geological assessment of coal mine roof conditions
TRANSCRIPT
University of Wollongong Thesis Collections
University of Wollongong Thesis Collection
University of Wollongong Year
Geological assessment of coal mine roof
conditions, southern Sydney basin
Ian J. StoneUniversity of Wollongong
Stone, Ian J., Geological assessment of coal mine roof conditions, southern Sydneybasin, Doctor of Philosophy thesis, Department of Geology - Faculty of Science, Universityof Wollongong, 1990. http://ro.uow.edu.au/theses/1394
This paper is posted at Research Online.
GEOLOGICAL ASSESSMENT OF
CXDAL MINE ROOF CXMDITIONS,
SCXJIHERN SYDNEY BASIN
A thesis submitted in partial fulfilment of the requirements
for the award of tJie degree of
DOCTOR OF PHILOSOPHY
from
THE UNIVERSITY OF WDLL0N30N3
•-•
by
UNIVERSITY OF WOLLONGONG
LIBRARY
IAN J . STONE, B.Sc. (Hons)
DEPARTMENT OF GEOLOGY
1990
r7^a:> . 7
Except vdiere otherwise acknowledged, this thesis represents the
authors original research \ iich has not been previously sutandtted to
any institution in partial or catplete fulfilment of another degree.
(IAN J. STONE)
ABSTOACT
Roof conditions in coal mines of the southern Sydney Basin, Australia,
are typically poor due to the effect of a relatively high horizontal in
situ stress field (horizontal to vertical stress ratio (.o^o^) is 1 3
approximately 2/1). The Permian Bulli Coal seam is mined frcm a
portion of the basin v*ich has undergone relatively little tectonic
deformation apart frcm faulting and regional warping. The o
orientation acting on mine roadways is determined using the mining
induced shear fractures and is ccnparable to results from in situ
overcore measurements. The angle between a., and the mine roadway (0sr)
together with the o.. magnitude and tJie o./o^ ratio defines the range of
roof conditions txD be ejqjected in a mine roadway. A twelve point scale
of stress induced roof failure has been developed to rank the severity
of stress acting across the mine roadway. For a given stress field the
roof conditions expected over the range of Osr is defined by a Roof
Failure (Turve. A number of Roof Failiice Curves are able to define roof
conditions for a varying stress field. The distribution of Roof
Failure CXirves represents the relative changes in stress field
intensit:y across the mapped area. Mapping techniques are able to show
the variability of both relative stress field intensity and lateral
stress field orientation. Successful management of the in situ stress
effects in mine development drivages and around longwall blocks is
crucial tx> the economic viability of coal mines in the southern Sydney
Basin.
Tto further understand the origin of the in situ stress field a
technique was developed to measm^e strain anisotropy in the coal
maceral vitxinite. Vitrinite mean maximum reflectance (R max), using
oil immersion, was measured from oriented sections nomal to bedding
and results indicate that the vitrinite in medium volatile bituminous
coals has biaxial optical properties. The range of true maximum
reflectance (R max) of vitrinite in the study was between 1.04% and o
1.48% reflectance. The orientat:ion of the R max can be determined frcm
the long axis of the elliptical Calculated Bedding Plane Section of the
Indicating Surface (CBPSIS). The biaxial nature of the vitrinite is
thought to result from asymtretrical growth of its molecular structirre
and to be related to stress fields vMch developed siinultaneously with
coalification. The R max direction is formed normal to lateral o
cotpressive forces. The CBPSIS figure fron the bituminoiis coals
studied is not usually elliptical but commonly takes the shape of two
superirrposed ellipses and, therefore, has two R max peak directions,
indicating overprinting of successive stress field orientations.
Results from studies of R max orientations indicate that they show
palaeostress patterns around faulted areas (including small faults with
<10m displacanent) consistent with fault formation, and are also able
to shew variation of regional palaeost:ress events.
The R rrax directions and in situ stress directions were determined frcm
study areas in different coal mines. Five palaeostress directions are
identified, two of vMch were recognised in all of the study areas.
The same two palaeostress directions are coincident with the two in
situ lateral stress field directions (NNW and ENE) recognised within
the study area. The ENE stress field is coincident with a palaeostress
active during sedimentation, prior to uplift. The NNW stiress field
orientation has been linked with a major wrench faulting episode in the
area, following the cessation of sedimentation, but during
coalification. Vitrinite reflectance data is able to record st:ress
field evaits vMch have been_irrprinted and locked into strata around
the Bulli Coal seam, indicating that the in situ stress field acrting in
the southern Sydney Basin has a strong residual caiponent. The study
shows that the use of vitrinite as a tectcaiic fabric indicator is
viable in weakly deformed terrain and is able to provide information
concerning palaeostrress regimes.
ACKNOWLEDGEMENTS
I wish to acknowledge the contribution of Professor A.C. Cook, vho
presented the opportunity, both by the introduction to the topic of coal
mine i oof conditions, and his early work with vitrinite properties . I am
indebted to Associate Professor B.G. Jones v^ose time was graciously
provided, and \^ose advice was gratefully received. Dr P.F. Carr remained
a judicious prcmpt at critical stages, thankfully.
Permission to carry out field work at mine sites owned by Kembla Coal and
Coke, BHP, Clutha Development, and BP Coal Australia is gratefully
acknowledged. I wish to thank the assistance provided by the many mine
personnel during the tenure of the field work. In particular I t±ank the
patience of Tahmoor Mine imnageirs, C. Taylor and B. Nicholls, and fellow
employees.
During the course of work the encouragement and assistance of associates in
the coal mining industry was appreciated, the contribution of P.W. Goodwin,
Dr W.J. GalOf and W.A. Williams is especially noted.
The continuing and patient support of ray family, particularly Julie, has
enabled the ccsipletion of this study. Special thanks to iry sister Marita
who did much of the tiyping.
TABLE CF OCWTEMTS
OCVPTER 1
INBRCDOCTICW p a g e
1 .1 AIM OF STUDY 1
1.2 STUDY AREA AND STRUCTURAL SETTING 2
1 .3 APPROACH 7
CHAPTER 2
MEmODS OF STODY
2.1 INTRODUCTION 11
2.2 COAL MINE ROOF CONDITIONS 11
2.2.1 PREVIOUS V O ^
2.2.2 ROOF C(»OITia^ OASSIFICATIC^I 13
2.2.2.1 Morphological Mine Roof Classification 14
2.2.2.2 Cfenetic Roof Fall Classification 19
2.2.3 METHODS OF MAPPING AND ANALYSIS 22
2.3 VITRINITE REFLECTANCE 23
2.3.1 INTRODUCTIC^I
2.3.2 METHOD 26
2.3.3 STUDY AREAS 30
2.3.4 SAMPLE SCHEME 30
2.3.5 RESULTS 32
2.3.5.1 Calculated and Jfeasured Reflectance
2.3.5.2 Random and Non-Random R max Orientations 34
2.3.5.3 R max Orientations 37 o
2.3.5.4 Replication Measurements 38
2.3.5.5 Reflectance Measurements in the Bedding
Plane 43
2.3.6 INrERPRETATia} AND DISCUSSION OF RESULTS 48
2.3.6.1 Uniaxial or Biaxial Vitrinites? 48
2.3.6.2 Reflectance in the Vicinity of Faulting 50
2.3.6.3 Molecular Structure in Biaxial Vitrinite 51
2.3.6.4 Strain Overprinting in Vitrinite 58
2.3.6.5 Flatrock and Scarborough Faults - CBPSIS
Interpretation 61
2.3.7 FURTHER APPLICATI(»IS OF THE CBPSIS 62
2.4 POINT-LOAD FRACTURE CKIENTATIONS 64
2.4.1 INTRODUCTICN
2.4.2 AIM 65
2.4.3 TECHNIQUE 65
2.4.4 RESULTS FROM THE SOUTHERN COALFIELD 66
CHAPTER 3
WEST CLIFF Cnri.TERY - CASE STIJDY
3.1 INIRODUOTK^ 71
3.2 GBOIJOGICAL STRUCTURES 73
3.3 ROOF MORPHOLOGY 77
3.4 VITRINITE REFLECTANCE - AREA A AND B 85
3.4.1 REFLECTANCE AND R^MAX O^ENTATIONS; AREAS A AND B 87
3.4.2 CBPSIS - MULTIPLE REFLECTANCE PEAKS 93
3.4.3 STRAIN MAXIMA - AREA A AND B 99
3.4.3.1 Fault Intersection - Area A 105
3.4.3.2 Normal Favilt Termination - Area A 106
3.4.3.3 South Normal Fault - Area A 107
3.4.3.4 Strike-Slip Fault - Area B 107
3.4.4 INTERPRETATI(3N OF STRAIN EVENTS - AREA A AND B 108
3.4.4.1 Normal Faults 108
3.4.4.2 Strike-Slip Faults 112
3.5 POINT-LOAD FRACTURE ORIENTATIONS 114
3.5.1 POINT-LOAD FRACTTJRE ORIENTATICX^ AND STRAIN MAXIMA 118
3.6 VITRINITE REFLECTANCE - AREA C 118
3.6.1 REFLECTANCE RESULTS - AREA C 121
3.6.2 R MAX (KIENTATIONS - AREA C 121
o 3 . 6 . 3 INTERPRETATION OF R MAX CKEENTATIONS - AREA C 125
o 3.7 IN SITU STRESS, PALAEOSTRAIN AND STRUCTURE - CONCLUSIOIS 128
CHAPTER 4
CASE gPUDY - KEMIRA OOLLIERY
4 . 1 INTRODUCTION 131
4 .2 ROOF CCMDITIONS - C4 PANEL 140
4 . 2 . 1 HEI(3TT OF R(XIF FALLS 140
4 . 2 . 2 TYPE OF ROOF CX)NDITI(XNS 141
4 . 2 . 3 GENETIC OiASSIFICATION OF ROOF FAR^ 145
4 . 3 VITRINITE REFLECTANCE 149
4 . 3 . 1 RESULTS 149
4 . 3 . 2 INTERPRETATION 158
4.3.3 RELATION OF R^MAX SETS A, B, C 159
4.4 POINT-LOAD FRACTURE CRIENTATIOIS 162
4.5 DISCUSSIC2N 165
4.5.1 ROOF CONDITIONS 165
4.5.2 STRAIN EVENTS 168
CHAPTER 5
FfflRRT aORANS VALLEY - CASE STODY
5.1 INIRODUCTICN 175
5.2 STRUCTURE 176
5.3 MINE ROOF CCNDITICNS 184
5.3.1 MINE ROOF COOITIONS - OAKDALE COLLIERY 187
5.3.2 MINE ROOF CCM3ITI(3^S - NAITAI BULLI COLLIERY 190
5.4 VITRINITE REFLECTANCE STUDY 192
5.4.1 RESULTS 194
5.4.2 RELATION OF STRAIN, STRUCTORE AND ROOF O^OITIONS 198
5.4.3 INTERPRETATION AND DISCUSSION OF RESULTS 198
5.4.3.1 Strain History of Domains A and B
- Interpretation One 202
5.4.3.2 Strain History of DortHins A and B
- Interpretation Two 205
5.4.3.3 Relation Between Inferred Palaeostress,
In Situ Stress and (Geological Stmicture 209
5.4.4 VITRINITE STRAIN PATTERNS AROUND POST-COALIFIC^fflON
STRUCTURES - NATTAI NORTH COLLIERY 218
5.4.4.1 200 Area Nattai North Colliery 219
5.4.4.2 Reverse Fault - Nattai North Colliery 223
5.5 COCLUSIONS 226
CHAPTER 6
TAHMXR OCBJJERY - CASE STUDY
6.1 INTRCXXJCTIQN 229
6.2 STRATIC3RAPHY 230
6.3 GEOLOGICAL STRUCTURE 233
6.4 ROOF COmiTlCm 240
6.4.1 TNTRODUCTION 240
6.4.2 ROOF CLASSIFICATION 242
6.4.3 MErpCOS USED P(5l ROOF MAPPING 244
6.4.4 DISTRIBOTI(3N OF ROOF FAILURE TYPES 246
6.4.5 ROOF FAILURE IN THE NW PANEL 247
6 .4 .5 .1 Short Term Roof Fai lure 247
6 .4 .5 .2 Long Terra Roof Fa i lure 254
6 .4 .5 .3 Cdipariscai Between Short Term and Long Term
Roof Fai lure 258
6.4 .5 .4 Relationship Between Order of Drivage and
Total Long Term Roof Deformation 263
6.4.6 DEVELOPMENT OF RCOF CXM)ITIC»NS TTiR(XIQK)UT TAHMOOR
MINE 270
6.5 THE IN SITU STRESS FIELD 275
6.5.1 METHODS USED TO DETERMINE STRESS FIELD ORIENTATION 276
6.5.2 STRESS FIELD CBIENTATION 281
6.5.2.1 Sigma 1 Orientation 281
6.5.2.2 20 Situ Stress Jfeasurements 285
6.5.2.3 Cfcirparison of Methods Used to Determine
Sigma 1 Orientation 285
6.5.2.4 Sources of Error in Sigma 1 Orientatiion
from Rock Fractxire 285
6.5.2.5 Ratio of Sigma 1 and Sigma 2 289
6.5.2.6 Summary (Guide to Using Roof Fractures
to Identify the Stress Field 290
6.6 THE RELATIONSHIP BETWEEN STRESS FIELD ORIENTATION AND
MINING CCXOITICXNS 296
6.6.1 INIRODUCTION 296
6.6.2 THE PREFERRED LOCATION OF SHCHT TERM RCOF FAILURE 297
6.6.3 ROOF CCMDITKXNS AND THE ANGLE OF SI(31A 1 TO THE
MINE ROADWAY 298
6.6.4 LONG TERM RCOF CONDITIONS AND 9sr 300
6.6.5 SHORT TERM ROOF CCXNDITIONS 302
6.6.5.1 Roof Failure Curve 304
6.6.5.2 Ccnparison of Short Term Mining Conditions 305
6.6.6 VARIATION OF STRESSFIEU) AND ROOF FAILURE~CURVES 311
6.6.6.1 Stressfield Magnitude from Roof Failure
Curves 312
6.6.6.2 Sigma 1/Sigma 2 Ratio from Roof Failure
Curves 314
6 . 6 . 7 PREDICTION OF ROOF C0NDITI(3NS, ROOF SUPPORT AND
PR(XXX:TION RATES 3 1 4
6.6.7.1 Prediction of Roof Conditions 314
6.6.7.2 Roof Support Options 316
6.6.7.3 Roof (Conditions and Production Rates 316
6.7 VITRINITE REFLECTANCE 317
6.7.1 INTRODUCTION 317
6.7.2 RESULTS 317
6.7.3 STRUCTURAL DEVELOPMENT IN THE TAHMDOl AREA 321
6.7.4 COJCLUSIOJS 329
CHAPTER 7
SIMMARY AND OCNCLUSIOS
7.1 INTRODUCTIC^I 331
7.2 ROOF CONDITI(»JS AND THE IN SITU STRESS FIELD 331
7.3 CBPSIS FIGURES 336
7.4 PALAEOSTRESS AND IN SITU STRESS 341
REFERENCES 349
APPENDICES
I OBTAINING THE BQUATICN OF AN ELLIPSE GIVEN THREE
POINTS AND THE ORIGIN 363
II POINT-LOAD TEST RESULTS 364
III VITRINITE REFLECTANCE DATA 368
IV STRESS ORIENTATICWJVND LONG TERM DEFORMATION
NW PANEL - TAHMDCR MINE 382
IN BACK POCKET - supporting papers.
U S T OF FIGURES
CHAPTER 1
DNTRODOCTICM
Fig. 1.1
Fig . 1.2
Fig . 1.3
CHAPTER 2
MFfgCDS OF STUDY
Fig. 2.4
Fig. 2.5
Fig. 2.6
Fig. 2.7
Fig. 2.9
page
3
4
5
Fig. 2.1
Fig. 2.2
Fig. 2.3 31
17
24
36
39
40
45
Fig. 2.8 45
46
Fig. 2.10 47
Fig. 2.11 52
Fig. 2.12 59
Fig. 2.13 59
Fig. 2.14 69
Fig. 2.15 69
QiAPTER 3
WEST CLIFF (X3LLIERY - CASE STUDY
Fig. 3.1 72
Fig. 3.2 74
Fig. 3.3 75
Fig. 3.4 79
Fig. 3.5 79
Fig. 3.6 81
Fig. 3.7 84
Fig. 3.8 86
Fig. 3.9 91
Fig. 3.10 92
Fig. 3.11 94
Fig. 3.12 95
Fig. 3.13 96
Fig. 3.14 97
Fig. 3.15 98
Fig. 3.16 100
Fig. 3.17 101
Fig. 3.18 104
Fig. 3.19 109
Fig. 3.20 HO
Fig. 3.21 116
Fig. 3.22 117
Fig. 3.23 119
Fig. 3.24 120
Fig. 3.25 123
Fig. 3.26 126
Fig. 3.27 126
Fig. 3.28 129
CHAFi'iai 4
KEMIRA COLLIERY - CASE STUDY
Fig. 4.1 132
Fig. 4.2 133
Fig. 4.3 134
Fig. 4.4 135
Fig. 4.5 138
Fig. 4.6 142
Fig. 4.7 147
Fig. 4.8 151
Fig. 4.9 153
Fig. 4.10 154
Fig. 4.11 155
Fig. 4.12 157
Fig. 4.13 160
Fig, 4.14 163
Fig. 4.15 164
Fig. 4.16 169
CHAPTER 5
BORRAGCRANG VALLEY - CASE STUDY
Fig. 5.1 177
Fig. 5.2 179
Fig. 5.3 181
Fig. 5.4 185
Fig. 5.5 188
Fig. 5.6 189
Fig. 5.7 191
Fig. 5.8 - 193
Fig. 5.9 196
Fig. 5.10 197
Fig. 5.11 199
Fig. 5.12 200
Fig. 5.13 203
Fig. 5.14 206
Fig. 5.15 208
Fig. 5.16 210
Fig. 5.17 212
Fig. 5.18 215
Fig. 5.19 221
Fig. 5.20 222
Fig. 5.21 224
CHAPTER 6
TAHMXR OOEUIRY - CASE STUDY
Fig. 6.1 231
Fig. 6.2 232
Fig. 6.3 234
Fig. 6.4 235
Fig. 6.5 236
Fig. 6.6 239
Fig. 6.7 241
Fig. 6.8 242
Fig. 6.9 250
Fig. 6.10 255
Fig. 6.11 256
Fig. 6.12
Fig. 6.13
Fig. 6.14
Fig. 6.15
Fig. 6.16
Fig. 6.17
Fig. 6.18
Fig. 6.19
Fig. 6.20
Fig. 6.21
Fig. 6.22
Fig. 6.23
Fig. 6.24
Fig. 6.25
Fig. 6.26
Fig. 6.27
Fig. 6.28
Fig. 6.29
Fig. 6.30
Fig. 6.31
Fig. 6.32
Fig. 6.33
Fig. 6.34
Fig. 6.35
Fig. 6.36
Fig. 6.37
256
257
257
259
261
265
267
273
278
282
284
293
299
301
303
306
307
309
315
315
318
319
323
324
327
327
CHAPTER 7
SUMMARY AND (XMCLUSICKS
F i g . 7 .1 333
F i g . 7 .2 343
LIST OF TABLES
Table 2 . 1
Table 2.2
Table 2 .3
Table 2.4
_
C31APTER 2
MEnHDS OF STUDY
CHAPTER 3
WEST CLIFF CQLLIHiy -
Table 3 .1
Table 3.2
Table 3 .3
Table 3.4
Table 3 .5
Table 3.6
CEffiPTIR 4
CASE STUDY
KEJGRA OOTJ.TERY - CASE STUDY
Table 4 . 1
Table 4 .2
Table 4 .3
Table 4 .4
Table 4 .5
page
20
34
35
42
83
88
90
102
114
122
141
143
150
173
174
CHAPTHl 5
BORRAGCRANG VALLEY - CASE STUDY
Table 5.1 195
Table 5.2 213
CHAPTER 6
TAHMOOR OOBJLIERY - CASE STUDY
Table 6.1
Table 6.2
Table 6.3
Table 6.4
Table 6.5
Table 6.6
Table 6.7
Table 6.8
CHAPTER 7
SLMMARY AND (XNCLOSICNS
243
248
271
286
288
291
313
320
T^le 7.1 342
CHAPTER 1
INTRODOCnCW
1.1 AIM OF grUDY
The southern Sydney Basin, New South Wales, Australia, contains an
iirportant Permian coal resource (Fig. 1.1). Uhderground mining itethods
are used to extract the coal from depths which range frcm 300m to over
50Qm. The Bulli Ctoal seam is the uppermost seam and lies at the txp of
the Illawarra Coal Measures beneath the overlying Triassic sandstones
and thinner claystone and shale sequences of the Narrabeen Group, and
the Hav^esbury Sandstone. The top of the sequence contains the shales
of the Wianamatta (Group (Sherwin and Holmes, 1986). Figxrre 1.2 shows a
schematic cross-section of the sequence above the Bulli Coal through
the thesis study area.
Roof conditions in collieries which mine the Bulli Coal seam are
generally poor due to the effect of high horizontal stiresses in the
roof and floor strata. Shej^erd and (Gale (1982) reviewed the range of
geological features vdiich affect coal mine roof stability. They
attribute the abnormally high horizontal stresses as the principal
reason for the difficult roof conditions at what are, on a worldwide
stage, relatively shallow depths.
Mine development delays and \anfavourable stress concentrations around
roadways used for the high capacity longwall mining syston can be
caused by the in situ stiress field. Mines can and have become
uneconomic if the in situ stress field is not vinderstood to allow the
use of appropriate control procedures.
The aim of this thesis is twofold;
(i) To understand the effect-that the high horizontal stress field has
on the rectangular coal mine opening by;
(a) using field mapping methods to record the orientation of the
lateral stress field and relative magnitude of roof failure,
and
(b) determining the relationships bet::v en the in situ stress field
and the type of roof conditions in each study area.
(ii) To develop methods of measuring tectonic fabric and potential
palaeostijoss directions from hand specimen size sanples, in the
weakly deformed terrain of the southern Sydney Basin, to help
define the nature of the in situ stress field, its origins and
potential variability.
1.2 STUDY AREA AND STRUCTURAL SETTING
The stixiy area consists of a series of eight coal mines spread unevenly
across the southern Sydney Basin. The mine locations are shown in Fig.
1.1. The Coal Cliff, Vfest Cliff and Kanira Collieries are located on
the eastern part of the NW dipping limb of the main synclinal
structure, the Camden Syncline. Tahmoor Ctolliery and the four mines in
the Burragorang Valley group are located to the west of the meridonal
Nepean Fault structure which is the approximate division between the
Woronora Plateau and the west:em Illawarra Plateau (Berabrick et al.,
1980).
The principal fold structure is the north-plunging Camden Syncline
\ hich forms the axis of the basin (Fig. 1.3). A series of NW trending
monoclinal structures are present around the edge of the basin and, in
the coastal area, ESE trending folds are superintposed on the eastern
Fig. 1.1 Location plan of the study area in the southern Sydney
Basin, New South WcLles, Australia.
ssw NNE
. ^
Or Inlerfingering
Regression
Transgression
Palaeocurrent direction
Unconformity, disconformity
^
Otford Sandstoney Member
.^
m -~—~
Dark grey shale and lamlnlte
Grey shale/clayslont
Claystone, chocolali and grey mottled In parts
Cream clay pellet sandstone
Interbedded sandstom and slltstone and lamlnlle
LIthIc sandstone
Ouartzose sandstont
16041
Fig. 1.2 Schematic cross-sect ion of the s t r a t a overlying t h e Bul l i
Coal seam through the study area ( a f t e r Sherwin and
Holmes,1986).
2 0
!._
- 1 - -- - f -
SCALE
2 4 6 8
Kilometres
Fault
Monocline
Anticline
Syncline
Linear feature
10
LINDSAY" /.V,f. DOME ' W
.MT MURRAY v..
v
Fig. 1.3 Major structvural features of the study area (after Sherwin
and Holmes, 1986).
limb of the Camden Syncline. These later features are believed to have
been active during Late Permian (Sherwin and Holmes, 1986). Jakanan
(1980) concluded that the present-day Bulli Coal structural trends were
largely imprinted by Middle Triassic.
The Nepean Fault structure is a high angle reverse fault zone
characterised by discontinuous en-echelon west dipping faults
indicative of a ccrrponent of wrench movement (Herbert, 1989). This is
a major structure with maximum throws of approximately 100m and a
strike length of at least lOOlon. The Nepean Fault is the southern
extension of the Lapstone Structural Conplex (Branagan and Pedram,
1990). Deformation history of the structure is believed to be long and
complex (Branagan and Pedram, 1990). Bishop et al.(1982) reported that
the most recent movements on the structure v^re older than 8Ma, whereas
Branagan (1975) suggested that the structure is related to the opening
of the Tasman Sea between 80-60 Ma. Herbert (1989) suggested the Nepean
Fault was forrr^ in the Late Triassic. To the west of the Nepean Fault
are the Oakdale and Thirlmere Monoclines.
Sherwin and Holines (1986) concluded that the Sydney Basin was subjected
to E-W ccitpression from the commencement of sedimentation until the
Cainozoic, with intervening periods of NE ccnpression. (Gray (1982)
suggested that the current carpression is N-S and has been active since
the Cainozoic.
There is little agreement in the literature concerning the uniformity
of stress direction measured either at the Bulli seam horizon or, as
inferred from stiKiies of earthquakes, in the basement underlying Sydney
Basin sediments.
studies of the Robertson earthquake (Cleary, 1963; Denham, 1980), the
Burragorang (or Picton) earthquake (Mills and Fitch, 1977; (Gray, 1976),
both of vhich were in or adjacent to the stixJy area, have not produced
agreement. Denham (1980) believed that the pressure axes determined
from earthquakes vary over short distances. Shepherd and Huntington
(1981) showed the stress field ccnpression in the West Cliff area to be
N-S yet Enever et al. (1989) suggested the major horizontal stress
ccrrponent is E to NE.
1.3 APPROACH
The aims of this thesis were approached hy initially defining the data
gathering methods that were feasible and likely to produce the required
resiiLts. A series of case stxxLLes were conducted at different mine
sites across the southern Sydney Basin to iirplement the thesis aims.
No attempt was made to gather data from all available mine sites in
order to interpret an in situ or palaeostress model for the developnent
of the post-Permian basin. Instead small areas were chosen to relate
the in situ stress field and associated meso- and rtacro-scale tectonic
fabrics. Mining activity, after all, is conducted over no more than a
few square kilcmeti^es at any one time and the stress field influence
needs to be understood at that scale.
Chapter 2 describes the development of methods used in gathering and,
to some extent, interpreting data.
Each of the case study areas was treated similarly but, because of the
different character of the mine area available at the time, different
aspects are eitphasised. As with normal coal mine development only a
relatively small area of the mine area is accessible at any one time.
8
Chapter 3 studied West Cliff Mine. (Good exposure to stress-affected
mining conditions beneath a sards tone roof was available. In additJ-on,
a variety of faults were available for stvidying the manner of strain
developnent in their vicinity.
Chapter 4 looked at a small study area in Kemira Colliery. Extranely
variable mining conditions beneath variable sedimentary roof types, and
the presence of stone rolls, were considered with respect to the stress
field.
Chapter 5 looked at the regional variation of stress across, four
adjacent colliery holdings in the Burragorang Valley. This study
concentrated on the variable imprinting of tectonic fabric to hand
specimen size sanples.
Chapter 6 stxidied the roof conditions developed as a new mine expanded
over a number of years. It was an ideal area because of the access
available and the stress field variability encountered. The main theme
of the relationship between roof conditions and the in situ stress
field was developed at Tahmoor,
Each chapter draws conclusions about the relationships recorded at each
site. Chapter 7 incorporates summary results from each case study,
provides comments and draws conclusions concerning the general and
regional significance of the accumulated data.
Throughout the thesis azimuths are relative to (Grid North imless
2 specified. The symbol X is used throughout to refer to the Chi-square
statistical test.
The i :pendices contain the following data. The method for calculating
the long axis of an ellipse ( jpendix I), data from point-load testing
(Appendix II), a list of all reflectance data (J^pendix III) and a list
of stress orientations and roof deformation at Tahmoor mine (i 3pendix
IV).
10
11
CHAPTER 2
METHJDS OF STTOY
2.1 IMRODOCnCN
The purpose of this study was to look at coal mine roof conditions from
a geological standpoint. In particular the effect of lateral stress on
the mine opening, and the relationship of the in situ stress, if any,
to the palaeotectonism of the stixiy area.
Three different data gathering procedures were used in this stvidy.
Firstly, information was recorded about mining ccmditions, particularly
mine roof conditions. This inclixied information on the in situ stress
field. Secondly, a study of palaeostrain (and palaeostress) was
attenpted using the optical anisotropy of the coal maceral vitrinite.
Uiconf ined axial point-load tests of coal mine roof strata vere used as
the third method. This latter procediire was applied to indicate any
non-random fracture inherent in the rock sanples.
Each of these three procedures will be described in this chapter.
2.2 COAL MINE ROOF OOMDITICKS
2.2.1 PREVIOUS WCRK
Uriderground coal mines in the Southern Coalfield of N.S.W. have roof
conditions which are reported as being the worst in the state (Williams
and Wilson, 1976). The stability of mine roadways is irtpoirtant for
safety reasons, for access to the coal-twinning face and ultimately for
the economic viability of the mine. Excessive roof failure can make
12
roof support a major consideration both technically and economically in
the mining operation.
In this study en iiasis is placed on the roof conditions vrfiich are
related to the high horizontal in situ stress field typical of the
southern Sydney Basin (Jaggar, 1967; Williams and Wilson, 1976; and
(Gale et al., 1984a). Stress related roof failure is the dominant
influence on roof stability in the study area.
Each study area in this thesis has had part of the coal mine roadways
mapped to record the roof condition. A roof condition classification
system was used vhich incorporated both morphological and genetic
aspects. Previous work reported from the Sydney Basin described
aspects of geological featirres which have affected the mining
conditions.
Williams and Wilson (1976) commented on the roof rock type, stress and
discontinviities (faults, joints and bedding planes) as inportant
factors in roof conditions. The relationship of sediitentary and
structural features for strata surrounding the coal in the Southern
Coalfield was discussed by Diessel and Moelle (1965) and Diessel et al.
(1967).
Shepherd and (Gale (1982) provided an overview of the role of geology in
colliery roof stability, and provided exanples from the Sydney Basin.
They regarded lithology and in situ stress as the two most inportant
factors affecting roof conditions. In addition to Shepherd and (Gale
(1982) and Williams and Wilscai (1976), other authors have reported on
13
the effect of high horizontal stresses, e.g. Connelly (1970), Yeates
(1977), Nicholls (1978) and Hamment (1983).
Yeates (1977) provided a 10 point classification of roof conditions
which was a combination of roof fall description, failure related to
location, and failure related to geology. Shepherd and Burston (1977)
mapped areas of a colliery with a descriptive classification of roof
conditions v iich was predefined and non-genetic.
Many articles have been conpiled about the roof conditions found in
overseas coal mines. These are not reviewed here in detail because of
the variation in general mining conditions found in different
coiintries. The irtportant effect of high horizontal stress, however, is
recognised, e.g. Parsons and Dahl (1971), Aggson (1978, 1979) and
Jeremic (1981).
Two distinctly different approaches to classifying roof conditions were
proposed by Patrick and Aughenbaugh (1979) and Hylbert (1978). The
former authors proposed that roof falls be classified on a geometric
basis. This system is independent of causative factors. Hylbert
(1978) used a geologically based classification for poor roof
conditions. He combined various geological parameters into each of
four roof condition categories. However, detailed roof types rather
than roof fall morpiiology were enphasized.
2.2.2 ROOF OCKDinCN CLASSIFICATICW
The roof condition classification used in this study to gather data is
twofold. Firstly, there is a descriptive system based on the roof
morphology. It is modified from Shefherd and Burston (1977) to take
14
account of local conditions. Secondly, at each roof fall site
geological paraiteters were recorded so that a genetic classification of
roof falls might also be made. Both systems are described below.
2.2.2.1 Morcholoqical Mine Roof Classification
LJpon mapping underground coal mine roof conditions the lateral
extent and height of the falls are recorded on a mine plan of
suitable scale (usually 1:50). The roof condition morphology is
recorded in one of the categories listed below.
Type I (Good or stable roof.
As the nane suggests it refers to roof v iich has not
undergone any deformation. Strictly speaking, stable
roof may refer to the condition of a roof fall after
deformation has occurred. This is not the meaning used
in this work.
Type II Roof Fall Cavity Classification.
(a) Scaly Roof - (Fig. 2.1a) refers to thin (<0.3m thick)
areally irregular falls of roof ply. May be found to
occur in most roof rock types and under most geological
conditions. It is not regarded as a serious factor in
overall ixof stability. Areas prone to scaly roof
should be regarded as a safety problon and supported
accordingly.
(b) Flat top falls - (Fig. 2.1b) refers to falls which are
greater than 0.2m high and have a roof formed by a
bedding plane. In plan it is approximately
equidiirensional about its centre or is rectangular. The
15
sides of this fall type may be steep (e.g. along a
jointing plane) or form as a dome shape. This category
is often referred to as done falls,
(c) Inverted V-shape falls (Fig. 2.1c-e); this category of
fall has a general inverted V-shape in its sinplest form
or may have an irregular shape fall without a flat top
in its most general form.
There are three inportant practical and distinct
subdivisions of type 'c' falls:
(i) Low angle conjugate shears (Fig. 2.1c). This
failure type is <0.3m in height, is serpentine or
straight in plan view and iray occur either in the
centre part of the heading or adjacent to the
ribside. There is some overlap with the gutter
classification (see c(ii) below). The main
difference is that low angle conjugate shears occur
with or soon after mining and need not necessarily
occur against the ribline.
(ii) (Gutter falls (Fig. 2.Id). This type of fall has a
genetic association with high horizontal stress
fields. Morphologically they occur as inverted
V-shape falls of width less than one-third the
roadway width and length greater than width.
(Gutter falls are so defined because they are
located in the roof immediately adjacent to the
rib. However, gutter falls may cross the heading
at an oblique angle, continiring along the opposite
rib line. In this thesis the terminology gutter
16
Fig.2.1 Morphological mine roof classification. Figures a to h
provide plan and section views of each roof type. The width
(w), height (h), and length (1) of types a to e are defined.
17
(a)
MINE ROOF CLASSIFICATION SECTION VIEW PLAN VIEW
^ JLJ, of roadway
Scaly Roof —
h<0.3m ^ i
rlb&ide\
T
(b)
h
K- w -H
Flat Top Falls
l>w or w>l
h>0.2m
Y- I H
(c)
V-shaped Falls - low angle conjugate shears
l » w and h<0.3m
- /
(d)
(e)
V-shaped falls - gutter falls
l »w -^•i--.-.-.-.-, '••• v . - i - . . ; . . L , , . , L i 7 ~
I
V-shaped falls - arch falls w>l or l>w
h>0.3m
(t)
Cantllevered roof
(g)
Cracked and/or Sagged roof
(h)
Heavy roof
18
fall is restricted to falls which occur in the roof
area immediately adjacent to the rib line. The
continuation of the gutter fall across the heading
is referred to as an arch fall (c(iii)).
(iii) Arch falls (Fig. 2.1e); as the name implies
form an arch profile with a height greater than
0.3m, located in the roof away frcm the ribside.
The width may be variable but the length is usually
greater than the width. Like low angle conjugate
sheairs, arch falls may be serpentine or straight in
plan views. Arch falls rray occur at the mining
face or eventuate frcm time dependent failure.
Type III Uhstable Roof - Not Fallen
This type of roof vhich has not fallen, most likely as
the result of roof supports, may also incorporate Type
II roof conditions.
(a) Cantilever roof (Fig. 2. If); the roof drops down
significantly on the side which has guttered giving the
appearance of having pivoted about the opposite ribside.
(b) Cracked and broken roof (Fig. 2.1g); incorporates ixxof
vhich is cracked and broken. It is conmon for this roof
to sag down in the centre area of the roadway. Hence
the term sag is used v^ere perceptable movement can be
visually recorded. Both tensile and shear cracks are
included in this classification.
(c) Heavy roof (Fig. 2.1h); this is an arbitrary and
svibjective term applied to roof which is placing
19
significant weight on roof supports, it is not a roof
fall description but refers to a very general rxoof
description, normally as the role of an adjective in
describing other roof condition types. It can be used
as an extreme example of Type Ill(b) above.
In all the case studies carried out on roof conditions only one
(Tahmoor in Chapter 6) was reviewed over a period of time.
Therefore the classification of roof conditions was based on those
present at the time of majping and is not necessarily
repi?esentative of the final state of equilibrium. It would be
unlikely that the roof conditions would change significantly from
those mapped without further mining activity.
2.2.2.2 (Genetic Roof Eall Classification
A full range of the geological parameters observable at each fall
site were mapped so that factors likely to have contributed to the
fall could be assessed. Such parameters included roof sequence
and lithology, bedding details such as thickness and continuity,
likely planes of separation, joints and other tectonic structures,
and mining induced features including indicators of the direction
of strata movement.
A simple four corponent genetic classification of roof falls was
developed for conditions in the Southern Coalfield. Table 2.1
indicates the classes and their most \iseful and common
svibdivisions.
20
TAEaCiE 2.1
(gMETIC CLftSSIFICAnCW OF ROOF FALtg
A. FAILURE PRIMARILY DUE TO HIOI AN3LE FEATURES:
(i) normal fault planes
(ii) strike-slip fault planes
(iii) joint planes
(iv) d^es
B. FAILURE PRIMARILY DUE TO LOW ANGLE DISCONTINUITIES:
(i) reverse faiiLt planes
(ii) bedding plane slip
(iii) ply separation
due to mechanically weak stratum
due to geometry of strata, e.g. foreset beds
in conjunction with seme other feature
C. STRESS:
(i) Horizontal Stress
shearing and gutter failure
shearing and stirata deflection (sag)
mining induced tensile failirre
(ii) Vertical Stress
strata deflection
mining induced tensile failure
D. LATERAL SEDIMENTARY CHANGE
21
This classification of roof falls is intended to be geometrical so that
it can be more readily used in roof support design. High angle and low
angle discontinuities need different support design. The influence of
the dominant stress direction on discontinirlties is also important
(Williams and Wilson, 1976). Roof failure related to stress factors in
general requires the resistance of shear forces.
The subdivisions of Classes A and B (Table 2.1) are self explanatory.
No distinction of the origin of applied stress is made in Class C. The
attitude of the stress field gives different failure modes. Horizontal
stress produces failxire oriented normal to the applied stress (Shepherd
and (Gale, 1982) except where modified by mining induced factors. For
exairple, horizontal stress releases itself by forming gutter failures
v iich are not necessarily normal to the applied stress. However, the
area in the top comer of the rectangular shaped cross-section of the
coal mines rxoadways has a high stress concentration (Aggson, 1979),
which acts as a locus for guttering. Enever and Shepherd (1979) also
record tensile fractures oriented in the plane of the two local
principal in situ stress direcrtions, sigma 1 and sigma 2 around the
mine roadway.
Vertical stress produces a different set of failure modes characterised
by strata deflection, tension cracks and shearing along the ribs
(Yeates, 1977).
The full developnent of techniques to interpret roof fracturing and the
associated stress field will be detailed in Chapter 6. In that chapter
elonents of the above roof condition classifications are expanded.
22
The roof lithology (Class D) is correctly considered as a very
inportant aspect of roof stability. In the context of this thesis the
roof lithology can be incorporated as part of the description within
any of the four genetic classifications. Where lateral variation of
lithology occurs, the boundary may be a distinct physical discontinuity
with either a high or low angle relative to bedding. An exarrple could
be an erosive sandstone channel within the immediate roof.
2.2.3 MKEHODS OF MAPPIMG AND ANMiYSIS
The details of the roof conditions were recorded onto 1:50 scale plans.
In each heading distances were either paced out, or a tape measure was
laid out and referred to. The areas available to be mapped in any of
the locations were limited by safety of access. Therefore some areas
which would have added considerably to the spread of the data base were
not considered.
In two of the study areas (Kemira and West Cliff) some of the mapping
was done between three months and two years after mining. Therefore
the conditions vhich existed at the working face were interpreted from
experience but were imlikely to have changed significantly frcm those
majped.
Analysis of the data recorded by mapping roof conditions is treated
separately in each of the case stixiies. Work on roof conditions was
greatly expanded at the Tahmoor Mine v^ere access over tine and a broad
range of mining conditions was available. Chapter 6 contains the
Tahmoor information.
23
2.3 VITRINITE REFLECTANCE
2.3.1 INIRODUCTION
The coal maceral vitrinite datonstrates the ability to flow and undergo
deformation (Cook et al., 1972a, plate 26; Jones and Creaney, 1977;
Figs 15 and 16). For exairple, strain shadows have been noticed in
vitrinites occurring around more dimensionally stable inclusions.
Interest in the coal maceral vitrinite arises from the need to have a
readily available indicator of palaeostress within the coal mining
environment. In an area such as the Southern Coalfield, vhere
tectonic deformation is low in accord with flat lying sedimentary
rocks, a palaeostress indicator would need to be sensitive. Vitrinite,
even at low rank (e.g. 0.647% reflectance - Davis, 1971), shows signs
of anisotropy in response to load pressure from deposition and burial.
Tteichmuller and Tfeichmuller (1975) noted that vitrinite is more
responsive than most other indicators of metamorphic grade. Vitrinite
also has the advantage of being present in most coals and, therefore,
at most mining sites.
Vitrinite is generally considered to have a uniaxial optical character
(Hevia and Virgos, 1977). That is, reflectance values measured in all
possible sections of a vitrinite would define an oblate spheroid v^ose
short axis is normal to bedding (Fig. 2.2a).
The minimum reflectance is normally considered to be perpendicular to
bedding, although Petrascheck (1954) found the position of the minimum
departed from being perpendicular to bedding in a folded sequence.
Since bedding in the coal measures studied in this thesis is
24
UNIAXIAL INDICATING SURFACE
OBLATE SPHEROID
BIAXIAL INDICATING SURFACE
OBLATE ELLIPSOID
Fig. 2.2 Idealised reflectance indicating surfaces for (a), uniaxial
negative vitrinite and (b), biaxial negative vitrinite.
25
essentially horizontal the minimum vitrinite reflectance value is taken
as vertical. Thus for uniaxial vitrinite a bedding plane section
should give a true maximum reflectance (R max) on all positions of
stage rotation.
Vitrinite with \miaxial negative optical properties should have at
least one true maximum reflectance (R max) upon a ninety degree
rotation of the microscope stage. Ctolique sections show the R max and
an apparent minimum reflectance.
If a vitrinite is optically biaxial then the shape of the indicatrix
(Fig. 2.2b) places constraints on the sections from which R max may be
measured. Values of R max may only be determined from the bedding
plane section (ab plane), and a family of sections parallel to the b
axis of the indicatrix. The minimum reflectance measured in the
bedding plane section (a-b plane. Fig. 2.2b) is from a family of
sections parallel to the a axis. This reflectance is the intermediate
reflectance (R int). The R min can be measured from vertical sections. o o
Other sections of the indicatrix will give apparent R^max and R^min
values.
Cook et al. (1972b) provided evidence to suggest that the plane
containing the R max may lie at a small angle to the bedding plane.
Therefore, if the true R max is to be measured with certainty it should ' o
be from a vertical section parallel to the b axis of the indicatrix
(Fig. 2.2b).
Cook et al. (1972b) proposed a nimiber of ejqjlanations for the biaxial
character of the anthracites which they studied. One proposal was the
26
existence of anisotropy of lamellar elements of vitrinite in the
horizontal as well as the vertical planes. They argued that the
polyarcmatic chains of the vitrinite were either distorted or grew
asymmetrically, both resulting from the influence of a triaxial stress
field. The asymrretric lamellae in the vitrinite would grow normal to
the applied force. Therefore, in a given triaxial stress field the
resultant optically negative biaxial vitrinite is oriented with its
long axis normal to the maximum lateral stress field.
Although the work by Cook et al. (1972a, b) was based on the biaxial
characteristics produced in anthracites it was thought worthwhile in
this stxxiy to investigate the existence of any biaxial character that
might occur in coals in the Southern (Coalfield. The aim being to
determine if any existing biaxiality could be related to strain in
vitrinite produced by a triaxial stress field. In particular it was
thought that by determining the exact orientation of the R ITBX (or
maximum strain) in an oriented coal block it would be possible to infer
the lateral palaeostress orientation as being normal to the azimuth of
the same Rjnax. The method, results and relationships between the
Rjnax direction, associated tectonic structures and the inferred
lateral palaeostress at two locations are presented in this chapter.
2.3.2 METHOD
In the early stages of this investigation it was not considered
practical to measure the direction of the R max from a bedding plane
section becaiase the R max does not necessarily lie exactly in the plane
of bedding of a vitrinite band. Furthermore, it is difficult to be
certain that the bedding plane section is parallel to bedding.
27
especially if the vitrinite band is very thin or has an irregular upper
or lower surface.
An alternative is to measure the nean maximum reflectance values
(Rjmax) of vitrinite in each of a series of differently oriented
vertical sections from the one sample. Such R max values could then be
related to the elliptical ab plane (Fig. 2.2b) of the negative biaxial
indicating surface. By using the R^nax values, and the azimuth of the
vertical sections, the shape and orientation of the ellipse which lies
very close to the ab plane is defined. This ellipse, representing the
strain ellipse formed by stress active diaring coalification is called
the ^Calculated BecMing Plane Surface of the Indicating Surface' or
CBPSIS.
Strictly speaking if the vitrinites are biaxial a vertical section not
parallel to the b axis (Fig. 2.2b) cannot contain a true R max. Its o
maximum reflectance lies between R max and R int. Therefore a mean o o
maximum ref lec tance (R max) coiild not be obtained from a ve r t i ca l o
section of biaxial vitrinite as it would from a uniaxial vitrinite.
Hevia and Virgos (1977) recognised the invalidity of using R max for
sections normal to bedding in biaxial s\±>stances. Kilby (1988) agreed
and suggested the term apparent maximum reflectance be tised for biaxial
vitrinites.
The terminology R max will be retained in this thesis. It is a
recognised term indicating the average value of maximum reflectance
measured from any sample, including vertical sections. The true maximum
reflectance is designated by R max.
28
Precise definition of the shape of the CBPSIS would require a large
number of vertical sections to be measured. It is more practical to
measure a limited number of oriented vertical sections and to calculate
the orientation of the R max (the procedure is outlined in i^pendix A).
Three vectors are able to define an ellipse located at an arbitrary
origin. The azimuth and R max value of three vertical sections are the
vectors \ised in this stucty.
All the combinations of three vertical sections are then used to define
a number of ellipses \^ose major and minor axes (equivalent to the
R max and the minimum reflectance in the bedding plane, or intermediate
reflectance (R int), respectively), aziimiths of the major axes, and
2
eccentricities can be determined. Both X ard Rayleigh tests of
significance were used on the major axis direction of each calculated
ellip)se to determine if it were randomly or non-randcmly distributed
about the mean, and appropriate limits of significance were designated.
The small sairple size of ellip»se calculations puts restrictions on the
2 2
validity of the significance of the X tests. The X test can be
insensitive, especially for low sairple sizes, but the Rayleigh test is
not applicable for small sairple sizes (n>5). Consequently for sanples 2
with n<6 significance levels are defined by the X test in the absence 2
of a more rigorous method of evaluation. The X test value is reported in tables of results.
A high degree of significance (or non-random distribution) for the
CBPSIS R max direction indicates that the R max values of each vertical
section forms a smoothly elliptical CBPSIS figure. Calculated ellipse
orientations vhich have a random distribution nay be due to:
29
(a) measirranent errors; (b) measurement of a uniaxial vitrinite; (c)
measurement of a sample v iich has neither a circular nor elliptical
CBPSIS; (d) or a combination of these factors.
The method of obtaining CBPSIS orientations was modified during the
study. Initially from each oriented coal sanple collected, four
polished sections, cut normal to bedding in known orientations, were
prepared for incident light coal microscopy. Later, six oriented
vertical sections were used from each sanple for two reasons. Firstly,
CBPSIS figures could be drawn in more detail from the raw data, and
secondly, more combinations (20) of three sections could be calculated
from six sections, giving a statistically better R max value.
Reflectance measurements were taken at 545nm in oil of refractive index
1.518 at 23°C using a flourite lens of numerical aperture 0.95. Thirty
maximum reflectance measurements v^re made on each section to determine
the R max. The arithmetic mean and the standard deviation were o
calculated for the vitrinite reflectance in each section. Measurements
were made on band vitrinite - that is, vitrinite A occurring in
relatively massive layers (O.lnin to lOmm in thickness) which do not
contain inclusions of other macerals or minerals (Brown et al., 1964).
The sane band of vitrinite was measured in each section of the specimen
in order to minimise reflectance variability caused by interband
maceral variation. To eliminate operator bias toward any particiiLar
coal block orientation each block was measured without knowledge of its
direction relative to north, this latter data being kept in a separate
file.
30
2.3.3 STUDY AREAS
In choosing a set of study areas to test the biaxial characteristics,
if any, of vitrinite a nvunber of considerations were important.
Definition of the regional stress field is best established away from
the zone of influence of the strain field developed around any tectonic
or structural feature or features (e.g. nonral faults, strike-slip
faults, joint zones). However, the range of the field of influence
from any structure is unknown.
(Dne approach to this problem is to sanple away from an isolated
structure until it can be reasonably determined if the regional strain
is being measured. The above rationale was used in selecting the study
sites. FaiiLts are an inportant structvire in the Southern Coalfield
with respect to their influence on coal mining. Their frequency of
occurrence, accessibility and relative ease of definition make them
ideal features around vdiich to stixiy any variation of the biaxial
characteristics of vitrinite. A demonstration of the resiiLts, obtained
via this vitrinite reflectance technique, and a girlde to its
applicability are given in this chapter for two faults from the Coal
Cliff Colliery (Fig. 2.3). Further, and more detailed, investigations
using this technique are provided in later chapters.
2.3.4 SAMPLE SCHEME
In the Coal Cliff Colliery, located in the Southern Coalfield, Sydney
Basin, New South Wales, two normal faults were investigated (Fig. 2.3).
They are the Flatrock Fault and the Scarborough Fault, chosen because
they were as distant as possible from other known tectonic structures.
The Scarborough Fault is a growth faiiLt (Ocamb, 1961) with a throw of
55m and dips between 50-60° NE. At different sites along its leigth it
31
SAMPLING AREA
MINE WORKINGS
UNMINED AREA
FAULT
SYDNEY BASIN
SOUTHERN COALFIELD i^^SYDNEY
OLLONGONG
STUDY AREA
WOLLONGONG
Fig. 2.3 Location plan of sampling traverses around the Scarborough
and Flatrock Faults, Coal Cliff Colliery.
32
consists of from one to three fracture planes. The throw of the fault
decreases vertically so that in the Late Triassic sequence movement was
greatly reduced. On the downthrow side of the fault the Bulli Seam is
thicker due to additional plies at the top of the coal - further
evidence of the contenporaneous nature of the faulting. The Flatrock
FaiiLt has a throw of 8m and forms the eastern-most fault in a 400m wide
zone of faults trending approximately north-south. The fault plane
dips at 66° W and slickensides on the fault plane suggest that at seme
stage a minor corponent of strike-slip movement occurred.
Preliminary work suggested that R max orientations were more likely to
vary close to the faiilt. Therefore, sanple spacing decreased toward
each fault, although sanple site choice was restricted by mine layout
and safety conditions. For the Flatrock FaiiLt sanples were collected
in a traverse (Traverse 1) approaching the fault on the upthrow side.
Sanpling traverses were conducted on both the upthrow side (Traverse 2)
and the downthrow side (Traverse 3) of the Scarborough Fault. All
sanples contained vitrinite and were taken from plies in the middle of
the coal seam.
2.3.5 RESULTS
2.3.5.1 Calculated and Ifeasured Reflectanoe
To give a more coiplete set of data regarding reflectance in this
area of the coalfield the bireflectanoe (R max - R min) is given o o ^
for a set of oriented sanples taken in a fault zone frcm 410 Panel
in Coal Cliff Colliery. Results (Table 2.2) show that the
biref lectanoe (using R max as the largest Rjiax measured) varied
between 0.18% to 0.32%. Apart from background data, the Rjnin was
33
not measured for all the sanples in this thesis because it
appeared unable to provide infonration about lateral strain.
The calculated R^max is used to define the true reflectance of the
sanple because the largest measured R max value from a series of
vertical sections fron any one sanple may not be the true R max.
Cne possible difficulty in this procedure is the presence of
irregularly shaped CBPSIS figures causing the calculated R max to
be out of proportion to the measured R max values. (Generally,
calculated R max values are either equal to, or within 0.03%, of
the largest measured R max value. The calculated R max is
o o disregarded and the measured R max is used as an estimate of the
true R max if R max exceeds the highest R max by 0.03%. o o ^ o -
Vitrinite R max's measured on vertical sections from around the o
two faults range from 1.29% to 1.47% (Table 2.3, columns c and d)
- that is, within the category of medium volatile bituminous coal.
Measured R max values listed in column d are the lowest measured o
for the sanple and are therefore an estimate of the intermediate
reflectance (R int). Just as the calculated R nax is determined o o
for each sanple, so too is a calculated R^int. The difference
between these two values is used to determine the CBPSIS
biref lectanoe (calculated R max minus calculated R^int). CBPSIS
o o
biref lectanoe values are generally small (Table 2.3, column g).
^proximately half of the calculated CBPSIS biref lectances are
0.04% or less. Therefore, from reflectance values alone it is
difficult to be certain that the calculated CBPSIS biref lectances
do actually represent biaxiality of vitrinite.
34
TABLE 2.2
R max's and Rmin's from 410 Panel Coal Cliff Colliery -tD o ^^ — ^
Sairple
102
103A
104
105
106
107
R max o
lyfeasured
1.28
1.26
1.31
1.42
1.34
1.35
R min o
Measured
1.04
1.08
1.06
1.10
1.05
1.04
Biref lectanoe
(R max -•• o
- R min) ' • • o •
0.24
0.18
0.25
0.32
0.29
0.31
2.3.5.2 Random and Non-Random R.itex Orientations o
Orientations of calculated R max directions for vitrinites frcm o
the two faults, together with their statistical significance, are
given in Table 2.3, columns i, j and k. Approxinately fifty
percent of the CBPSIS figures from these two faults were
statistically non-random. A CBPSIS, however, does need to plot as
a relatively smooth ellipse in order to give a statistically
significant R max direction if the biref lectanoe in that plane is
low.
The results in these tables show that the degree of significance
of the calculated R max orientation is not necessarily related to
the CBPSIS biref lectanoe (Fig. 2.4). Therefore, a large CBPSIS
bireflectance is not necessarily associated with a significant
R max orientation, o
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36
5 r
LU 0-1
< >
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•01 -
•001 -=0= L _L X J_ J • 02 04 -06 '08 -10 12
CBPSIS BIREFLECTANCE
Fig. 2.4 CBPSIS bireflectance is not a guide to the statistical
significance of R max orientation. Statistically
significant R max at p<0.1 are indicated with a horizontal
2 bar (refer to Table 2.2). Open circle has a X value of
1.90 X 10"^.
37
By comparing CBPSIS figures drawn from the reflectance data of
each measured section it was found that most randomly oriented
Rjnax's were derived frcm irregularly shaped CBPSIS's. In a later
chapter it will be shown that CBPSIS shapes are of equal
iirportance to R max orientations in determining strain directions.
2.3.5.3 R_max Orientations —o
On sanpling traverses 1 and 3, from the Flatrock and Scarborough
Faults respectively, the orientation of the statistically
significant R max directions change as the fault is approached
(Figs 2.5 and 2.6). Furthermore, there is some similarity in the
pattern of variation in significant R max orientation towards the
fault on both traverses.
The angular relationship between the fault direction and the
significant R max orientation best distinguishes this pattern.
The non-random R max orientations developed farthest from both
faults (i.e. sanples 123 and 238) are oriented within 25° of the
fault direction. For ease of reference, sanples with this angular
difference will be called Type 1 Rjrax orientations. Towards the
faults the next substantial change in orientation is shown by
sanples 120 and 236 which have an Rjrax direction greater than 60°
from the fault direction (Type 2 R^max orientations).
Imrediately adjacent to both faults Rjnax orientations are within
35° of the fault direction (i.e. sanples 118, 214 and 217) (Type
3 R max orientations). Sample 119 appears to be transitional with o
the above angular relationships. The distance that each 'type' of
38
R max orientation occurs, both along each traverse and from each
fault, is variable for the two faults.
UsefiiL information nay be provided by the shape of CBPSIS figures
even if their R max orientation is not significant. For exanple, o
the change of R max orientations between sanples 123 and 120 is
shown to be gradational by the CBPSIS figures (Fig. 2.5). That
is, the N-S trending elongation of the CBPSIS of sanple 123
gradually overprinted an E-W trending corponent which becomes
dominant at sanple 120. Oi this basis it is likely that there may
be sone gradational j^se between adjacoit areas of different
R max orientation types.
The length of traverse 2 toward the Scarborough Fault (Fig. 2.6)
was limited by inaccessible mine workings. Traverse 2 has only
two significant R max orientations, both of v^ch have Type 2
R max orientations relative to the fault. Closer to the fault, o
sanples 212 and 213 have directional (ZBPSIS elongations related to
Type 3 R max orientations. This is consistent with the Type 3
R max orientations of Traverses 1 and 3 v iich also occur adjacent
to the faults.
2.3.5.4 Replicaticxi Measurements
To support the above results a series of replication measurements
were made on sanples from two previously sampled sites whose R max
orientations were different (Flatrock Fault - sanple sites 119 and
123) to determine the possible variability of the Rjnax value and
orientation within and between different vitrinite bands. At
sanple sites 119 and 123 four oriented blocks were taken from
39 LU
m
z o < H Z UJ CC
o X CD E o
oc
O O z < oc z o z
z o p z UJ cc o X (0 E o
oc
o o z < oc
10
UJ
cc
w Q.
u
LU 1 CC
o V) UJ
z
X < cc o u. UJ -I < u
Fig. 2.5 Development of strain in vitrinite on the upthrow side of
the Flatrock Fault. Non-random R max orientations have o
PKO.10. The axial lines of the CBPSIS figures represent
the orientation of sections normal to bedding and their
lengths are related to their reflectance value about the
centre (1.31% reflectance).
236
-A CO
r M G
EN
D
UJ -J
BE
R
s Z
O z <
TIO
N
LO
CA
UJ -J 0.
S < (0
z
ATI
O
h-
z UJ
o K (0 E 0
oc
MD
OM
< oc
z o z
z
ATI
O
K-Z UJ £ o X (0
E 0
oc o o z < QC
UJ O
TR
A
$ O
PTH
R
UJ O < oc
o oc z
OW
NT
=5 Q
1 1
u.
3 < U.
U.
UJ er
FIG
UI
w w 0. CQ
a
CN 6" •
-1 u. UJ
oc O O'*
U) UJ
z _J
XIA
L
E
FOR
A
-J < O (/)
o lOi
o o
10
Fig. 2.6 Development of strain in vitrinite around the Scarborough
Fault. Non-random R max orientations have IKO.IO. The o ^
axial lines of the CBPSIS figures represent normal to
bedding section orientations and their lengths are related
to the reflectance value about the centre (1.27% reflectance).
41
different seam heights. A set of four oriented polished secUons
cut normal to bedding were made from three of the sanpled blocks
and at least six sets of four oriented vertical polished sections
containing the one vitrinite band were made from the fourth block.
The results of the replication measurarent are given in Table 2.4.
The non-random Rjrax orientations of sanples from different seam
heights show a degree of consistency at both sanple sites (Fig.
2.7). An exception is the result for sanple 245 which is the
vector mean of six sets of R max orientations from the same o
vitrinite ply (Fig. 2.8). In contrast, five sets of non-randcm
R max orientations from sanple 240 (Fig. 2.8), also from the one
vitrinite ply, have a vector mean trend which is consistent with
that of other sanples from sanple site 119. Except for the sets
of sanple 245, R max orientations at the one sanple site have a
similar trend both within and between vitrinite bands.
By using four sets, each having sections with the sane
orientations, from one vitrinite band at one sanple site, sixteen
oriented sections can be used to determine an R^max orientation
instead of the four normally used. Sets 240-1,2,3,4 and
245-1,2,3,4 were chosen and by using section R^max and orientation
values in ccmbinations of three, parameters of 256 CBPSIS's v^re
obtained at each of the two sites. For sanple 240 the result
(Fig. 2.9) is in accord with the general trend at that location,
but for sanple 245 the R max distribution (Fig. 2.9), in addition
to a N-S subset had its main trend approximately 50° away from the
trend defined in Fig. 2.7 by sanple 123. The vector mean R^max
orientations obtained in the above manner were statistically
42
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43
non-random for both sanples 240 and 245 (Table 2.4, columns i and
k).
2.3.5.5 Reflectance Measurements in the Bedding Plane
The usual technique for determining the R max direction of
vitrinite for this thesis is from polished sections of vitrinite
cut normal to the bedding. Sanple 119 also had a polished block
oriented parallel to the bedding prepared and neasured to
determine the R max direction, o
Cook e t a l . (1972a) found tha t the R itax occurred a t a sna i l o
angle to bedding. "Rjnax" determined from becMing plane sections
would probably not be the true R nax. The beciiing plane secrtion
from sanple 119 is reported to show the cxarparison of measurerents
made by both methods.
The beclding plane secrtion was prepared so that one edge of the
polished block had a known azimuth. The angular relationship with
the polarizer (set at 45°) and the edge of the polished block was
then determined. Therefore, rotation of the microscope stage to
the position of maximum reflectance could be translated to define
the azintith of the R max measured at that point. In acMition to
defining the position of the R max, reflectance measurements were
made at each 10° of stage rotation at twelve different points so
that the indicating figure of the bedding plane section could be
cxjnstructed. The average of the twelve reflectance measurements
for each 10° interval was used to define the indicating surface
for sanple 119 (Fig. 2.10).
44
Fig. 2.7 Non-random R max orientations (p<0.10) of sanples from
different heights within the seam at sanple site localities
119 and 123 (Table 2.4). Original R max orientations of
sanples 119 and 123 (Table 2.3) are included for
corrparison. Sanples 240 and 245 represent vector mean
R max orientations of their respective subsets with
non-random CBPSIS's.
Fig- 2.8 Non-random R^max orientations (pKO.lO), of subsets (frcm
one vitrinite band) frcm sanples 240 and 245 which c:ane
from sanple sites 119 and 124 respectively (Table 2.4).
Numbers on Rjtax orientation lines indicate each subset.
45
SITE SITE
119 123
A
SITE 119
SITE 123
sample 240 sample 245
46
A ri
245: 1-4
240: 1-4
Fig. 2.9 R max direcrtions calculated from the sixteen oriented
sections normal to bedding of four subsets (from the one
vitrinite band), for samples 240 and 245. Each histogram
represents 256 R nax direcrtions.
47
Fig. 2.10 CBPSIS figure for sanple 119 constructed frcm measurements
taken on a bedding plane section. The original R max
orientation of sanple 119 is marked. Centre of CBPSIS
figure equals 1.29% reflectance.
48
The indicating figure measured frcm the bedding plane section
(sanple 119) gives a similar R max direction to the CBPSIS
constructed from four sections cut normal to bedding (Fig. 2.5).
The R max frcm the bedding plane section is 1.36% oriented 030°
and the R int is 1.31%. The calculated R^max of sanple 119 is o o
1.41% oriented 040° and the R^int is 1.30%.
The bedding plane section method appears to give a reasonable
comparison with the CBPSIS figure and may be developed as a
reliable alternative with a more thorough understanding of the
subject. However, at this stage of knowledge of biaxial
vitrinite, it is thought that using sections cut normal to bedding
provides the surest forum for investigation.
2.3.6 nmERPRETATICM AND DISCOSSICM OF RESULTS
Further exanples of the response of vitrinite to stress, in various
geological environments, are given in later chapters. In this section
it is appropriate to discuss the results so far presented and to
develop a basis upon v^ch further work may be analysed.
2.3.6.1 Driiaxial or Biaxial Vitrinites?
Corrpared to anthracites (e.g. Cook et al., 1972b) the sanples from
this stuciy of the two fault areas have only slight calculated
biaxial character in the bedding plane section (i.e. bireflectance
of between 0.02% and 0.05%). It is conceivable that some of this
biaxiality might be explained by the statistical error in the
reflectance measurements (standard deviatican ranging from 0.01% -
0.02%). To detemdne vdiether vitrinites used in this study have
biaxial properties it is first useful to assume, vhat is now
49
conventionally accepted, that vitrinite is optically uniaxial in
character. Therefore, R^max measured in each section nomal to
bedding shoiiLd be equal. If the Rjaax values neasured were not
equal, due perhaps to some feature such as operator error, machine
error or maceral variation, then the results should still give a
CBPSIS figure vdiich had a randomly oriented R max. This is not
strictly true, however, because a number of CBPSIS determinations
may by chance give non-random R max orientations. For the 43
results reported around the two faults mentioned above (including
replication results) 27 liave non-random R max orientations (63%).
It would appear that the non-random R max orientations of the o
vitrinites studied are probably not chance results from uniaxial
vitrinites. Furthermore, the bireflecrtance measured (up to 0.11%)
are unlikely to be due to randcan measurements or uniaxial
vitrinites on the basis of the stanciard deviation of measurements.
Another explanation for consistent non-uniaxial behaviour by
vitrinites may be due to natural plant anisotropy. Rjrax
orientations in this circumstance should be randomly distributed
and similar patterns, as developed around the Scarborough and
Flatrock Faults, would be unlikely to occur by chance as would
consistency in the replication measuronents. It is concluded that
although the biaxiality of the vitrinites is snail, the C3PSIS of
nost sanples could be a significant measure of strain rather than
arising from artefacts of measurement error, or being relict
natural anisotropy of the original plant material.
50
2.3.6.2 Reflectance in the Vicinity of Faulting
The cjuestion of rank increase in the vicinity of faulting has, at
thiis stage, not been answered conclusively in the literature.
TeichmLiller and Teichmuller (1966) showed evidence of a rank
increase from the Sutan overthrusts. They attributed shearing
movenents or frictional heat, or a cxanbination of both as cause of
the rank increase. Unless there is an intense release of strain
energy accompanying faulting, Teichmuller and Teichmuller (1975)
proposed that frictional heat is norirally able to cilssipate
without having any effect on the coal. Taylor (1979), reported
that there was no rank increase associated with localised
irylonitisation of the Bowen Seam in the Bowen Basin.
The difference between 'background' R max values and 'fault
influenced' R max values is only snail in the Southern Coalfield o •'
and therefore may be masked by factors such as maceral variation,
vitrinite band thickness, vertical position of the sanple in the
coal seam, and natural rank increase with depth on the more
steeply dljping hanging wall strata adjacent to the fault (e.g.
Sc arborough Fault). Qi the hanging wall of the Scarborough fault
there is a 0.10% ref lecrtance increase down-dip toward the fault.
Expected downhole reflectance gradient values of 0.05%/lOOm (Cook,
1975) and 0.07%/lOOm (Diessel, 1973) for the Sydney Basin account
for 0.03% of this reflectance increase on the hanging wall. Data
in Table 2.4 show that higher R max values occur lower in the coal
seam which is in agreement with the results of Jones et al.
(1972). R max values of sanples determined frcm particulate
blocks (made frcm a representative sanple of the full seam) around
the Scarborough Fault (Table 2.2 Column 1) show the sane general
51
reflectance increase tcfward the fault as do R max values frcm
individual plies.
However the sanple nearest the fault has a lower relative R max o
than ejqjected from the R^max value trend (Fig. 2.11). R max o ^ o
trends frcm the Flatrock Fault also support the increase in
reflectance noted at the Scarborough Fault. Much more work is
recjuired to be done to determine the paraneters vhich would
control a rank increase adjacent to faulting. In partic:ular it is
relevant to determine if there is a zone of relatively depressed
reflectance caused by a localised pressure build up prior to
faulting, and if frictional heat subsecjuent to brittle failure is
intense enough to increase the coal rank in that vicinity.
Pressure is a well documented inhibitor of chemical coalification
(Huck and Patteisky, 1964; Teichmuller and Teichmuller 1968; and
McTavish 1978).
2.3.6.3 Molecular Structure in Biaxial Vitrinite
The reflectance properties of coals (including maximum
reflectance, bireflectance and bedding plane bireflectance) are
dependent on both the chemical properties and physical structure
of the coal. Vitrinite reflectance increases with an increase of
arcmatisation of the humin 'molecules' of vitrinite (Teichmuller
and Tteichmuller, 1975). The nature of the chemical and physical
properties of vitrinite are discussed briefly. Both van Krevelan
(1961) and Stach et al. (1975) have detailed reviews of this
subject.
"Vitrinite is corposed of various humins vMch consist of an
aromatic nucleus surrounded by peripheral alij^tic groups. With
52
1.47 r
1.45
1.43 UJ
O z u y 1.41 u. UJ OC 3?
1.39
1.37
R max (SF) o
R max (FF)
I
R max (SF) •• o
100 200 300
DISTANCE FROM FAULT (m)
400
Fig. 2.11 Relationship of R max and R max ccmpared to distance from
the Scarborough Fault (SF) and the R max ccmpared to distance from the
Flatrock Fault (FF).
53
increasing rank the peripheral groups (CH, COCH, CH^) are lost and
the arcmatic nuclei become larger." (Stach et al., 1975, p.67).
Coal, including vitrinite, is a non-crystalline substance
(turbostratic) which has arcmatic crystalline entities, or
crystallites, immersed in an amorphous 'cenent'. The crystallites
consist of stacks of flat polyarcmatic lamellae vhose ordering and
size increase with increasing rank. The relative parallelism of
the arcmatic stacks also increases with rank and is attributed to
pressure loading - normally parallel to becMing in flat lying
strata.
Hirsch (1954) cx)nsidered coals could be grouped into three
categories based on their structure and rank. Below 85% carbon
they have randomly oriented lamellae, between 85% to 91% carbon
there is sore lamellae orientation and above 91% carbon a greatly
increased lamellae orientation exists.
Funcianental to the cjuestion of beckling plane bireflectance is the
manner of lamallae orientation in coal and the in situ geological
history. Background information regarding optical anisotropy, the
influence of pressure and tesiperature and the mechanics of
molecular alignment are worthy of brief discussion.
The main anisotropy v iich forms in vitrinite is noticed optically
as bireflectance and is due to a preferred orientation of planar
arcxratic ccmplexes. Normally such preferred orientation occurs in
the beciding plane in response to load pressure frcm overburden and
increases with rank (Stach et al., 1975). Stach et al. (1975)
54
indicated that the anisotropy was not a measure of rank, which was
confirmed ioy Pfower and Davis (1981a) who correlated it with depth
of burial. The optical anisotropy is predominantly physically
conditioned (Teichmuller, 1975) and is not a feature dependent on
chemical coalification. It has been recorded that increases of
rank without pressure increase leaves the anisotropy unaltered
(Chandra, 1965a).
Clearly reflectance is not a measure of the degree of alignment of
the arcmatic lamellae as is bireflectance. Deformation ((3iosh,
1970) and an increase in density (Ergun and McCartney, 1960) have
been reported to increase vitrinite reflectance presumably without
alteration of chemistry. Shear zones have caused the localised
increase of bireflectance (Teichmuller, 1975). Much further work
remsdns to cjuantify rank, temperature and pressure conditions
where pressure is able to change reflectance paraneters without
affecrting arcmaticity.
(aenerally coalification proceeds under the dominant influences of
time and temperature but is also subject to the effecrts of
pressure (Teichmoller and Teichmuller, 1975, p.42). In this
context the chemical rank increases with the jiiysical alignnent of
the arcmatics into the plane of beckling due to overburden
pressure. To ascertain if both pressure and temperature are
necessary to recxsrd biaxial optical anisotropy in vitrinite,
studies of the dominant effecrt of either are discussed.
The effect of teirperature on raising vitrinite reflectance is well
shown by studies of contact metamori^iism adjacent to an igneous
55
intrusion (Chandra and Taylor, 1975). Results of studies of
vitrinite reflectance for cxoals of the same chanical rank
suggested that a thermally altered coal will have a higher
ref lecrtance than an unaltered coal (Chandra, 1963).
The influence of pressure on chemical rank is carplex, sore
studies have shown that pressure retards coalification (Davis and
Spackman, 1964; Bostick, 1973) v>hereas Oiosh (1970) indicated that
deformation was able to increase reflectance without an increase
of chemical rank. Similarly Huntjens and van Krevelan (1954)
noted that coal with the sane rank (based on proximate and
ultimate analysis) but having slightly different physical
structures may have a range of reflectance. Experimentally
Chandra (1965a, b) recorded that pressure (4Kb at 350°C) may
increase vitrinite reflectance. However studies showing isorank
lines parallel to bedding in folded secjuences indicate that the
post-ccalif ication tecrtonic stresses are unable to change the rank
(Teichmuller, 1975). The effect of pressure is seen in other
ways, for exanple:
(i) producing anomalously low moisture content in a low rank cxal
(Berkowitz and Schein, 1952);
(ii) reorientation of vitrinite anisotropy frcm parallel to
bedding into an oblicjue position by fold pressure
(Petrascheck, 1954; Hower and Davis, 1981b)
In view of scare of these exanples Teichmuller and Teichmuller
(1975, p. 47) comrrent that: "No doubt the anisotropy of
56
vitrinite is a result of orientation of micelles
perpendicular to the direction of pressure".
If the polyarcmatic entities are oriented by pressure, what models
exist to explain the nechanisms of this ordering? Bonijoly et al.
(1982) proposed a model for the development of anisotropy in
planar arcmatic ring structures. A model of crumpled sheets of
paper is used whereby air spaces between the sheets are
representative of microscopic pores within the coal (formed by the
escaping gases) and the aromatic layers form as separate stacks
sub-parallel to the pore surface. Over an area containing many
large non-aligned pores there would be an essentially random
alignnent of arcmatic layers. Pore space is reduced fcy compaction
and there is an increase in the alignment of the separate groups
of arcmatic stacks. An alternative view was expressed by Spiro
(1981) on the basis of a viable space filling model of coal
molecules. Spiro (1981) developed a mechanism for the development
of plasticity during themal decxmposition \*dch is generally
agreed to follow the sane trend as coalification (van Krevelan,
1961). In Spiro's mcdel alijiiatic, alicyclic and hydroaromatic
groups, vhen split off from the flat arcrratic planes, form spacers
and lubricants for the mcfvement of those sub-parallel arcmatic
planes.
Overburden pressure applied to coal during basin subsidence acts
essentially vertically and the main anisotropy produced is
parallel to the becMing plane (or normal to the applied pressure)
(Teichmuller and Teichmuller, 1975). It is proposed that lateral
stresses will produce anisotropy in the beckiing plane. The
57
maximum reflectance of the biaxial vitrinite would develop nomal
to the principal lateral, stress direction (Stone and Cook, 1979),
Statistically non-random Rjiax orientations provide information of
the maximum lateral strain direction frcm v iich the principal
lateral st:ress direction may be inferred.
Hower and Davis (1981b) reported that the orientation of the
maxirrum reflectance was:
(a) normal to the greatest tectonic stress; and
(b) together with the intermediate ref lecrtance, fomed a plane
parallel to the axial plane of the fold from v rlch the
samples v^re taken.
Some experimental evidence of high cxjnfining pressure and
temperature being able to reorient the R max direction in the
plane of the beckiing has been provided for anthracites (Bustin et
al., 1986). Bustin and cxo-workers ware able to increase the rank
in conjunction with reorienting the CBPSIS but were unable to
confirm if there was an accompanying increase of arcmaticity and
size of arcmatic clusters. Clearly further work is recjuired
before the conditions of burial history and the coalification path
of lower rank cxals can be reproduced with respect to the
reflectance indicating surfac:e.
Asyntretric growth of the polyarcmatic layers in coal may be
caiparable to the growth of minerals in a triaxial stress field.
It is suggested that the maximum growth rate occurs normal to o.^
in the direction of lowest potentJ.al energy (Dumey, 1976).
58
2.3.6.4 Strain Overprinting in Vitrinite
If it can be assumed that the biaxial properties of vitrinite are
real and not just neasuraient errors or natural artefacts then the
measured reflectance peaJcs in CBPSIS's represent strain in that
direction. The work of Bustin et al. (1986) cxonfirmed that the
R max orientation could be altered experimentally with temperature
and pressure. Also, if the configuration of the strain gives a
smooth elliptical CBPSIS figure it is likely that a statistically
significant R max orientation exists. In nany CBPSIS figures
there may be at least two reflectance peaks, and from the
prec:eding assunptions these may represent the overprinting of two
separate strain events. If overprinting is complete then the
CBPSIS has only one reflectance peak (e.g. samples 123 to 120,
Fig. 2.5).
Figure 2.12 demonstrates a simplified exanple of overprinting an
existing strain by a 90° change in the lateral stress field
cilrection. It follows that the maximum reflectance value of the
old strain direction will tend, upon further coalification,
towards the intermediate reflectance value of the reoriented
strain direction.
Therefore, in sanples with the sane coalificaticm history,
vitrinite subjected to changes in strain direcrtion will have a
smaller CBPSIS bireflectance than vitrinite which had a constant
strain direction. As a corollary, given an area with only one
strain j^se, the vitrinite with the highest R max will have the
greatest CBPSIS bireflectance. For the two faults studied there
is only a weak positive correlation between R max and CBPSIS
59
STAGE 1
t
"max Rjnt
STAGE 2 STAGE 3
i:ig_^J^ Schematic representation of a 90° shift in the lateral
stress field direction (arrow) and its effect on Rmax
orientation.
•02 04 06 08 -10 .^2 C B P S I S BIREFLECTANCE
Fig. 2.13 Relationship between R max and CBPSIS bireflectance for
sanples around both the Flatrock and Scarfxorough Faults.
Line of best fit: y = 1.37 + 0.68x (r^ = 0.27).
60
bireflectance (Fig. 2.13). This would indicate that some CBPSIS
figures demonstrate effects of strain reorientation.
Replication neasurements at sanple site 123 have a range of R^max
orientations (Figs 2.7 and 2.8) including some vAiich are similar
to those developed in sanples more proxinal to the fault. This
may suggest that overprinting of strain is not only a gradational
process but that it may not be homogenous at hand specimen scale.
Bustin et al. (1986) also refer to inhomogeneity of overprinting
frcm experinental reorienting of the reflectance indicating
surface.
With acrtive coalification occurring, reorientation of strain
direction may be recorded by the asynmetric growth of the
polyarcmatic micelles in the new strain dlrecrtion rather than by
mechanical deformation of the existing micelles. Therefore
CBPSIS's with a randomly oriented R max direction may still
provide useful information by the number and orientation of their
reflectance peaks. The accuracy of defining exact strain
directions may be limited by the azimuth and number of sections
used to define the CBPSIS. If the number of different CBPSIS
determinations is large enough this limitation may be overxxme. A
limit on the number of sections used will be decided largely on a
practic:al viewpoint. After coalification is completed, it is not
certain if the bedding plane anisotropy is affecrted by subsecjuent
tectonic events. It is unlikely that the rank is increased but
there may be seme minor reorientatican of the polyarcmatic layers
in the beciding plane. This may be sufficient to be recorded as a
change in the shape of the CBPSIS. No answer to this problem will
61
be achieved until detailed experimental neasurenents are
completed. Bustin et _ al. (1986) was able to achieve a
reorientation of the CBPSIS using high cxDnfining pressure and
temperature with anthracites but further work is necessary to
extrapolate these findings to lower rank cxoals.
Research on the viscoelastic behaviour of coal has indicated a
similarity between creep behaviour in cxal and synthetic
macrcmolecular networks (Howell and Pejpas, 1987). They noted
that the increase in ccaipressive strain at the end of each episode
of cyclic loading was attributed to "densification of the cross
linked cxal structure". However creep behaviour or the retention
of permanent strain was inproved at higher temperatures, toward
the "glass transition teirperature" (Howell and Pejpas, 1987) of
350°C (approximately), vdiere the crosslinking is more easily
modified than at lower tenperatures.
2.3.6.5 Flatrock and Scarborout^ Faults - CBPSIS
Interpretation
In this section a set of stress regimes, some of localised extent,
is attributed to explain the pattern of R max orientations about
the Flatrock and Scarborough Faiilts. Prior to normal faulting the
maximum lateral stress in the vicinity of the fault would,
theoretically, be parallel to the strike of the fault (Hobbs et
al., 1976). Raleigh (1974) presented supporting data from in situ
neasurements in the vicinity of a normal fault. For the
Scarborough and Flatrock Faults Type 2 R^max orientations
correspond to this stress dlrecrtion being oriented greater than
62
60° to the fault direction (remanbering that non-random R max
orientations are oriented normal to the maximum lateral stress).
Type 3 R max orientations overprint the Type 2 R max orientation,
and are probably related to a post-failure stress reorientation
similar to that proposed by Price (1974). Price gave a
theoretical assessment of stress patterns in an undefomed
sedimentary basin. He suggested that with stress relief after
brittle failure, the direction of least lateral conpressive stress
becomes the principal horizontal coipressive stress direction.
The Type 3 R nax orientation is restricted to the immediate ^^ o
vicinity of the faulting. For these two faults Type 1 R max
orientations do not appear to be related to the faulting, and are
probably associated with a stress regime developed on a more
regional scale. A study of the far-field stress is developed in
follcjwing chapters.
2.3.7 FURTHER APPLJCATICWS OF THE CBPSIS
The use of the optical indicating surface of vitrinite appears to be a
method of gaining information about part of the strain history for an
area. Ideally individual strain events might be explained frcm CBPSIS
figures giving a corplete stress history. Many difficulties obstruct
this proposition in respect of CBPSIS figures, not least of \diich is
deciding up to which stage in the coalification history can strain be
inparted into the vitrinite.
Both physiochemical and mechanical processes might be envisaged forming
asymmetrical growth in the molecular structure of the vitrinite. But
if mechanical processes are found to be a corponent, then strains
63
developed after the nain coalification jtese, and in the absence of a
temperature increase, may be imprinted in vitrinite. Answers to these
questions cannot be put forward on the basis of information frcm the
Scarborough and Flatrock Faults. Following chapters in addition to
investigating the broader relationships of CBPSIS's and roof stability
factors show exanples v iich provide evidence and further cjuestions as
to the nature of CBPSIS's.
CBPSIS's liJce those frcm the Scarborough and Flatrocdc Faults do provide
a picture of relative stiain events, although not the total strain
history. In the siirpler tectonic areas many c3ata points would be
needed to build up a corplete strain picture even if the method used
(e.g. CBPSIS's) was fully understocxi. The value of CBPSIS's does
appear to be in the comparison of results from adjacent sanple points.
Coal seams generally having a continuous nature and accessible from
surface mining, underground mining or boreholes provide an ideal
setting for sanpling to define relative changes in the orientation of
the lateral strain field. Case studies in following chapters will
further investigate the relation of local and regional CBPSIS's,
showing the iirportance of their differentiation for the successful
amplication of this technicjue.
64
2.4 POINT-IOAD FRACTURE ORIENTATICKS
2 . 4 . 1 iwmoDUC?ncM
The point-load method is a siiiple technicjue for determining the tensile
strength of a rock sanple. It involves loading a rock between two
aligned points until fracture occurs. The load applied is used to
calculate the point-load strength index v*dch is a ratio of the applied
load P to the square of the distance D between the two loading points
(Bieniawski, 1975). The relationship between the point-load index and
the uniaxial strength of the rock have been established for certain
sanple size specifications (Bieniawski, 1975). Brcxrh and Franklin
(1972) gave a detailed account of the methods and stardard testing
procedure for the point-load strength test.
Another application of the point-load test is to determine the
existence of any preferred tensile fracture direction in oriented
sanples. Apart from a preferred parting of sediments parallel to
bedding, tensile fractures commonly have a non-random distribution vhen
the rock sanple is loaded normal to bedding (Friecirran and Bur, 1974).
Fracture anisotropy in a rock is reliably gained by the point-load test
(Peng, 1976) and would develop normal to the direction of minimum
tensile strength in the plane normal to the load axis (Frieciman and
Logan, 1970).
Reik and Currie (1974) reported that "Paulman (1966) demonstrated that
for an isotropic concrete aggregate corposed of c«rent and fine grained
sand, discs would develop randomly oriented tensile failures in respect
of azimuth".
65
Friedman and I/sgan (1970) studied preferred directions of tensile
fractures normal to bedding _vdrlch they attributed to the state of
residual strain or prestrain in the rock. Other studies have
attributed the existence of non-randcm distributions of tensile
fractures to microcracks in the rock fabric (for exanple, Friedman and
Bur, 1974). The relationship of microcraclcs to the history of ajplied
tectonic loading is not unicjue. A field study by Reik and Currie
(1974) showed that the microcracks (and the induced tensile fractures)
were oriented normal to the tectonic loading. The microcracks being
produced in the uplift phase. Experimental work supports this
interpretation (lajtai and Alison, 1979) although load-parallel
microcracks nay be produced in certain conditions (Lajtai and Alison,
1979; (Gallagher et al., 1974).
2.4.2 AIM
Point-load fracture anisotropy has been investigated on some coal mine
roof sanples from case stuciy areas detailed in later chapters. The aim
was to determine firstly, if rocks from the case study areas had a
fracture anisotropy and secxondly, if this direcrtion was related to
palaeostrain.
2.4.3 TECHNIQUE
Samples used for point-load testing in this study are cores prepared in
accordance with recxmmended procedure (Broch aiKi Franklin, 1972). Sore
sanples were prepared to determine the point-load strength index.
Cores with their ends ground parallel and a length to diameter-ratio of
1.1 were used.
66
The strength results ajpear in T^pendLx II. The majority of sanples
from vrfiich point-load fracture orientations were determined had
variable length to diameter ratios. Many were thin discs sectioned
frcm the core. The length of the specimens used did not appear to
affect the direcrtion of fracturing.
Oriented sanples were centred between the two points and loaded
manually at a consistent but uncontrolled rate. The azimuth of each
fracrture radiating fron the centre load point was measured for both the
upper and lower end of the core. At least four fractures were counted
for each sanple tested.
2.4.4 RESULTS FRCM THE SOLTIHERN COMJIEED
Williams (1977a) is the only published account of point-load fracture
anisotropy in the Southern Coalfield area. He has recorded a preferred
trend of point-load fractures oriented between 010° and 060° with an
average of 025° (Williams, 1977b).
In view of these results reporting fracrture anisotropy, an outcrop of
(Zoal Cliff sandstone was drilled to obtain oriented cores for
point-load testing. The Coal Cliff Sandstone directly overlies the
Bulli Coal seam in the Southern Coalfield (Hanlon et al., 1954). In
the area drilled the Coal Cliff Sandstone is a 10m thick light grey,
medium- to coarse-grained, cjuartz-lithic sandstone. Twenty cores (54nm
diameter) were tested for fracture anisotropy. Figure 2.14 shows the
induced point-load fracture distribution. The main orientation is
between 020° and 030° with a smaller secondary peak from 110° to 120°
(Fig. 2.14).
67
A rx3se diagram of joints measured in the vicinity of the core sanple
locations shows the NNE trending set subparallel to the point-lcsad
fracture directicm (Fig. 2.15). A minor ESE trending joint set is
parallel to the secondary ESE point-load fracture direction.
The result from this sanple site supports the ciata of Williams (1977b).
Fracture anisotropy does exist and there appears to be preferred NNE
trend of the induced fracture direction. Although not proven from the
limited amount of data in the above sairple there is some indication
that jointing and irduced tensile fracturing are related geometrically
if not genetically.
More detailed analyses of point-load fracture anisotropy is presented
in sore of the c:ase studies.
68
Fig. 2.14 Rose diagram of point-load fracture orientations frcm Coal
Cliff Sandstone core sanples from a rock platform. Ten
degree intervals.
Fig. 2.15 Rose diagram of joint orientations measured from a rock
platform of Coal Cliff Sandstone. Point-load sanples were
taken fron the sane platform. Ten degree intervals.
69
\ \
15 I I
\ \
\
\ I \
30
I /
/
/ /
70
71
CHAPTER 3
WEST CLIFF OCEXJERY - CASE STUDY
3.1 INTRODOCTICW
Vtest Cliff Colliery was chosen as an ideal extension to the earlier
vitrinite reflectance investigations of the Flatrock and Scarborough
Faults because it had normal faults and a later generation of
strike-slip faults. Therefore, the investigation for a reccjgnisable
strain pattern for strike-slip faults and the extent of strain
C3verprinting of the succeeding fault generation was of interest.
Vfest Cliff (Zolliery is located 4]cm from i^in (Fig. 1.1). Wbrk for
this thesis was carried out within the initial two years of mine
producrtion from the Bulli Coal. Detail of the structural geology in
the mine area is therefore limited. Figure 3.1 shows the structiure as
ejqposed by mine workings. Also shown in Fig. 3.1 are the three
specific areas of sanpling, nanely Areas A, B and C. Area A contains
three structures around which vitrinite sanples were taken for CBPSIS
determination. The structures are: an intersection of a dextral
strike-slip fault and a normal fault; a normal fault termination; and a
normal fault (Fig. 3.2). Area B contains a strike-slip fault and has
also been sanpled to determine CBPSIS patterns over the area. Part of
Area B has had the roof deformation mapped in detail. Detailed
sanpling around a strike-slip fault was undertaken at Area C to study
the nature of vitrinite bedding plane bireflectance.
The extent of the detailed roof stability mapping in Area B is limited
as it was typical of the directional roof deformation in that portion
of the mine. This size area shcjuld also delineate the types of
72
Fig. 3.1 Location plan of the study areas A, B, and C in West Cliff
Colliery. Location of fault structures indicated are shown
in detail in subsequent figures.
73
geological variation that might cloud any direcUonal relaUcn betvveen
non-uniaxial optical vitrinites and roof failure parameters.
3.2 GEOLOGICAL STRUCTURES
The location of West Cliff with respect to the major structures found
in the Southern Coalfield is described in Chapter 1.
The smaller scale geological structures found in the study area in the
Colliery are normal faults whose vertical nraveirent range fron 10m at
the southern fault (I - Area A, Fig. 3.2) to nil at a fault terminaUon
(Marshall et al., 1980). Typically the normal faults in this study
area have throws less than Im. The southern nomal fault has a trend
of 060° but subsequent mining has shown that it swings and becoies
sub-parallel to the nain trend of the other normal faults (that is; NNE
to NE). In the eastern part of the lease two large nonral faults
trending NW to SE are predicted (Marshall et al., 1980).
The other main structures in the stuciy area are snail strike-slip fault
zones which trend approximately 125°. Zones of very strong jointing
accorpany the faulting. At some exposures they have up to 10cm net
vertical movement. Detailed work has been c:arried out on the fracture
patterns in the vicinity of the strike-slip faults (She^ierd and
Creasey, 1979; Marshall et al., 1980) because these faults are loci for
gas and coal outbursts (Fig. 3.3).
In stucty Area A the strike-slip fault has dextral movarent and
displaces the normal fault laterally by 0.5m. Shepherd and Creasey
(1979) believed that both sinistral and dextral movements occur on
different faiilts and that some demonstrate multiple movement.
74
AREA B
r
j SYDNEY 1 BASIN
L \
~ ^ • • ^
- ^ - N . / ~ |
r,^j/sYDNEY
/SOUTHERN COALFIELD
WOLLONGONG
LEGEND
NORMAL FAULT
STRIKE-SLIP FAULT
STUDY AREA
MINE WORKINGS
Fiq* 3.2 Location plan of study areas A and B with detail of
faulting. I: normal fault; II: normal fault termination;
III: intersection of dextral strike-slip fault and normal
fault.
75
joints minor faults in seam 0 2 4 metres
L_J 1 I I
Fig. 3.3 Jointing associated with strike-slip faulting typical of
area, after Shepherd and Creasey (1979).
76
In the vicinity of the strike-slip fault in area B two main joint
trends are present, that is, a NW to SE set and an E-W set (Fig. 3.4).
More than 20m from the fault the najor joint sets are oriented
approximately NE to SW and NW to SE (Fig. 3.4). Figure 3.5 indicates
that the cleat in Area B has a similar orientation to the regional
joint direcrtion.
In Area A vhere roof conditions were good, jointing is rare. A weak
^jointing' occurs as fine fractures in the sandstone a few millimetres
above the interface between sandstone and coal. Although only weakly
penetrative into the sandstone, they are conspicuous in the roof of the
mine roaciways having a ^brush' like texture or appearance (Fig. 3.6).
These structures appear to be related to the cleat in the immediately
underlying coal and cxaly shale ply, as t h ^ have similar firequency and
lateral continuity.
In some parts of the area stixiied a thin band (20mm) of crushed coal,
usually concordant with bedding in the top plies of the seam but also
seen oblique to bedding, suggests a j iase of bedding plane slip
movement. It is unknown if it is associated with strike-slip faulting
or another phase because of the lack of suitable markers to judge
movement.
At only one location, across a strike-slip fault zone, there appears to
have been lateral displacement of the fault plane between the coal and
overlying sandstone (the roof having an apparent northward movenent
relative to the ccDal). Although the displacement of the fault between
coal and roof is clear at C3ne site it is not seen elsevdiere and may
have been fomed at the time of strike-slip faulting.
77
3.3 ROOF MCRPHG03GY
The Area B was chosen for detailed roof mapping and is typical of the
style of mining induced roof deformation in that part of the mine (Fig.
3.2). In other parts of the mine workings, including much of the area
where vitrinite sanples were obtained, roof conditions were good. The
roof deformation was mapped in accordanc:e with the outline in Chapter
2.2.2.
Figure 3.7 shows the roof deformation in Area B. The height of the
roof falls are also shown in Fig. 3.7. They generally range between
0.2m and 0.6m above the top of the nomal roof of the Bulli seam. The
areal distribution of scaly roof is shown in Fig. 3.7, and consists of
rxDof ply falls less than 0.2m. The roof lithology is consistently
sandstone but has irregular patches of conglomerates. At the
intersection of 19 crut-through and F heading a roof fall shows that a
O.lm thick shale horizon occurs above 0.4m of sandstone in the
inmedlate roof.
The main feature of roof conditions is the difference between the
amount of undefomed roof in the heading direction when ccmpared to the
cut-through direction. Expressed as an amount per metre of roadway the
headings have 0.66m per netre of undefomed roof and the cut-throughs
0.17m per netre of undefomed roof. Roof deformation is not expressed
as an area because different failure types, by their nature, have a
variable extent.
Table 3.1 presents a synthesis of different morphological types of roof
failure (also shown in Fig. 3.6). In this table the failure types are
expressed as an amount of failure per netre of mine roadway. All
78
Fig. 3.4 Orientation of jointing in Area B. Subdivided to identify
joint orientation within 20m of the stirike-slip fault zone
frcm joints in the remainder of the stucfy area. Joint
directions are similar to Fig. 3.3.
Fig. 3.5 Cleat orientation in Area B.
79
WITHIN 20m OF
STRIKE-SLIP FAULT
> 20m FROM STRIKE-SLIP FAULT
\ \ \ 1
30 I
\
\
I \
40 I
I
I
80
intersections of headings and cut-throughs were included as heading
statistics.
In the headings scaly roof is the most common type of failure. (Sutter
failure and crack/sag types of failure are found mainly at the
intersections. The higher falls found in the headings have been
located near intersections or in the close vicinity of the strong joint
zones associated with the strike-slip faulting.
In the cut-throughs cracked/sagging roof accounts for 0.59m per netre,
scaly roof 0.36m per netre and gutteiring 0.17m per metre.
The association of these failure types at any one site is instructive.
Where falls have occrurred at the face during mining there is a much
decreased tendency for sagging to occur. Where no falls occur the
sagging is most severe (for example, 20 cut-through between C and D
headings).
(buttering is not a common primary form of failure. Normally any early
stage failure and roof falls /diich occur at the face will involve
deformation of the centre area of the roof (providing the source for
the flat top and V-shaped or arch falls - Table 3.1). In this study
area guttering occurs with the sagging and cracking of the centre of
the roaciways. The formation of the guttering appears to be secondary
to the sagging and forms in a top comer of the roadway vdiich is
normally unsupported. As the residual reinforcement capacity of roof
bolts arrests and supports the sag movement at the centre of the
roaciway strain relief in the form of roof failure then transfers to the
unsupported gutter area of the roof. Once started guttering has a
Fig. 3.6 Waakly penetrative jointing in the sandstuone of the
imnediate roof (Area A ) . This "brush" texture appears
to mimic the cleat development.
82
83
TABLE 3.1
PRQPCRTICW (3F ROOF FAILURE TYPE PER METIRE
TYPE OF
ROOF ctrr-THROuais HEADINGS
FAILURE
20 19 18 17 TOTAL B C D E F TOTAL
SCALY 0.27 0.43 0.48 0.30 0.36 0.10 0.12 0.20 0.33 0.24 0.20
FLAT TOP 0.09 0.02 0.07 0.01 0.05 0.03 0.04 0.05 0.10 0.28 0.09
ARCH 0.14 0.10 0.02 0.00 0.07 0.00 0.00 0.01 0.00 0.06 0.01
CRACK/SAG 0.95 0.75 0.65 0.09 0.59 0.04 0.04 0.04 0.07 0.05 0.05
GOTTER 0.05 0.24 0.04 0.00 0.17 0.00 0.04 0.02 0.00 0.04 0.02
tendency to ^run' along the rib line until deflected or stopped by
installing extra support or by following natural planes of vjeakness.
The intersection of mining induced low angle conjugate shearing often
produces linear zones of roof failure and falls or linear roof sagging.
The applied lateral in situ stress is thought to act normal to the
linear failure direction. The cut-throughs do not show consistent
orientation of such mining induced failure except for a tendency to be
sub-parallel to the roadway direction. In the headings, roof ply
failure is cormonly linear and oriented obUquely to the roadway
direction. Figure 3.8 shows the trends of these mining induced shear
failures. The principal SSE trend has an average orientation of 158°
(Standard deviation 5.1°). Therefore, a doninant lateral stress
direction of 068° nay be postulated for this area. Such a stress would
make an angle of 55° with the cut-through direction.
84
Fig. 3.7 Roof deformation style and distribution. Study Area B.
Note that the fault narked is a strike-slip fault with
negligible vertical displaconent.
FHEAIHNQ
jaM tone
<sa. *'
Fv! l " 1 ^ ^
»*•
b3m
r
LEGEND
I I GOOD ROOF
SCALY ROOF
FLATTOP
V-TOP (IMCL GUTTER)
l A I SAG/CRACK
HEAVY ROOF
85
The secondary trerd of low angle conjugate shears oriented nearly
norrral to the principal shear trend is thought to represent the
secondary horizontal stress direction. The majority of failure in both
the heading and cut-throughs results fron the applied lateral stress.
Sore areas are affected by high angle discontinuities such as joints
and strike-slip faults. In the headings a minor portion of the roof
ply falls are related to isolated joint planes.
3.4 VrmiNITE REFLErniANCE - AREAS A AND B
Sanples taken in West Cliff Colliery can for ease of presentation be
divided into three separate Areas A, B and C (Fig. 3.1). Areas A and B
will be considered together.
(feological structures such as nomal fault termination, strike-slip
faulting and the intersection of a normal and strike-slip fault have
been sanpled and the vitrinite strain patterns studied in Areas A and
B. Six polished block sections were used to obtain the CBPSIS figure
for each sanple in these two areas. There are two reasons for
increasing the number of sections from four as used in the work
described in Chapter 2. Firstly, it gives a better statistical base
for determining the significance of non-randcm R^max orientations.
Secondly, the strain ^ellipse' drawn from the raw data is more
detailed.
Area C is an investigation of a strike-slip fault using four polished
sections from each sanple and is presented separately in Chapter 3.6.
86
Fig. 3.8 Trace of low angle conjugate shears in the roof of Area B.
Average direction of main trend is 158°.
87
3.4.1 REFLBCEftNCE AND RJMAX ORIENTflTIONS; AREA A AND B
The R^max of the sanples studied ranges between 1.26% and 1.48%, and
the CBPSIS biref lectances range between 0.01% and 0.12% with an average
of 0.05% (Tables 3.2 and 3.3). These tables indicate the sanples \diich
have statistic:ally significant R nax orientations. No clear
relationship was found between the R max value and the distance of the o
sanple from the nearest fault.
Statistically non-random R max orientations in the vicinity of the
nomnal fault and the terminated normal fault do not display the sane
corplete pattern (Figs 3.9 and 3.10) as those from the Scarborx>ugh and
Flatrock Faults (Figs 2.5 and 2.6).
The southern normal fault (Area A) has one non-random R max (sanple
248) oriented at 071° (Type 2 orientation) and distal to this an R max
oriented 23° to the fault (sanple 251). Close to the normal fault
termination is a zone of non-random R max orientations within 35° of
the fault (sanples 295, 301, 303, 304) vdiich are Type 3 R^nax
orientation equivalents (Fig. 3.9). Sanples 300 and 308, further fron
the fault have Type 2 orientations, being greater than 45° to the fault
direction. Alternatively they may represent a more regional strain.
At the intersection between the nomal fault and the strike-slip fault
no consistent relationship exists between each type R^max orientation
and its relative location to the fault (Fig. 3.9).
In Area B R nax orientations have two trends (between 030° and 075°,
and 125° to 160°) as shown in Fig. 3.10. There does not appear to be
any consistency between the Rjrax orientation and distance frcm the
fault and a pattern of the two R^max directions is not apparent.
88
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91
Fig.3.9 Non-randcm and randan R max orientations in vitrinite o
sanples frcm Area A. Three d i f fe ren t strucrtiices sanpled
fron north t o south a r e : intersecrtion of s t r i k e - s l i p faiiLt
ard normal f au l t ; normal f au l t termination; and a normal
f a u l t .
92
Fig. 3.10 Randan and non-randcm R max orientations in vitrinite o
sanples from Area B. Strike-slip fault shown. Refer to
Fig. 3.9 for legend.
93
Overall the orientation of Rjnax's gives a cxrtplex picture of strain
development in Areas A and B. Figure 3.11 shows a sunmary of
non-randcm R max orientations for both areas, o
3.4.2 CBPSIS - MULTIPLE REFLETTiaNCE PEftKS
If the CBPSIS bireflectance of vitrinite is real, and not neasurertent
error or natural artefacrt, then individual reflectance peaks of the
CBPSIS's also represent strain irtprinted in the vitrinite. If strain
cxDnfigxrrations give smcoth elliptical CBPSIS figures it is likely that
a statistically significant R max orientation exists.
In many CBPSIS figures, particailarly those observed in the West Cliff
exanples (Figs 3.12, 3.13, 3.14 and 3.15) at least two reflecrtanc:e
peaks are present, and frcm the preceding assunptions these may
r epresent two separate strain direcrtions derived by one having
overprinted the other. If overprinting is cortplete then the CBPSIS
would have only one reflectance peak. CBPSIS's with randcmly oriented
R max directions may still provide information frcm reflectance peaJcs.
Precise definition of the reflectance peak orientation on any CBPSIS,
is limited by the azimuth and number of sections used to define the
CBPSIS. In practice the strain caiponents are detemined by visual
inspection. Obviously reflectance peaks will be defined by oriented
polished secticons vhich have higher R max values than adjacent
sections. If the reflectance peak is defined by one oriented section
then the peak or strain maxima assumes that partictilar orientation. If
two or more oriented sections have the same Rjnax, and also define a
reflectance peak, then the average angle of the oriented sec:tions is
the strain maxima direcrtion.
94
A
ri
\
AREA B AREA A
o AREA A
O- _ AREA B
Fig. 3.11 Non-randcm CBPSIS orientations for Areas A and B.
95
i N I 10m
LEGEND
116
CBPSIS FIGURE
0 0-1 I . 1 SCALE FOR AXIAL LINES % REFL
Fig. 3.12 CBPSIS figures for normal fault. Area A - (refer to Fig.
3.2). Axial lines of (2BPSIS figures represent normal to
bedding section orientations and their lengths are related
to the reflectance value about the centre (1.25%
reflectance).
96
>o REFL
SCALE FOR AXIAL LINES
Fig. 3.13 CBPSIS figirces for normal faiilt termination. Area A.
Axial lines of CBPSIS figures represent section
orientations; reflectance value of centre is 1.25%
reflectance. CBPSIS figure with dashed outline has a
centre value of 1.15% reflectance. Refer to Figs 3.9 and
3.12 for legend.
97
Fig. 3.14 CBPSIS figures for intersection of normal and strike-slip
faulting, Area A. Axial lines of CBPSIS figures represent
section orientations; reflectance value of centre is 1.25%
reflectance. Refer to Figs 3.9 and 3.11 for legend.
98
Fig. 3.15 CBPSIS figures for Area B. Axial lines of CBPSIS figures
represent section orientations; reflectance value of
centre is 1.20% reflectance. Refer to Figs 3.9 and 3.12
for legend.
99
The limited nimiber of sections preclixles any statistical analysis to
define each peak. For individual sanples the orientation of strain
maxima will be controlled to at least seme extent by the orientation of
the polished secrtions. The subjectivity of determining strain maxim
directions can be minimised by virtue of the relatively large number of
strain determinations that can be readily measured in any one area.
3.4.3 STRAIN MAXIMA - AREA A AND B
As demonstrated by results in Section 3.4.1 non-randon R max o
orientations frcm Areas A and B exhibit corplex and apparently non-
systanatic distributions coipared to those frcm around the Flatrock and
Scarborough Faults (Chapter 2).
Non-randon strain maxima calculated frcm each CBPSIS in Chapter 3.4.1
cover a wide range of orientations (Fig. 3.11). The problem to be
solved is how to differentiate individual strain maxima and assign them
to separate strain events. This is attorpted by considering that
strain events in Areas A and B may be related to the observed
geological structmre.
CBPSIS strain maxima are shown by the CBPSIS figures around the three
structirces in Area A (Figs 3.12, 3.13 and 3.14) and Area B (Fig. 3.15).
The ref lecrtance peaks of each CBPSIS fron Areas A and B are identified
using the procedure described in Section 3.4.2 (Figs 3.16 and 3.17).
Table 3.4 lists the orientations of strain maxima of each sanple.
For exanple, the stress field diiring strike-slip faiiLt movement may be
expected to be oriented within 45° of the fault. For dextral movement
on the fault this would nean a doninant stress field orientation of
100
•?-<
I 60 m
T7
'x*
/ -
k-«
<
\
iC
'.t
t
<
y y
^y Fig. 3.16 Reflectance maximum of CBPSIS figures. Area A. Thin bar,
a Type 1 R max orientation related to normal faulting;
thick bar, an R max orientation related to strike-slip
faulting; and the clashed bar, an R max orientation related
to strain reorientation after normal fault formation.
Refer to Fig. 3.9 for sanple numbers.
101
^ / -
o mi
V
- V - ^
- ^
\l
Fig. 3.17 Reflectance maximum of CBPSIS figures. Area B. Thiii bar,
a Type 1 R max orientation related to normal faulting;
thick bar, an R max orientation related to strike-slip
faulting. Refer to Fig. 3.9 for sanple numbers.
102
TftBLE 3 . 4
SfiMPLE NO. R.MAX AZIMUIHS ( - ) SAMPLE NO. R_MAX AZIMtTIHS ( " ) _Q _Q
Southern Fault - Area A
247 166, 065 250 037
248 146 251 060, 114
249 059, 148 Fault Termination - Area A
294
295
296
297
298
299
300
301
309
310
311
312
313
314
315
273
274
275
276
277
009
021,
130,
135,
033,
084,
049,
034
022,
023,
029,
053,
058,
059,
018,
070,
055,
021,
073,
046,
064,
060
050
113
167
142
135
Fault :
134
111
125
133
163
144
120
Strike
149
163
127
160
136
302
303
304
305
306
307
• 308
Entersection
287
288
289
290
291
293
Slip Fault -
278
279
280
283
284
021,
043,
042,
015,
060,
120
027,
- Area A
039,
038,
064,
068,
063,
059,
Area B
068,
081,
043,
062,
035,
082
148
159
076, 140
138
058, 128
108
127
152
143
148
149
152
135
140
110
145
103
between 120° and 165°. Reflectance strain maxima, forming normal to
the applied stress field, would then be expected between 030° and
075°.
A range of expected strain maxima can be established for each
structure in Areas A and B (Fig. 3.18).
(a) Dextral strike-slip faults: discussed above, would have
expecrted maxiita oriented between 030° and 075°.
(b) Normal faults: there are three normal fault zones, with
two broadly different orientations in Area A. Lateral
stress associated with faulting would be oriented
arbitrarily in a range of 20° either side of the fault
direcrtion. Strain maxima measured by reflectance should
be oriented as follows:
- Southern fault (I - Fig. 3.2): 145° to 185°
- Other normal faults in Area A (II and III in Fig.
3.2): 109° to 149°.
Post-faulting strain, relaxation and reorientation
adjacent to normal faulting would be expected to have
ref lecrtance maxima as follows:
- Southern fault: 055° to 095°
- Other normal faults: 019° to 059°
These maxima are normal to the expected pre-f ault strain
peaks and were previously classified as Type 3 strains in
Chapter 2.
The orientation range for strain maxima associated with formation of
the normal faults and the strike-slip movement are essentially
discrete. However there is overlap between the normal fault Type 3
orientation and the strike-slip field (Fig. 3.18). The Type 3
104
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3 < u. - J < CC
o z
<
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s <
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< u. t -
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<
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c 0 '-^ •^ Csj O CO
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-
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3 O « 2 "• o>
11 =
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i .2>
CM
O « 3 o
CQ
< LU QC <
Reflectance maximum distribution of sanples frcm each
structure in Areas A and B. The e3q)ected strain fields
for each structirce are indicated by dotted boxes.
105
strains could be isolated because they should be located close to
the normal fault plane. The discrete normal fault and strike-slip
fault fields would then be carparable with CBPSIS maxima.
In Figs 3.16 and 3.17 different symbols were used to identify
strains attributed to each expected reflectanc:e maxima range
identified in Fig. 3.18. A summary of the strain maxima
distribution for each structure is presented in Fig. 3.18.
The pattern of strain maxima about each structure is described below
followed by an inteirpretation of the secjuence of strain events.
3.4.3.1 Eavtlt Intersecrtion - Area A
The pattern of ref lecrtance maxima around the fault intersecrtion
is the least variable of the struc:tures studied. Maxima
associated with strike-slip fault formation (thick bar - Fig.
3.16) but not located near the normal fault, have a consist
angle between 42° and 77° fron the strike-slip fault (Fig.
3.18). One sanple, 315, is oriented cxitside the ej^ected
range. Sanples next to the normal fault have strain maxima
(dashed bar - Fig. 3.16) vdiich fall in the expected range (Fig.
3.18) and do not overlap with the 'strike-slip fault' maxima
just discussed.
All sanples have maxima in the range of normal fault formation
(Fig. 3.18). They have a 46° range and fall either side of the
expected range.
Two sets of reflectance maxima are clear. The strike-slxp
fault strain and the localised post-normal faulting strain have
106
similarly oriented, but separate, maxima. The cjuestion arises
whether the dashed bars in Fig. 3.16 the post-normal fault
strains, are indeed that, or strike-slip fault strains
reoriented slightly around the pre-existing normal fault.
3.4.3.2 Normal EaiiLt Termination - Area A
The pattern of reflectance maxima around the normal fault
termination structure is corplex. The difficulty is attenpting
to differentiate between maxima in the expected range of
strike-slip fault formation and post-normal faulting.
Figure 3.18 shows that there is C3verlap betvveen these two
maxima even though eacrh tends toward one end of the dcmain.
The presence of the strike-slip fault maxima will always make
definition of the post-normal fault strain difficult.
The normal fault formation maxima (113° to 167° in Fig. 3.18)
occurs in the expected range except for two sanples (299,304),
v rlch may be related to formation of the southeni normal fault.
107
3.4.3.3 South Normal FaiiLt - Area A
Once again it is difficult to pick between strike-slip fault
formation strain and post-normal faulting strain, especially as
this normal fault has a slightly different orientation (Fig.
3.16). The strains assumed in Fig. 3.16 do fall into expecrted
ranges (Fig. 3.18). Strains irelated to normal fault formation
are interesting in that the limited number measured have
shifted orientation corpared to the previous normal faults and
fall into the ej ected range, apart frcm one widely discrepant
sanple (number 251, Fig. 3.9).
3.4.3.4 Strike-Slip Fault - Area B
Sanples up to approxinately 200m frcm the strike-slip fault
were gathered. Similarly oriented reflectance maxima occur in
sanples close to and remote frcm the strike-slip fault.
i )art fron two sanples all strain related to strike-slip fault
formation fall into the expected range (Fig. 3.18).
The second reflectance maxima aligns with the range of
reflectance maxima related to normal fault formation found
around the three structures in Area A (that is, between 110°
and 163°).
The variability of the distributicxi of strain maxima
orientations in Area B is illustrated by the variation of the
intensity of overprinting of the two strains at one sanple
site, that is 280 (Fig. 3.15). At site 280 samples were taken
fron different heights within the 2m seam. The upper sanple
108
has a non-randon R max oriented in a NE direction (and strain o
maxima oriented 065°) -whereas the lower two sanples (281, 282)
have higher R nax values and randcm R nax orientations, but ^ o o
have CBPSIS's with similarly oriented pairs of reflectance
maxirra of 043° and 154° corpared to 063° and 149° (Fig. 3.19
and Table 3.3). It is unknown if a particular level of the
seam is more responsive to transmitting and recording strain.
3.4.4 ItTTERPREEZynCW OF STRAIN EVEKTS - AREA. A AND B
The most distinguished feature of the pattern of reflectance maxima
is the presenc:e of two, admittedly broad, orientation domains, (Fig.
3.20). Irrespective of any prospective subdivision within each
dcmain the division points exit that reflecrtance maxima are not
randcm. Clalculation of non-randcm R max orientation, fron a series
o '
of vertical sections, is unable to isolate two consistently oriented
reflectance maxima in CBPSIS figures.
Maxima fron CBPSIS figures obtained fron at least six secrtions is a
viable methcxl of strain analysis in vitrinite.
The two ref lecrtance maxima orientation donains are generally related
to either normal fault formation or strike-slip fault formation.
3.4.4.1 Normal Faults
The strain assigned to expected normal fault formation is found
both adjacent to normal faults and in areas ranr»te from normal
faulting (for exanple. Area B). Therefore the Type 1 and Type
2 strains defined for Chapter 2 work are equivalent in the Vfest
109
N
1. -280
Scale for Axial Lines 0 0.1
— I
% REFL
2 . -281
-282
Fig. 3.19 CBPSIS figures fron sanple site 280. Conparison of
figures with location in the seam: sanple 280, fron the
top of the seam; sanple 281, 0.5m frcm top of seam;
sanple 282, 1.2m frcm top of seam. Centre of CBPSIS
figures is 1.20% reflectance.
110
15 -I
10 -
> o z UJ 3 O lU oc u.
s -
STRAIN COMPONENT AZIMUTH (deg.)
Fig. 3.20 Histogram of CBPSIS reflectance maxima orientations.
Area A and B. Type 1 R max corponent, or "regional"
strains represented by shaded area between 100° and
170°. Type 3 R nax corponents are unshaded, and
strike-slip fault strain ccxrponent is the shaded area
between 0° and 90°.
Ill
Cliff study. In other words the normal faulting strain is a
widespread event, covering at least the study area.
The strains associated with formation of the south normal fault
and the other (slightly) differently oriented normal faults in
Area A are theoretically separable (Fig. 3.18). The results
fron the south normal fault are in the expected zone (Fig.
3.18). However results frcm Area B, vMch contains no nomal
faults, cover the same orientation range as all of the normal
faults in Area A.
Two explanations are offered:
(a) only one strain event occurred, the variability being
caused by: natural variability of the strain, localised
variation of strain on the hand specimen scale, variation
inherent with the limited vertical secticm coverage, or
inccarplete inprinting;
(b) the south fault and the other normal faults of Area A were
separate events. The strain fron the south fault has a limited
record through the area, possibly due to incorplete
Cfverprinting of a previous or subsecjuent event. There is a
modest indication of a secondary peak fron 160° to 170° in Fig.
3.20.
The evidence points to the probability of two separate 'normal
fault' events. The nean strain orientation for reflectance
maxima of the southern normal fault is 154° (sd = 7.8°), and
for the other normal faults is 132° (sd = 12.6°). Nevertheless
112
further investigations should be aware of the possibility of
the 160° to 170° events.
3.4.4.2 Strike-Slip Faiilts
Area B most clearly shows the range over vAiich the reflectance
maxima associated with strike-slip fault formation occurs, that
is, fron 21° to 81° (Fig. 3.18). No other regional, or study
area wide, pattern can be subdivided. It must be concluded
that the natural variability of strain, measuronent design, and
vitrinite iirprinting causes the range of results noted.
It is difficult to isolate Type 3 strain, that is strain
associated with post-normal fault stress reorientation frcm the
strike-slip fault jiiase. Results fron the strike-slip fault -
normal fault intersection in Area A show tightly grouped
reflectance maxima (frcm 22° to 38° and frcm 53° to 68°) which
might be associated with each of these two phases of faulting
(Fig. 3.18). This distinction is not as well defined for other
Area A normal faulting.
Fig. 3.20 records the distribution of CBPSIS reflecrtance maxima
in Areas A and B. The dcmain between 0° and 90° shows the
distribution of reflecrtance peaks frcm the Type 3 phase
(unshaded area) and the reflectance peaks frcm the strike-slip
fault event (shaded area). The 'average' strike-slip strain is
050° and excludes possible Type 3 strains.
An interpretation of the sequence of stress development in Area
A and B is summarised in Table 3.5 by assuming that strain
113
directions recorded in vitrinite are normal to the applied
stress.
The NE trending stress field associated with the formation of
nomal faulting is considered the oldest recxognised and occurs
across the stuciy area. The nomal fault is displaced by
strike-slip movement. The mpre ENE trending noimal fault was
probably formed during the same jiiase of normal faulting. The
stress field during this time would have been oriented between
NE and ENE.
Localised strain relaxation occurs in the post-failure period
of normal faulting. A Icxoalised SE trending stress field would
have existed in the post- faulting phase.
Strain related to movement along strike-slip favilts is the
youngest event arecognised fron vitrinite reflectance. A stress
field oriented SE was responsible for strike-slip faulting and
vitrinite inprinting.
The current in situ stress is recognised frcm roof deformation
of mine roadways. This stress field is oriented ENE and aligns
most closely with the ENE stress field associated with
formation of the southern normal fault.
114
TABLE 3.5 INTERPRETED STRESS DIRBCTICWS AND THEIR SBCXJENCE
- AREA A AND B - WEST CLIFF
SEQUENCE DIRBCTIC J EXPECTED STRAIN MEAN STRAIN EVIDENCE OF STRESS OF STRESS MAXIMA MAXIMA AZIMLTTH EVENT ORIENTATION (ST. DEV.)
NE
ENE
SE
SE
NOTE: ENE
109° - 149'
145° - 185'
019° - 059"
030°-075'
139° (16°)
154° (7.8°)
039° (12°)
050°(20°)
Related to normal fault developnent. Also recorded in sanples remote frcm structure. Probably two independent events, but difficult to sequence. Localised event around nomal faulting. Occurs during time of NE event. Related to localised relief of the NE stress in post-failure pericd of normal faulting. Related to the strike-slip event. Widespread distribution. Current in situ stress field.
3.5 POIMr-LQAD ERACTORE CRIFWEATICWS
Point-lead tests were carried out on fine-grained to coarse-grained
sandstones forming the immediate roof strata in the West Cliff study
area. If the fabric of the rock were isotropic, fractures induced by
point-load tests loaded nomal to bedding should be randcmly
oriented. Fractures that are preferentially oriented are related to
lateral tensile strength anisotropies. Point-load fracture
directions were determined in this study to establish v^ether any
preferred fracture directican existed and hew it would corpare to
vitrinite strain orientations. Between 14 and 38 oriented cores
115
24.5mm in diameter and 24.5mm long, v^re prepared fron each sanple
in accord with standard methods (Brcxh and Franklin, 1972;
Bieniawski, 1975) for axial strength determinations and then they
were loaded to failure. Tests were also carried out on shorter
cores with smaller length to breadth ratios (i.e. <1:1). The
fracture orientations, measured frcm the centre of the upper and
lower core surfaces for both size cores (that is, four neasurorents
for each planar fracture), were found to be similar. The results of
the point-load fracture orientations are shown in Figs 3.21 and
3.22.
Figure 3.21 shows the fracrture distribution in sanples taken in Area
B. Three trends or fracture frequency maxima are noticeable in this
suite of sanples. All sanples except site 155 have a NNE fracrture
direcrtion. Many of these sanples also have strong to medium
fracrture directions sul^arallel to the strike-slip fault (that is,
ESE). In sanple 158, located immediately adjacent to the
strike-slip fault this ESE trend is dominant. In sairple site 155
the SSE fracture trend is doninant and can be noticed as a
subordinate trend in many of the other sanples.
Figure 3.22 shows rose diagrams of the fracrture distribution frcm
two sanples taken firm near the southern normal fault in Area A.
Sanple 135 has the main fracture orientation N-NNE, similar to that
found in Fig. 3.21. Subordinate peaks are N and NE. Sanple 134 fron
iirmadiately adjacent to the faults, has strong fracture trends just
south of east. This trend is more closely oriented to the
strike-slip fault direction than the adjacent normal fault.
116
Fig. 3.21 Point-load fracture orientation rose diagrams of
sanples 154 to 159 frcrm Area B. Dashed circle on each
diagram represents 10% frecjuency level. Nurnber of
cores tested frcm each sanple indicated adjacent to
diagram.
i v 10 m
117
/
/
15^0
\
\ \
/ /
10%
\ ^
X /
y
Fig. 3.22 Point-load fracture orientation rose diagrane of
sanples 134 and 135 frcm the normal fault. Area A.
Twenty three cores were tested frcm sanple 134 and
sixteen cores were tested fron sanple 135. -
118
3.5.1 POIWr-K)AD FRACTORE CRIEKCATIONS AND gERAIN MAXIMA
The oldest recrognisable vitrinite strain direction in this stuciy is
oriented SE or SSE, vdiich iirplies that the corresponding lateral
palaeostress maximum event trended NE or ENE. If this stress was
'locked' into the asscxriated mine roof strata, point-lcsad fractures
of load-parallel origin would be oriented NE-ENE, ard those of
load-nomal origin, SE-SSE. Figure 3.23 demonstrates that the
point-load fractures are not in close agreement to this predlcrtion.
It appears that point-load fractures located adjacent to faults have
been influenced by the faulting process, and they were not included
in the ciata used in Fig. 3.23. The close association between the SE
trending 'load normal' direcrtion and the trend of the strike-slip
faults makes it difficult to assess the possible contribution to
point-load fracrture by the strain event associated with strike-slip
movements. These results indicate that point-load fracture
direcrtions nay derive both from an older prestrain event, than
recognised frcm vitrinite strain maxima, and fron subsequently
formed microdefects acting in conjunction with microfabric.
Therefore, the use of point-load fracrture direcrtions to predict
lateral stress orientations should be used in with other indicators
of palaeostresses and in situ stresses.
3.6 VITRINITE REFLECTANCE - AREA C
Twenty four sanples were collecrted on two parallel traverses 60m
apart across a strike-slip fault in Area C vAiich is located north of
Area A and east of Area B (Fig. 3.1). The location of the sanples
is shown in Fig. 3.24. Sanples were taken on both sides of the
fault to a distance of up to 80m away. At the stage in the project
when these sanples were measured vitrinite reflecrtance was
119
i IM
POINT-LOAD FRACTURES
STRAIN COMPONENTS
Fig. 3.23 Corparative rose diagrams of point-load fracture
orientation and interpreted vitrinite strain
ccarponents. Type 1 R max orientation corponent trends
SE; strike-slip fault strain corponent trends NE. 631
point-load fracrtures and 67 strain corponents were
plotted. Point-load sanples 134 and 158 and Typ© 3
R max strain corponents were not included.
120
SCALE
O S T O 15 20 metres
Fig. 3.24 Non-randcm R max direcrtions (bars) and randcm R max o o
sanples (circles) frcm Area C. Sanple numbers are
denoted. Fault marked is a strike-slip fault plane.
121
determined fron four polished sections and the R max calculated fron o
the CBPSIS.
3.6.1 REFLBCnaNCE RESULTS - AREA C
The Rjnax of the sanples studied ranges between 1.25% and 1.41%
reflectance, and the average bireflectance of the CBPSIS is 0.04%.
Table 3.6 presents further infomation about the CBPSIS figures of
each sanple and indicates those with statistically significant R nax
orientations. There dcDes not appear to be any significant or
recognisable relationship between the reflectance as represented by
the largest measured R max value and distance frcm the fault (Fig.
3.25). Likewise R max values fron particular sanples (sanpled frcm
the full seam), and average R max values frcm the four polished
blocks used to gain the R nax, do not relate reflectance value with
distance fron the strike-slip fault (Fig. 3.25).
3.6.2 R MAX CRnMTATIOKS - AREA C -o
CBPSIS figures of sanples measured in Area C are drawn in Fig. 3.26.
The non-randcm orientations of this set of sanples are shown in Fig.
3.24. Table 3.6 indicates the R nax orientations and strain maxima
orientations fron statistically randcm sanples. Of the 24 sanples
measured only 5 have randcm R max direcrtions.
There does not appear to be a consistent Rjnax trend at any one
location with respect to the fault or as a sequenUal trend away
fron the strike-slip fault.
122
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DISTANCE (m) 50 60 70
Fig. 3.25 Relationship between the distance fron the fault and
the largest measured R nax for each sanple.
Fig. 3.26 CBPSIS figures around a strike-slip fault in Area C.
Axial lines of the CBPSIS figures represent section
orientations. Reflectance value of centre is 1.25%.
Refer to Figs 3.9 and 3.12 for legend.
125
3.6.3 IWrERPRETATICN OF R MAX CRIENCATICNS - AREA. C
The statistically non-randon R^max orientation as calculated fron
the CBPSIS has been used to identify vitrinite strain direcrtions in
Area C. It is considered that the four polished sections used for
obtaining the Rjnax's do not provide enough detail fron v iich to
identify strain maxima as was done in Chapter 3.4.2. The main
problem with using 4 sections to calcrulate the R nax orientation is
that the calculated answer may be the average of two strain maxima.
Depending on the bedding plane biref lecrtance this will give an
average of both reflectance peak ciirecrtions or a randcm R nax
orientation.
In Area C sanples 139 and 184 may be exanples of this. Another
limitation of four sections is that statistically significant
non-randon R nax orientations can only occur fron sanples with one
apparent strain maxima. Normally sanples with two strain maxima
would produce a randcmly oriented R nax and be rejected fron the
interpretation. In view of the interpretation of sanples fron Areas
A and B, sanples frcm Area C with recognisable strain maxima fron
each CBPSIS figure (Fig. 3.26) are used in conjunction with
non-randon R max direcrtions for interpreting strain.
Figure 3.27 shows the distribution of vitxinite strain directions in
Area C. Reflectance maxima fron CBPSIS figures and calculated
non-randon R nax direcrtions are plotted independently. The ranges o
of expected reflectance maxima determined in Areas A and B are also
used in Area C.
126
CBPSIS PEAKS
NON-RANDOM Rj,max
EXPECTED STRIKE-SLIP FAULT RANGE
20 40
EXPECTED NORMAL FAULT RANGE
60 -h i- + -f- -i h i 1-
80 100 120 AZIMUTH (degrees)
140 160 180
Fig. 3.27 Distribution of non-randon R max directions and o
reflectance maxima determined fron CBPSIS figures
created fron four vertical sections. The expected
strain ranges for the normal fault and the strike-slip
fault are marked.
127
It ratains inconclusive v^ether the 160° to 170° maxima are a
separate event related to the south nomal fault (Area A) as
postulated in Area A and B ciata (section 3.4.4.1).
Inspection of Fig. 3.27 shows that there are no preferred
orientations exclusive to the expected range for normal or
strike-slip fault formation. Many of the CBPSIS reflectance maxima
do fall into the expected range except for a group oriented between
160° and 170°. The non-randon R nax orientations have an even less o
clearly defined asscciation with the expected ranges. These
orientations are spread fron 0° to 180°.
Do the i esults frcm Area C invaliciate the relationships between
vitrinite reflectance and faulting noted in Areas A and B? The
consistency of results obtained in Areas A and B instead prorpt the
cjuestion of vhat factors may mask a clearer interpretation fron Area
C.
The use of only four sections limits the precision of determining
both non-randon R nax directions, and reflectance maxima fron CBPSIS
figures. For exanple, it is possible for the non-randcm Rjnax
direction to be the average of two reflectance maxima. The CBPSIS
figures, with the exception of sanples 143 and 175, had only one
recognisable reflectance peak. In Areas A and B it was coimon to
observe CBPSIS figures constructed fron 6 vertical sections to have
two recognisable reflectance maxima. It is therefore deduced that
four vertical sections nay result in a scatter of reflectance
maxima.
128
The data fron Area C is not conclusive, but taken in conjunction
with reflectance maxima frcm Areas A and B confirms the existence of
two regional palaeostrain directions oriented NNE to ENE and ESE to
SSE.
3.7 IN SITU STRESS, PAEABOgTRAIN AND STRUCKIRE -
OCMCLUSICKS
The data collected fron West Cliff Ctolliery has provided infornation
on the direction of the dcminant lateral stress, the lateral
palaeostress direcrtions, as inferred frcm vitrinite reflectance
results and geological structures such as normal faults, strike-slip
faults, joints and cleats in the croal. What relationship exists
between these features?
Figure 3.28 provides a gecmetric relationship between the above
mentioned features. The following is a sumnary of likely
relationships:
1. There is a NNE to NE trend for the secondary joint
ciirection, seconciary cleat direcrtion and the primary
point-load fracture direction. This is reasonably
coincident with the oldest recrognised palaeostress
direction (042°), It is also possible that the joint,cleat
and point-load directions are related to an earlier NNE
stress field not recognised in the vitrinite.
2. The oldest palaeostress, inferred frcm reflecrtance naxima
associated with noimal faiilts, is related to normal fault
foimation. Two j iases of stress are postulated within this
timespan: a ENE stress field associated with the south
normal fault; and a NE stress field associated with the
129
N
M JOINTS (^
0 "''" 0
270*
Fig. 3.28 Summary of gecmetrical relationship between lateral
palaeostress directions, inferred fron vitrinite
reflectance data, the in situ stress directions,
geological structures such as joints, cleats and faults
and point-load fracrtures.
130
remaining normal faults. A localised secrondary SE stress
field occurs immediately adjacent to the normal faults
and represents post-fault stress reorientation.
3. The youngest palaeostress recognised is oriented 20° fron
the strike-slip fault direction, and is cotpatible with
dextral movement on the strike-slip fault. The 20° arc
between the palaeostress and the strike-slip fault defines
the principal joint and cleat direcrtions.
4. The NE and NW palaeostress directions nay be genetically
related to part of the point-load fracture population and
the cleat measured in the coal. Not all of the
palaeostress directions ajpear to be associated with
joints, cleat, or point-load fractures, nor is all the
joint, cleat and point-load population represented by
palaeostress events recorded in vitrinite.
5. Palaeostress events recorded in vitrinite aire related to
the faulting in the stuciy area. The ENE palaeostress is
also parallel to the in situ stress field. The in situ
stress field is thought to have been iirprinted in the
inmedlate mine roof strata at the time it was inprinted in
the vitrinite. Interestingly, the ENE palaeostress does
not appear to be asscxriated with any of the joint or cleat
fabric of the rock nass, further suggesting ciifferent
ages for these events.
131
CHftPTBR 4
KEMIRA OOaXIHg - CASE STODY
4.1 INTRODUCTICN
Kemira Colliery is located in the Southern Coalfield to the south of
Coal Cliff and Vfest Cliff Collieries (Fig. 1.1). Kenira Colliery,
C4 Panel, was chosen to study the roof conditions in association with
three different parameters, namely variation of irmedlate rxoof
lithology, the effect of stone rolls and the influence of an apparently
dlrecrtional, doninantly horizontal stress field. The palaeostress
evidence gathered fron reflectance measurements of vitrinite sanples
will be corpared with the in situ lateral stress field.
In C4 Panel the area studied included a sandstone channel in the
immediate roof sediments in contrast to the surrounding shale laminites
(Fig. 4.1). Within the normally medium- to coarse-grained sandstone
are patches of cronglcmerate v^ch extend up to approximately 10m along
the headings. Isolated evidence of cross-bedded strata was obtained
frcm roof falls and the direcrtion of current beciding is shown in Fig.
4.2.
Stone rolls are common in the area napped in C4 Panel. Morphologically
they are longitudinal ridges of carbonaceous shale and siltstone on the
floor of the seam and extend variable heights into the seam. Diessel
and Moelle (1967) described and discussed aspects of the stone rolls
found in the Southern Coalfields of the Sy±iey Basin. They concluded
that stone rolls are "analogous to washouts, and represent silted up
stream channels" (1967, p.619). The cross-sectional shape and size of
the stone rolls vary as shown in Figs 4.3 and 4.4.
132
Mine Roodwoy
Lominite
Stone rol Is
SCALE METRES
Fig. 4.1 C4 Panel stuciy area showing the immediate roof lithology
and location of stcane rolls. Locations I to V indicate
stone rolls profiled in Fig. 4.3.
133
*
' I »
Fig. 4.2 Current beciding diagram of cross-bedded sardstone strata in
C4 Panel roof. Orientation of log in roof shown by dotted
line. Limited exposure provides only 14 ciata points.
134
o <N
<0
E
o o
C4 Csi
II
I
>
UJ - J < O
Fig. 4.3 Cross-section of stone-rolls in headings of C4 Panel. The
locaticms I to V are marked on Fig. 4.1.
135
Fig. 4.4 Photographs of parts of stone rolls showing the irregular
outline and the intricate association of sote bright
vitrinite layers continuous between coal and the ciark grey
shale of the stone roll.
137
The boundary of the stone rolls nay be either sharp or may have
vitrinite bancis continuous between the stone roll and the adjacent coal
(Fig. 4.4). Figure 4.1 shows the plan view of where the stone rolls
occur in the ribside. It is very difficult to define continuous stone
rolls vAiich have a subparallel trend as reported by Diessel and Moelle
(1967). In this small area the individual stone rolls may divide along
their length or abruptly disappear. Some stone rolls which appear to
have been cxontinuous occur on either side of headings. The neasured
trend of these rolls has an average direction of 355°, and ranges frcm
348° to 008°.
Another guide to the likely trend of the stone rolls is the attitude
and orientation of the planar fracrtures vhich are propagated around the
stone rolls as a result of differential ccnpaction. In C4 Panel the
joint trend and the trend of the moi?e inclined fractures (60° to 70°
dip) which extend frcm the edge of the stone rolls are similar.
Diessel and Moelle (1967) indicate that fractures caused by
differential corpaction nay extend for 25m on either side of a stone
roll. Therefore, the joints found in C4 (Fig. 4.5) nay represent
ciiffeirential corpaction rather than a regional joint pattern.
Joints measured in the roof ajproximately 1km NE fron the study area
have a different naxima orientation 015°-025° (Fig. 4.5).
Approximately 300m NE of the study area is a zone of jointing
sulparallel to the d^^e and noimal fault oriented at 110°. The joints
measured near the bounciary of the sandstone channel tend to be oriented
slightly more E-W, possibly due to stress reorientation in the vicinity
of the sandstone channel. A number of strike-slip fault zones, with
vertical throw less than O.lm have been napped at the inbye end of C4
138
Fig. 4.5 Rose diagram of joints measured in C4 Panel stuciy area
(shaded area), and joints measured in a Panel Ucm away
(non-shaded area). The orientation of strike-slip faulting
mapped in C4 Panel is shc»wn.
139
Panel (Fig. 4.1). They occur parallel to the jointing and nay have
used the pre-existing joint planes as loci for movorent. It is likely
that the SE trending joints in the C4 Panel have a more regional
character than just a localised association with differential
corpaction around stone rolls.
The shear zones have a crushed rock or mylonite zone less than O.lm
across in both the coal and surrounding strata. The roof in their
vicinity is very fractured, with calcite being conmon as an infilling
mineral of joints and tension gashes. At the interface between the
Bulli Coal and roof sediments there is an apparent offset of the shear
zone. The roof appears to have moved east relative to the coal seam.
Ot±ier obvious signs to support this movement are inconsistent,
especially a lack of beciding plane slickensiciing, so that the apparent
horizontal dislocation of the shear zone nay represent only a path of
least resistance at the time of deformation.
The intense mining induced shear failure of the roof sediments in the
cut-th3X)ugh indicates that an in situ horizontal stress is present and
is an inportant cause of observed roof conditions. Detailed roof
mapping of the headings and cut-throughs demonstrated the variation in
roof failure types to be found between heaciings and cut-throughs.
140
4.2 ROOF OCMDinCMS - C4 PANEL
The area of C4 Panel mapped is shown in Fig. 4.6. Only the inbye
portion of this panel was investigated in detail as this was considered
adequate to define representative types of roof failure. Initial
inspection showed mining-induced rcxDf deformation in both heading and
cut-throughs. Detailed mapping of failure t 'pes was used to isolate
any differences. Failure types used are outlined in Chapter 2.
4.2.1 HEIGHT OF ROOF FALEg
A breakdown of the roof fall height distribution in the area mapped is
provided for both shale, laminite and sancistone roof material. The
height of each roof fall was counted as an individual event so that
each roof fall was equally weighted statistically, irrespecrtive of the
area extended by the fall cavity. Data recording the height of falls is
listed and grouped in Table 4.1.
The nost conmon roof fall height in all roaciways was less than O.lSra
(76.7%). In cut-throughs the 0.15-0.50m and the 0-0.15m high falls
occurred with similar frequency. Both sandstone and laminite have a
similar proportion per metre of roof falls less than 0.15m high (T^le
4.1). Taking into account the ratio between the length of headings
with sandstone roof compared to laminite roof was almost 2:1 (i.e. 415m
to 211m) the laminite roof tends to have a greater proportion of the
higher roof falls, although they are a snail part of the total. In the
cut-throughs the roof falls are higher without an apparently
significant difference between the sandstone and laminite roof
materials.
141
HEIC3fr OF
FALL (M)
0.15
0.15-0.5
0.5-1.0
1.00
TOTAL
TABLE 4.1
ROOF EALL HEIGHT ERBQUENCY IN C4 PANEL (PERCENT)
HEADIN3S
lAMINITE
ROOF
19.8
6.0
1.7
0.9
28.4
SANDSTONE
ROOF
46.6
5.2
0.0
0.0
51.8
CUr-THR0LK3B
LAMINITE
ROOF
6.0
1.7
1.7
0.0
9.4
SANDSTOJE
ROOF
4.3
5.2
0.9
0.0
10.4
TOTAL
76.7
18.1
4.3
0.9
100.0
4.2.2 TYPE OF ROOF CXUDITICWS
Figure 4.6 indicates the distribution of the six different types of
rcx>f conditions. Table 4.2 lists the proportion per metre of each of
the roof condition types, in heaciings and cut-throughs for both
sandstone and laminite roof. These percentages v^re calculated by
measuring the length parallel to the roadway of each roof fall in each
roadway and dividing this ty the total roadway length beneath a roof
lithology type in a heading or cut-through. By this method there may
be more than one netre per metre of total roof failure as different
failure types nay occur adjacent to each other.
Scaly roof is the predoninant type of failure in the headings formed
under both sandstone and laminite roof. In the cut-throughs broken/
cracked roof is the dcminant failure type under both sandstone and
laminite roof. Scaly roof in laminite and scaly and flat top roof
142
Fig. 4.6 Plan of C4 Panel showing roof condition types mapped.
Boundaries of changing sedunentary rcof type are marked and
the position of stone rolls marked on the mine roadway
outline.
w
v\
' • t
[1
CD
LEGEND
GOOD ROOF
E 3 ? ] SCALY HOOF
FLAT TOP HOOF
V-SMAPE FALL - AHCH
CRACKED/BROKEN HOOF
GUTTER
143
-TABLE 4.2
PROPORTICW OF ROOF FATTJII^ TYPE PER METRE
TYPE OF HEADINGS CUT-THROXaB
ROOF FAILURE LAMINITE SANDSTCa^ TOTAL LAMINITE SANDSTONE TOTAL
SCALY
FLAT TOP
V-SHAPE-ARCH
EROKEN/CRACKED
GUi'i'ER
Wrr FALLEN
0.32
0.17
0,01
0.00
0.11
0.50
0.03
0.00
0.06
0.03
0.43
0.08
0.01
0.04
0.06
0.38
0.56
0.16
0.00
0.94
0.00
0.28
0.37
0.19
0.54
0.00
0.42
0.27
0.10
0.73
0.00
0.02
failure in sandstone are inportant subsidiary failure types in the
cut-throughs.
Assuming that general mining conditions (for exanple, stress
conditions, mining rates, roof sujport parameters, and roof lithologies
and strengths) in the heaciings are similar and the mining conditions
between the cut-throughs are similar then the influence of roof
lithology on the roof morj^ology can be assessed.
In the headings, scaly roof cccurs proportionally more in the sandstone
than in the laminite, whereas both flat top falls and guttering are
more conmon in laminite roof.
In the cut-throughs the scaly roof and flat top falls are more
extensive in the laminite and sancistone respectively, vhich is a
reversal of the distribution found in the headings. The proportican of
144
scaly roof per metre is similar in both the cut-throughs and headings.
However broken/cracked ground^ in particular, and flat top falls have
significant increases in the cut-throughs.
A number of ciifferences appear in the proportion of various
morphological types of roof falls between the crut-throughs and
heaciings. The cut-throughs have a greater proportion per metre of flat
top falls (0.27/m cf. 0.08/m) and cracked/broken (0.73/m cf. 0.04/m)
types and no gutter failure (whereas headings have 0.06/m gutter
failure). Inverted V-shaped arch failure type is low in both headings
and cut-throughs.
The amount of roof not fallen is much greater in the heaciings. Almost
the vdiole length of the cut-throughs have seme type of roof failure.
A very inportant feature of the roof failure in the crut-throughs,
irrespective of morphology, is that it occurs in the middle of the
cut-through. The inverted V-shape failure present would be classified
as arch failure (see Chapter 2, failure type Il-c-iii). It is likely
that the flat top failure is also an arch type failure but has the top
of the fall defined by a beciding plane.
Therefore, although the failure morphology can be different, the same
origin can be attributed to the roof failure as discussed in the next
section (4.2.3). An understanding of the failure type for each
lithology, and use of extenscmetry methods to monitor roof
displacement, provides a good basis for roof support design.
145
4.2.3 GENETIC CLASSIFICATION OF ROOF Eflllfi
Each roof condition type is- classified into one of three genetic
categories based on the feature or reason nost proninent in its
formation. They are: (a) high angle discontinuities (for exanple,
strike-slip faults and associated shears); (b) low angle
discontinuities (for exanple, separation along beciding planes); (c)
ccrtpressive stress related fcd-lure (for exanple, mining induced shear,
producing the features such as guttering and roof sagging).
Seme particular relationships were noted across 04 Panel. Firstly, in
headings, areas of laminite roof are predcminantly affected by the high
angle discontinuities of closely spacred joints (spacing 70nin) and
strike-slip faults within the joint zones (Fig. 4.7a). At least seme
of these discontinuities in C4 Panel are related to differential
corpacrtion around stone rolls. Within the sandstone roof section only
a minor nuniber of falls are related to jointing.
Secondly, sandstone roof in the heaciings mainly produces small falls of
roof along beciding planes, usually cross-becided strata (Fig. 4.7b) and
is classified as being due to low angle discontinuities. On the
bounciary of the main sancistone channel the laminite roof has parted
along the bedding plane - low angle ciiscontiniu.tY falls.
A small anount of guttering is found in both shale and sancistone roof
in the heaciings.
Thircily, the roof failure in the cut-throughs appears to be related to
ccnpressive shear failure of the roof irrespective of lithology. In
the cut-throughs the roof is seen to fall in the centre of the roadway
146
Fig. 4.7(a) Closely spaced jointing associated with minor strike-slip
faults are exanples of roof conditions affected by high
angle ciiscontinuities.
Fig. 4.7(b) Roof fallen at the mining face caused by separation of
cross-becided strata. This is an exanple of low angle
discontinuity falls.
Fig. 4.7(c) Arch failure of roof at the mining face. Lateral
carpressive stress oriented at a high angle to the
roaciway results in shearing of the roof strata in the
centre area of the roadway.
147
149
and in seme places has fallen at the mining face before roof supports
could be placred (Fig. 4.7c).. Very lew angle mining induced shear
planes (less than 20° dip) are common throughout this fall. The
majority of roof failure in the headings trerds across the roaciway
v^ereas the roof failure is located in the centre of the cut-throughs.
This roof failure is probably related to a stress field vhich has a
najor near-horizontal corponent oriented approximately normal to the
cut-through direcrtion. Fron the evidence the in situ lateral stress
ciirection is approximately 060°. The failure nodes noted suggest that
the maximum principle stress is near horizontal.
4.3 VITRINITE REFLBCTAtCE
Ten vitrinite sanples were cxDllecrted frcm C4 Panel to establish the
pattern of beciding plane bireflectance. Although the area studied in
C4 Panel is relatively snail, vitrinite reflectance patterns here might
be influenced by any of three factors. Firstly, the regional stress
pattern, and regional stress history, vhich includes the in situ stress
field apparent from the mining induced roof failure. Secondly, the
localised effect of strike-slip faulting and, lastly, the localised
effects of differential corpaction around stone rolls. Each of these
factors nay produce distincUve beciding plane bireflectance patterns
which nay be overprinted to varying degrees ty later stress fields.
4.3.1 RESULTS
Table 4.3 records the vitrinite reflectance and bedding plane
bireflectance characteristics of the sanples. Figure 4.8 shows
locations of each sample taken fron 04 Panel. Reflectance measurements
were nade according to the procedure described in Chapter 2 except that
CBPSIS figures were constructed frcm six vertical sections rather than
150
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151
Fig. 4.8 Location plan of coal sanples taken for vitrinite
reflectance measurement (for exanple, 261) and rock sanples
taken for point-load testing (for exanple, R141).
Non-randcm R max orientations of 4 sanples are narked t^
bars adjacent to the sanple site.
152
four. The maximum reflectance of sanples varies frcxn 1.18% to 1.26% and
the bedding plane bireflectance ranges fron 0.02% to 0.07%.
Of the ten sanples measured in C4 Panel fomr had CBPSIS figures which
gave a statistically significrant R max direction. None of these R max
ciirecrtions have a consistent trend (Fig. 4.8). Inspection of the
CBPSIS figirces, however, show that they all have at least two sets of
peaks (Figs 4.9, 4.10 and 4.11).
Therefore, the reflectance peak directions were identified and their
orientations listed in Table 4.3. Subsequent analysis of vitrinite
strain refers to the reflectance peak directions.
The directions of reflectance maxima measured fron sanples taken near
or above stone rolls are indicated on the CBPSIS figures in Figs 4.9
and 4.10. The location of the sanple within the seam relative to
the stone roll is also shown. Sanple 265 (Fig. 4.11) was taken
approximately 2m laterally frcm a stone roll.
Rose diagrams of reflecrtance maxima directions have been drawn for each
sanpling dorain. For exanple, the sanples from both stone rolls are
shown separately in Figs 4.12a and 4.12b. Sanples 262, 263 and 264
were considered separately as they were taken frcm around a stone roll
located between strike-slip faults. Sanple 265 is included in Fig.
4.12b because it occurs within 2m of a stone roll. Sanples remote from
stone rolls (266 and 267) are shown on a separate rose diagram (Fig.
4.12c).
153
262 264 263
Seom Roof
•262 •263
262-264 ^ SAMPLE LOCATIONS
Seom Floor
0 ) 2 3 '• I I -I V, . 1.
^ 258-261
; ^
Fig. 4.9 CBPSIS figures of sanples taken fron around stone rolls in
04 Panel. The locations of sanples relative to the stone
roll are shown. Refer to Fig. 4.8 for additional sanple
locations. Reflectance maxima on CBPSIS figures are shown
by bars extending frcm each CBPSIS figure.
154
258 259 260 261
Seom Roof
.259
258.
260
2 3 - I I
\
•261
S«om Flo
Fig. 4.10 CBPSIS figures of sanples taken frcm cux)und and adjacent
to a stone roll in C4 Panel. Reflectance maxima are shown
on each CBPSIS figure. Refer to Figs 4.8 and 4.9 for
sanple locations.
155
Fig. 4.11 CBPSIS figures of sanples taken fron 04 Panel. Sanples
were located away frcm stone rolls except 265 \diich was 2m
frcm a stone roll. Reflectance maxima are shown on each
CBPSIS figure.
156
Fig. 4.12 Rose diagrams of (ZBPSIS reflectance naxina grouped as
follows:
(a) Sanples 262,263 and 264 frcm around a stone roll
between strike-slip faults.
(b) Sanples 258-261 and 265 frcm around a stone roll.
(c) Sanples 266and 267 remote fron stone rolls.
(d) All sairples.
157
$
(a)
I
(b)
I
(d) (c)
158
In the three sanpling dcmains represented in Figs 4.12a-c, the NNW
trending reflectance maxima is conmon. Reflectance maxima oriented
between E and ESE are found frcm sanples located near the stone rolls
and between the strike-slip faults, and frcm sairples 266 and 267
located remote fron stone rolls. Only sanples 258-261 and 265 all of
which are located near to stone rolls have maxima trending NE. One
sanple in each of the sanple dcmains has a third reflectance maxima
trending NE. In addition one sanple in each sanple dcmain has a third
reflectance maxima oriented between N and NNE (that is, sanples 260,
262 and 266).
Figure 4.12d presents a sunmary of the orientations of all reflectance
maxima directions in C4 Panel.Three peaks are clearly present but the
330° to 340° peak is dcminant.
4.3.2 INTERPRETATION
Vitrinite with a non-randcm R max orientation inplies that the
reflecrtance maxima of the CBPSIS is equivalent to the R max. What then
defines the R max of vitrinites v^ose R max orientation is random? This o o
nay occur vdien the CBPSIS has two reflectance maxima. In this stixiy
reflectance naxima are deemed equivalent to R max peaics. Even if a
CBPSIS has two or more reflectance maxima each is referred to as a
R nax peak, o ^
Fron these results the influence of stone rolls upon R max peak
orientations is not conclusive, because the two stone rolls studied
have ciifferent vitrinite reflectance patterns.
159
In a further attempt to find systematic R nax orientation trerds the
orientation of the peaks on. each sanple were ccxrpared with other
sanples irrespective of location within 04 Panel.
It was found that crertain sanples have the same pair of R max peaks.
Three groups of sanples were defined (Fig. 4.13).
(a) Set A has peaks oriented NNW and NE (sanples 258, 259, 261 and
265).
(b) Set B has peaics oriented NNW and E-W (sanples 263, 264 and 267).
(c) Set C has three R max pea3cs oriented NNW, NNE and E-W (sanples
260, 262 and 266).
The observed pairing or coupling of R max peaks is interesting in that
it shows the ubicjuitous NNW orientation but more inportantly provides a
basis for dividing and grouping the R max peaks oriented between north
and east. The division between the NE R max peaics of Set A and the o ^
E-W peaks of Set B is distinct. However, R nax peaks for this cjuadrant
(0 - 90°) fron Sets A and 0 are not readily grouped
until both the NNE and E-W peaJcs of Set C are separately defined (Fig.
4.13), giving three groups of R max peaks between N and E.
4.3.3 RELAnOM OF R max SETTS A, B, C cr —
The three sets of sanples A, B and C cannot be explained ty virtue of
their location with respecrt to local observed structure. No zonal
R max orientations are evident, carparable, for exanple, to the
Scarborough Fault (Stone and Cook, 1979). Interpretation of the
relationship between R max orientation sets A, B and C is ciif f icult
because they have no apparent or unicjue relaticanship with the observed
structure. Fron this particular study area it is equivocal whether the
160
GN.
W-
Fig. 4.13 Orientation of R max peaks. Sets A, B and C each contain
samples with the same pair of R max peak ciirecrtions. S,
to S. represent individual strain events whose mean
orientations are shown.
161
observed sets developed simultaneously or as a response to a series of
strain events. Previous work presented indicates that sequential
strain events are recorded (for exanple, the Scarborough Fault) but, if
true in the Kanira stixiy, the cjuestion raised is why all the sanples
were not iirprinted with these events? At least a partial answer might
be given in Chapter 3 which shows how vitrinite, collected fron
ciifferent levels within the seam, fron the same site, has the sane
strain events inprinted unevenly between the sanples.
Extending this line of argument further, the data frcm Sets A, B and 0,
suggest that scrme strain events may not be recorded in all parts of the
coal seam.
Differentiation of R max peaics of Sets A, B and 0 enables four discrete o
R max peak orientation dcmains (S, to S.) to be established, vAiich
have nean orientaticans of 335°, 014°, 053° and 272° respectively (Fig.
4.13). The assunption is made that each dcmain represents at least one
ciiscrete strain event.
These four strain directions can be interpreted as being two orthogonal
sets, that is, S ^ and S^ plus Sj and S^.
For reasons not apparent, all strains are not inprinted into vitrinite,
and for the sanples taken, R max peaks are seen to occur in three
ccmbinations. Sets A and C have at least both members of an orthogonal
strain pair. Set B has R max peaks representing the dcminant strains
of each orthogonal pair (that is, S^ and S^). All sanples contain the
S, strain event. No significance can yet be placed on vhich strains
162
are found in any one sanple except this interpretation has allowed the
identification of orthogonal R max peaks.
4.4 PODCT-LQAD HUCTORE CRIEWTATICNS
Point-load fracturing of cored sanples was carried out to establish if
any preferred ciirection of tensile fracture exists in the sandstone
roof rocks of the Kemira Colliery study area. Sanples R141, R142 and
R144 were taken fron the sancistone roof at locations shown in Fig. 4.8.
The crores, each cirilled nomal to bedding, were of two types. Firstly,
those vhose length to diameter ratio conformed to the stanciard for
point-load fracture strength testing (Broch and Franklin, 1972) and
seconcily, those vhose length was shorter were used to establish
point-load fracture direcrtions. AjpendLx II lists the strength of
cores loaded to failure. Fracture ciirections were measured as
described in Chapter 2.
Figure 4.14 shows the ciistribution of point-load fracrture orientations
for sanples R141, R142 and R144. These figures were constructed by
using a moving 10° area at 2° intervals.
A number of dcminant fracture frecjuency peaks are found for each
sanple. Seme of the sanples have carmon peaks but all peaks are not
ccmmon to each sanple. Figure 4.15 shows the cembination of data for
the three sanples as (a) a weighted mean, giving equal credencre to each
sanple, and (b) the total number of fractures measured. Both are
similar except the 121-123° peak is stronger in ciiagram (a).
163
ui -I a S < (Ji
lU -J
a <
UJ
Q.
<
Fig. 4.14 Histogram of point-load fracture orientations for sanples
R141, R142 and R144. The histogram was constructed using
a moving 10 degree arc at two degree intervals. The peak
ciirections are narked for each sanple.
164
o
<
o »-
UR
ES
O < QC UL
Fig.
HTE
D
30
EIG
^ 1
4. 15
(fi UJ QC
Histogram of point-load fracrture orientations for all
sanples as follows:
(a) a weighted fracture total giving each sanple the same
credence, and
(b) total fractures neasured frcm each point-loaded
sanple. Peak frequencies are indicated.
165
In the 000° to 090° range four strong peaics ajpear at 001°, 023°, 047°
and 073°. The peak at 121° is the only one in the 090° to 180° sector.
No firm conclusions nay be drawn fron the point-load fracture
orientations because of the polymodal nature of the peak pattern.
4.5 DISCOSSIOW
4.5.1 ROOF OCKDITIOMS
The data presented suggests that the presence of either laminite or
sancistone in the roof will produce a different type of failure.
However, this failure may be ciifferent between heaciings and
cut-throughs. The apparent dependence on mine roaciway direction is
exorplified by the change in proportion of failure type per metre, e.g.
scaly roof failure changes frcm laminite/sancistone = 0.32/0.50
(heaciings) to 0.56/0.12 (cut-throughs). Therefore, the mechanisms of
failure involved for the headings will very likely be different to
those in the cut-throughs.
In the heaciings sandstone has a greater proportion of scaly roof per
metre than laminite, although the number of irdividual falls per metre
is similar (Table 4.1). This is accounted for by the nature of the
failure.The sandstone fails along beciding planes, either inclined
foreset becis or horizontal becis, and tends to extend further laterally
than the laminite falls which fail along high angle geological
discsontinuities such as joints and strike-slip faults. The extent of
the falls in the headings is restricted because the joints trend across
the rc)adway. The majority of sancistone failure in the headings is
along beciding planes,which tends to limit the heights of the falls (see
Table 4.1) so that the scaly type is predoninant.
166
In the crut-throughs laminite has the greater proportion of scaly roof
type. The failure mechanism ajpears to be different to that found in
the headings. The action of a dcminant near horizontal stress field
acting at a high angle to the thinly bedded laminite appears to have
caused the rock to delaminate by a cembination of shearing and
buckling. This mechanism applies to each of the failure morphologies
whose developnent depends mainly on how cjuickly and, therefore, how far
upward this proceeds before being supported. Broken and cracked roof
is also cannon in the laminite roof and represents thin broken plies
vhich probably result frcm continued delamination after the placement
of roof supports.
Sandstone also has a broken and cracked roof as a major failure type in
the cut-throughs. However, the sandstone terds to be more blocrky due
to the thicker nature of the beds. The most inportant change of
failure mode of sancistone in the crut-throughs, crcarpared to the heading,
is the tendency for falls to be higher.
This is becrause sandstone no longer parts along the basal beciding
planes but is prone to shear at a higher level. As a result flat top
falls, irregular top falls and brokoi and cracked roof occur instead of
the scraly type of roof failure.
The presence of gutter failure, (low angle shearing of roof adjacent to
rib) so often used as an indicator of horizontally applied stress, is
restricted to small sections of the headings (generally near
intersections). It is likely that the guttering is an extension of
failure originating in the cut-through because the doninant horizontal
stress field is oriented sub-parallel to the headings. Stress induced
167
roof failure should be minimised in this orientation. Low angle stress
failure in the cut-throughs is restricted to the centre region of the
roadway roof. Apparently shear failure extends above the roof bolts
forcing the lower roof plies downward as roof failmne extends upward.
Therefore, the immediate roof shows tension cracks and becores dead
weight to be held by the remaining support capacity. Alternatively the
roof shears and delaminates, falling at the face prior to support
placement due to the high lateral stress field.
The total proportion of roof not fallen or broken per metre in the
cut-throughs is 0.02 corpared to 0.38 in the heaciings. This suggests
that the roof lithology is not the main cause for such a variation. In
acidltion the ciifferent genetic failure modes between headings and
cut-throughs would irdicrate that the horizontal stress is oriented
060°. It is interesting to note that the minor amount of guttering
v*iich does occur in the headings is oriented approximately parallel to
the principal horizontal stress, but as mentioned previously this
appears to have originated frcm the cut-throughs.
The contribution to roof failure made by the presence of stone rolls is
unclear because of the adjacent strike-slip fault line. Not enough of
the surrounding Panel was napped to indicate if the stone rolls caused
the faulting and associated joint formation.
Evidence from other areas of the Southern Coalfield show zones of
strike-slip faults, (Shepherd and Creasey, 1979) without associated
stone rolls, of similar trerd.
168
4.5.2 SPRAIN EVENTS
A number of different interpretations of the stress/strain data may be
derived in 04 Panel. Each of the strain events recognised in the
vitrinite reflectance data are apparently significant responses to
applied stress. Interpreting the origin, ciirection and sequence of the
applied stresses is problematic because there is no theoretical basis
for determining the likely response of vitrinite to stress. Therefore,
enpirically based judgements are used to interpret possible
stress/strain histories, assuming that a R max pieak ciirection was
oriented normal to the dcminant lateral palaeostress.
In 04 Panel the vitrinite reflectance patterns appear to be carplex in
their association with geological strucrture. Interpretation of strain
patterns based on sequential crverprinting such as described for the
Scarborough Fault (Stone and Cook, 1979) are not obvious in 04 Panel.
However, sequential overprinting forms the basis for the proposed
history of strain events presented below. The major difficulty is not
being able to assign a reliable sequence to the strain events because
the vitrinite reflectance patterns are not localised about a particular
structure to show the stages of cfverprinting.
This limitation apart, the interpreted palaeostress events are
presented in Fig. 4.16 (the strain is assumed to have developed normal
to the applied near horizontal stress). The trend of associated
geological structure in 04 Panel is also shown in the figure.
The strain associated with palaeostress-S, is proninent in all the
sanples examined and is also sulparallel to the doninant present day
169
Fig. 4.16 Sunmary ciiagram showing angular relationships between
fault strucrtures, joint orientations, point-load fracture
orientations and lateral stress directions for stress
events S, to S.. The in situ doninant lateral stress
direcrtion is shewn.
170
lateral in situ stress. The questions which arise about
palaeostress-S, and the lateral in situ stress are:
(a) is the in situ stress strongly residual and recorded in the
vitrinite?
(b) is the in situ stress recorded in the vitrinite as a recrent
tectonic event (that is, post-coalificaticm)?
(c) is the in situ stress not recorded in vitrinite at all but is
oriented coincidently with an older stress event?
These uncertainties cannot be resolved frcm the Kemira study but an
interpretation of palaeostress order is presented. It is based on
linking reflectance ciata to the coalification period. It is probable
that the strongest recognisable strain inprinting in the vitrinite
occurred during croalification. Furthermore these strains would have
been recorded near the end, or have been the last strain j iase, of the
coalification period. Low beciciing plane biref lecrtance, typical of the
Bulli Coal, indicates that the older strains inprinted in the vitrinite
during coalification would normally have been corpletely overprinted by
subsecjuent events toward the end of coalification. Unfortunately there
is no evidence to exclude two reflectance naxima fron the main
coalification pericd. Stress fielcis applied in the pxost-croalification
pericd nay possibly be imprinted in the vitrinite over time, but are
unlikely to C3verprint strain or reflectance naxina fron the erxi of the
coalification pericd.
Table 4.4 surrmarises the different stress/strain j iases and their
likely association with observed geological features. The S,
palaeostress event is inprinted in all Kanira vitrinite sanples, and is
presumed to be the oldest recognised from vitrinite reflectance. The
171
ENE S^ palaeostress event is probably also inprinted to the roof and
flcxDr strata of the Bulli Goal as the residual in situ stress field.
The remaining palaeostresses, S2-S., are not able to be placed in
definite secjuence. The palaeostress-S^, oriented E-W, forms almost
normal to the doninant point-load fracture ciirection (023°), and the
regicDnal joint ciirection napped outside 04 Panel, as well as being
parallel to the ciyke, high angle fault/joint zone just outside the area
of 04 napped in detail (Fig. 4.16). S2 is possibly older than S,
becrause of its potential relation to regional jointing.
Palaeostress-S., oriented N-S, is almost orthogonal to palaeostress-S2.
Apart frcm being parallel to the point-lead fracture direcrtion 001° it
is not associated with any observed geological feature.
The strike-slip movemant in C4 Panel, including movement on the dyke
slightly outside the stuciy area, is related to palaeostress-S^
orientation (NW-SE). The West Cliff exanple fron Chapter 3
demonstrated the relatively late stage movement on similiarly oriented
strike-slip fault structures. This stress field is also normal to the
047° pxoint-load ciirection.
The Kemira study area has produced an interpretation having four
possible stress events and five point-load fracture directions. This
is seemingly more cemplex than the West Cliff case study in Chapter 3.
Do the multiple point-load fracture peaks reflect different applied
stress events? Table 4.5 shows which stress events are gecmetrically
related to point-load fracture directions. Interestingly there is a
172
cembination of load nomal pxoint-load fracture directions (023°, 047°)
and load parallel point-load fracture ciirecrtions.
Further analysis of this stress event and point-load fracture
relationship will be presented in Chapter 7 and will include other
stuciy areas.
As stated earlier in this chapter the vitrinite reflectance pattern may
have been influenced by any one of four factors. They were, regional
trends, in situ horizontal stress field, localised effecrt of
strike-slip faulting and differential ccmpaction about stone rolls.
The ciistribution of reflecrtance peaks at the ciifferent sanple locations
suggests that localised effects were not recognised and each of the
strains influenced more than the stucty area in 04 Panel. The
relationship of the dcminant R nax peak direcrtion with the in situ
horizontal stress raises the possibility of coincident origins and
indicates that the in situ stress field is probably strongly residual.
173
TABLE 4 .4
STRESS DIRECTICM NATURE OF RBOCRD IN VTmiNITE AND ITS
RELATIONSHIP TO CTOXIGICAL STRUCTURE
Palaeostress-S,
(ENE-WSW)
Palaeostress-S,
(E-W)
Palaeostress-S-
(SE-NW)
Palaeostress-S.
(N-S)
The doninant R max ciirection is recorded in all o
sanples. Subparallel to the present dominant in
situ lateral stress ciirection as determined frcm
roof crondltions. Sulparallel to the 073°
point-load fracture direction. Possibly oldest.
Strain recorded in only a few sanples but in all
ciifferent structural associations in 04 Panel.
Subparallel to ciyke and normal fault outside
area of detailed work in C4 Panel. Forms normal
to more regicanal jointing and the major 023°
point-load direction. May also be the oldest
strain present.
A strong ciirection but containing a wide spread
of R max peaks. This strain is found in sanples o
near stone rolls. Although not dcminant in the
stone roll between the strike-slip faults seme
evidence of weak R max peaks exist in sanples 263
and 264. This stress p^se may be related to the
strike-slip movemant found on joints near stone
rolls. Stress direction is also nomal to the
047° point-load fracture direction.
Strain recorded in samples remote frcm stone
rolls, and above stone rolls in strike-slip zone.
May be related to formation of dcminant N - N N E
point-lcsad fracture set.
174
TAEBLE 4.5
gmESS EVEMTS AND EOINT-LQAD FRACTURE DIRBCTICM5
POINT LOAD FRACTURE ORIENTATION JOINTS
001° 023° 047° 073° 123° LOCAL REGIC» AL
Parallel to
Stress Event S. - - S, -
Normal to
Stress Event - S^ S. - - - S^
Note: S., for exairple, refers to the stress event v iicrh
caused the S. strain - assumed to be nomal to the
S. strain ciirection.
175
CHAPraR 5
BURRAQCRAMS VALI£Y - CASE STUDY
5.1 IWmODUCTICN
Mines in the Burragorang Valley are located on the western side of the
southern Sydney Basin (Fig. 1.1). The bedding plane bireflectance
characteristics wei e measured on oriented coal sairples of Bulli Coal
collected from four mines (Brimstone No. 1, Nattai North, Nattai Bulli
and Oakciale) in the Burragorang Valley. The pjurpose of this part of
the study was to examine a large sanple area (approximately 50km ), and
determine the range of variation of the vitrinite CBPSIS figures. The
sanpling pattern was not a systanatic coverage of the area because it
was limited to recently mined and accessible areas.
Apart from stuciying vitrinite reflectance, a regional assessment of
mining corditions was undertaken. Historical information of mining
conciitions is not very well documented in published reports, although
seme unpublished reports do exist and will be referred to. Seme
details of roof conditions, mapped by the author, will be presented.
Generally there are quite well defined areas with poor mining
conciitions.
Detailed geological structure will be presented in Chapter 5.2, but
this study area has relatively little structural deformation apart frcm
a zone of faulting and seme monoclinal flexuring (Mclean and Wright,
1975).
This chapter investigates two ideas:
176
(a) to look at vitrinite reflectance CBPSIS figures on a regional
scale in the Burragorang Valley group of mines, and irelate
them to geological structure and to variable mining
conditions; and
(b) to look at the response to vitrinite reflectance CBPSIS
figures frcm areas affected by deeply incised valleys
crverlying the coal seam and associated strata.
The above approach may give results from areas v iich have been
subjected to applied in situ stress of ciifferent age, duration and
orientation.
5.2 gmUCTORE
The Burragorang Valley mines are located on the western side of the
'controlling syncline' of the southern Sydney Basin (Wilson et al.,
1958) and have strata dipping at approximately 1 in 20 to the ENE.
Small monoclinal flexures are ccmmon in this region. Two larger N-S
trending normal faults, the Nepean and Oakciale Faults, occur to the
east of the mine leases (McLean and Wright, 1975). These structures
form a hinge line along vhich seciimentary thickness increase on the
east side of the faults. In the mine area the main structural feature
is a zone of NNW trerding normal faults (less than IQm throw) with a
hinge zone centred about Oakdale Colliery (Fig. 5.1). The sense of
throw changes at either end of this zone via an apparent scissors
movement. Associated with the faults are a series of c^es, which
ccmmonly trend ESE or are sulparallel to the nomal faults.
On the eastern side of the fault zone the normally poorly defined
monoclinal flexures, vdiich occur throughout the mining leases, beccme
177
^KT c1.
\
NATTAI NORTH
200 area^ i3 '
c3
N
t
normal faults
strike-slip faults/dykes
1km
BRIMSTONE
OAKDALE COLLIERY
\ ' I 8 North
NATTAI BULLI \ V
F i a : _ 5 j J : ^ faults d e v e l c ^ isi the a^agorang Valley i ^ ,
^ . i d u a l s ^ ^ are i ^ ^ ^ ^ ° ^ t 0> and cleat <c>
Stations are indicated.
178
more pronounced. In the more southern collieries (Oaicciale and Nattai
Bulli) east of the fault zone,- the flexures have steeper gradients but
shorter vavelengths although the overall gradient is similar to the
more consistent grades of the northern area. The eastern extent of the
flexuring is not well defined but borehole seam levels indicate
alternate areas of steepening and flattening of the gradient. Coal
seam analyses suggest that the monoclinal flexuring was active during
sedimentation (McLean and Wright, 1975). A regional scale BMR gravity
plan (Mayne et al., 1974, plate 5) shows a steepening of the gradient
in the vicinity of the eastern portion of the Burragorang Valley mine
leases.
The main two joint sets are oriented to the E and SSE. In the western
workings of Oakciale the E trending set is oriented ENE vrfiich is rotated
slightly northward of the crorparable trend fron the western mine
workings.
Joint ciata from recent mine workings are presented as rose diagrams in
Fig. 5.2. Half of each rose diagram is a summation of joint frecjuency
per 10° arc at 2° increments. The joint stations have major frequency
maximums at 003° 025°, 120-125° and 155° (magnetic).
Cleat ciata are presented in the same manner as the jointing (Fig. 5.3).
The nain cleat directions are reasonably consistent and trend NNE and
ESE.
The western boundary of the mine workings is defined by an escarpirent
of Triassic and Permian strata. The Bulli Coal crops out on the
western edge of this escarpirent.
179
(ii) (J2)
Fig. 5.2 Histograms of joints measured in 5 locations fron mine
workings of the Burragorang Valley mines. The location of
each site is marked with a ^ j' in Fig. 5.1. Histogram is
constructed using a 10° arc at 2° intervals. The peak
joint ciirections are marked.
180
(i3)
MN
t (i4)
MN
!
' ^
/i
Fig. 5.2 contd.
181
(C4) »f
Fig. 5.3 Rose diagrams of cleat measured in 6 locations frcm mine
workings of the Burragorang Valley mines. The location of
each site is marked with a ^c' on Fig. 5.1. Rose diagrams
in 10° intervals. Histograms with each ciiagram are
constructed using a moving 10° arc at 2° intervals, the
pjeak cleat directions are narked.
182
(C4)
Fig. 5.3 contd.
183
MN
Fig. 5.3 contd.
184
5.3 MINE ROOF CCNDITICNS
In the Burragorang Valley Collieries studied, the complete Bulli Seam
is mined to a height vMch varies between 1.5m and 3.0m
(approximately).
i^art fron the aciverse effects of local features, such as deeply
incised overlying gullies (Enever and McKay, 1980) and faults, the roof
conditions of the mine roaciways to the west of the NNW-trendlng fault
zone are generally considered to be very gcxxi. This is also true of
those mined areas in Brimstone 1 and 2 Collieries, vdiich are east of
the fault zone but closer to a northern escarpment vhere the Bulli Ctal
crops out.
However, east of the fault zone in Oakciale and Nattai Bulli Ciollieries
the mining conditions are atypicral of previous Burragorang Valley
ej jerience (Nicholls, 1979). Ifere roof conditions are generally poor
(Fig. 5.4) with the style of failure indicative of dcminant lateral in
situ stresses (e.g. Aggson, 1979) vMch preferentially deform
north-south oriented mine roaciways. Frcm a study of mining induced
failure, the principal stress direction is thought to be near
horizontal and oriented between ENE and E which has been conf imed by
an in situ stress measurorent (Gale et al., 1984b). The area of poor
roof conditions coincides approximately with the zone of more
pronounced monoclinal flexures.
The distribution of roof rock types throughout the mines varies.
Experience has shown that \ihere the immediate roof consists of a
massive ciark to mid-grey siltstone or mucistone more than one metre
185
i]
TYPICALLY
GOOD
ROOF
CONDITIONS
:^
\^
^^MAkEA OF
riCULT
fp/TlONS uLalera/ Stressed
^
Fig. 5.4 Area of difficult roof conditions in the Burragorang Valley
caused by a high horizontal stress field. Vitrinite sanple
locations are narked by dots.
186
thick, roof conditions are good. Areas which bound N-S trending
sancistone channels (McLean and Goociwin, 1973) have been affected by a
thinning of the siltstone and are prone to falls, via separation along
beciding planes or slickensides caused by differential corpaction. A
third sedimentary roof type is a thinly interbecided (less than 0.2m)
sequencre of shale, siltstone and sandstone. Because of the thinly
bedded nature of these rocks seme falls occur via beciding plane
separation.
In the eastern area of Oakciale and Nattai Bulli Collieries which are
affected by horizontal stress-related rcx?f failure, the roof is an
interbedded secjuence of siltstone, shale and sandstone. The ciark to
mid-grey siltstone is less than one metre thick in areas with stress
induced roof failure. However, good roof conditions have been recorded
from areas in Brimstone 1 and other collieries vMch have interbedded
sedunents and laminites in the immediate roof O&iLean and (Goodwin,
1973).
One problem frcm the point of view of this stuciy is that areas of good
roof do not fall and so the characteristics of the roof sediments
remain unknown. It wcxild appear that areas which are affected by
stress cannot be correlated solely to interbedded roof sedlnents.
Hovrever, the stronger massive siltstone seciinents, vdien greater than
one metre thick, do appear to resist stress failure slightly better
than interbecided secjuences.
A description of the poor roof conditions fron the Oakciale and Nattai
Bulli Collieries is provided below.
187
5.3.1 MINE ROOF OCMDITICWS - OAKDALE OCOJERY
Detailed napping of the 8 North Panel within Oakdale Colliery (Fig.
5.1), vdiich has severe roof deformation, is presented in Fig. 5.5.
This area is typical of roof deformation found in the eastern and more
recent workings of the Nattai Bulli and Oakdale Collieries (Nicholls,
1979).
8 North Panel has headings trending N-S which were preferentially
deformed. The E-W crut-throughs were in good condition. Gutter failure
formed by lew angle shearing of the roof strata, or shearing along
beciciing planes resulting in roof sag, were the main stress induced
failure types.
By measuring the orientation of the few lew angle conjugate shears
whicrh developed in the 8 North Panel (Fig. 5.6), the inferred principal
lateral stress direcrtion is 076°. This assumes that the low angle
cronjugate shears form nomal to the direcrtion of the lateral stress
field. The set of roof fractures oriented NE to ENE are thought to
originate from the effect of the seconciary lateral stress ciirection
(oriented at 323° - Fig. 5.6).
Most of the shear failure of the N-S mine roaciways is parallel to the
roaciways and forms as guttering. The roof stability mapping shown in
Fig. 5.5 shows the effect of a style of mining, called "pillaring on
the acivance" (Nicholls, 1979) carried out in difficult areas in
Oakciale. Briefly, as 8 North Panel developed fron south to north, a
pillar of coal on the imneciiate west of the panel was extracted. The
intention being to relieve the ENE oriented in situ horizontal stress.
This proved to be successful toward the middle area of the panel. At
188
LEGEND
I I Gcx>d R<x>f
ScaJy Roof
Flat Top
L W V-Top - Gutter
XJ Sag/Crack
^ Heavy Roof
V
Fig. 5.5 Mapping of roof failure conditions in 8 North Panel,
Oaicciale Colliery.
189
Fig. 5.6 Orientation of oblique lew angle conjugate shears in the
roof strata of 8 North Panel, Oakciale Colliery.
190
the northern end of the panel heaciings were driven ahead of the
extracted pillars. The poor rxoof conciitions and style of roof fciilure
in this area is shown in Fig. 5.5.
Figure 5.7 shows that 8 North Panel in Oakdale had an interbedded
secjuence of shale, sandstone and siltstone in the immediate roof. In
recent workings to the east of the 8 North study area, roof conditions
improved as the thickness of the ciark to mid-grey siltstone increased
but, locally, the presence of the monocline structure also decreased.
The roof conciitions east of the nain N-S fault zone are worse than on
the west side of the zone.
5.3.2 MINE ROOF OCWDITIOKS - NATTAI BULLI
The eastern mine workings in Nattai Bulli Colliery have very similar
failure characteristics to those described in Oakciale. In Nattai a set
of three or four headings were driven eastward into virgin ground
conpletely remote from surrounding mine workings. Severe roof failure
occurred in the N-S trending crut-throughs and the style of failure
(roof sag and guttering) indicated that the rocks were deformed by a
dcminant lateral E-W in situ stress.The in situ stress is thought to be
oriented between ENE and E, vhich is consistent with a number of in
situ stress neasurenents (Gale et al., 1984b). In a panel driven
northwards frcm this eastern development at Nattai Bulli Colliery, the
N-S trending heaciings were being deformed by the in situ stress
oriented with the najor principle stress dLrecticm (sigma 1)
approximately E-W and near horizontal.
A crude indicator of the time dependent failure prcperties of fcxu:
headings (A, B, C and D), driven 3Qm apart at a high angle to this
191
ISOPACH OF DARK GREY SILTSTONE IN IMMEDIATE ROOF(M)
FINE-MEDIUfvl SANDSTONE. INTERBEDDED SANDSTONE/SHALE
DARK GREY SILTSTONE
EROSIVE SILTSTONE CHANNEL IN UPPER PART OF SEAM
Fig. 5.7 Local sedin^tary and structural geology majped fron the
Bulli Coal seam roof, 8 North Panel, Oakdale Colliery.
192
stress field, are shown in Fig. 5.8. The roof of the first driven
heading. A, was found to break up as the mining face progressed. Ihe
mining of heading A was subject to the full in situ stress nagnitude
and the roof failed at the face. The immediate roof failure then gave
sore stress relief to B heading which did not break up until 14 days
after mining. C heading failed only 7 days after mining because of the
reduced rate of stress relief it obtained fron B heading. Lastly, D
heading had a further reduced tine to failure being 3 days. Fig. 5.8
shows that headings furthest frcm A heading receive less stress relief
and, therefore, had nore stress energy available to break up of the
roof. The first driven roaciway will break up higher into thQ roof
strata, thereby providing a better shield to an adjacent roadway than a
roaciway with a lower height of roof breakup.
This brief exanple of mine ix»f failure fron Nattai Bulli gives a crude
demonstration of how ciirecrtional in situ stress has a changing effect
on the roof conditions if mining metheds give any stress relief.
5.4 VITRINrTE REFLBCngJCE STUDY
Oriented vitrinite sanples were taken frcm the four mines studied.
Their location was limited by the location of recent workings although
in Nattai Bulli the western sanples are fron old workings. Old
workings usually have crushed and broken ribs vhich do not allc w sinple
crollecrtion of truly oriented sanples. The sanple locations were made
to give as wide a cxoverage as possible in the four mines as well as
looking at any local variation crver snail areas.
193
30 60 Distance from A Heading (m)
Fig. 5.8 (3rap showing tine taken before onset of observable roof
failure relative to distance fron the first driven
roaciway, Nattai Bulli Colliery.
194
5.4.1 RESULTS
The measured R max values of. the CBPSIS figures of sanples studied
range between 1.04% and 1.14% (Table 5.1). CBPSIS figures cormonly
have two sets of distinct reflectance peaks, except sanples taken
adjacent to faulting vAiere only one peak is evident. In judging
variations in the regional trend, results from these more localised
fractures were not used (i.e. sanple numbers NNl, NN3, NN4, NN5) Ixit
are presented later in this chapter.
Figure 5.9 shows the R max peaks of CBPSIS figures representing
different sanple sites in the four Burragorang Valley mines. They are
listed in Table 5.1. In view of the sanples commonly having more than
one set of reflectance naxima in the CBPSIS figures, it was not thought
worthvMle to calculate vhich sanples had non-randcm R max mean
ciirections as was done in Chapters 2, 3 and 4. Instead reflecrtance
maxima of the CBPSIS figures are determined by the procedure outlined
in Chapter 3.4.2, and used to make inferences of the vitrinite strain.
An analysis of the reflectance naxima p)ea]<;s of the vitrinite CBPSIS
figures reveals two separate Dcmains, A and B (Fig. 5.10). The
development of ciifferent vitrinite strain patterns in each Dcmain is
the basis of their identity. Figure 5.10 shows the rose diagrams of
the strain maxima frcm sanples in each Donain. The main ciifference
between the strain patterns of the two areas is the orientation of the
NE trending peak: in Domain A azimuths generally range frcm 047° to
074°; and in Dcmain B the range is 011° to 034°. One sanple NNIO from
Domain A has a strain peak at 020° v iich lies outside the normal range
for Donain A.
195
la
§,
^
C/D & a, <
w -J P-.
1/3
oi
<<< << CQ CQ CQ CQ CQ CQ CQ CQ CQ
O r H O r — ( 1 — l O O t — t O i — ( O i — 1 0
X ^ >i_ v... k >* x_ I ^ .-I .J i 1 -. >t v_ \j J (—t I—1 - 3- u i ^3" i_^ t„j *^ t o O^ O O^ I—< C^ O t ^ rH * 0 ^ ^0 C^ C^ CD <7 r~v O t^
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1 — ( i — < O r H O O O r - ( O O O O r - ( i — I O C 3 0 0 0 0 0 0 r - l i — l i — ( 1 — l i — ( O i — ( 1 — ( O O O e - ( I—( o o r-ir^
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rH r-l r-( rH rH O O O O O
O O O O O
o o
o CD
O
CD
o O
O
CD
O
O
O
o o
o C3
CD
CD
O O
O O
O
CD
O
o CD
O
O 0 0 O
CO ' d - t ^ t ^ vO C I CD CTl r H O CD
CD CD
hO O
Ln
o LO o o o
CTl o o o
O 1—I O 1—I t—I
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196
BRIMSTONE b4
"WSf
nnl.
nn3-
nn4. nn5
\
NATtTAI NORTH nnIO
nn12
nnll
b3
oa6
oa5.
OAKDALE
<»7 oa2~ \ oal
NATTAI BULU nb12 UA '3 /nb2
Fig. 5.9 Orientation of R max peaks of CBPSIS figures fron sanples
taken in Burragorang Valley mines.
197
Fig. 5.10 Location of Dorains A and B defined ty different R^max
peak orientations. Rose diagrams of R^mx peaks in ten
degree intervals. The number of samples measured, not the
number of R^nax peaks, is shown with each rose diagram.
198
The SE strain peak ciirection has crverlapping orientations in both
Dcmains A and B (A: 115° to 167°; B: 097° to 150°), although in Domain
B there is a relative anticlockwise rotation of seme strain peak
orientations as was also found for the NE trending strain peaics (Fig.
5.10). The exact nature of the bounciary between Domains A and B is
un]cnown although the two western-most sanples in Nattai Bulli Colliery
are approximately 40m apart and show strain patterns belonging to each
dcmain. On a regional scale this is an abrupt change.
5 .4 .2 RELATION OF STRAIN, STRUCTURE AND ROOF (X3NDITI0KS
Figure 5.11 shows the superposition of plans of geological structure,
poor roof conditions and the two dcmains with ciifferent vitrinite
strain patterns. The Domain B strain field and the area of poor roof
conditions, resulting fron a dominant E-W trending lateral stress, are
reasonably coincident.
5.4.3 INTERPRETATIOW AND DISCUSSICWS OF RESULTS
The vitrinite reflecrtance results show that for the area studied
regional strain patterns are cronsistent within each structural dcmain.
Such consistency of results verifies that non-uniaxial behaviour
related to strain cran be found in coals with as low as 1.00% vitrinite
reflectance.
Figure 5.12 provides detail of the ciistribution of CBPSIS peaks of
sanples fron Dcmains A and B. Except for one sanple, Dcmain A and B
have ciifferently oriented groups of NE trending strain peaics. The
Dcmain B group is oriented NNE (midpoint of the range being 023°) and
the Dcmain A group is oriented NE to ENE (midpoint of the range being
061°). There aire two sets of SE trending vitrinite strain peaks in
199
^'^^K-t^ROOF CONDITION BOUNDARY
Fig^_5^ superposition of the boundaries of different roof
conditions and different reflectance maxi^ orientation
with the fault zone.
200
N
o DOMAIN B
DOMAIN A
Fig. 5.12 Distribution of R max pea]cs frcm Dcmains A and B.
Midpoint of each group of strain peaics is narked with ^*'
201
each Dcmain (Fig. 5.12). Their orientation within Dcmains A and B
vary. In general the orientation of the strain peaks in Dcmain B
appear to be rotated anticlockwise to those of Domain A.
Irrespective of the strucrtural significance of any of the strain peaics,
the NE tirendlng peaks are the clearest inciicators of strain variation
between Dcmains A and B. There is an overlap of these strain peak
orientations between Dcmains A and B and, therefore, they cannot be
used to identify either Dcmain.
Various evidence suggests that the area defined by Dcmain B is a
distinct structural entity ccmpared to Domain A. This evidence is
dlscrussed below.
A. Domain B has higher in situ stress which is consistent with the
observed variation in mining conditions. In Dcmain B, roof
failure induced by high horizontal in situ stress fielcis is
markedly different frcm the good mining crondltions of Domain A.
The extent of the influence of the escarpment, situated on the
northern and western bounciary of the Burragorang Valley mines, as
a stress relief agent is unknown.
B. Although the escarprent probably does offer some stress relief
eastward it is unlikely to ejq)lain the higher strain evident in
Dcmain B. Furthertnore, stress relief from the escarpment is
unlikely to cause different vitrinite strain patterns between
Dcmains A and B.
202
0. Different patterns of vitrinite strain peaics between Domains A and
B suggests that the two areas had ciifferent strain histories. Two
interpretations of the strain pattern interpretation are discussed
belcw. Each alternative looks at the possible relation between
individual strain events in Dcmain A and Dcmain B.
5.4.3.1 Strain History of Domains A and B - Interpretaticm
One
The two NE strain peak orientations in the domains are interpreted
as being the same generation of strain. An anticlockwise rotation
of approximately 38° (betv^en the midpoints of eacrh group,of NE
strain measurements) is involved across the bounciary frcm Dcmain A
to Dcmain B (Fig. 5.13a).
Looking within Donain B the NNE to NE strain pea3cs of Oakciale
Colliery are oriented more northerly than those of Nattai Bulli
Colliery (a rotation of 12° using the midpoint of each group of
strain peaks. Figs 5.9 and 5.12). This may be evidence of a
natural rotation of strain within Dcmain B and be supportive of
the NE reflecrtance peaks in Dcmains A and B being the same
generation of strain.
Close inspection of Fig. 5.12 shows there are two sets of NW-SE
trenciing strain peaks within each dcmain. Furthermoi?e, there is
also an apparent anticlocrkwise rotaticm of the two sets frcm
Domain A to Domain B. The 338° set of strain peaks of Domain A is
sub-parallel to the general structural trend in the Burragorang
Valley mines. This Domain A set can be rotated 15° to correspond
with the midpoint of the ecjuivalent set in in Dcmain B. Similarly
203
N
t \ /
\ (J DOMAIN B ^
. ^ V.'\ t> DOMAIN A 0
/ / o
f \
*o \ \ \
Fig. 5.13 Evidence of rotation of three sets of R max peaks between
Dcmain A and Dcmain B. (a) Interpretation 1, and (b)
Interpretation 2. Note in (b), peak orientations Al and
Bl are orthogonal pairs vhereas peak orientations A and B
represent the one direcrtion rotated between dcmains.
s \
^ ^ ^ \
B Al
?
Bl
A1
204
a rotation of some 17° is apparent beti en midpoints of the second
northwesterly set in Domains A and B (305° rotated to 287°).
Within either Dcmain there is no apparent pattern to the areal
ciistribution of the strain peak sets. The cronclusion to be drawn
fron this is that the earlier of the two strain events, within
either Donain, was not corpletely overprinted by the following
event.
Frcm the ciata presented, three strain events are interpreted in
each Dcmain (Fig. 5.12). Dcmain A has strain p)eak midpoints at
061°, 305° and 338° whereas Dcmain B has strain peak midpoints at
023°, 287° and 323°. One explanation for the rotation of strain
between Dcmains A and B is the existence of ciifferent structural
donains as controlled by differential movement within the
basement. Dcmain B contains the hinge zone around vhich the sense
of throw on the normal faulting changes and the intensity of the
monoclinal flexure increases. Thus Domain B possibly represents
an area of more active basement tectonism, vhich transmits an
inhemogeneous strain pattern into the Permian seciimentary
secjuence.
The three strain events recorded in the vitrinite show ciifferent
amounts of rotation betvreen Dcmains A and B, which nay imply that
strain transmitted frcm basement tecrtonics has varied with time
(rotations are 38° and 15-17°), and has been active over a period
of time. This is in accordance with the variation in raw ash
crontent (excluding ncn-coal bands) of the Bulli Coal ac2X)SS the
moncxrlines in the Burragorang Valley collieries, v^ch suggests
205
that these structures v^re acUve at the tine of Bulli Coal
deposition (McLean and (Soociwin, 1973).
This interpretation, stated briefly, requires that the three
recorded strain events are rotated across the boundary between the
two structural Domains A and B (Fig. 5.13a) Assuming that the
strains form nomnal to applied lateral stresses. Domain A would
have palaeostresses oriented NE, ENE and NNW. These are rotated
to NNE, NE and NW to WNW respectively in Dcmain B. As shown in a
schematic model of the lateral stress rotation in Fig. 5.13a the
sense of rotation is the same.
It cannot be assessed frcm the ciata available which of the
dcmains, if either, is an indicator of the regional pattern. The
structirral character of Domain B appears to be slightly more
intense, whereas the western and northern bounciary of Dcmain A
borders an incised river system whose escarpment forms the western
bounciary of the mine leases. The origin of this geomorphological
feature may have been related to basement tectcanics.
5.4.3.2 Strain History of Domains A and B - Interpretation TViO
There are two different lines of evidence v iich are not well
ejqslained by sinple anticlockwise rotation of strain across the
bounciary between structural Dcmains A and B. Firstly, the sense
of rotation of cleat between Domains A and B is clockwise (Fig.
5.14) and is, therefore, opposite to that of the vitrinite strain.
The sense of rotation of cleat was determined by plotting the
cleat orientation maxima for both Domains A and B. The two major
sets were orthogonal and appeared consistent between Dcmains A and
206
< S o o
CQ
z < s O
O OO
o
o
o C>4
Z S - w
O E « rt> r" *-D O ) «5 fl) = Q N <
o
o
o Csl
4- O
Fig. 5.14 Dominant cleat orientations in Dcmains A and B. The sense
of rotation between the zcanes is marked.
207
B if a clockwise rotation of approximately 10°-15° is allowed.
Using this same rotation five cleat direcrtions in all are
correlated across both dorains.
The reason for this opposite sense of movement is not ejqplicable
by interpretation 1 unless the cleats were formed at a ciifferent
time to the vitrinite strain vhen there nay have been a different
sense of strain being transmitted fron the basenent.
Seconcily, pirevious experioice (Chapters 3 and 4) has shown that
strain peaics are conmonly found as pairs. Pairs of vitrinite
strain peaics can be found in Dcnains A and B, however, this
involved pairing ciifferent sets of strain peaks ccnpared with
interpretation 1. For exanple, in Dcmain A the 061° and 338°
(midpoint of sets) sets are orthcgonal, as are the 023° and 287°
sets from Domain B. The two strain sets whicrh remain are the 305°
set (Domain A) and the 323° set (Domain B) shown in Fig. 5.13b.
These two remaining strain sets have a coincident orientation with
the najor NW cleat set orientation in their respecrtive structural
dcmains (Fig. 5.15).
Frcm the above information a second interpretation is proposed
(Fig. 5.13b). The strain event recorded in Domain A (305°
midpoint) is postulated to be rotated approximately 19° clockwise
across the Dcmain B bounciary. Both the vitrinite strain
directions and the sense of rotation are very similar to the
interpretation of cleat variation between the two structural
-dcmains. This strain event would occur simultaneously in each
dcmain. A similar rotation across boundaries is the only evidence
208
. \
. ^N
0 CLEAT 0
\ RoTTiax
\ ^ PEAKS 0
Al Bl B
A l
Bl
Fig. 5.15 Ctnparison of R nax peak direcrtion with the doninant cleat
orientation in Domains A and B. Refer to text for
explanation.
209
to tie this vitrinite strain to the formation of the cleat.
Dcmains A and B each have a uniquely oriented conjugate set of
vitrinite strain peak directions. For Donain A these are the 061°
and 338° sets and for Domain B the 023° and 287° sets. It is
unknown if the equivalent strain sets in the two domains formed at
the same time via an anticlockwise rotation across the structural
domain boundary, or if the strain recorded in each dcmain was a
separate and localised phase.
In summary, interpretations one and two vary on the basis of
whether the strains noted in each domain are rotated across the
domain bounciary, are rotated ciifferently over tine or are separate
events recorded independently in each domain. In either
interpretation there are at least three stress events vhich nay
have relevance on a regional scale.
5.4.3.3 Relaticn Between Inferred Palaeostress, In Situ Stress
and Geolocri-cal Structure
The expression of tectonic structure in Domains A and B is
similar. Perhaps an increase in the monoclinal flexuring on a
small scale, as explained previously, and a reversal in the sense
of threw of faulting are the nain differences between the
structural dcmains. A penetrative expression of structural
variation between the two donains is not apparent, apart frcm the
cleat. The joint pattern (Fig. 5.16) does not appear to shew any
rotation between the detrains.
Taidng the analysis a step further, by assuming that the vitrinite
strain forms normal to applied lateral palaeostress fielcis, the
210
o
o
o CM
O
o
o «1
o 06
z S
N
o
o
o CM
< Z
o Q
z < S o
Fig. 5.16 Conparison of p r inc ipa l j o in t ciirections between Domain A
and Donain B.
211
relationship of these interpreted palaeostresses to the in situ
stress and geological structure nay be briefly explored.
To date CSIRO have nade measurements of the in situ stress
at a number of sites in the Burragorang Valley (Walton and
Fuller, 1980; Enever and McKay, 1980; C5ale et al., 1984b). Figure
5.17 gives a summary of the maximum near horizontal corponents,
and Table 5.2 a summajcy of the overcoring results. In situ stress
measurements in Dcmain A, vdiich are not located beneath incised
surface valleys, have maximum principal near horizontal stress
directions oriented 039°, 060° and 115°. Their magnitude (7-10
MPa)is approximately equal and of the order expected for that
amount of overburden (Enever and McKay, 1980).
The magnitude of the in situ stress measured in Domain B is cjuite
ciifferent. The absolute value of the naximum principle stress
ciirection (a..) has doubled to 22 MPa and the ratio of horizontal to
vertical corponents is nearly 2:1, (Table 5.2). The orientation
of o.. is 063° v iich is similar to one of the directions measured
in Domain A, and compares to the in situ stress ciirecrtion of 076°
determined from mining induced shear failure of mine roaciways in
Oakdale Colliery (Dcnain B), and the approximate E to ENE
direction inferred fron Nattai Bulli Colliery (Dcmain B). The
escarpment to the west and north is an inportant fact in reducing
stress magnitudes in Domain A.
The interpretation of palaeostress directions found in vitrinite,
in situ stress, and the geological structure of the Burragorang
212
,-
•nje
i.
- ^
Fig. 5.17 Location and sumrary of principal horizontal in situ
stress corponents neasured by the overcore technique.
213
LO
m H CO
hH
o
o
CO
CO
CO CO
c/)
HH C/D
in
CJ C/D 1—1
c:) ? HH 1 ^
nl PQ
CO
< ? O C/5
rt
rt
03
W HH
- J
8 HH CO
r—\ I—\ /—\ O O O O OO 00 oo 00 CTl CTl Cr> CT> rH
^ ^ ^ ^
^ ;2 uB" uD" otr oir
> !H
(1)
w w
o •M rH CO
M 00 0>
o u 1/5 fH
a, (U
1 — I 0} e3
o o o o \ o 00 CO o r "^ r
o o o CN o LO cr> 00 O C3 rH
Csl K ) r o
LO o o to • • • •
LO LO LO hO
O O O O CT) O r H •<* O hO r H vO t o CsJ
I I
O O O O ro rH LO LO LO t~ rH cn v£) K) O hO O rH to
hO rH "^ OO O
d- t~ vO O t--
o CT r H
1
o rH rH
o oo ( N
o r-^ r
LO
1
O O O O O c n LO o t o r^ rH CTl \ 0 ' ^ rH <N1 CNl O (N
LO to vO LO UD
00 cn r-~- r~~ c-j rH (
s s s s ^ § g g g ^ 2 Z :z: 2 PQ HH HH HH HH HH
< < < < <
S S S e < pq U Q W
214
Valley mines is presented in Fig. 5.18. In Dcmain A, palaeostress
directions are oriented NE (035°), ENE (068°) and NNW (331°).
The NW-SE trending in situ stress field is ciifferent to the other
neasurements because the ^vertical' stress is o^ (Table 5.2)
instead of being the a- corponent. It is oriented parallel to the
main ESE dyke direction, but appears unrelated to the SSE
palaeostress ciirection.
The remaining two in situ measurements are aligned with the two
approximately NE trenciing palaeostresses but cannot be reliably
assigned to a particular event.
The NE family of palaeostress ciirections do not appear to be
related to the fault structures of the Burragorang Valley mines.
Nor do they appear related to the monoclinal system with its
nomal faults inplying an extensional system toward the ENE. The
SSE trenciing palaeostress is subparallel to the normal fault
system and nay be a relicrt of that episode.
Within Donain B, the palaeostress oriented at 017° does not appear
coincident with any geological structure or in situ stress. The
palaeostress direction oriented 113° is coincident with seme ciyke
ciirections, however, unlike the d dces this palaeostress is not
recorded in vitrinite from both Dcmains A and B. The third
palaeostress (oriented 054°) is oriented 9° from the in situ
stress measurement and 13° from being nomal to the structural
trend.
215
N
, DOMA/N A
DOMAIN B
< P = Palaeostress < • M = In situ stress-overcore method <- R = Stress determined from roof fractures
Fig. 5.18 Sunmary of geolcDgical structures, neasured la teral in si tu
s tress ccmponents, the la tera l stress direction inferred
f ixxn mining induced shear and palaeostress ciirections
determined frcm v i t r i n i t e .
216
The in situ sti:ess in Domain B is nomal to the structural trend
and the axis of the monoclines. It is unknown if the 054°
palaeostress (Fig. 5.18) is related to, or is a major corponent of
the in situ stress because of the uncertainty of its origin.
However in both Donains A and B the NE to ENE palaeostress
ciirection has had reasonable agreement with the in situ stress
direction.
Qureshi (1984) reported a gravity anemaly along a N-S line
inmedlately to the east of the Burragorang Valley area, ( le et
al. (1984b) postulated that normal faulting and increased in situ
horizontal stress in Nattai Bulli Colliery, were caused by
basement faulting. Movement within the basement, transmitted to
the strata surrounding the Bulli Coal is the likely origin of the
monoclines and strucrtural trends.
It is postulated that at seme stage a left-lateral wrench movement
in the basement caused the nomal fault zone, and the series of
cross-cutting strike-slip fault zones, in the overlying strata.
The angle between the ccmjugate set of faults is approximately
60-65°, and they represent a pair of synthetic and antithetic
strike-slip faults (Harding, 1974). The orientation of the faults
is cronsistent with a wrench zone oriented slightly east of north.
It would be expected that the nomal faults have a considerable
strike-slip corponent.
Limited accress to this fault system ciid not allow a firm
conclusion to be reached as nomal fault novement was the norm.
(Dblique movement was noted at limited sites. The reverse fault in
217
Nattai North is oriented sympathetically with this orientation but
it nay also have its -origins with forces caused by valley
incision.
A left-lateral wrench system in the basenent nay explain the
rotation of palaeostress noted between Dcmain A and Domain B. The
mechanics of basonent wrenching affecting ciifferently oriented,
and presumably concurrent stress events, is not understood.
Superirrposed on the basement movements are a series of lateral
tectonic stresses which may be rotated when crossing structural
bounciaries.
One interpretational difficulty encountered with regional strain
patterns neasured via vitrinite reflectance is relating them to a
particular geological event. Strain recorded in vitrinite around
single structures generally ajpears to be consistent with the
formation of that strucrture. Ifcwever, on a broader scale it is
presently unknown vhich events are recorded in the vitrinite and
which stress pulses remain unrecorded. Hence, the interpretation
of Burragorang Valley vitrinite strain figures is uncertain except
to say that the two areas have different strain regimes as
recorded by both the lateral strain release evident from the roof
and floor strata upon mining and from vitrinite reflectance
results.
218
5.4.4. VITRINITE STt AIN PATTERNS AROUND POST-<X)ALIFICAnOK
SmUCTORES - NATTAI NCKEH CXMJERY
A poor funcianental knowledge concerning the mechanism of inprinting a
penetrative strain to the vitrinite is restricting the full
interpretation and understarding of the strain figures. Two
suggestions for the mechanism of inprinting have been proposed (Stone
and Cook, 1979):
(i) the anisotropic growth of polyarcmatic micelles during
coalification due to unecjual lateral stresses; or
(ii) a type of nechanical distortion of the vitrinite
structirre.
Some evidence for the type (ii) inprinting mechanism might be
interpreted in Nattai North Colliery. Here surface valley incision
above the mine workings has produced localised high lateral stresses
vhich have caused roof failure during creal mining. More inportantly
the presence of a number of Ic w angle (20-30°) reverse fault planes is
possibly attributable to the directional increase in lateral stress,
and the decrease of vertical loading, in the vicinity of the valleys.
The lew angle reverse faulting is confined to areas of incised valleys
and it has unicjue structural trencis within the Burragorang Valley. The
incised valleys are probably of Tertiary age, being formed after the
nain pericxi of coalification (Diessel 1973). The effect of valley
incisions has been recorded in outcrop near the study area (McELroy,
1969). Stress dlstrihxitions expected in the area of influence of
incised valleys are reported by Pariseau (1971), Worotnicki (1969) and
Enever et al. (1978). Enever and McKay (1980) have related in situ
stress measurements in Nattai North Colliery to the overlying incised
valleys.
219
This section will look at the vitrinite strain pattern in two areas in
Nattai North Colliery vhich occur in the vicinity of deeply incised
surface valleys. First is an area (200 Area, Nattai North Colliery) in
which roof deformation occurs in response to localised lateral stress
beneath a valley. The second area vhich also has preferentially
deformed roaciways, looks at a lew angle reverse fault v trlch is
considered to have fomed due to stress field redistribution caused by
valley incision. This area has higher in situ stress magnitude than
that of 200 Area (Enever and McKay, 1980).
Enever and McKay (1980) have made a detailed stuciy of the response of
in situ stresses to valley incision in the two areas mentioned abcrve.
In the present stucty the sane two areas were sanpled and the vitrinite
strain patterns determined. Both areas represent two different
intensities of in situ stress. Therefore the response of vitrinite to
post-c»alification stress fielcis of different nagnitude can be gauged.
5.4.4.1 200 Area Nattai North Golliery
The nagnitude of the localised in situ stress in 200 Area, due to
valley incision, should decrease frcm west to east, as the D/H
ratio (Enever and McKay, 1980) changes fron 0.56 to 1.29 (where D
= depth of cover above coal seam, and H = height of relief above
valley floor). Enever and McKay (1980) reported that for D/H
ratios greater than 0.5 the roof conditions should be similar to
those expected without any valley present. I/)calised stress
induced roof failure beneath the valley suggest that roof failure,
although minor, persists to larger D/H ratios, although this would
depend on the strength of the imnediate roof strata.
220
Low angle shear failure is an integral part of the roof failure
beneath the valley. -The tracres of conjugate shears are
subparallel to the trend of the valley v iich is consistent with an
applied stress oriented normal to the shear trace (Fig. 5.19).
The doninant horizontal in situ stress is found to form normal to
the valley trend (Enever and McKay, 1980).
In situ stress neasureirents (Table 5.2) at sites B and C shew near
horizontal principal stress ccnponents vhich can be related to the
valley orientation. However, Enever and McKay (1980) concluded
that, because their D/H ratio is approximately equal to 1,, then,
"the stress fielcis neasured at sites 1 (0) and 2 (B) may be
expected to be substantially unaffected by the presence of the
valley" (p. 19). This is supported by the good roof conditions
found near the test sites. At stress test site D, Walton and
Fuller (1980) have produced a result (Table 5.2) vhich has o..
oriented approximately nomal to the valley trend. The nagnitude
of these measurements may be affecrted by the closer than usual
vicinity of the test to the roof (approximately 2m abcrve - the
purpose was not to monitor virgin in situ stress but to give a
useful guide to stress conditions at roof bolt horizons).
Figure 5.20 shews the horizontal ccnponents of in situ stress
neasurements relative to the topography. Also shown are the
vitrinite strain peaks for sanples in 200 Area. Three of the
sanples (NN9, NNll and NNl 2) are consistent with vitrinite strain
patterns found in other parts of Dcmain A, and show only general
agreement with the NE trend of the in situ stress field. The
221
N
\ 12
y
Fig. 5.19 Orientation of mining induced shear failure in the mine
roof in an area located beneath a deeply incised valley,
Nattai North Colliery.
222
Fig. 5.20 Horizontal ccnponents of the in situ stress measurement
sites B, C and D (refer to Table 5.2 for magnitudes) and
the orientation of R nax ciirecrtions from vitrinite o
sairples.
223
fourth vitrinite sample (NNIO) is atypical of Dcmain A and is not
obviously asscxriated with the in situ stress.
Therefore the above evidence would suggest that the level of in
situ stress resulting from the incision of the valley iias not
altered the vitrinite strain fron the regional pattern. The
resultant stress is however strong enough to cause mining-induced
rock failure.
5.4.4.2 Reverse Fault, Nattai North CDllierv
Beneath a deeply incised valley in the northern part of Nattai
North Colliery (Fig. 5.1) there are a number of localised lew
angle reverse faults. The location and extent of the fault
studied is shewn in Fig. 5.21. It consists of two fault planes
(with individual threw smaller than Im) and possibly formed as a
response to the localised increase in stress magnitude beneath the
incised valley. Enever and McKay (1980) report values for the
principal stress corponents (Table 5.2, Site A). These show that
the near horizontal ccnponents are doninant (o^ = 0 MPa), with
o./Oy ratio being over 4. If the stress nagnitude is sufficient,
these are ideal conditions for reverse faulting. In fact a^ is
normal to the trend of the reverse fault vhich occrurs in this
area.
A high angle nomal fault (85° dip) occurs normal to the reverse
fault. The normal fault has a variable throw less than Im and is
parallel to the dcminant joint ciirecrtion in the area. No
intersection of the two structures has been exposed ty mining.
224
Fig. 5.21 Orientation of Rjrax peaks around a normal fault and
intersecting reverse fault structure. The area is beneath
a deeply incised valley which has a high N-S trenciing
lateral stress field.
225
Vitrinite sanples have been taken near the two faults (Fig. 5.21).
The reflectance results of these sanples (NNl, NN3, NN4 and NN5)
are presented in Table 5.1. The interpreted strains in the
vitrinite, fron the two sanples (NNl, NN3) nearest to the reverse
fault, have a similar trend to the fault but dissimilar to any of
the regional strain patterns. Sanples NN4 and NN5 have strains
vhich fit corponents of the regional trend of Domain A vitrinite
reflectance patterns. Sanples NNl and NN3, adjacent to the fault,
have vitrinite strain directions consistent with the formation of
the reverse fault (i.e. the near horizontal stress oriented nomal
to the fault).
It cannot be directly determined if the strain was inprinted to
NNl and NN3 before or after faulting tait the strain pattern
would suggest that it is related to the reverse faulting. Sanples
NN4 and NN5 fit the regional trend and do not appear to have
been altered by the superinposed in situ stress field. Only those
sanples nearest the fault reflect the superinposed stress. The
maximum reflectance values do not increase toward the fault. The
above evidence suggests that strain is possibly recrorded in
vitrinite after the corpletion of regional coalification,
especially around specific fault structirres. However, it still
cannot be resolved with certainty, frcm this field evidence, if
vitrinite strain inprinting is associated with the physiochemical
process of coalification or is a mechanical distortion of the
micellular structure. Much further work neecis to be done to
establish the mechanism and conditions of this iirprinting.
226
5.5 OONCLUSICKS
Significant anisotropy of CBPSIS figures fron coals with Remax as low
as 1.00% has been neasured and interpreted as strain in vitrinite
sanples from the Bulli Coal in the Burragorang Valley.
By analysis of the main lateral strain ccnponents frcm vitrinite
measured frcm Burragorang Valley cxoal mines, strain patterns of more
regional significance have been neasured and two Domains of strain
identified. Within each structural dcmain the strain ccnponents have
relatively constant orientations vhich at least demonstrates that
vitrinite nay record regional strain patterns away from areas of
increased localised stress such as faulting.
Dcmain B is coincident with a greater release of strain energy frcm the
rock strata during and after mining. Poor coal mine roof conditions
result fron the higher stresses in Dcmain B. On the scrale of the mine
leases in the Burragorang Valley the structural style (monoclinal
flexuring) is similar although, on a smaller scale, the flexuring is
slightly better defined in the area with poorer roof conditions. A
direct relationship betv^en the variaticai in vitrinite strain figures
and the higher strain state in the rock mass cannot be proved, but at
least nay provide an enpirical indicator of a region -with a ciifferent
strain state. The origin of both vitrinite strain and in situ stress
is interpreted as a combination of strain transmitted from ciifferential
basement movements and from tectonism transmitted vdthin the
sedimentary pile, not necessarily associated with local basement
movement.
227
Vitrinite appears to be able to recx)rd subtle changes of strain but the
inprinting mechanism and timing of the strain events in geological time
are fundamental aspects which need further research. For weaJdy
defomed areas vhich have limited penetrative structures this technicjue
of strain determination should be a useful means of aiding structural
interpretation, especially as related to assessing mining conditions.
228
229
CHAPTER 6
TAHMXR OQLLIBRY - CASE STOTY
6.1 INIRODUCnON
Tahmoor Colliery is located on the western side of the coal leases
being mined in the Southern Coalfield (Fig. 1.1). Mining operations in
the Bulli Coal seam began on a producrtion scale in 1979. Data on roof
conciitions, structural geology, and inferred stress ciirection were
collected as mining progressed.
The initial mine development resulted in a number of mining panels
being driven in different directions into virgin conditions away from
any possible influence of adjacent mine workings. Tahmoor Colliery
provided a unicjue opportunity to assess the relationship betv^en roof
conciitions and the in situ stress field.
The development of a range of mining crondltions has been closely
monitored from the beginning of production. Mining conciitions becane
progressively more complex as mining proceeded enabling their stucfy to
develop secjuentially from the siirpler to the more corplex roof failure
types.
One panel, the NW Panel, was chosen for detailed study because it was
driven into virgin ground away from other mine worldngs. Many of the
fundairental relationships regarciing roof conditions were develcped in
the NW Panel. However the full range of mining conditions are not seen
in this panel, therefore the majority of other mine development was
also studied - but is not reported in the same detail as the NW Panel.
230
Stucty of the vitrinite optical indicatrix to identify palaeostrain
directions was undertaken to find any association with the geological
stress field.
In this chapter information is given regarciing:
(i) the stratigraphy
(ii) the geological structure
(iii) directional properties of the deminantly horizontal
stress field
(iv) mine roof conditions
(V) the causal relation between the in situ stress field and the
mine roof crondltions
(vi) the assessnent of palaeostrain ciata from vitrinite
reflectance.
6.2 STRATIGRAPHY
In the Tahmoor Colliery Coal Lease area the Rilli Coal is neminally the
uppermost unit of the Permian Illawainra Coal Maasures. The Permian
strata are overlain by the Triassic Narrabeen Groap, the Ifev^esbury
Sandstone and the Wiananatta Group which increase in thickness toward
the SE fron 370m to 450m. Representative thickness of individual
formations typical of the Tahmoor area, is shc wn in Fig. 6.1.
The interbecided strata v iich immediately overlies the Bulli Coal at
Tahmoor is significant in the context of mine roof conciitions. Figure
6.2 shows a section of the immediate roof. Its thicrkness varies from
approximately 3m to 9m over the mine coal lease area and cronsists of
interiDecided shales, mucistones and laminites overlain ty cearse-grained
cross-bedded sandstones approximately 25m thick. The laminites
231
TAHMOOR GEOLOGY /P\ fA / > \ A
SIC
T
RIA
S
r
MIA
a. UJ 0 .
SA
ND
ST
ON
E
cc
m U3 Ul
1 I
_ 200m •
GR
OU
P
NA
RR
AB
EE
N
400m •
05 UJ
WA
RR
A
CO
AL
M
EA
SU
f
CD
O
o
3
ILL
/
GENERALISED SECTION BULLI SEAM
/ ^ i
Jm-^^^^^I^Bj^
.Finely Interbedded Sltlstone Mudstone and Fine Sandstone
. Coal Bright and Dull (18m - 2.2m)
Interbedded Coal and Shale (0.0 - 0.3) . Sllty Mudstone/Slltstone (0.0 - 0.6) "Coal (0.0 - 0.25)
• Sllty Mudstorw/Siltstone
y
Fig. 6.1 Generalised s t ra ta section a t Tahmoor Colliery.
232
Abov« Rulli $«om Roof 5 5 m—1
D.DH. 28
LEGEND
i--^.'-' ' * ' ' ' • • ' " ' ' f ' ' f ' / i
Sondifon* 5 0 I
4 -5 ,
Shale
Mud»fon«
SiU»fon«
Lominit*
4 0m —
3 5 m —
30 I
2-5 m —
Thickness Rang» Throughout Ltas9
UNIT C 0 6 to 7 8m
2 0 1
1 5m —
1 0 m —
05 1
)m — I
I-** h,hA**^%^^
^7-yp-^-!r iJ"-J-^^J- i_ '—•<•
UNIT B 02toh6m
UNIT A 08to2-7m
TAHMOOR COLLIERY BULLI COAL-TYPICAL ROOF STRATA
Fig. 6.2 Typical sec t ion of roof s t r a t a above the Bul l i Coal,
Tahmoor Col l ie ry .
233
(Diessel and Moelle, 1965) are thinly interbedded (less than 20nm
thick) light and mid to dark -grey mudstones, shales and fine to very
fine lithic sancistones. Laminites are the dcminant rock type in the
initial metre of the roof. The large number of possible bedding plane
partings in the laminites make than a potential problem for mine roof
control.
Examination of core fran ej^loration boreholes over the Colliery lease
shows that the interbedded unit overlying the Bulli Coal can be divided
into three sections (Fig. 6.2). Unit A consists mainly of laminites
which vary in carposition between 35% and 85% of ciark shale beds., Unit
B is diagnostic and contains a massive mudstone, ccninonly clayey, vhich
may be underlain by a fine sandstone bed. ISiit 0 is variable.
Proportions of sandstone, laminite, shales, siltstones and mudstones of
Unit 0 change from borehole to borehole in the lease.
6.3 (SOBJOGICMi STRUCTURE
The Tahmoor Coal Lease lies in an area dipping gently to the NE with NW
trending monoclines. The Thirlmere Monocline extencis into the lease
area but the influence of the Bargo Syncline is not noticed locally
(Fig. 6.3). The main tectonic structure present in the lease is the
southern extension of the Nepean Fault (Fig. 6.4).
Within the colliery lease, the structure consists of two areas with
steeper NE trending gradients either side of a centrally located flat
area (Fig. 6.5). Tto the west of the lease a possible extension of the
Oakdale FaiiLt and Thirhrere Monocline systan may influence the
structural pattern within the mine lease.
234
OAKDALE
NORTH Trut Vflj
MITTAGONG
CAMDEN
CAMPBEUTOWNl
lAPPIN
LEGEND:
- + — Monoclint
Y - Sfnclint
' f « Ant id int
u D
• 1 1
Foull
Toftnship
Tohmcor Colliery Holding
TAHMOOR COLLIERY HOLDING STRUCTURAL SETTING
Fig- 6.3 Structural set t ing around Tahnoor Colliery (after Gcxxiwin,
1979).
235
I-
<
O I
hs 00 Q U Ul
Z
> •
LU >
D to
y
03 UJ CO
2 UJ Q s <
I-UJ
(KOjddB) »|B3S |S3|M»A
Fig. 6.4 Interpretation of the style of movonent on the JHepean Fault
structure, based on seismic data (after Herbert, 1989).
^""
A'
./^
.30. ,0- -\o-
Fig. 6.5 Structure contours of the Bulli Coal seam floor in the
Tahmoor Mine Lease.
237
i )art fron the Nepean Fault no other large faults have been interpreted
within the lease. The Nepean Fault structure had been thou^t of as an
easterly dipping normal fault (Willan, 1925; Branagan, 1975; Sherwin
and Holmes, 1986) before Herbert (1989) produced seismic evidence of a
v^sterly dipping, discontinuous high angle reverse fault system, which
he believes has significant wrench movonent (Fig. 6.4).
Mining to ciate has shown that a number of small faults are present
(vertical throw less than 2m). These are mainly discontinuities with
horizontal strike-slip movement (Fig. 6.5). A number of ciifferent
orientations of these structures have been observed ranging between
110° in the northern area and 138° further south. The strike-slip
faults occur in well developed joint zones and movanent appears to have
taken place along pre-existing joint planes. The extension of
strike-slip faults appear to have been via en-echelon movanent between
discontinuous joint planes, l^lonite and breccias associated with the
strike-slip faults vary fron a few millimetres up to a metre thick.
The nylonite thickness is usually greater in the coal than in the roof
rocks, and typically has well developed horizontal slickensides.
Strike-slip faults are in places associated with concorciant altered
igneous dykes up to 1.5m thick. The parUcular cembination of
strike-slip fault and d^^e is associated with instantaneous gas and
coal outbursts, v iich have ejected up to 350 tonnes of coal and
associated strata.
The di^es v iich are associated with the strike-slip structures are
highly altered and consist nmnly of clay minerals. At each exposure
the dyke is strongly fractured by randomly oriented highly poUshed
238
slickenside surfaces, and follows joint planes in an irregular and
discontinuous nanner. Strikerslip movanent appears to post-<3ate dyke
orplaconent along pre-existing joint zones.
In the NW Panel and 201 Panel a number of zones, oriented approximately
050°, contain a nest of low angle thrust faults in the Bulli seam and
the immediate roof. These faults have throws of less than 0.2m, and
occur as nests of conjugate reverse faults. Fault planes are seen to
flatten and extend along the bedding planes of roof and floor strata.
In the same area are nests of small conjugate reverse faults forming
zones oriented approximately 140°. These two zones are approximately
normal to each other. 400 Panel contains a 3.5m displacement nomal
fault oriented approximately 320°. Slickensides indicate only vertical
movanent on the fault plane, with little fracturing of the coal
adjacent to the fault plane. The normal fault is oriented seme 20°
from the direction of a nearby strike-slip fault/ciyke structirre.
Joints in the roof strata, above the Bulli seam, occur as distinct
zones. A number of joint zone directions exist in mine workings
e qjosed to date. In 100 Panel, in the southern part of the mine,
jointing is predeminately unidlrecrtional with an ESE trend and is
associated with strike-slip faults and ci es. In the eastern part of
the mine jointing is oriented NNW to NW. A summary of the joint
distribution is presented in Fig. 6.6.
(Geologists errployed by the mine owner, under the supervisicm of the
author, used the scan-line technique (Shepherd and Fisher, 1981) to
assess the variation in cleat ciirectican. Briefly this method uses 5
measuronents of each cleat set per site frcm which the median value
239
Fig. 6.6 Joint frequency distribution within Tahmoor Colliery
workings. Joints measured from roof strata of Bulli Goal.
Number of sanple points noted with each rose ciiagram. Ten
degree intervals.
240
becanes the representative value for each set. Sanple site spacing at
Tahmoor was 40m. (Generally, the cleat orientation is consistent in the
area studied as demonstrated by Fig. 6.7 vhich incorporates the
representative cleat directions fixm each station. Principal cleat
directions form an orthogonal set between 300-320° and 030-050°.
In general joints are developed independently of cleat. Most jointing
in the roof strata is not continuous into the coal of the Bulli seam.
6.4 ROOF (XMDITICWS
6.4.1 INIRODUCTION
Mining at Tahmoor Ctolliery was originally carried out using the bord
and pillar method to create main development panels or panels for
subsequent extraction. Roaciways driven to form pillars of coal
(ranging in size fron 35m x 115m, to 27.5m x 40m) are left to support
the roof. In extraction panels the coal pillars are subsequently
removed. Refer to Martin (1986) for a cxanprehensive description of
Australian mining practice. Longwall mining was cxrarenced in 1987 as
the principal source of production. Nicholls and Stone (1986) described
the history of roof support methods used in Tahmoor Mine, v iich was
based around roof bolts held by chemical cartridges.
In Tahmoor the early panel development involved drivage of three main
development panels (NW Panel, 100 Panel and East Intakes Panel) each in
a different direction (Fig. 6.8). The mining conditions in each of
these panels was the result of interaction with virgin ground
condLticais.
241
$
^ 20% -^
270 090
Fig. 6.7 Summary rose ciiagram of mean cleat dlrecticans determined
fron scan-line survey across Tahmoor Mine. 115 cleat
stations were measured. Ten degree intervals.
242
The NW Panel was chosen for detailed assessment of roof conditions
because it was initially driven for 1.5km as a 4-heading development
into virgin cxinditions, remote frcm any adjacent workings.
Roof conditions gradually deteriorated and became more cxantplex as the
NW Panel developed. The sequential deterioration of roof conditions
has significantly helped in the urderstandlng of the process causing
poor roof. The full range of roof conditions do not occur in the NW
Panel and are described from work carried out in subsequently developed
sections of the mine. This secrtion on roof conciitions intends to
describe the type ard ciistribution of conditions vdliich occur at Tahmoor
(Zolliery.
6.4.2 ROOF OASSIFICaTICW
The classification of roof conditions as used at Tahmoor is modified
from the classification used in previous case studies reported in
Chapters 3-5. Rcx)f cxjndltions are divided into two groups which are
readily identifiable in the field:
(i) short term roof conditions are those vhich occur at the
mining facs;
(ii) long term roof conditions are those vhich develop after
the roof support systan is set. This is a time dependent
roof condition.
Table 6.1 lists the classification of short term and long term roof
conditions. Short term roof conditions are related to the degree of
low angle conjugate shearing within the thinly interbedded roof strata.
The trace of the conjugate shears may be parallel or oblique to the
LEGEND
H B ARCH FAILURE
^ H SEVERE PARALLEL SHEAR
^ H PARALLEL SHEAR
I I PARALLEL/OBLIQUE SHEAR
H OBLIQUE SHEAR J
^ B SEVERE PARALLEL SHEAR
^Mi PARALLEL SHEAR
1 1 PARALLEL/OBLIQUE SHEAR
OBLIQUE SHEAR
m NO SHEAR
(In order of decreasing sever
ASSOCIATED WITH >-MINING INDUCED FRACTURES
(TENSIONAL)^
243
TABLE 6.1
Basic Roof Condition Classification Used At Tahmoor Colliery
1. Short Term Roof Conditions
(a) Arch failure
(b) Low-angle conjugate shearing - oblicjue
- parallel
- severe parallel. (c) ( ood
Nc>te: Mining induced fractures may occur with
rcof conditions (a) and (b).
2. Long Term Roof Conditions
(a) (3ood rcx>f
(b) Gutter fa l l s
(c) Cantilever gutter fal ls
(d) Sagged roof
(e) Scaly ixxjf
(f) Canplete roof failure - fa l l s .
*'^'w'rwa.r\.'^i^'Kr^i=^.i.Trm9-.'rx^v.
244
roadway direction and is classed as severe if shearing extends more
than 0.3m up into the roof- strata. Mining induced fractures are
tensional fractures induced ahead of the mining face in response to the
stress conc:entration around the acivancing mining face (Enever and
Shepherd, 1979). The mining induced fractures can occur with short
term shearing of the roof strata.
Arch failure refers to very severe shearing vhich causes the roof to
fall at the face. The natural arch so formed in Tahmoor usually has
good long teim stability.
The roof condition classification outlined in Chapter 2 has been
modified at Tahmoor to provide a better description. In particular the
arch failure type at Tahmoor has a minimum height limit of 0.5m instead
of 0.3m. Ccffisequently conjugate shear failure has an upper height
limit of 0.5m.
Roof conditions caused by variation in sedimentary style in the
immediate roof were not considered because of the similar roof found
across the Tahmoor Mine. Poor roof associated with minor faults and
ciykes were treated as separate events and no attarpt was made to
assimilate them within a typical Tahmoor roof classification.
6.4.3 MEIHGDS USED FOl ROCF MAPPING
Each mine roadway was mapped according to the roof classification of
Table 6.1. Description of these roof condition types is prc3vided in
Chapter 2. The basic unit mapped was the roaciway between each
intersection, which is a variable distance within panels and between
different areas of the mine. The range of lengths of ciiscrete roadway
245
units varies fran 120m to 27m. For the purposes of mapping roof
conciitions the unit roaciway length is not critical.
During the development of the NW Panel, roof conditions v ere
consistently mapped and re-napped. Both initial face conditions and
time-dependent failure were recorded. Roof conditions were mapped onto
mine plans so that their position and area of influence could be
traced. Assessment of the time-dependent failure for each roaciway
segment was not done at a fixed time after mining. Re-mapping of roof
conditions was carried out fron three to eighteen months after any
roaciway had been formed.
The extent of each roof failure type is recorded by the length of its
development along the mine jxaciway segment and is expressed as a
distance per metre for each secrtion of roaciway recorded. Alternatively
individual long term failure types are expressed as a proportion or
percentage per metre, vhich is also equivalent to the distance of
failure along each roaciway length. The dimensional characteristics of
ciifferent failure types means that failure may spread across the vhole
vddth of the roaciway, for exanple, sagged roof or be cxnfined to less
than one third or one cjuarter of the roadway span, for exanple,
guttering. Different failure types may occur side hy side or
superinposed on each other at the same distance along a roadway. Each
separate expression of a failure l^pe is recorded independently by its
length parallel to the roadway.
Therefore, the total of different failure types may sum to a ratio
greater than 1.0 per netre of roadway, if more than one failure type is
present.
246
6.4.4 DISIRIBOTIOW CF ROOF FAHJIRE TYPES
Both short term roof conditions and long term roof conciitions have been
intensively mapped in certain areas of Tahmoor Colliery.
Short term failure types have been mapped over much of the Tahmoor
Ctolliery mine workings. Figure 6.8 depicts the distribution of the
short term failure type deoned typical for each length of roacivay
between intersections. Inspection of Fig. 6.8 indicates that although
sane areas have consistent short term roof conditions other areas have
a range of roof failure types. The most usual dlfferenc^e is between
headings and cut-throughs or, in other worcis, adjacent roadways, mined
in a different direction (usually normal to each other),
Different areas of the mine workings have characrteristic roof failure
types. Mining panels such as 100 Panel, 200 Panel and Main East
Intakes (Fig. 6.8) have seveire mining conditicans at the mining face.
The short term roof conditions are extranely bad. By contrast 300
Panel has very good short term roof conditions, and other panels such
as the NW panel and 102 Panel and 103 Panel have variable short term
mining conciitions.
A detailed stuciy of the NW Panel is inportant toward understanding
short term roof conditions. The next section, 6.4.5, describes the
progressive change in the NW Panel toward poorer roof conditions which
allowed development of understanding of roof conditions in Tahmoor.
A later section, 6.4.6, lises the concepts developed in the NW Panel to
understand roof conditions in other panels of the mine wdth more
intensely deformed roof.
247
6-4.5 ROOF FAILURE IN THE NW PANEL
6-4.5.1 Short Term Roof Fai1iirp>
Low angle conjugate shears are the main type of short term roof
mapped in the NW Panel. Low angle conjugate shears are subdivided
into those vdiich are oriented parallel to the heading and those
v*iich cx:cur oblique to the direction of the mine roadway. The
oblicjue shears are recorded by their length carponent parallel to
the heading. Table 6.2 lists the distance per netre of low angle
conjugate shear failure and the distance per netre of severe
parallel shear and arch failure for both headings and
cut-throughs.
The higher (>0.5m) arch type falls, vhich occur at the face as the
ccal is being cut, are exanples of short term rocik failure. The
natural arch vdiich is formed in the roof as a consequence of the
fall appears to give stable long-term roof conditions.
At the inbye end of the section of the NW Panel studied in detail
(near 13 cut-through) mining induced fractures occurred in
conjunc:i:ion with low angle conjugate shearing against the ribside
(Fig. 6.9a).
The origin of these mining induced fractures is not cxxrpletely
understood but sane eirpirical observations give a partial
e3q)lanation. Before progressing further the term ^mining induced
fracture' should be more clearly explained. Strictly speaking any
fracture or rcxjf failure caused by mining is a mining induced
fracture or failure. In this thesis mining induced fractures
refer to curvilinear tensile fracture planes, not unlike joints.
248
TABLE 6.2
ROOF FAILURE TYPES RECORDED NEAR THE MINING FACE. N W PANEL
LOCATION FAILURE TYPES (DISTANCE PER METRE)
LOW ANGLE CONJUGATE SHEARS SEVERE ARCH FALLS PARALLEL TO OBLIQUE TO HDG TOTAL PARALLEL ( 0.3m) HEADING PARALLEL COMPONENT SHEARS
(0.3-0.5)
TOTAL ALL FAILURE TYPES
A HEADING (a) 0-1 1-2 2-3 3-4 A-5 5-6 6-7 7-8 8-9
9-10 10-11 11-12 12-13
B HEADING
0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9
9-10 10-11 11-12 12-13
(b) 0.00 0.00 0.15 0.29 0.03 0.38 0.18 0.55 0.87 0.54 0.38 0.85 1.08
0.00 0.11 0.23 0.00 0.04 0.07 0.00 0.42 0.78 0.33 0.37 0.60 1.10
(c) 0.06 0.09 0.01 0.10 0.14 0.16 0.48 0.38 0.02 0.41 0.19 0.07 0.08
0.00 0.04 0.00 0.24 0.00 0.11 0.15 0.32 0.02 0.35 0.32 0.25 0.07
(d) 0.06 0.09 0.16 0.39 0.17 0 .54 0.66 0.93 0.89 0.95 0.57 0.92 1.16
0.00 0.15 0.23 0.24 0.04 0.18 0.15 0.74 0.80 0.68 0.69 0.85 1.17
(e) 0.00 0.00 0.14 0.00 0.07 0.00 0.03 0.03 0.51 0.18 0.06 0.00 0.08
0.00 0.00 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.11 0.00 0.22
( f ) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.06
0.00 0.00 0.05 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
(g) 0.06 0.09 0.30 0.39 0.24 0.54 0.69 0.96 1.40 1.13 0.63 0.92 1.30
0.00 0.15 0.31 0.24 0.04 0.18 0.15 0.74 0.80 0.68 0.80 0.85 1.39
249
(a) 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-13
D HEADING
0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-13
Cut-throughs
1 2 3 4 4 exp*. 5 6 7 8 8A 9 10 11 12 13
(b) 0.00 0.17 0.00 0.00 0.02 0.00 0.05 0.15 0.73 0.63 0.67 0.93 0.76
0.00 0.00 0.00 0.00 0.04 0.10 0.02 0.08 0.48 0.10 0.25 1.00 0.76
0.34 0.62 0.66 1.14 0.68 0.76 1.19 0.98 0.93 0.71 0.35 0.52 0.71 0.94 0.74
(c) 0.00 0.00 0.00 0.00 0.02 0.02 0.11 0.33 0.31 0.38 0.20 0.07 0.26
0.00 0.00 0.03 0.03 0.00 0.09 0.46 0.26 0.38 0.10 0.58 0.20 0.23
0.00 0.21 0.18 0.48 0.30 0.19 0.24 0.33 0.00 0.00 0.02 0.07 0.06 0.04 0.38
(d) 0.00 0.17 0.00 0.00 0.04 0.02 0.16 0.48 1.04 1.01 0.87 1.00 1.02
0.00 0.00 0.03 0.03 0.04 0.19 0.48 0.34 0.86 0.20 0.83 1.20 0.99
0.34 0.83 0.84 1.62 0.98 0.95 1.43 1.31 0.93 0.71 0.37 0.59 0.77 0.98 1.12
(e) 0.00 0.00 0.06 0.00 0.00 0.00 0.00 0.02 0.03 0.03 0.00 0.20 0.00
0.00 0.00 0.06 0.00 0.00 0.00 0.00 0.00 0.00 0.20 0.04 0.00 0.00
0.00 0.00 0.00 0.08 0.08 0.04 0.00 0.00 0.33 0.28 0.14 0.18 0.08 0.03 0.08
(f) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.07 0.07 0.00 0.00 0.15
0.00 0.00 0.13 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 0.00 0.04 0.33 0.00 0.00 0.00 0.33 0.33 0.34 0.00 0.00 0.00 0.00
(g) 0.00 0.17 0.06 0.00 0.04 0.02 0.16 0.50 1.14 1.11 0.87 1.20 1.17
0.00 0.00
. 0.22 0.03 0.04 0.19 0.48 0.34 0.86 0.40 0.87 1.20 0.99
0.34 0.83 0.84 1.74 1.39 0.99 1.43 1.31 1.59 1.32 0.85 0.77 0.85 1.01 1.20
* Is extens ion of 4 cu t - th rough i n to v i r g i n coal on LHS of pane l .
250
Fig. 6.9a Mining induced fractures located in the roof near the
ribside, where the fracture plane dips at a high angle and
makes an angle of less than 20° to the roaciway direction.
Shear fractures are associated.
Fig. 6.9b Mining induced fractures cnjrve across the roaciway and dip
in the direction of drivage, that is, fron left to right.
251
252
253
vhich form in the immediate roof as the coal is being mined. Failure
of this type has been described from Leichhardt Ctolliery, Queensland,
by Hanes and Shepherd (1981). At Tahmoor the context of mining induced
fractures recorded in the NW Panel is more specific. The following
provides a description and partial explanation.
The mining induced fractures occ ur in the initial 0.4m (normally
between O.lm and 0.3m) of the coal mine roof. In plan view,
looking in the direction of mining, a mining induced fracture
located in the roof above the coal rib runs parallel to the
roaciway and then curves across part of the roaciway (Figs 6.9b and
6,20a). The fractures appear to form just ahead of the mining
face because they are well defined v^en the ccal is taken to
expose the roof. The frecjuency of cx currence is variable fron
approximately 10 per netre to 1 per 10m.
Mining induced fractures in the NW Panel normally extend half vay
across the roadway. Rarely do they extend more than
three-cjuarters across the roaciway.
Mining induced fractures dip in the direction of mining at an
angle vdiich decreases as the angle between the dip direction and
the roaciway ciirection increases. In the centre of the roaciway the
dip varies between 25° and 60°, but is nearly vertical over the
rib side.
Mining induced fractures occur consistently (greater than 90% of
fractures) on one ribside in any given roadvay segnent. It is
254
assumed that these tensile fractures are fonred parallel to the
plane containing the local sigma 1 (a..) and sigma 2 (a«) as they
are reoriented aixsund the rectangular face of the mine entry
(ffenes and Shepherd, 1981).
6.4.5.2 LcTKj Ttenn Roof Failure
The progressive development of each failure type is traced inbye
along each panel heading on the basis of order of drivage. The
secjuence of mining each heading was the same betvieen 1 and 9
cut-throughs but changed fron 9-12 cut-throughs and reverted to
the original method toward 13 cut-through (Fig. 6.10,). A
caiparison can be made on headings which have been ciriven in a
similar mining configuration, i^pendix IV contains a tabulation of
long term roof condition data.
The long term roof conditions (good, sag, cantilever and gutter)
as measured in headings are plotted against location (Figs 6.11,
6.12, 6.13 and 6.14). The amount of good roof in headings
decreases inbye along the NW Panel toward 8 cut-through and then
varies with respect to order of drivage (Fig. 6.11). The
proportion of the different types of roof failure (sag, gutter and
cantilever) increased as the amount of good roof decreased inbye
along the NW Panel (Figs 6.12, 6.13 and 6.14). (Generally each of
the failure types have their greatest develc^irent in different
locaticais in the NW Panel. Sag failure is inportant between 7 and
11 cut-throughs, overlapping slightly with cantilever failure
vhich increases markecily inbye 10 cut-through. (Sutter failure
affects more roaciways between 5 and 9 cut-throughs than the
further inbye headings.
255
CUT-THROUGH
MINING DIRECTION
ONE
MINING \
CYCLE
0 - 9 CUT-THROUGH
Ficu_6a0 Order of drivage i n one mining cycle , for d i f fe ren t areas
of the NW Panel.
256 lOOr
90
80
70
60
50
40
30
20-
O o cc
O
</> t -
z Ul
U
10
-» FIRST DRIVEN
• SECOND DRIVEN
• THIRD DRIVEN
-»LAST DRIVEN
LOCATION-CUT-THROUGH NUMBER.
Fig. 6.11 Plot of good roof in heaciings fron 0 to 13 cut-through
along the NW Panel. The order of drivage is indicated. 100
LOCATION- CUT-THROUGH NUMBER
Fig. 6.12 Plot of sagged roof in headings fran 0 to 13 cut-through
alcsng the NW Panel. The order of drivage is indicated.
100 r
90
80
o o oe ce. lU
> Ui .J
t-V < 1-
z Ul
Of
70
(SO
50
40
30
20
10
257
-•- FIRST DRIVEN
. «- SECOND DRIVEN
* THIRD DRIVEN
~ir LAST DRIVEN
4 5 6 7 8 9
LOCATION-CUT-THROUGH NUMBER
10 11 12 13
Fig. 6.13 Plot of cantilever roof in heaciings fran 0 to 13
cait-through along the NW Panel. The order of drivage is
indicated. 100
90
80
70
u 6 0 -
-1 FIRST DRIVEN
+ SECOND DRIVEN
• THIRD DRIVEN
-t LAST DRIVEN
U-
o o QC Ui
50
/o
30
20
10
0 5 6 7 8
LOCATION-CUT-THROUGH NUMBER
12 13
Fig. 6.14 Plot of gutter roof in headings fran 0 to 13 cut-through
along the NW Panel. The order of drivage is indicated.
258
The development of ciifferent failure types in the cut-through is
shown in Fig. 6.15. The-proportion of good roof is much less in
the cut-throughs than headings. Sagged rcx f is the pipedaninant
failure type through much of the panel although cantilever becanes
inportant from 11 c:ut-through to 13 cut-through.
The roof conditions between cut-thrxjughs and heaciings in the same
area of ,the panel may be cjirlte different. Average values (percent
per m) of failure types in each of the headings A, B, C and D were
calculated and corpared with cut-through values (Fig. 6.16a-d).
The following were the main points of caiparison between long term
roof conditions:
- the proportion of good roof is mach less in the cut-throughs
than in the headings (Fig. 6.16a).
- both headings and cut-throughs trend to poorer roof conditions
inbye along the NW Panel.
- both headings and cut-throughs have similar proportions and
tirends of gutter and cantilever roof failure types (Fig. 6.16c
and d)
- sagged roof is more ccmmon in cut-throughs than heaciings (Fig.
6.16b).
6.4.5.3 (jonparison Between Short Term and Long Term Roof
Failure
The amount of face failure appears to be indicative of the
proportion of total long terra failure in both the heaciings and
cut-throughs. Fig. 6.17a and b show the trend of total failure at
the mining face (distance per metre) and total long term sag.
259
z Ul U
>-
o z O u
o oc
/
-t-GOOD ROOF
+ SAG ROOF
•CANTILEVER ROOF
4 GUTTER ROOF
\
\
\
/
/
/
JL. uL 4 S 6 7 6 9
L O C A T I O N — CUT-THROUGH NUMBER
10 )) 12 13
Fig. 6.15 P lo t of long term roof conditions in crut-throughs along
the NW Panel.
260
Fig. 6.16 Ccsrparison of long term roof cxarditions between heaciings
(H) and cut-throughs (C.T.) along the NW Panel.
(a) Perc:entage of gocd roof.
(b) Percentage of sagged rcof.
(c) Percentage of gutter roof.
(d) Percentage of cantilever roof.
261
(a) 100
UJ CL
z UJ u Q: UJ Q-
GOOO
LOCATION
(b) 100 T
Q: UJ
z.
g Q.
LOCATION
JOO T
(c)
UJ
a. 2 Uj o or UJ
50 .
262
LOCATION
GUTTER
:d) JOO T
oc UJ Q-
UJ
o UJ Q.
JU -
•
50 .
0
CANTILEVER
C.TN
1 1 — I — • — 1 — ^ — 1 1 1 1 —
/A '• / / \
/ /
- t 1 1 1 i
10 (3
LOCATION
263
gutter and cantilever failure (ciistance per netre) for the first
driven heading and the cut-throughs. The first driven heading and
the cnit-throughs are formed with the least shielding effect of
adjacent roaciways and are considered to be carparable because they
were mined in virgin conditions.
6.4.5.4 Relaticjnship Between Order of Drivage and Total Long
Tenn Roof Def omation
Another factor worthy of discussion is the influence of the order
of drivage of heaciings (Fig. 6.10), in one mining cycle, upon the
long term stability of headings. It is noticeable frcm Fig. 6.11
that the first driven heading canmonly has the greatest amount of
deformation. Two seguences of drivage exist in the NW Panel (i.e.
0-9 cut-through cf. 9-12 exit-through), so the effecrt of the change
of secjuence may give an insight to the iirportance of the order of
drivage on long term roof conditions.
To determine the effect of the order of drivage on long term roof
conciitions the following procedure was used. For each cycle of
driving the four headings, the roof conditions of the four
heaciings were ranked fron best to worst. The relative quality of
the heaciing (v^rst, 2nd worst, 3rd worst and best) was then
tallied with the order of drivage as shown for 0-9 cut-throughs in
Fig. 6.18a-d and for 9-12 cut-throughs in Fig. 6.18f-i.
264
Fig. 6.17 (a) Plot of total short and long term roof failure for
first driven headings along the NW Panel.
(b) Plot of total short and long term roof failure for
cut-throughs along the NW Panel.
(a) 150 .^ 265
Ul oc ^ 100 -
ti.
U QC
50 -
150-,-
(b)
100-
oc
U oc Ul
a.
5 0 -
SHORT TERM
LONG TERM
3 5 7 9 n
LOCATION- CUT-THROUGH NUMBER
13
SHORT TERM
— • LONG TERM
-T r 7
T r 9 3 5
LOCATION- CUT-THROUGH NUMBER
A ' 13
266
In order to cjuantify the quality of roof condition vath respect to
order of drivage each roof condition in the drivage secjuence was
weighted as follows:
4 X for worst roof,
3 X for 3rd best roof,
2 X for 2nd best roof, and
1 X for best roof.
The order of drivage with the highest weighted value would have
the poorest roof conditions.
The weighted roof condition ranking is cofrpared to the drivage
secjuence between 0-9 cut-throughs (Fig. 6.18e) and 9-12
cut-throughs (Fig. 6.18j).
In the first sequence of drivage fron 0-9 cut-throughs, the four
headings were ciriven consecutively frcm left to right. Note that
only data fran inbye 2 cut-through was used because of low
deformation in outbye headings. The weighted roof condition
ranldng for the sequence used between 0 and 9 cut-throughs (Fig.
6.18e) shows that the first 'driven heading has the vrorst, and the
second ciriven heading has the best, long term roof conditions.
The fcxirth ciriven heading has slightly better roof condlticns than
the third heading.
These results vrould point to stress relief in adjacent headings
being dependent on the amount of failure in the previously ciriven
heading. The greater the failure in one heaciing vrould suggest
nore stress relief in the subsequently ciriven adjacent heaciing.
5
4 .
3
2
I
(o)
WORST
1 2 3 4
(b) 267
2nd WORST
FL T T
2 3 4
(c)
3rd WORST
1 2 3 4
ORDER OF DRIVAGE
id)
BEST
1 • T f -
2 3 4
(e) o o oc
• ^ -IT
Oo
Ui *-' h-X
o
30
20
10-
-1 , 1 — I 2 3
ORDER OF DRIVAGE
5 .
z ^ 3 i S2 cr. ^ I
( f ) WORST
(g) 2nd WORST
(h) 3rd WORST
T 1—"—r
1 2 3 4 1 2 3 4 1 2 3 4
ORDER OF DRIVAGE
ACTUAL
PREDICTED
SHORT TERM
( I ) BEST
—J 1
1 2 3 4
( J ) u.
o o oc
o w z ^Q
ED
RA
C
ON
DIT
1 -I O U l
^
15 •
10 •
K •
\
1
1
• • ^ ^ — • » .
\^^ ^ ** —
V
1 2
ORDER OF
^ '^• '^CxV
1
3 DRIVAGE
V-\
4
ACTUAL
PREDICTED
SHORT TERM
Fig. 6.18 Cfcirparison of the f recjuency of the roadway with the worst
mining condition in each mining cycle and the order of
drivage of roaciways in each mining cycle, in the NW
Panel, (a) to (e) represents 0-9 cut-throughs, and (f)
to (j) represents 9-12 cut-throughs.
268
The effect of distance between the adjacent roaciways would have an
effect on the degree of stress relief.
If stress relief was a factor in the relative roof conciitions
between adjacent roaciways in a single mining cycle as described
for 0-9 cut-throughs then a most likely ranking of roaciways can be
derived. The first driven roadvjay is most likely to have the
worst roof and the subsecjuent stress relief would provide the best
roof for the second ciriven roacJvay. The third ciriven roacivsay, not
subject to significant stress relief from the second driven, vail
have the second worst roof conciitions, whereas the last ciriven
heaciing will have the third worst roof conditions.
A theoretical weighted ranking curve may be cirawn by assigning
worst to best conciitions, as described above, to the first, third,
fourth and second driven heaciings respectively and multiplying by
the weighting factor given above. In Fig. 6.1 Be the theoretical
long term trend and the actual trend are very similar.
The extent of short term roof failure in first ciriven roacis ays is
indicative of the long term failure as shown in Fig. 6.17a and b.
This relationship may also be confirmed for each roadway in the
mining c ycle. Figure 6.18e shows that the weighted raiJdng of
short term failure for each heading, in order of drivage, does not
follow the pattern for actual (long term) roof failure. Only the
first driven heading clearly has the poorest short term and long
term roof conditions. The ciistance of 40m between the centres of
adjacent roaciways may be too great for clearly defined patterns of
short term stress relief.
269
To summarise for the 0-9 cut-through sequence pattern, the
relative roof conditions-will tend to oscillate fran poor to good
based on the degree of deformation in the adjacent heading. The
incranent of relief to be gained gradually decreasing as more
heaciings are driven. The amount of stress relief available will
also be controlled ty the spacing between heaciings but this factor
is constant at 40m fran 0-9 cnit-throughs.
The change of sequence fron 9-12 cut-through is shown in Fig.
6.10. The same set of calculations made for the 0-9 cut-through
secjuence was made for the 9-12 cut-through sequence and is
presented in Fig. 6.18f-j. The theoretic:al weighted ranking (Fig.
6.18J) shows that the order of drivage has the sane relative roof
conciitions except that the last driven heading would be expected
to have the best conditions as it is driven between existing
heaciings (Fig. 6.10).
Fran 9-12 cut-through the heading with the best condition is the
last ciriven, as would be expected, since it was driven between
existing roadways (Fig. 6.18J). The first and second driven
headings do not have clearly defined ciifferences of roof
conditions. This is unexpected and is probably explained by the
presence of a fault vdiich is subparallel to, and crosses, the
second driven heading between 9 and 11 cut-through. The third
driven heaciing has the second worst condition vhich is consistent
with being driven 80m frcm an adjacent heading (Fig. 6.10). In
the 0-9 cut-through sequence, 40m was the greatest spacing between
rcjadways. Figure 6.11 shows that between 11-12 cut-throughs, which
is away fran the faulting influence, the ranking of headings fron
270
worst to best with respect to order of cirivage is 1, 3, 2 and 4
vdiich would be expecrted of this cirivage secjuence.
Short term roof conditions for the 9-12 cut-through sequence
inprove as more headings are ciriven (Fig. 6.18j). Together with
the 0-9 cut-through secjuence, the relative short term failure of
the later ciriven heaciings of a cycle is not necessarily inciicative
of relative long term roof conditions. Long term roof conciitions
are best forecast by consideration of the overall cirivage geanetry
of the panel. Absolute stress relief vd.ll vary in accordance vdth
heaciing spacing, in situ stress magnitude, stiiength of roof strata
and the sequence of cirivage. However, the above exanples
demonstrate that the amount of relative roof deformation is
related to the sequence of drivage.
6.4.6 DEVEDOFMENT (F ROOF CXIOITICWS THROOGHOOT T?fflMCCR MINE
The NW Panel constitutes only porticm of roadvay development majped at
Tahmoor. Not all types of short term roaciway conditions are observed
in the NW Panel. Table 6.3 shews the range of short term roof
conditions distinguished at Tahmoor, vdth seme of these conditions
being found in the NW Panel. The 12 crategories listed in Table 6.3 are
an ej jansicMi of the general list of short term ixx)f condlticais in Table
6.1. In Table 6.3 short term roof conditions are ranked in decreasing
severity of deformation. This is a qualitative ranicing based on years
of observation of roof conciitions in Tahmoor.
En^hasis is placed on mapping short term roof conditians because:
- variation of roof support methcxis make caiparison of long term
roof conditions ciifficniLt;
271
-TSLBLE 6 .3
StCRT TEIM RCOF CXUDITICW SCfilg
- TMMXR MINE -
12 Arch Hei^t of cavity >0.5m
11 Severe Parallel Shear vdth mining Height of cavity between
induced fractures on both ribsides 0.3m and 0.5m
10 Severe Parallel Shear with mining
induced fract ures on 1 ribside
9 Parallel Shear with mining induced Height of cavity <= 0.3m
fracrtures on both ribsides
8 Parallel Shear vdth mining induced
fractures on 1 ribside
7 Severe Parallel Shear
6 (X)licjue and Parallel Shear
vdth mining induced fractures
5 Parallel Shear
4 Oolique Shear vd.th mining induced
fractures
3 CS licjue and Parallel Shear
2 caolique Shear
1 No Shear
272
- short term or ^face' conditions are most easily cxatpared
between ciifferent areas because mining technicjues have a
reduced effect;
- short term roof conditions vd.ll or can ciic:tate the roof support
which is placed during mining;
- understanding short tenn roof conditions has direct application
to rxxDf support techniques.
Short term roof conditions have been mapped in mine roacivays throughout
Tahmoor. Figure 6.8 represents short term conditions of individual
roadways based on the classification in Table 6.3. For ease of graphic
presentation the division of mining induced fractures vhich occur on
one side or on both sides of the roaciway is not recognised in Fig. 6.8
- effectively allowing for 10 short term roof condition categories.
For tabulation and further assessment 12 categories of short term roof
conditions have been used.
Inspection of Fig. 6.8 shows a number of inportant aspects of short
term roof conditions. The following are included:
- areas of the mine which have markecily ciifferent roof conditions
frcm each other;
- areas where one roaciway drrection is markecily worse than the
adjacent roaciway;
- areas vhere both roaciway ciirections have similar short term
roof conditions.
Three areas of the mine have the worst short term roof cxonditions (Fig.
6.19), namely 100 Panel, 200 Panel and the area near No. 2 Shaft (the
Main East Panel).
273
BP Cod Autlrala
Roof Condition* Ng,l.l« r
M
Worst Roof Conditions
Best Roof Conciitions
274
275
The 100 Panel and 200 Panel areas are located imrediately to the south
of different ESE trending strike-slip fault zones but the Main East
Panel is not associated with faulting. Not all areas mined on the
southern side of these strike-slip faults have such poor roof
conciitions. 300 Panel area contains the best short term roof
conditians. It is located between areas vd.th poor roof ccnditions,
such as 100 Panel and the Main East Panel.
In attarpting to assess the reasons vhy roof conciitions varied it was
realised that the mining direction was not the carmon thread. The in
situ stress field at Taiimoor was stuciied and is reported in the next
section. These results are linked vdth roof cxarxiition ciata in section
6.6.
6.5 THE IN SITO STRESS FIELD
Behaviour of the roof strata in Tahmoor indicated that roof fracturing
was caused by lateral shortening across the roacivay - consistent vdth a
dcminant lateral stress field. A stuciy programme was set up to
establish the orientation of the lateral stress field and the
significance of:
- variation of the stress field orientation;
- possible relations between the stress field and variable roof
conciitions.
The stress field was mapped in Tahmoor in a range of mining
circomistances. In roaciways ciriven into virgin areas, remote from
adjacent workings the stress field acting on the roaciway vdll closely
represent the virgin in situ stress field. In many roaciways, ciriven
276
next to existing roadways there may be Iccalised mcdification of the
stress field. In areas adjacent to goaf there is likely to be
significant modification to the virgin in situ stress field as it is
reoriented around mine workings, or relaxed into the goaf.
The degree to vhich the virgin stress field has been modified by mining
activity cannot be accurately judged when measuring roof fracture
orientation. In the context of this thesis the stress field being
assessed is that vrfiich acts on the mine roaciways. A partial aim of
this stuciy is to judge to what degree and in vhat mining configuration
there is significant reorientation of the virgin stress field.
6.5.1 METHODS USED TO DETTERMINE STRESS FTKTD (KEEJSrEftTICJJ
The mapping and assessnent of mining induced shear and tensile
fractures is used to determine the orientation of the horizontal
components of the stress field in any roaciway segment.
The axial trend of low angle conjugate shear fractures vdiich occur at
an angle between 0° and 90° to the roaciway ciirection are assimed to
develop normal to the principal horizontal carponent of the stress
field (Fig. 6.20a). Shear fractures are mapped in each roadway segnent
between intersections and the average orientation calculated. A
principal lateral stress orientation can be obtained for each
individual roadway or for a number of adjacent roaciways.
In seme roaciways low angle conjugate shears may occur in two directions
oriented approximately normal to each other. It is assumed these
represent the response of the roof strata to both principal horizontal
stress field corponents, o.. and a^. In order to determine vhich shear
dLrection represents a. other features are ccansidered:
(Q O
o o
<
15 0 o Q. W CQ H -
c o • • • •
o o Im
• • •
o 0) JC w 43 V)
E "TO
*^ t; <D CQ Q -J 6
o a .
0) Q.
"(3 •*-LL
E° 0)
I-
o 0)
c o o
(8
> c TO Q.
279
SIGMA 1 STRESS TRAJECTORY
CONCENTRATION
SUBJECT TO
FAILURE
MINING DIRECTION
Fig. 6.20b Schematic plan view presenta t ion of a dcminant l a t e r a l
s t r e s s conc:entration forming around one s ide of a mine
roaciway. Dotted l i n e frcm face, p a r a l l e l t o sigma 1, w i l l
i n t e r s e c t the r i b s i d e prone t o shear f a i l u r e .
280
1. The relative condition of adjacent heaciings and
cut-throughs. The assunption is that the roaciway direction
wdth consistently poorer roof conciitions is oriented at a
higher angle to the stress field.
2. Location of short term shear failure. The majority of low
angle conjugate shear is oriented parallel to the roaciway.
Usually it is preferentially located on one side or in the
centre of the roaciway. If located to one side of the
roaciway it is related to the stress field as shown in Fig.
6. 20a and b. This sinplified two dimensional model of ,
stress concentration around one corner of the roaciway (Fig.
6. 20b) is in accord with 3 dimensional carputer modelling
((Sale and Blackwood, 1987). The side of the roaciway most
likely to develop shear fracture is gauged by the following
rule of thumb.
"Shearing of the roof strata occairs on the existing ribside
intersected by an imaginary line drawn through the mining
face parallel to the principal horizontal stress
ciirection."
3. The tensional mining inducted fracture is derived frcm
a similar stress reorientation and concentration across the
mining face. The mining induced fractures form as c:urvilinear
tensional fractures, ahead of the face, in the plane of the
reoriented a. and a^. Where mining induced fractures occur on
only one side of the roaciway they are a reliable guide to the
quacirant of a, orientation.
281
To summarise, the average trend of the low angle conjugate shears is
used to determine the principal lateral stress directions and the
cjuadrant of o.. c:an be determined by the:
- re la t ive condition of adjacent roaciv^ys;
- location of parallel shears;
- loc:ation of mining induced fractures.
6.5.2 STRESS FIELD CRIFKIATICN
6.5.2.1 Siqna 1 Orientaticpn
The trend of individual shear traces was measured in each
accessible roaciway. Data vas then ccmbined fran a number of
adjacent roaciways so as to determine the average o.. ciirection in
2 an area approximately lOQm . The size of this basic ^unit' varies
vdth the width and pillar design of different panels.
Figure 6.21 shows in detail the distributican of shear traces
collected from the NW Panel. All ciata between and including, each
c:ut-through is represented on frecjuency diagrams, and the a^
dlrectican, inferred from the average shear trace orientation is
noted. Each shear trace is identified as being caused hy the
primary or seconciary lateral stress.
In the NW Panel shear traces, caused by lateral shortening
parallel to o.., are dcminant over the shear direction related to
the seconciary horizontal stress dlrectican. Inbye along the NW
Panel two factors vary:
(a) the frequency of shear fracture traces increases, and
(b) the frequenc y of shear traces related to the secondary
horizontal stress ciirection increases.
13 CT 282
019 N
J9
1.34
10 c r ,
^019 NORTH-WEST PANEL
013
19
v40 /0I6
,25 .014
i -=—• "^Sfi'i prmclpl* stress orientation
y^^22 frequency of 5 ~ T
/number of shear plonej measured
,009
12
5 CT
02
.003
I
100
METRES
200
1 C.T
Fig.6.21 Lateral stress ciirections determined from the orientatian
of conjugate shear traces measirred in heaciings and
cnit-throughs of the NW Panel. Each rose diagram represents
the shear traces measured between each cut-through. Ten
degree intervals.
283
The orientation of a^, as inferred from shear traces, was
determined for the majority of mine workings in Taimeor (Fig.
6.22). The principal horizontal stress ciirection has a N-S trend
for much of the northern part of the mine. Sigma 1 is oriented
NNE at the northern end of the NW Panel but farther east it is
rotated seme 60° to a SE trend in the Main East Panel. Toward the
south, in 100 Panel o^ maintains a N-S trend.
The variaticai of a- orientation alreacfy mentioned is gradual
carpared to two areas of the mine vhere the apparent a., ciirection
changes through 90° within 100m. One location is the Main East
Panel, vhich at the time of drivage was ranote from other workings
- 300 Panel had not been formed. The change of apparent o..
direcrtion v^s very distinct as roadway conditions cjuickly changed
(Fig. 6.19). The orthogonal change of a, orientation in the Main
East Panel most likely reflects the orientation of the virgin
stress field.
A variation of o.. dLrection also occurs in the 100, 102 and 103
Panel area. The 102 and 103 Panels, developed fron 100 Panel,
were driven, at least in part, adjacent to an area vhere the cxal
had been fully extracted (goaf). It is not possible to state if
a. in part of the area represented the virgin in situ stress field
or had been modified by mine workings; but the southern portion
should be unaffected by goaf and represent the true stress field.
284
' ^ CSIRO 3/4
?
CSIRO 1
t N
Fig. 6.22 Lateral stress directions (small bars) across Tahmoor Mine
workings, determined from the trace of mining induced
conjugate shears. Larger bars represent in situ lateral
stress orientation determined by CSIRO using overcore
methocis. Test sites 1 to 4 are indicated.
285
6.5.2.2 In Situ Stress Measurements
Four in situ stress field determinations were obtained by CSIRO in
Talimoor Colliery using an overcoring technique (Wbrotnicki and
Walton, 1976). Table 6.4 gives results of the four overcore tests
fron three sites (Walton, 1983). Figure 6.22 shows the location
and orientation of the CSIRO results vhich show o.. to be oriented
approximately N-S.
6.5.2.3 Ccmpariscxi of Methocis Used to Determine Siqtra 1
Orientation
The in situ stress field neasurements conducted by CSIRO provide a
benchmark to test the reliability of low angle conjugate shear
traces as an indicator of o.. orientation. Both methods show
agreement in the orientation of a., vdthin 10° and cxjnfirm that
there is clockwise rotation of a, inbye along the NW Panel (Fig.
6.22).
6.5.2.4 Sourc:es of Error in Sigma 1 Cteientation frcm Rock
Fracture
The o.. orientation is calculated using the trace of low angle
conjugate shears in the roof strata, in both heaciings and adjacent
cut-throughs. If shear fractures occur at approximately the sane
density per metre of cirivage in both roaciway directions (heaciings
and cut-throughs) and there is no ^local' deflecrtion of the stress
field across individual roaciways there will be no bias in the
results. In most panels the ^unit' area used to calculate a^ vdll
contain a greater length of one roaciway ciirection (usually
headings) carpared to the other (usually cut-throughs).
286
TABLE 6.4
CSIRO C3VERCCRE RESULTS
SITE 1** SITE 2 SITE 3 SITE 4
SIGMA 1
Azimuth
Magnitude (MPa)
Elevation
SIGMA 2
Azimuth
Magnitude (MPa)
Elevation
SIGMA 3
Azimuth
Magnitude (MPa)
Elevation
E-W CCMPONENT
Ifegnitude (MPa)
180°
21.3
-30°*
305°
13.0
-45°
070°
11.6
-30°
12.1
171°
20.5
-8°
077°
12.8
-24°
227°
9.8
-65°
12.4
198°
18.0
0°
108°
14.6
-7°
291°
11.3
-83°
14.9
202°
19.2
-3°
112°
13.4
0°
033°
9.9
-87°
14.2
SIGMA 1/SI(3^ 2 1.64/1 1.60/1 1.23/1 1.43/1
* Negative value indicates a below horizontal
inclination in the orientation direcrtion.
** Refer to Fig. 6.22 for locatican of each site.
287
Bias of stress data due to unequal sanple populations frcm
heaciings and cut-throughs vdll only occur if the stress field is
deflected across the roaciway. The possibility of bias was tested
for the NW Panel data.
In each unit area of the NW Panel the average stress ciirection was
calcoilated for heaciings and for cut-tiirougiis. The ciifference vas
noted. Table 6.5 lists the results.
For the 14 cut-throughs mapped in the NW Panel there is an average
ciifference of 13.7° between the principal stress ciirection as
mapped in the headings and in the cut-throughs. Furthermore the
average stress ciirection, measured in the cut-throughs, was
consistently less than the ^unit area' average stress direction
(Table 6.5). The stress ciirection neasured in headings was
consistently greater than the ^unit area' average stress
ciirecrtion.
The average stress ciirections determined for adjacent heaciings and
cnit-throughs suggests that the in situ lateral stress, may be
deflected across the mine roadway so as to increase its angle to
that roadway by 7°. A bias would be introduced to the calculation
of the "unit' average stress ciirection if there v*as not the sane
number of neasurenents fron headings and cut-throughs for the
"unit area'.
Two reasons exist vhich make it difficult to allow for any
potential bias in the calculation of the "unit' average stress
direction:
1. A proven theory or mcxiel is not available to account for
288
TftBLE 6 . 5
DIFFERENCE BETWEEW MEAN SIQSi 1 DIRBCTICN OF THE FH^ST ERIVHI HEADINGS
AND COT-THROOGHS, NORffl-WEST PANEL
LOCATION SIGMA 1 ORIENTATKXJ MEAN SIGMA 1 DIFFERENCE FROyi
MEAN
CT NUMBERS
0-2
2-3
3-4
4-5
5-6
6-7
7-8
8-9
9-10
10-11
11-12
12-13
HDG
016
008
010
017
016
020
017
015
021
028
019
030
AVERAGE
CT
351
357
358
004
009
006
357
352
Oil
018
021
013
DIFF
25
11
12
13
7
14
20
23
10
10
2
17
13.7
OF UNIT AREA
001
003
006
009
014
016
014
013
019
027
019
027
HDG
+15
+5
+4
+6
+2
+4
+3
+2
+2
+1
0
+3
+3.9
CT
-1.0
-6
-8
-5
-5
-10
-17
-21
-8
-9
2
-14
-9.6
289
the deviation of stress across mine openings.
2. It is unknown if the amount of postulated stress deflecrtion
is dependent on the angle between a., and the roaciway
direction.
In view of the unknown limits of the potential bias and the
limited data frcm the NW Panel the unit average stress ciirections
are used in an uncorrected form.
6.5.2.5 Ratio of Sicyna 1 and Signs 2
CSIRO in situ stress neasurements show an increase in the relative
magnitude of o^ from test site 1 tc ward test site 3. The c7Va„
ratio decreases from 1.64/1 to 1.23/1 between these two sites.
The frecjuency of low angle conjugate shears oriented normal to a„
also increases inbye along the NW Panel (Fig. 6.21). Other panels
of Talimoor also have roaciways wdth shear traces oriented
approximately normal to each other. Where the numbers of shear
traces from either ciirection are approximately ecjual other
methods, described in section 6.5.1, are recjuired to identify
vhich is the a., direcrtion.
The presence of significant numbers of low angle conjugate shears
related to o^ c:an be a guide to a relative increase in the
strength of a_. Oblicjue low angle conjugate shears are not always
present and, as vd.ll be explained in the next section, the above
guide is not at all conclusive.
290
6.5.2.6 Summary ( uicie to Using Roof Frac:tures to Icientify the
Stress Field _
The previous secrtion irdicated that the i elative nagnitude of a,
and a„ (the principal horizontal stress ccnponents), can vary
vdthin the mine, in acidltion to changes of o. orientation. Field
mapping of the roof lias identified the types of roof failure to be
fouTKi in the vicinity of in situ stress neasuranents. Areas with
different CJ,/a^ ratios also have ciifferent ixxjf failure styles.
Table 6.6 presents an outline of the methodolcgy recjuired to
establish the ciirection of a, in areas where there is a dominant
stress direction and in areas vhere neither horizontal stress
direction is significantly greater.
Four main criteria are available for assessing the o.. ciirecrtion:
- relative condition of adjacent headings and cut-throughs;
- orientation of low angle conjugate shear fractures;
- mining induced tensional fractures; and
- location of shear failure in roof.
The expression of each of these features varies in different
roaciways depending upon:
- the angle between the roaciway direcrtion and the o.
orientation (9sr);
- the relative magnitude of o.. and a„, assuming both
are the principal horizontal caiponents of the stress field.
Each criteria is examined separately.
291
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292
Relative CondLtion of Adjacaent Heading and Cut-Througji
This information can cietermine only the quadrant of the o^
azimuth. Roof conditions will be better in heaciings oriented vdth
Osr <45° than those oriented vdth Osr >45° (Fig. 6.23). However
vhere 9sr = 45° and where the magnitude of 02 approaches a. the
conditions in headings and cut-throughs should be similar.
Factors such as order of cirivage of adjacent roaciways can make a
greater ciifference to relative roaciway condition. First driven
headings and cut-throughs provide the best basis for caiparison.
Oblicjue lew Angle Ocxi jugate Shears
These oblicjue shears can provide the most accurate o.. orientation
of the four criteria. Usually one shear ciirecrtion is more
frequent but two conjugate shear directions are ccmmon. The
relative frequency of the conjugate shears is not a reliable girlde
to vhich set is related to a... Other criteria are required to
determine o.., for exanple, the relative condition of headings and
cut-throughs.
Oblique low angle conjugate shears are present for a limited range
of Gsr and stress magnitude (Fig. 6.23).
For areas with:
(i) a dcminant horizontal stress ciirection the oblicjue shears:
- occur more frecjuently in roaciways vhere Gsr <45°;
- are not as frequent in first driven roaciways carpared to
suiosequently driven adjacent roacivrays;
- are rarely seen when Gsr >60° for any roaciway or in areas
vhich iiave higher stress magnitudes (as irdicated by the
t 293
z S I -u UJ cc 5
z i {^ Ol CD
WORST MINING DIRECTION
- MAXIMUM HORIZONTAL
STRESS DIRECTION
I <45
2. Low Angle Conjugate Shears
Mining Direction
3. Mining Induced Fractures
>45
MIT'S ON
ONE SIDE
mif's
MIPS ACROSS ROADWAY
Osr - . 90
OR
Sigma 1 >= Sigma 2
4. Location of Shear Failure
0»r < 55 to 60
Shear blasted to one side
Shear in centre of roadway
Osr > 55 to 60
OR Sigma 1 >= Sigma 2
Fig. 6.23 Summary of c r i t e r i a used t o determine the principed
hor izonta l s t r e s s ciirecrtion acrting across adjacent
roaciways. "mif's" = mining induced fracrtures.
294
severity of face conditions) as parallel shear is dominant;
- are more likely to be oriented normal to o...
(ii) principal horizontal stress ccnponents vd.th almost equivalent
magnitude, the oblicjue shears:
- are not as ccmmon because the majority of shearing will be
parallel to the roaciway;
- could be oriented normal to either a, or o^-
Mining Induced Tensional iiactures
The location of so called mining induced tensional fractures is a
good guide to the cjuadrant of a., direcrtion.
The mining induced fractures occur either preferentially on one
side of the roaciway or on both sides of the roadway. A dcminant
lateral stress direcrtion causes mining induced fractures to occur
preferentially on one side of the roaciway. This side of the
roadway is determined by the orientation of the stress field
relative to the roaciway as shown in Fig. 6.20a. However if the
dcminant lateral stress is oriented at a high angle to the roadway
it is also likely that mining induced fractures could occur on
both sides of the roaciway. Mining induced fractures also occrur on
both sides of the roadway in areas of similar horizontal stress
cxxiponents.
Rcaciways vd.th jointing in the roof strata have localised patches
of mining induced fractures, presumably vAiere local stress
concentrations develop. These sites usually do not contribute to
any stress analysis of the far-field stress.
295
Mining induced fractures do not occur in all roadways. They
appear to be associated, vdth more severe roof conditions. The
conclusion is cirawn that they occur at higher stress levels,
either with one dcminant or two nearly ecjuivalent lateral stress
field ccmponents. No in situ measurements are available to
directly confirm tliis observation.
Locaticxi of Short Term Shear Failure
The location of low angle conjugate shear vhicdi forms at the
mining face can indicate the quacirant of o.. orientation. Shear
location is the most useful tool of all because even if the, shear
traces do not form normal to the o.. orientation, there is usually
a preferential locration to inciicate quadrant.
In areas which have a daninant lateral stress field, shear ccc:urs
preferentially on one side of the roaciway. Different areas have
short term shear located either in the gutter area, (the
intersection between the roof and ribside) or approximately iialf
way between the ribside and the centre of the roof.
The one special case is vhere a., occurs at a high angle to the
rcjadway. Shear vd.ll then be preferentially located in the centre
of the roaciway. The relative condition of headings and
cut-throughs vdll then be a deciciing factor in determining a^
orientation.
Where lateral stress magnitudes are nearly equivalent the short
term shear failure vdll preferentially ocxrur in the caitre of the
roaciway.
296
6.6 THE RELATig^BHIP BBIWEEN SmESS FIEED ORIENiaTICK AND MDilNG
6.6.1 INmODOCTICW
In section 6.4 it was suggested that changes in roof conditions along
the NW Panel were related to a change of the in situ stress field. The
direction of a., and the ratio of the lateral stress caiponents were
shown to change along the NW Panel by in situ stress field measurements
(Walton, 1983) and roof fracture mapping. Section 6.5 also outlined
the methocis, based on roof conditions, used to assess the stress field
orientation.
The NW Panel is a good exanple of the type of stress field and roof
condition variation encxaintered in a development panel. The
relationsiiip between stress field and roof conditions vdll be presented
in this section. In doing so the following aspects of the stress field
vdll be considered:
- stress field orientation
- stress field magnitude
- relative strength of both in situ horizontal stress ccnponents
- the angle between a. and the mine roaciway (Gsr).
Each of these four factors vary in ciifferent mining areas of Taiinoor
and produce a different set of roof conditions requiring different roof
support. In additican to establishing the relationsiiip between the
stress field and long and short term roof conditions, the aim is to
develcp a predictive tool vhich allows roof conciitions to be forecast
for a laiown or predicted stress field.
297
6.6.2 PREFERRED LOCATICW OF SH3RT TEt M ROnP FATTJIRR
Mapping the short term roof failure in the NW Panel indicated that the
low angle conjugate shearing occurred mainly on one side of the
roaciway. Mining induced fractures were also located on the sane side
of the mine roaciway.
The orientation of the stress field relative to the mine rc adway
direction and the ciirection of cirivage appear to determine on \*iich
side of the roaciway low angle conjugate shears and mining induced
fracrtures develop. Short term roof failure vdll occur on the side of
the face area, and therefore the side of the mine roaciway vhich
develops the greater concentration of stress during mining. This
relationsiiip is useful in determining stress field orientation, as
presented in secrtion 6.5.2.6. The ^rule of thumb' for determining
vhich side of the roaciway vdll be subject to shear is: "the existing
ribside which is intersected by a line dravm through the centre of the
mining face parallel to o,".
The abc3ve relationshuLps hold true throughout Tahmoor except:
- v^ere a., is at a high angle to the roaciway (>60°) causing
failure to occrur in the centre area of the roadway
- in the area around intersections v^ere the stress field is most
prone to be locally reoriented.
Williams and Turner (1981) indicated that gutter formation occurs on
the ribside which first intersects a designated joint or cleat set in
the immediate roof strata. In Taiimoor the orientation of the stress
field causes roof shearing irrespective of roof joint orientation.
Sites exist where the axis of lc3w angle conjugate shears traxis vdthin
298
10° of strong jointing, highlighting the independence of shearing in
response to the stress field..
Roof support practice in Taiimoor Colliery lias been successfully
modified so that extra roof bolts are placed on the ribside designated
by the above ^rule of thumb' to suffer short term shear. Longer term
propagation of such shearing iias been restricted by this procedure.
6.6.3 ROOF OCgiPITICMS AND THE AISGLE OF SlQtA 1 TO THE MINE RQftPWZg"
The principal cause of ciifferent roof conditions noted between headings
and cut-throughs along the NW Panel in Taiimoor is the angle between o..
and the roaciway direction (Gsr). Mjacent headings and cut-tiiroughs,
normally oriented at 90° to each other vdll intersect a.; one at less
than 45° and one greater than 45° (that is, Gsr <45° and Gsr >45°).
The worst roof conditions occrur in roadways oriented with Gsr >45°.
Appendix IV contains talxilation of stress orientation ciata for the NW
panel.
Ccnparison of the amount of good roof in first ciriven roadways and
cut-throughs of the NW Panel wdth Gsr for each roaciway shows a
significant decrease in the amount of good roof for values of Gsr above
40° (Fig. 6.24).
Gsr is a critical factor in determining roof conditions in stress
fields vhere o^ is dominant over a^, for exanple, the NW Panel. The
case of a biaxial stress field is discussed in section 6.6.5.
299
2 O <
o ®
S < O i^ 0$ Cii
O
S 2 CO I:::
U j ^
u 2
/
/
• ^
• /
/ •
/
I 1 I 1 1 1 1
o o o ^
jood aooD %
Oi
.o CO
uo N
o CO
CD
o
_o
Fig . 6.24 Increase of roof deformation vdth increasing Gsr, for
f i r s t driven heaciings i n the NW Panel.
300
6.6.4 I O C TEKM ROOF OONDITIONS AND OSR
In section 6.4.5.2 the ciistribution of long term roof conditions was
presented for the NW Panel. The changes of long term failure types
along the NW Panel is related to Gsr in Fig. 6.25.
Each of the four nain long term roof failure categories, vhich occupy
above 20% of each ixaciway segment, develop over a different range of
Gsr.
Good roof occrurs for the Gsr range 0° to 40° (approximately). It
overlaps slightly vdth roof sag, vhose range in the NW Panel e ctends
frcm 33° to 88°. Sag rcof and gcxxi roof are the most oemtnon types over
the full range of Gsr.
(Sutter and cantilever roof failure types occur over a reduced Gsr
range. C5utter failure being restricted between 46° and 50°, whereas
cantilever failure occurs in two small ranges of Gsr: 29° to 33° and
53° to 61°. The separation of Gsr ranges for gutter and cantilever,
vdiich are two similar failure types, is noteworthy. (3utter, the lower
intensity failure type, has a lower Gsr value than the main cantilever
range, possibly indicating a Icwer effective stress level.
The existence of the lower Gsr range of cantilever failure (29°-33°) is
probably due to the action of a^ in roaciways partially relieved of a.,
In ttiis case the Gsr for o.j woiiLd be 57° to 61°.
Cantilever and gutter are asymmetrical failure types which occur when
Gsr is approximately between 45° and 60°. In this range short term
failure types are biased to a particular sicie of the roaciway. Above
301
RANGE OF DOMINANT
LONG TERM ROOF CONDITIONS
GOOD
> 1 33 88
I 1 I 1 29 33 53 61
SAG
CANTILEVER
GUTTER 4€ 50
-1 1 1 1 1 1 1 1 10 20 30 4I5 60 70 80 90
Osr
Fig. 6.25 Dis t r ibut ion of ciifferent long term roof conditions in the
NW Panel vdth respect t o Gsr.
302
60° short term roof failure tends to be located in the centre area of
the roaciway giving rise to longer term sag failure.
Sag failure covers a wide spectrum, including the Gsr range of
cantilever and gutter failure types. Effective roof support in areas
most prone to cantilever and gutter failure will lead to a general roof
sag, vhiich explains the broad Gsr range. Sag roof does beccne
proninent at r values above 60°.
The variation of long term conciitions along the NW Panel is related to
Gsr. Figure 6.26 shows the relationship between Gsr and the long term
roof failure found in the first driven roaciway.
There is evidence frcm the NW Panel to suggest that long term roof
failure types (good, sag, gutter aixi cantilever) are dependent on Gsr.
Furthermore, for conparable stress magnitudes Gsr may provide a guide
to the amount of good roof, and if applicable, the types of failure.
6.6.5 SEERT TERM ROOF COMDITIONS
The developnent of a Short Term Roof Condition Scale (Table 6.3) for
Taiimoor roof conditions v^s based on extensive mapping and the severity
of roof deformation. It could be expected that for a given stress
field magnitude the short term roof cx)nciition scale would develop as
Gsr changed frcm 0° to 90°. Tb generalise:
- values of Gsr <45° provide oblicjue shear
- values of 45°>Gsr<60° vdll pixrvide shear biased to one side
of the roacivay
- values of Gsr>60° vdll provide shear in the centre area of
the roaciway.
303
150 _
100 -
a c u
50 -
Location - Cut-Through Number
Fig. 6.26 Relationsidp between Gsr and the amount of long term roof
fai lure, in the f i r s t driven heaciing, along the NW Panel.
Roof conditions deteriorate significantly as Gsr > 45°.
304
Gsr is only one of tlrree variables of the in situ stress field which
affect short term roof conditions. The three variables are:
1. Gsr (which also accounts for stress field orientation)
2. Magnitude of a.
3. Ratio of a., and a^ (assuming that they are both
horizontal).
In Tahmoor each of these three variables changes in different areas of
the mine.
The variation of any of these stress field characteristics vdll effect
the short term or face mining conciitions. An analysis of the full
range of short term roof conditions in an area may be false unless each
of the possible stress field variants are noted. Ccnparison between
areas, and forecasts of future mining conditions, vdll be invalid
unless the stress field in each area is recorded and any variations
incrorporated.
6.6.5.1 Roof Failure Curve
The Rcof Failure C arve is a graphical representation of short term
roof condition versus Gsr for a given area. The Roof Failure
Curve represents the short term roof conciitions esqpected over a
range of Gsr if the stress field iias consistent magnitude and
orientation. Areas of the mine which have a ciifferent Roof
Failure Curve can be expecrted to iiave ciifferent stress field
cenditions.
An area of the mine vhich is represented by a single Roof Failure
Curve iias consistent stress field magnitixie parameters.
305
A typical Roof Failure Curve is shown in Fig. 6.27 and displays
tliree characteristics:
1. a ciistinct ciiange of roof conciitions either side of Gsr =
45°, reflecrts the ciifferent roof cx)nditions ccmmonly
noticed between adjacent heaciings and c:ut-tiirouglis.
2. the relative intensity of roof failure, and the relative
intensity of the stress field is easily represented for a
range of mining ciirections.
3. a guide to the relative intensity of the two principal
horizontal stress field ccnponents is given loy ccnparison of
failure intensity when Gsr is greater and less tiian 45°.
The Roof Failure Curve in Fig. 6.27 represents the NW Panel
iDetween 0-7 cut-tlrrouglis. The changing stress field along the NW
Panel means that four ciifferent Rcof Failure Curves are required
to represent short term mining conciitions.
6.6.5.2 (jonpariscan of Short Term Mining CondLticns
Five ciifferent Roof Failure Curves iiave been identified to
describe the range of short term roof cx)ndltions and stress field
conciitions noted in Talnnoor development panels (Fig. 6.28). The
Roof Failure Curve (except for cnrrve 2) are defined only for a
limited range of Gsr (25° to 65°), because no mining iias taken
place at the extreme values toward 0° and 90°. Figure 6.29 shows
the areas of the mine associated vdth eacdi Roof Failure Oirve.
The five Roof Failure Curves each characterise a particular area
and the siiape of each curve indicates the relative dlfferenc e
between the stress field in different areas.
12 -I
306
UJ -J < o CO
o
Q
O o ti. o o Q:
9 -
! I 6
3 -
r
-T~ 30
~T~ 60
"1 90
ANGLE OF STRESS TO ROADWAY (Gsr) (degrees)
Fig. 6.27 Typical exanple of a Roof Failure Curve for Talmcor.
Curve is a plot of short term roof conditions versus Gsr.
307
12 -,
Ul - I < o CO z o H Q z o o Ii. o o Q:
C 6
3 -
. -y. j_ r / •
7
T I 1 1 1 1 1 r
30 60
CD O r-H
m
v> H
90
ANGLE OF STRESS TO ROADWAY (Gsr) (degrees)
Fig 6.28 Set of Roof Fa i lure Curves recjuired t o define roof
conciitions i n Taimoor workings.
308
Roof Failure Curve 1 (in Fig. 6.28) represents the best roof
conciitions and presumably is an area vdth a relatively low stress
field magnitude. For exanple, in the NW Panel the area on the
north side of a strike-slip fault iias a relatively low stress
magnitude and is represented loy Curve 1.
Roof Failure Curve 2 covers a wide range of Gsr. This curve is
typical of one horizontal stress direcrtion (a.) Iseing stronger
than the other (o^). The worst short term rcof conditions are not
acJiieved until liigh values of Gsr. The CSIRO site 2 stress
measurement (Table 6.4) inciic:ates a o../o^ ratio of 1.60/1.
Roof Failure Curve 3 is similar to Roof Failure Curve 2 except
that it has worse short term conditions for values of Gsr just
greater than 45°. No in situ stress field measurements were taken
in areas represented by this Roof Failure Curve but it probably
represents the greatest o../o^ ratio; or is at least as great as
for Roof Failure (Zurve 2.
Roof Failure Curve 4 represents a siiift to poorer short term
conditions for Gsr <45°. It also signifies a decrease in the
^Y^^2 ^ " io* ''^^^ is confirmed \yy in situ stress field
measurenent csn the Ixsunciary of the area represented loy Roof
Failure Curve 4 (Site 3, Table 6.4). The o^/o^ ratio being
1.23/1.
Roof Failure Curve 5 represents the worst mining conditions. One
mining ciirection is just worse than the other for the range of Gsr
observed. Areas represented Isy Roof Failure Curve 5 have a nearly
Artwork Prepared by-'TWO-CAN DESIGN'
Fig. 6.29 Areas of Taiimoor Mine \diich are represented by the same
Roof Failure Curve. The nuntiers of Roof Failure Curves
defined in Fig. 6.28 are noted, and matched to each area.
311
biaxial stress field. All mining directions would therefore be
nearly ecjually ciifficult.-
Most of the development roaciways driven in Taiimoor have been
mapped for roof conciition and stress direction. This data allows
a Roof Failure Curve to be assigned to each area of the mine (Fig.
6.29). The areas vhich iiave ciifferent mining conditions and
ciifferent stress field conditions can be identified (Fig. 6.29).
Frcm Fig. 6.29 the area denoted by Roof Failure Curve 1 iias the
lowest stress field magnitude and Roof Failure C urve 5 represents
the area with the most severe mining conditions. The pattern
fomed over the mine workings is not definitive but there is a
suggestion of ^zones' vdth similar stress field character. The
virgin stress field picture is possibly masked hy the influence of
adjacent goaf areas, for exanple, 103 Panel at the southern end of
the mine (Fig. 6.29). Construction of a zonal stress field
picture vdll need to take account of such effects.
6.6.6 VARIATICN OF gTOESS FIELD AND ROOF FAILDRE (JIRVES
Jfeasurarents of the in situ stress field liave shown tiiat there is seme
change in magnitude and ojo^ ratio of the horizontal stress field
corponents (Section 6.5.2.2) wdthin Tahmoor Mine.
Study of roof conditions has allowed a series of Roof Failure Curves to
be ocHistructed vhich are peculiar to each area of the mine, vdth
presumably, similar stress field ccaidltions. Roof Failiire Curves
provide an indicator of the relative stress field magnitude and
horizontal stress cxxrponent ratios. Roof Failure Curve 1 represents
312
the lowest stress field intensity and Roof Failure Curve 5 the
relatively greatest stress field intensity. These are cjualitative
judgenents, but how may they be better linked to actual stress field
parameters?
6.6.6.1 Stress Field Maqnitucie fran Roof Failure Curves
Stress field magnitude is difficult to assess frcm Roof Failure
Curves. Inspection of in situ stress field results fran Table 6.4
shows that sites 1 and 2, represented by Roof Fcdlirre Curve 2, and
sites 3 and 4 representative of Roof Failure Curve 4 iiave a.
average magnitudes of 20.9 MPa and 18.6 MPa respecrtively (Table
6.7). This is the reverse to expected as Roof Failure (Turve 4,
being the worst roof condition, should be associated vdth the
Irlgher stress magnitude.
It vould be expected tliat for high values of Gsr (80° to 90°) rcof
conditions would be very poor, ranldng at least 10+ on the short
term roof condition scale (Table 6.3). This v^uld be true for the
range of o magnitudes likely to be found in Taiimoor. Therefore
the relative strength of the stress field magnitude would be
difficxilt to judge frcm roof conditions at iiigh values of Gsr.
However for Gsr just above 45° there is more variation in roof
conditions for each Roof Failure Curve 1 to 5. The relative o.
magnitudes are therefore best judged at Gsr between 45° and 60°.
Table 6.7 shows the average E-W ccnponent of the horizontal stress
field for sites 1 and 2, and sites 3 and 4. This stress is
approximately ecjuivalent to that acrting across the NW Panel
roaciways in the Gsr = 45° to 60° range. The E-W ccnponent is
313
liigher for Roof Failure Curve 4 (14.6) than for Roof Failure Curve
2 (12.3) as might be expecrted frcm observation of roof conditions.
Greater stress field intensity occurs at the Gsr = 45° to 60°
range for areas with iiigher o^ values, given a constant a.. The
c7-j/02 ratio makes an inportant contribution to stress field
intensity.
Ody two Roof Failure Curves can be linked vd.th actual
measurements, liifortunately the ciifference in stress magnitude
between each Roof Failure Curve frcm 1 to 5 is not known to he
equal and can only be approximated. Using Roof Failure Curves 2
and 4 as tenchmarks it is possible to approximate the relative
stress field at Gsr = 45° to 60° (approximately) for the other 3
TAHTiR 6.7
STRESS FTKTn PARAMETERS RELATED TO ROOF EAELDRE CURVES
E-W
CURVE STRESS MEASUREMENT CCMPGNENT ^i^^o
SITE (TABLE 6.4) MAG. (MPa) (MPa) RATIO
2 1 and 2 20.9 12.3 1.62/1
4 3 and 4 18.6 14.6 1.33/1
Note: 1. The table gives average resiiLts of the two stress
measurement sites taken in each Rcof Failure Curve area.
2. Stress sites 3 and 4 occrur near the bounciary of a Roof
Failure Cacve 1 and a Roof Failure Curve 4 area. Results
are assumed to be indicative of Roof Fcdlure Curve 4 because
the Roof Failure Curve 1 area is a localised effecrt around a
fault zone.
314
Roof Failure Curves (assuming ecjual ciifference between the stress
magnitude of each Rcxjf JFailure Curve). This is represented in
Fig. 6.30.
6.6.6.2 Sigma 1/Sigma 2 Ratio frcm Roof Failure Curves
The ciifference in roof conditions alcove and below Gsr = 45° for
each Roof Failure Curve is a relative indicator of the o^/o^
ratio. Once again Roof Failure Curves 2 and 4 iiave benchmarks
frcm in situ stress measurements (Table 6.7). Roof Failure Curve
2 has the iiigher measured ratio, which matches the greater
difference in oliserved rcof conditions for heaciings and
cut-tiirouglis. Again if stress magnitudes Ijetv sen each Rcof
Failure Curve are assumed similar the o.Jo^ ratio for the other
three Rcof Failure Curves can be estimated (Fig. 6.31).
6.6.7 PRHDICnCN OF ROOF COMDITIOWS, ROOF SUPPORT AND PRODOCTICW RATES
6.6.7.1 Preciictlcn of Roof Conditions
Mining conditions wdthin future develepment workings are predicted
loy projection frcm adjacent vrorkings. Predicted roof conditions
vdll be test cliaracterised by assigning a Rcof Failure Curve to
each planned development area. The number of different Roof
Failure Curves required to cliaracterise one or more development
panels vdll be determined frcm adjacent vorkings.
315
16-T-
15 -
S
UJ *» Q ' * 3
< s tn (A tu GC
(A
lU
13
12 -
11 4
RFC NUMBER
Fig. 6.30 Projected relationsiiip between two measured E-W stress
magnitudes (dots) and associated Roof Failure Curve (RFC)
numbers.
2.0 -I
1.8
cc CM
< s g <A
< s (3
1.6 -
1.4 -
1.2 -
1.0 "T" 2
T 3
RFC NUMBER
Fig. 6.31 Projected relationsiiip between the two measured horizontal
stress cenpcanent ratios (sigma 1 and sigma 2), and
associated Roof Failure Curve numbers.
316
To determine the expected rcof conditions in headings and
cut-througiis of a new area, the following is needed:
1. exp)ected a. trend in the area
2. orientation of headings and cut-througiis
3. determine Gsr (frcm (1) and (2))
4. use the roof failure curve typical of the area to determine
the expected roof conditions for the Gsr values of headings
and cait-tlirougiis.
6.6.7.2 Roof Support Opticgis
Essentially tlrree options of support are currently used, that is,
6, 7 or 8 bolts per W-strap. Spacing between W-strap)s is reduced
as conditions deteriorate. Experience at Talimcor iias enabled roof
support recjuirements, or bolt density, to be related to the
intensity of short term roof conditions (Fig. 6.28). Bolt density
may differ in heaciings and cut-througlis dependent on short term
roof conditions.
The roof support options presented are based on current
experience. An investigation programme has been ccxrmenced to
detemnine the failure horizons, in areas characterised by
ciifferent Roof Failure Curves, to allcw optimum choice of roof
bolt lengtlis, type and patterns.
6.6.7.3 Roof Conditions and PrcducrtdLon Rates
Development roadway areas wiiich have ciifferent diaracteristic roof
conditians, as defined by their respective Rcof Failure Curves,
also tiave different production rates as measured tjy acivance per
sJiift. The average sliift acivance is calculated on a monthly basis
317
for each development area. The monthly production fran
development panels lias been determined since mining began in 1979
to provide a range of data related to various mining conditions.
The relationship tetween the developnent rate and the
characteristic roof conditions as rated by the Roof Failure Curve
is shewn in Fig. 6.32.
6.7 VrmiNITE REFLBCTAMZE
6 . 7 . 1 INTRODOCTICW
The biaxial nature of vitrinite sanples in Tahmcor was specifically
investigated to establish the regional pattern, A specific aim was to
ccnpare the orientation of the in situ stress field and the R max of
vitrinite. Sanples were not taken adjacent to particular fault
structures but over a ciistance of 1. 5km vd.th seme closely spaced in the
centre area to test reproduceability of results (Fig. 6.33).
Six secrtions cut normal to beciding vere prepared for each sanple and
the reflectance measurements taken using the procedure described in
Chapter 2. No atterpt was made to establish if a set of ellipses
calculated frcm the reflectance results vould give randcm or non-randcm
R max orientations. Instead the reflectance maxima of each CBPSIS were o
defined as the R max direction or ciirections for each sanple using o
criteria described in Chapter 3.4.2.
6.7.2 RESULTS
In the Tahmoor sanples neasured, the R max ranges between 1.06% and
1.16% reflectance. Bedding plane bireflectance is small ranging fjxm
0.01% to 0.05% reflectance. Results are summarised in Table 6.8.
5-1
4 -
318
hi -J < O
o u.
3 -
I -\
V
I I 1 1 1 \ 1 \ « I I ' 6 8 10 12 14 16 18
ADVANCE PER SHIFT (m)
Fig. 6.32 Variation of mine roaciway advance rate with roof
conditions.
319
LEGEND
CBPSIS Figure
0 0.1 L, 1 1 Scale for Axial Llr>e»
% REFL
Fig. 6.33 CBPSIS figures of samples taken frcm Tahmoor Mine
worldngs. The R max peaks are shewn on each figure. The
centre of CBPSIS figures is 1.00% reflectance.
320
Nbtvdtiistandlng the snail beciding plane bireflectance, reflectance
maxima were chosen from CBPSIS figures. Bireflectance (R max - R min) o o
varies between 0.19% and 0.24% reflecrtance for the sanples measured.
T\ro distinct groups of reflectance maxima (ecjuivalent to R max peaks)
are recognised from the sanples measured (Fig. 6.34). Qae group of
R max peaics lias a nean orientation of 064° and the second group,
approximately normal to the first, iias a mean orientation of 152°. It
is inferred tJiat these strains relate to palaeostress oriented at 154°
and 062° respectively.
The method of determining R max orientations frcm CBPSIS figures
appears to be reliable in the Tahmoor sanples even allcwing for bedding
plane bireflectance as low as 0.01%. The reproduceability of results
is confirmed frcm relatively closely spaced samples.
TABLE 6.8
VITRINITE REFLECTANCE D?a!A - TAHMDCR COLLIERY
SAMPLE
TI
T2
T5
T15
T20
T21
R MAX o
BEDDING PLANE BIREFLECTANCE
BIREFLECTANCE (R MAX-R MIN) (DRIENTATI(2J o o
(% REFLECTANCE) (%REFLECTANCE) (%REFLBCTANCE)
1.09
1.14
1.16
1.16
1.06
1.15
0.03
0.02
0.01
0.04
0.02
0.05
0.24
0.19
R MAX o VDTT<TvTP
PEAK
(DEGREES)
059,
057,
061
074,
-
070,
154
133
-
159
155
159
321
6.7.3 S'lRUL'lTFAL DEVELOPMENr IN THE TAHMDCR AREA
Prior to placing the palaeostrains derived frcm CBPSIS figures into any
reasonable context the relation between associated geological
structures must be assessed. The geological iiistory of tliis area
recjuires more than two episodes of applied stress to explain the
variety of structural relationsidps olDserved.
The structures mapped in Taiimoor can he placed into a relative
geological order frcm oldest to youngest.
(a) N-S to NNW joints (160° set). Ooss-cutting relationsiiipis
suggest tliis joint set precedes other sets.
(b) Formation of ^120°' joint ciirection, toth over wide areas and
as narrow zones crossing the pre-existing 160° set. Strike-slip
faults probably initiated prior to dyke intrusion.
(c) Dyke arplac:ement along ^120°' joint set.
(d) Lateral movement along ^120°' joint set giving rise to small
strike-slip faults, and shearing of the dykes.
Two phases of reverse faulting occur, forming as narrow linear
zones. One of these zones, oriented approximately 060°, most
likely formed vdth a phase of strike-slip movanent. The other
zone (oriented at approximately 150°) formed in a ciifferent stress
regime.
The gecmetrical relationsiiip of these structures is shown by Fig. 6.35.
The role of the Nepean Fault is inportant to the structural development
of the Tahmcor mine area. It is p»stulated the Nepean Fault structural
zone developed by a series of left-lateral v encii movements, instigated
by an active N-S trenciing basement structure. The intensity of this
322
Fig. 6.34a Rose diagram of the daninant lateral in situ stress field
ciirection as determined frcm traces of lew angle conjugate
shears in the mine roaciway roof (siiaded area). Data for
stress field orientation cxnes frcm 93 locations across a
wdde area of mine workings, as shewn on Fig. 6.22. The
non-siiaded area represents the orientation of R max peaks
frcm six CBPSIS figures frcm Taiunoor. Arrows inciicate the
lateral palaeostress ciirections inferred frcm R max peaics.
Ten degree intervals.
Fig. 6.34b Rose diagram of the dcminant lateral in situ stress field
ciirection determined frcm traces of low angle ccanjugate
shears. Stress field orientations are limited to the
areas frcm which the six CBPSIS figures, and R max peaks,
were determined. Arrows inciicate the lateral palaeostress
directicms inferred frcm R max peaks. Ten degree
intervals.
323
i (a)
IN SITU HORIZONTAL STRESS
R ,max PEAKS
4 . —"
(b)
IN SITU HORIZONTAL STRESS
R^max PEAKS
4 ' -
324
w- — E
Fig. 6.35 (Gecmetrical relationsiiip of faulting and other structural
features in Talmoor Mine. Palaeostress and in situ stress
directions are also included.
325
shear movement in Taiimoor is considered to he low becrause the mine is
located toward the southern end of the structure. Figure 6.36 shows
the orientation of a set of structures that can result frcm
left-lateral wrrenching of a shear couple (Harding, 1974). Many fault
strucrtures noted in Tahmcor mine v<orkings are accounted for ty tirls
model. Figure 6.37 shows the known faults associated vdLth each
potential fault orientatican presented hy the model. The synthetic and
antithetic strike-slip faults intersect the wrench strike at angles of
10° to 30° and 70° to 90° respectively. Wilcox et al. (1973)
considered tliat these conjugate fractures can te either joints or
faults, or both, depending on the intensity of v«:enciiing., The
principal lateral carpressive stress vd.ll bisect the conjugate fracture
set.
The follcwing sequence of geolegical events can therefore te postulated
for Taiimoor.
(a) The NW to NNW reverse faults are consideiTed to be the oldest
recognised fault structure in Taiimoor. The cleat and the NNW
jointing is protably older again, however, no direct proof exists.
C3ray (1982) and Sherwin and Holmes (1986) state that the southern
Syiiey Basin was subjecrt to a NE to E-W cxnpression at least until
the end of sedimentation. The ENE palaeostress direction is
thought to be related to tiiis stress field vAiich, apart frcm
limited, small scale reverse faults, and restricted areas of ENE
oriented in situ stress, is not strongly represented in Tahmoor.
(b) Initial movement along the Nepean Fault structure. HeriDert
(1989) attributed the discontinuous en-echelon iiigh-angle
reverse fault movenent of the Nepean system to oblicjue ccnpression
against a N-S trenciing bcisenent structure. Hertert indicated a
326
Fig. 6.36 Range of possible structures developed frcm left-lateral
movanent of a shear couple, (after Harding, 1974).
Fig. 6.37 (Ccnparison of structure orientations predicted from a left-
lateral wrench model vdth the actual strucrture orientations
in the Tahmoor Mine area. Both vitrinite derived
palaeostress ciirections are included.
327
N
K m
m > r-o < m S m z
ACTUAL STRUCTURE DIRECTIONS
N
PREDICTED STRUCTURE DIRECTIONS
K
>
328
Late Triassic age for the possible ccmmencement of movement.
Other authors (Bishop et.al., 1982; Branagan and Pedram, 1990)
iiave denonstrated a long iiistory of movement along the structure.
Associated with movement along the Nepean Fault structure would be
the follcwing structures found in and adjacent to the Bulli seam.
- Strike-slip joint and fault zones at 120° approximately.
- Potential formation of limited nonral faulting (150°
approximately).
- Developnent of lc3w angle reverse fault structures (050° to
060°).
- Development of a lateral stress field oriented at
approximately 150° (normal to reverse faulting and parallel
to normal faulting). This stress field matches the other
palaeostress recognised in CBPSIS figures. Figure 6.34 shows
the 154° palaeostress ciirection (determined frcm R max peaics)
is not parallel to the main trend of the in situ stress field.
However, Fig. 6.34b ccnpares the R max derived palaeostress
directions with rcof shearing measured in the area of vitrinite
sanpling. This provides a reasonable match between
palaeostress and in situ stress direction.
(c) Bnplacement of dykes along pre-existing ESE trenciing
strike-slip fault and joint zones. If cijdce enplacement occurred
during a time period when the wrench movement was active the ciykes
would not be oriented parallel to the principal lateral stress
dlrectican. Alternatively an otherwise unrecrgnised stress event
in Tahmoor, parallel to 120°, is required for c^e intrusion.
Dykes of this orientation do occur in eastern parts of the basin
vhere the presence of acrtive shear couples is unconfirmed.
(d) Shearing of the ciyke indicates further movement of the shear
329
couple associated vd.th the Nepean Fault.
Based upon the above interpretation there are two recognised stress
events vhich account for the majority of fault structures or movorent
in Taiimoor. Reactivation of movement alcaig the Nepean Fault strucrture
may account seconciary movanent on seme structures. Palaeostress fielcis
vdth similar orientations to the NNW and ENE stress fielcis are
recxognised frcm CBPSIS figures. TWo palaeostress events iiave been
inprinted to toth the vitrinite and Bulli Coal seam roof strata. The
recrognition of these events as vitrinite strain and an in situ stress
ciirection, does allow the possibility of predicting one knowing the
other. However, vitrinite can apparently record twD palaeostress
ciirecrtions but, not necessarily indicate vhich represents the in situ
stress direcrtion.
6.7.4 CCNCLOSIOMS
The in situ stress field, determined frcm both overcore technigues and
napping rock fracrture in mine roaciways, varies across the mine
workings. Two principal lateral stress field ciirecrtions are
recognised. Different in situ stress field directions appear to cxover
substantial areas of the mine rather tiian being restricted to loccil
structures. A graciual rotation of a. occurred around fault structures,
v^ereas seme areas, not associated vd.th fault strucrtures, exidbited a
90° change of a., ciirecrtion vdthin a ciistance of 100m. This
characteristic of a., infers tliat there is a strong residual stress
ccnponent in the roof strata of the Bulli Coal seam, derived frcm the
inprinting of palaeostress events. Kncwledge of how residucd stress is
inprinted to the rock mass, vhat is the variability of that inprinting.
330
both in recording one, or subsecjuent stress events is unknown.
Ifcwever, the seciimentary rcoks adjacent to the Bulli seam at Tahnoor
can apparently irrprint two generations of stress events. The
inccnpleteness of the inprinting may e35>lain the variability in °-\fOy
ratios, and the proneness to abrupt change of a., ciirection.
The roof conditions in Tahmoor Mine are linked to the in situ stress
dlrecticjn, the o../o^ ratio and the stress magnitude. In gaieral, the
roof conditions deteriorated as the angle of roaciway drivage to the
horizontal stress field increased. A ccnprehensive method was
developed to map the in situ stress direction; its relative stpength
was determined using a twelve point short term condition scrale, with
the angle tetv^en the horizontal stress and the roaciv ay (Gsr), to
define a Roof Failure Curve for each area vdth the same stress field
dimensions. Knowledge of the stress field dimensions, its likely
variation, and the type of roof conciitions to be encountered allcw
appropriate roof support design, stress relief methods, or panel layout
options to be considered.
In areas which have lew grade tectonic deformation, such as Tahmcor
Mine, the R max peak orientations are well matched with in situ stress
field orientations.
331
CHAPTER 7
SLMMARY AND CXHCLUSICWS
7.1 INTRODOCnCN
The aim of this stuciy has iaeen twofold. Firstly, to use suitable field
mapping methods to determine the relative strength and orientation of
the dcminant in situ horizontal stress field and its effect on coal
mine roadways. Secondly, to develop a method of measuring tecrtonic
fabric and potential palaeostress ciirections and, if possible, provide
ciata on the origin of the in situ stress field.
A number of case studies were conducted at ciifferent collieries in the
southern Sydney Basin to provide data for the study. Collectively the
erase studies presented an opportunity to determine vdiich relationsliip)s
were localised and vhich were ccmmon to the ciifferent stucfy areas.
7.2 ROOF CXUDrnCKS AND THE IN SITU STRESS FIELD
High lateral in situ stress fielcis are the principal cause of poor roof
conciitions in the southern Sydney Basin. Sigma 1 (a..) is approximately
twice the magnitude of the vertical a^. Mining conciitions of the Bulli
Coal seam liave been stuciied and the follcwing conclusions can te
reached, based on each of the case studies.
1. The in situ stress field orientation was mapped in coal mine
rcaciways frcm low angle conjugate shears, the relative condition of
adjacent roaciways, location of shearing in the roof and the presence of
mining induced fractures. Results frcm mapping a. frcm mining inducted
roof deformation agrees well vd.th in situ overcore measurements.
332
The in situ stress field in Tahmcor Ctolliery has two general
orientations NNW to N and ENE to E. In West Cliff, Kemira and the
Burragorang Valley mines the lateral stress field had a dcminant ENE
direction (Fig. 7.1). The NE oriented stress in the Burragorang Valley
is from an area not affected by iiigh horizontal stress.
Variation in the orientation of the in situ horizontal stress field in
virgin ground can be interpreted frcm both field mapping and in situ
measurements. For exanple, a., orientation ranges up to 20° from noirth
for the generally N-S trending a, in Taiimoor Colliery, Fig. 7.1. Seme
of this variability occurs as a gradual rotation around , small
strike-slip fault structures, however, in Tahmcor Colliery, there are
areas vhich liave a 90° ciiange of the o. direction over a ciistance of
100m vhich cannot te related to a localised structure.
Mapping technicjues are able to determine changes of a., due bo stress
concentrations heneath overlying incised valleys, around areas of the
mine vhere the ccal iias been fully extracted, and stress relaxation
around fault zones,
2. The relationsirlp between roof condition type, roof stability, and
the in situ stress field depencis cm four factors:
(i) the angle tetween the a., direcrtion and the roadway
direction (Gsr).
(ii) the magnitude of o...
(iii) the ratio between the two horizontal stress ccnpcanents
(o^/o^).
(iv) lithology and strength characteristicrs of the roof
strata.
333 UJ
o -00 o
o
o o • • « o
o
O) c
O) O n
« E t fc
^ i<i m ra
o
E
»2
Oi o •a
— Z
CD
o Csl
I
N <
o - o
Hi
ii o
</) UJ CC h-(/> O UJ < - I < Q.
ILCC u
3 • •*
(/i </> UJ a: H (/) D H (/>
IS ul S e
men
M (0 4>
s
Fig. 7.1 Ccnparison of in situ lateral stress ccnponents and
generalised R max dlrecticans for each of the four case
stuciy areas.
334
3. Variation of any of these four factors can cause a change in the
short teiom, or mining face, roof conditions. Recognition of short term
roof conditions is enphasised because the a., orientation, the roof
failure intensity, and the probable long term performance of the roof
are all inteipreted from the face conciitions. Short term roof
conditions also prcrvide a early indication of vhat roof support density
will be recjuired for long terra roof stability. The long term roof
failure types do not necessarily define the initial defomation types
or causes, nor do they clearly define in situ horizontal stress
conditions. Their use as a primary investigative tcol is limited.
4. A twelve step classification for mapping short term roof conciitions
vas developed and used to rank the severity of deformation (see Table
6.3). Both the type of roof deformation and its relative location in
the rcof of the mine roaciway v^re used to develop the
classification.The system vas graded so that each step was the result
of an apparently liigher lateral stress acting across the mine roaciway.
The ranking was established cjualitatively frcm observatican of roof
conditions in hundrecis of kilometres of coal mine roaciways in the
southern Syciney Basin, and backed up by available in situ stress
measurements.
The classification is suited to all mining situations subject to iiigh
horizontal in situ stress fields. It is specifically developed for
tiiinly interbedded roof types, vhich are susceptible to shear and
delamination, and show a more siibtle range of short term roof
conditions. Stronger rcof types may recjuire a classification liaving
fewer steps.
335
5. In a known and constant horizontal stress field, mining conditions
vdll vary as Gsr changes. Mine roaciway roof conditions are better when
Gsr < 45° but deteriorate vdien Gsr > 45°, especially as Gsr approaches
90°. The twelve step roof condition classification enables the
severity of roof conciitions to he recorded over a range of Gsr. A plot
of roof conciitions versus Gsr produces a Roof Failure Curve, vdiich
defines the irof conciitions experienc:ed over a range of Gsr for a
stress field of constant o.. magnitude and cr../ap ratio.
In Talmoor Colliery, for exanple, five Roof Failure Curves are recjuired
to define the range of roof conditions for ciifferent stress field
conditions. Each Roof Failure Curve lias a unicjue a., magnitude and
associated c7../a ratio. Higher o.. magnitudes cause a iiigher degree of
short term roof deformation, especially in roaciways oriented at greater
than 45° to a, . As the o./a^ ratio decreases and approaches 1.0 the
distribution of short term roof conditions change. Under such
conditions adjacent roadways vdll liave essentially ecjuivalent short
term deformation styles rather than one of the rcaciways having
obviously worse conditions. Tahmcor Colliery also lias distinct areas
where both the a. magnitude and the 0../O2 ratio vary markedly. Roof
Failure Curves are able to define roof conciitions over mappable areas,
which also neans that the extent of the stress field, unicjue to each
Roof Failure CXirve, can be defined.
6. Different roof litholc^gies will have ciifferent roof behaviour in a
given horizontal stress field. Stronger roof strata, such as massive
sandstones, are able to resist in situ horizontal stress vhich would
crause failure in laminites. Therefore, Roof Failure C irves must also
be specific for roof lithology in acidltion to stress field magnitude.
336
The orientation of shear failure in the roof acts independently of
jointing, however the joint zones may preferentially acrt as a focus of
the shear by being a plane of weakness in the roof.
The economic viability of coal mines, subject to high in situ stress
conditions, is linked to using the high capacity longv^ll mining
systan, partly to counter high roof support costs. Knowledge of the in
situ stress field allows operators to design appropriate roof support
density, appropriate stress relief methods and appropriate mine layout
for development roaciways. The in situ stress field can have a
significant effect on longwall performance: ty ciamaging longwall access
rcaciways during development; by delaying the development of longwall
access roaciways; and in unfavourably oriented longwalls, lay
concentrating the horizontal stress field across, and therei>y damaging
the gateroacis during extraction. Reducticn of annual longwall
production by 50% has been caused by horizontal stress fielcis affecting
roaciway stability. This is crucial to the mine when ciaily revenue from
an operating longvall is approximately $0.5m. Kncwledge of the stress
field for mine design to avoid stress induced problems is fundamental
to successfiiL mine operation.
7.3 CBPSIS FIGURES
To understand the nature of the stress field a tool was sought to allow
the palaeostress of an area to be determined. Vitrinite reflectance
characteristics have been used successfully to determine aspecrts of the
palaeostress and to infer cenpcanents of residual or ^locked in' stress.
Coals of the Southern Coalfield studied had R max ranging between 1.04%
and 1.48%, and showed that the reflectance indicating surface took the
337
shape of an oblate ellipsoid rather than an cfclate spheroid; i.e. in
other vjords the vitrinite reflectance envelope is defined by a biaxial
indicating surface. The biaxial or non-uniaxial nature of the
ellipeoid allows its orientaticai to be defined and related to a
palaeostress event.
Subsequent to the development of this technicjue to outline palaeostress
directions (Stone and Ctook, 1979) later workers have used the
orientation and shape of the full ellip»soid to define tectonic movanent
in st3x>ngly deformed areas (Hewer and Davis, 1981b; Kilby, 1988).
In areas vdth flat lying strata, such as the stuciy area, the CalcniLated
Beciding Plane Section of the Indicating Surface, or CBPSIS, will take
the shape of an ellipse for one applied lateral stress field. The
smooth elliptical CBPSIS shape allows the orientation of the Rjnax to
be calculated statistically frcm only foirr sections normal to the
bedding. The R max direction is inferred to develop normal to an
applied lateral stress.
Beciding plane bireflectance is small, ranging between 0.01% to 0.11% in
the stxxiy area, with the najority less tlian 0.05%. As discussed in
Chapter 2 the fact that a high proportion of non-randcm Rjnax
directions were determined indicated that the results were not an
artefact of neasurorent error or an intrinsic part of plant anisotropy.
This argument can be extended further. Six sections cut normal to
bedding instead of four enabled a more detailed CBPSIS figure to be
drawn. TVro R max peaics were sut>sequently noted as normal and vdll
reduce the probability of a non-randcm R max being calculated. The
338
high percentage of non-randcm R max directions noted in Chapter 2 vjere
obviously sairples deminated by one of the R max peaks.
An inportant conclusican cirawn fron the flat lying bituminous coals in
this study is that the normal shape of the CBPSIS is not a smooth
ellipse Ixit rather the superposition of two unequal size ellipses.
Each CBPSIS lias frcm one to tliree sets of R max peaJcs, each of vhich is
inferred to liave developed normal to a lateral stress field.
The test for the orientation of R max peaks not being a randcm event is
subjecrtive. It is ultimately judged by the tendency for a set of, R max
peaks, frcm sanples in one area, to define a consistent pattern
(ideally which fits surrounduig geology).
Exanples of the consistency are best derived frcm study areas vhere
sanples are remote frcm potential areas of local disturioance such as
faulting. The Kemira area, although difficult to interpiTet, produced
four R max direcrtions fron pairs of R max ciirecrtions. The Burragorang
Valley exanple produced consistently oriented strain ciirections on each
side of a strucrtural zone. The strain direction was rotated across the
structural zone. Tahmoor R max peaks were consistently oriented in two
ciirections vhich matched the two recorded in situ stress directions.
West Cliff, Area B, showed consistent R max orientations remote frcm
faulting and in Area A, vhich contained a number of faults,
reflectance maxima were able to be matched vd.th both local faults and
regional trencis.
In the Southern Coalfield faults develop in response to regicsnal
stresses vhich may be clearly i ecorded in vitrinite more than 50m frcm
339
faulting. The reflectance data around faulting needs careful
interpretatican as the stress, ciirecrtion related to the post-faulting
stress relief may be similar to a separately recognised stress event.
Conflicting evidence was recxarded regarding the increase of reflectance
toward a fault plane. In the mildly defomed Southern Ccalfield the
range of reflectance increase noted dcaes not appreciably exceed that
expected frcm normal in-seam ply variation. The full resolution of the
subjecrt is beyond the scope of this stuciy.
The question of whether R max peaics develop only during the
coalification phase is ecjuivocal. During the cxalification process the
reflecrtance vdll increase so that each new strain direcrtion should
ccnpletely overprint the preceding strain direction. Considering the
lew beciciing plane bireflectance values (0.01% to 0.12%) typical of the
Bulli Coal, ccnplete overprinting would be expected during
ccalification. However, the Bulli Coal sanples normally iiave two
reflectance peaks, vhich iirplies that the final shaping of the CBPSIS
was ccnpleted at or near the end of the main phase of coalificatican.
Seme phases of strain iirprinting noted in the coal may also rely on
mechanical iirprinting processes rather than purely physiochemical
processes underway during coalification. Experinental work of the type
reported by Bustin et al. (1986), v^ere the short term amplication of
tenperature and pressure to anthracites was able to modify the
orientation of the R max, may be the method to resolve the nature of o
R max peak develcpment in vitrinite.
The experinental work of Bustin et al^ (1986) reported imperfect
inprinting of the experimentally applied stress to the anthracite. The
340
sane effecrt is noted in the field where variability in each study area
neans that all R max directions are recorded evenly or any one is
markedly dcminant.
Bustin and co-workers recorded tiiat the experimentally induced strain
was rotated frcm the original direcrtion, inplying that the palaeostrain
of the antiiracite was destroyed. In fact they only used three sections
of the coal to define the orientation of the ellipse and may have
missed ronnant strain, i.e. the calculated Rmax may have teen a
ccnposite of the two strain directions. The use of further secticans
may have shown two separate peaks. This work raises questions, as to
the effects of strain rate, differential stress magnitudes and the
torperature on iirprinting strain to vitrinite. The answers await
further experimental v«rk.
In regimes vhere a number of stress episodes are able to inprint strain
to the vitrinite, as measured by the R nax orientation, the resultant
R max ciirection is cxansidered a ccnposite of dlffeirent episodes of
iirprinting (Levine and Davis, 1984). The intensity of the ccnpression
and the stage of coalification vdll dictate the extent to which the
original R max ciirection is superseded. In the Southern Coalfield it
appears that an analysis of individual R max peaks is preferable to
producing a ccnposite R max ciirection (using only 4 polished secrtions),
because it is generally able to prcavide two ciiscrete palaeostress
directicjns.
341
7.4 PALAEOSTRESS AND IN SITU STRESS
The case studies of each mine recorded the specific relaUonships
between the geological structure, the in situ stress field, and the
palaeostress ciirections of each study area.
Five ciifferent palaeostress dlrecticjns can be interpreted frcm the
stuciy of Rjnax peaks in vitrinite frcm each of the case study areas
(Fig. 7.1). Two palaeostress ciirections, ENE and NW to NNW, occrur in
all of the case stuciy areas. Of the remaining three palaeostress
directions, NE, occ:urs in the Burragorang Valley and West Cliff,
vhereas the N-S and WNW ciirecrtions only occrur in the Burragorang Valley
mines and Kemira.
Table 7.1 lists the possible geological association between structures
and the palaeostress directions. Figure 7.2 shc:ws the fault, joint,
cleat and point-lead ciistribution in each case study area together wdiJi
the five generalised palaeostress ciirections.
The Group A palaeostress ciirection (ENE) is found in each stuciy area,
but is not strongly associated vd.th geological structure, except for
the south normal fault (West Cliff) and reverse faulting in Taiimoor.
The NW to NNW orientation of the (iroup B palaeostress was also found in
each stuciy area. In Tahmcor this palaeostress is associated vdth a
range of fault structures caused by left lateral voench movement along
the Nepean Fault zone. This palaeostress direction at Tahmoor is a
result of the wrench movement. It is not known if the Group B
palaeostress has similar origins at Kemira and West Cliff but is
probably associated vdLth a left lateral wrench system in the
342
- TABLE 7.1
FIVE PALAEOSTRESS DIRBCTICWS AND POSTULATED STROCTURAL ASSOCIATICM
GROUP GENERAL (HIENTATI(3N ASSOCIATED FEATURES
A ENE - Related to dcminant in situ stress
ciirecrtion frcm study area.
- Reveirse fault - Talmoor.
- South fault - West Cliff.
- Load-parallel point-lead fractures -
Kemira.
B NW to NNW - ESE strike-slip faulting in each gtuciy
area.
- Sulparallel to Tahmoor in situ stress
field.
- Stress direction involved wdth left-
lateral v?renching.
C NE - Normal faulting - West Cliff.
- Load-parallel to point-load fractures -
Kemira and West Cliff.
- Load-normal to NW jointing.
- load-normal and parallel to cleat
ciirections.
D N-S - no associated structure.
E w to WNW - load normal to dcminant point-load
ciirecrtion and NNE joint direcrtion.
— <
o
— CD
UJ
I I I I 1 T I
I
T I
1 T I 1
UJ - J O
Ol
< cr S UJ
O z <
<
Ii
343
cr O O S X
S
•s (A u. « (A , cr
1 • i I ' Ol
o — 09
a
o o
I II
T I 1
T C
! "
==1
11 (A
(A
T
TCA| I
1 T
o ! CA|
O (A Ii
LU
° « o 4) 0) k. O) « •o
z I H 3 S N
2 <
e
O
o 00
T ^5 O < O - I »-
z O CL
H Z o
o z b <
Fig. 7.2 Ccnparison of selected strucrtural fabric features in each
of the case stuciy areas. The five palaeostress ciirections
(A-E) are inciicated.
344
Burragorang Valley. Irrespective of origin this palaeostress is
associated with strike-slip faulting, oriented WNW to NW, in all four
study areas.
(3roup C palaeostress direcrtions are oriented NE. They are coincident
vd.th the nomal faulting in West Cliff and with scne joint, cleat and
point-load fracture directions. No evidence exists to confirm if this
stress event precedes or was synchronous with joint and cleat
formation. The stress ciirection, if not the actual sliress event, are
related to ESE to SE trending folcis on the eastern margin of the Camden
Syncline, which were active during sedimentation.
Palaeostress ciirections from Groups D (N-S) and E (WNW) are not ccmmon
in the stuciy area and are not related to geological structure, except
that Group E may be related to the NNE joint ciirection.
Palaeostress ciirections frcm (Sroups A and B occur in each study area,
which means that these stress fields were either stronger over a longer
time span, and/or were inprinted more readily during a time of active
coalification. It is considered more likely that inprinting of lateral
strain in vitrinite is aciileved during coalification.
Diessel (1973) suggested that in the Southern Cbalfield 70% of
coalification was ccnpleted by the Micidle to Late Triassic, prior to
the ccmmencement of uplift. Therefore it may be concluded that
cxalif ication was largely ccnpleted by Micidle to Late Jurassic. C5ray
(1982), Sherwin and Holnes (1986) and Branagan et al. (1988), amcaig
others, refer to a NE to E-W ccnpression until the end of sedimentation
by Micidle Jurassic, although seme workers extend this until Cainozoic
345
(Sherwin and Holmes, 1986). Stuciy of vitrinite suggests that the ENE
oriented palaeostress (Group A), vhich was found in each study area,
represents tliis ccnpressive phase inprinted during the later stage of
coalification. In the Tahmoor area the NW to NNW palaeostresses of
Group B are related to wrenching of the Nepean Fault zone, but this
palaeostress direcUon is also found in each study area and was,
therefore, probably imprinted toward the end of coalification,
following the ENE palaeostress event.
Study of vitrinite suggested that the tasement movenents generating
vrrenching of the Nepean Fault zone appear to have created a NW to NNW
cxanpression in the Syciney Basin sediments, not only at Tahmcor, but
also in the other study areas.
The age of a significrant movenent on the Nepean Fault zone is Late
Triassic to Micidle Jurassic, lased cm the interpretation of the NW to
NNW palaeostress event iirprinted in the vitrinite toward the end of
cxalif ication. This agrees with Hei±ert (1989) vho postulated a Late
Triassic age for the main novemait on the structure. He argued tliat
convergent vnrenching was caused by oblique ccnpression of N-S trending
basement structures. Branagan and Pedram (1990) preferred an Early
Tertiary age for the main movement of the Nepean Fault structure to the
north of the study area but noted that the strucrture had a much longer
history. Evidence also exists which suggests movement along sections
of the Nepean Fault structure during the last 20Ma (Wellman and
McDougall, 1974; Bishop etal., 1982; Rawson, 1989).
346
The remaining three palaeostress ciirections are not represented in all
stuciy areas and may be remnant frcm older events due to uneven
overprinting. Group C NE palaeostresses may be a phase of the NE to E
ccnpression active during sedimentation, whereas the (iooup D and E
palaeostresses are coincident vd.th regional jointing vhich is thought
to have an early origin (Cook and Johnson (1970); Shepherd and
Huntington (1981).
Vitrinite reflectanc:^ results inciicate two dcminant palaeostress
ciirections v iich probably occurred in the Late Triassic to Early
(Zretaceous. Younger fault and ciyke structures do not appear to be
represented by recognised R nax peak directions in vitrinite.
Palaeostresses defined from vitrinite cover a limited span of
geological history and must be used in conjunction vdth tecrtonic
structure to define their nic±ie.
The two daninant ENE and NW to NNW palaeostress ciirecrtions are
reasonably coincident with the two general in situ horizontal stress
ciirections which occurred in the stuciy areas (Fig. 7.1). This iirplies
that the in situ lateral stress field has a significant residual, or
^locked in' strain ccnponent related to the palaeostress history and
was also recorded in vitrinite during the pericxi of coalification. The
ENE stress field occurs in each stuciy area and is probably related to
the NE to E ccaipressicjn, vhich vas generally agreed to exist at least
to the conclusion of sedimentation (Sherwin and Holmes, 1986). The NNW
stress field at Tahmoor exists in an area vhere the stress field was,
for seme part of its development, defined by vwendiing. The presence
of both in situ stress fields at Tahmoor is probably related to a
347
variable inprinting of strain in the roof strata, just as the
iirprinting of strain in vitrinite was shown to be variable.
In the Southern Coalfield sare reflectance naxima are able to define
the in situ stress field ciirection. The regional in situ stress
direcrtion is probably a "Icxrked in' or residual strain inprinted to the
roof strata by a ENE palaeostress field, and a subsecjuent overprinting,
if any, of the NW to NNW palaeostress field created by left lateral
wrenching transmitted frcm the basenent. Localised stress field
variation was noted around individual fault structures.
The coal mine roof conditions studied in the scxithem Sydney Basin are
largely controlled by the nature of the in situ stress field. Field
majping techniques were able to identify the relative strength and
orientation of the horizontal stress field and define its contribution
toward, and the nature of, cxal mine roof deformation. Stucfy of the
optically biaxial characrter of vitrinite has established a tectonic
fabric element distinguishable in flat lying relatively undefomed
strata. It has also enabled regional palaeostress direcrtions to be
linked vdth the in situ st:ress fielcis, and provides possible
ej^lanations for the origin of seme stress field variations. Mine
planning can utilise a more carplete kncwledge of the in situ stress
fielcis to minimise and control roof strata beliaviour problems and
improve mine productivity.
The methocis of studying in situ stress fielcis, palaeostress ciirections,
and ccal mine roof cx)nditions established in this study are
transferable to other geological areas. In more deformed terrains the
technicjues are particularly relevant, because this stuciy lias shown that
348
in situ stress fields, and their origins, can even be interpreted frcm
flat lying relatively undefomed strata.
349
REFERHCES
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363
APPEMDIX I
OBTAINING THE EQUATICN OF AN ELLIPSE GIVEN
THREE PODnS AND THE ORIGIN
The general ecjuation of a conic is;
2 2 Ax + Bxy + Cy + Ey +F = 0.
For a cronic whose cent re i s the o r ig in the ecjuation reduces t o ;
2 2
Ax + Bxy + Cy + 1 = 0
where x=rcosR and
y=rsinR,
(in practice r=% reflectance and R = azimuth of coal block section).
Solve for A,B,and C to obtain the ecjuation of the ellipse, oriented at
a angle R to the E-W reference axis.
The value of R is given by;
cot2R = (A-C)/B, or
R = 0.5tan~-'-(l/(A-C)/B).
To find the length of the major and minor axes and the eccentricity of
the ellipse, the reference frame must be changed to that of the axes of
the ellipse, by the follcwing transformation:
X = x'cos^.- y'sinot
y = x'sino< + y'cosoc
Substitution into the original ecjuation vdll give an equation of the
form:
A(x'^) + B(y'^) = X
If this is changed to the form
2 , 2 ^ 2.2 , X /a +y /b = 1,
then a and b are the lengths of the long and short axes respectively.
Eccentricity (e) is:
2 2 -1/2 e = c/a where c = (a - b )
364
APPENDIX II POINT lOAD TEST RESULTS
1. Coal Cliff Rock Platform. Axial tests to failure.
Sanple Number 11/5/1 1/3/1 1/3/2 10/5/1 11/4/2 10/2/1 1/10/1 3/4/1 10/5/2 10/1/1
2. Sanple
Sanple Numter 134-1 134-3 134-5 134-7 134-9 134-11 134-13 134-15 134-17 134-19 134-21 134-23 134-25 134-27 134-29 134-31 134-33 134-35 134-37 134-39 134-41
3. Sanple
Sanple Nunnber 135-1 135-3 135-5 135-7 135-9 135-11 135-13 135-15
Sanple Length(cm) 5.4 5.5 5.5 5.45 5.5 5.55 5.55 5.5 5.6 5.55
54nm crore diameter • Location: E. 297450. N. 1207710.
Max. Press. psi 1350 1350 1375 1350 1275 1350 1300 1450 1300 1350
134 - West Cliff Colliery. Locration E Sanple Length(cm) 2.6 2.6 2.5 2.7 2.6 2.7 2.7 2.6 2.6 2.5 2.6 2.6 2.7 2.7 2.6 1.7 2.1 2.3 1.7 1.1 0.7
. 283280 . N. Max. Press.
kPa 4200 4500 4500 4100 3900 4550 4200 4700 3900 4400 2700 3000 4300 2700 4600 3900 4200 4100 4600 2400 1500
135 - West Cliff Colliery. Location E. 283285.
Sanple Length(an) 2.55 2.70 2.6 2.5 2.9 2.7 2.7 2.2
Max. Press. kPa 4400 3100 3750 3000 3200 3800 3400 3200
Sanple Nunter 11/3/2 3/5/2 10/2/2 11/3/1 3/2/1 3/2/2 10/1/2 11/4/1 3/5/1 3/4/1
25nm core 1211232.
Sanple Number 134-2 134-4 134-6 134-8 134-10 134-12 134-14 134-16 134-18 134-20 134-22 134-24 134-26 134-28 134-30 134-32 134-34 134-36 134-38 134-40
Sample Length (cm) 5.45 5.5 5.5 5.6 5.6 5.45 5.5 5.5 5.6 5.5
diameter.
Sanple Length (cm) 2.6 2.6 2.7 2.7 2.5 2.6 2.6 2.5 2.5 2.6 2.7 2.65 2.7 2.7 2,3 2.3 1.7 1.6 1.0 0.9
25mm core diameter. N. 1211253. Sanple Number 135-2 135-4 135-6 135-8 135-10 135-12 135-14 135-16
Sanple Length (cm) 2.70 2.65 2.6 2.7 2.55 2.65 2.65 2.0
Max. Press. psi 1350 1400 1380 1350 1350 1340 1400 1300 1450 1400
Max. Press. kPa 4100 4700 4450 4200 4600 4500 4100 3900 1700 4400 4700 4300 4600 4100 3800 4200 3900 4000 —
1800
Max. Press. kPa 3100 3200 4000 3200 3100 3400 3000 3400
365
135-17 135-19 135-21
4. Sanple
Sanple Number 141-21 141-20 141-4 141-10
1.8 1.6 2.3
3100 2700 4100
135-18 135-20 135-22
141. Kemira Colliery. 38nm dlaneter Location E. 281484.
Sanple Length (cm)
Note: Majority of 25 <
Max. Press. kPa 3700 3600 3000 2000
X)res frcm this be used for strength testing.
5. Sanple
Sanple Number 142-1 142-3 142-5 142-7 142-9
6. Sanple
Sanple Number 144-1 144-2 144-3 144-4 144-5 144-6 144-7 144-8 144-9 144-10 144-11
7. Sanple
Sanple Nunter 154.21b 154.23a 154.7a 154.10b 154.3a 154.6a 154.14b 154.11a 154.18a 154.6b 154.21a 154.17b
N. 1196504 Sanple Number 141-5 141-11 141-16 141-2
sanple were
142 Kemira Ctolliery. 38nm diameter Location E. 281534.
Sanple Length(cm) 1.7 4.3 1.65 1.4 1.25
Max. Press. kPa 3300 4600 3000 2000 2300
N. 1196539 Sanple Number 142-2 142-4 142-6 142-8
144 Kanira (Colliery. 38nm diameter Location E. 281624.
Sanple Length(cm) 1.5 1.3 1.55 1.55 1.45 1.20 1.35 1.25 1.4 0.85 1.95
154 West
Max. Press. kPa 2900 2200 2300 2700 2400 2100 2300 2300 2500 1900 3600
Cliff Ctolliery. Location E. 282563.
Sanple Length (cm) 1.6 2.7 2.55 2.45 2.4 2.2 2.15 2.0 1.8 1.9 1.6 1.45
Max. Press. kPa 3100 4200 4000 3950 4300 3800 3500 3100 3200 3400 3000 2800
N. 1196601 Sanple Numher 144-la 144-2a 144-3a 144-4a 144-5a
144-7a 144-8a 144-9a 144-lOa
N. 1212399 Sanple Number 154.3b 154.10a 154.2a 154.2b 154.14a 154.4a 154.18b 154.23b 154.4b 154.17a 154.7b
2.1 1.6 2.0
cores •
Sanple Length (cm)
thin cores
cores. • Sanple Length (cm) 4.05 2.7 4.2 1.55
cores. • Sanple Length (cm) 0.95 1.4 1.2 1.35 1.60
1.0 1.1 1.3 0.65
•
Sanple Length (on) 2.6 2.65 2.7 2.4 2.25 2.15 2.05 1.90 1.80 1.95 1.50
4400 2900 3400
Max. Press. kPa 3900 1700 1200 3500
- not able to
Max. Press. kPa 4400 3700 4400 2750
Max. Press. kPa 2000 2500 2300 2200 2500
2000 2100 2300 1600
Max. Press. kPa 4000 4400 3900 3700 3800 3700 3100 3200 3100 3400 2900
366
154.13 154.9 154.12 154.2 154.19 154.8
8. Sanple
Sanple Number 156.1 156.3 156.6 156.8 156.4 156a.11 156a.2 156a.14 156a.4a 156a.4 156a.10
9. Sanple
Sanple Nunter 157.4 157.3 157.4 157.5 157.7 157.1
10. Sanpl
Sanple Number 158.3.1 158.5.2 158.7.2 158.3.2 158.2.2 158.1.2 158.8.1 158.7.1 158.4.1 158.16.2 158.20.3 158.20.1 158.25.2 158.17.3
2.7 2.7 2.65 2.75 2.7 2.65
156
Sanple
4400 4000 3900 4200 4300 4000
West Cliff Colliery. Location E.
Length(cm) 2.35 1.25
157
Sanple
282664. Max. Press.
kPa 4100 3400 6000 4900 5400 5100 6500 6600 6200 6150 5800
West Cliff Colliery. Location E.
Length (cm) 1.5 1.3 0.9 0.65 3.9 4.05
e 158
Sanple
282560 Max. Press.
kPa 2400 3000 2500 2100 6900 7400
West Cliff Colliery. Location E.
Length (cm) 2.55 2.70 2.65 2.7 2.7 2.7 2.55 2.55 2.1 1.6 1.1 1.2 1.3 1.4
282678 Max. Press.
kPa 4700 4700 4750 5200 4900 4750 4600 4600 4500 4600 3800 3600 3900 4100
154.1 154.24 154.16 154.20 154.15 154.9
38nm core
2.65 2.75 2.7 2.8 2.7 2.2
diameter. N. 1212425. Sanple Number 156.1.1 156.3.1 156.2 156.10 156.9 156a,7 156a.6 156a.8 156a.9 156a.13
38mm core
Sanple Length (cm) 1.40 .9
diameter. . N. 1212379. Sanple Number 157.11 157.4 157.7 157.3 157.11
25inm core
Sanple Length (cm) 1.45 1.0 1.0 4.1 3.95
diameter. . N. 1212402. Sanple Number 158.1.1 158.8.2 158.4.2 158.6.1 158.2.1 158.9.2 158.6 158.9.1 158.25.1 158.17.1 158.21.1 158.15 158.21.2 158.16.3
Sanple Length (cm) 2.7 2.7 2.7 2.65 2.65 2.6 2.6 2.4 1.5 1.2 0.9 1.3 1.0 0.8
4300 3900 4000 4250 4200 3700
Max. Press kPa 3500 2900 4700 5400 5400 6550
0 6200
0 6900
Max. Press kPa 2700 2800 2600 6500 6900
Max. Press kPa 4700 4800 5300 4700 4500 4950 4800 4750 4400 3900 2900 3900 2700 1700
11. Sanple 159 West Cliff Ctolliery. 25nm core d lane te r . Location E. 282676. N. 1212390.
Sanple Sanple Max. Press. Sample Sanple Max. Press. Number Length(cm) kPa Number Length(cm) kPa
367
159a 159c 159.4.2 159.2.2 159.19.2 159.8.2 159.11.2 159.18.2 159.23.2
2.8 2.9 2.8 2.8 2.8 2.75 2.8 2.8 2.85
3750 4100 4200 4200 3900 4100 4400 3800 3300
159b 159.6.2 159.9.2 159.3.2 159.20.2 159.5.2 159.13.2 159.10.2
2.75 2.75 2.75 2.8 2.8 2.75 2.8 2.8
3200 3700 4150 4200 3900 3600 3800 4150
368
Sanple Number 102
103A
104
105
106
107
118
119
120
121
122
123
124
125
APPENDIX Ill VITRINITE REFLBCnANCE DATA
Block Number 4337 4338 4339 4340 4333 4334 4335 4336 4329 4330 4331 4332 4341 4342 4343 4344 4368 4369 4370 4371 4372 4374 4375 4467 4543 4544 4545 4546 4670 4671 4672 4673 4551 4552 4553 4554 4555 4556 4557 4558 4559 4560 4561 4562 4539 4540 4541 4542 4563 4564 4565 4566 4567
ISG Location (E,N)
292065. 1209040.
291748. 1209920.
291590. 1209940.
291465. 1209965.
292145. 1209825.
292240. 1209810.
292730. 1211440.
292737. 1211445.
292741. 1211450.
292762. 1211460.
292793. 1211480.
292820. 1211495.
292872. 1211535.
292945.
R max o 1.28 1.27 1.26 1.27 1.26 1.24 1.22 i.21 1.29 1.31 1.29 1.27 1.40 1.42 1.33 1.36 1.32 1.31 1.33 1.34 1.32 1.35 1.33 1.34 1.39 1.41 1.40 1.40 1.40 1.38 1.33 1.33 1.38 1.38 1.38 1.37 1.37 1.36 1.38 1.38 1.37 1.36 1.36 1.34 1.35 1.35 1.36 1.37 1.37 1.38 1.35 1.37 1.38
Block Orientation 350 235 318 260 059 331 106 020 236 282 153 204 135 182 089 210 201 291 169 219 217 093 178 307 241 148 195 285 243 155 154 272 245 299 200 176 083 347 120 210 172 064 127 041 044 286 019 171 213 084 122 171 050
369
210
209
211
212
213
214
215
216
217
218
236
237
238
239
4568 4569 4570 5009 5010 5011 5012 5005 5006 5007 5008 5013 5014 5015 5016 5017 5018 5019 5020 5021 5022 5023 5024 5025 5026 5027 5028 5029 5030 5031 5032 5033 5034 5035 5036 5037 5038 5039 5040 5041 5042 5043 5044 5303
- 5304 5305 5306 5299 5300 5301 5302 5295 5296 5297 5298 5447
1211585.
293052. 1209495.
292951. 1209667.
293075. 1209528.
293109. 1209582.
293152. 1209585.
293269. 1209662.
293300. 1209645.
293342. 1209630.
293397. 1209615.
293480. 1209587.
293605. 1209590.
293670. 1209640.
293775. 1209605.
292737.
1.37 1.37 1.37 1.35 1.34 1.36 1.34 1.37 1.36 1.29 1.38 1.38 1.36 1.35 1.38 1.34 1.34 1.34 1.36 1.34 1.35 1.35 1.34 1.46 1.47 1.44 1.47 1.43 1.44 1.38 1.40 1.39 1.42 1.37 1.40 1.39 1.42 1.42 1.40 1.40 1.42 1.41 1.41 1.44 1.44 1.40 1.37 1.35 1.37 1.37 1.36 1.38 1.36 1.34 1.37 1.42
087 184 131 114 204 075 162 147 258 174 238 264 352 302 034 084 130 032 174 040 072 353 308 230 144 095 008 316 229 103 Oil 130 003 220 092 101 149 194 059 176 220 257 128 055 090 005 144 056 147 101 218 279 246 187 337 353
370
240-1
240-2
240-3
240-4
240-5
240-6
241
242
243
244
245-1
245-2
245-3
245-4
5448 5449 5450 5387 5388 5389 5390 5391 5392 5393 5394 5395 5396 5397 5398 5399 5400 5401 5402 5403 5404 5405 5406 5407 5408 5409 5410 5451 5452 5453 5454 5455 5456 5457 5458 5463 5464 5465 5466 5459 5460 5461 5462 5415 5416 5417 5418 5419 5420 5421 5422 5423 5424 5425 5426 5427 5428
1211445.
292737. 1211445.
292737. 1211445.
292820. 1211495.
292820. 1211495.
1.42 1.37 1,38 1.40 1.44 1.40 1,44 1.41 1.43 1.41 1,43 1.39 1.43 1.38 1.41 1.43 1.44 1.42 1.42 1.40 1.44 1.42 1.42 1.42 1.40 1.40 1.38 1.47 1.44 1.47 1.47 1.45 1.40 1.43 1.41 1.41 1.40 1.36 1.35 1.44 1.44 1.44 1.41 1.44 1.42 1.44 1.42 1.42 1.45 1.45 1.44 1.45 1.40 1.43 1.44 1.45 1.38
048 134 081 131 182 081 033 131 033 081 182 131 033 081 182 131 033 081 182 299 208 157 099 225 102 189 134 107 054 018 329 214 158 092 122 133 170 042 079 162 225 138 254 299 207 159 066 299 207 159 066 299 207 159 066 299 207
371
245-5
245-6
245-7
245-8
247
248
249
250
251
294
295
296
297
5429 5430 5431 5432 5433 5434 5435 5436 5437 5438 5439 5440 5441 5442 5443 5444 5445 5446 5502 5503 5504 5505 5506 5507 5508 5509 5510 5511 5512 5513 5514 5515 5516 5517 5518 5519 5520 5521 6052 6053 6054 6055 6056 6057 6058 6059 6060 6061 6062 6063 6064 6065 6066 6067 6068 6069 6070
283278. 1211234.
283280. 1211232.
283282. 1211242.
283285. 1211253.
283292. 1211285.
283314. 1211381.
283311. 1211411.
283287. 1211397.
283297.
1.42 1.44 1.42 1.41 1.45 1.44 1.41 1.43 1.43 1.43 1.44 1.42 1.42 1.41 1.42 1.42 1.45 1.42 1.39 1.29 1.35 1.36 1.34 1.32 1.30 1.34 1.27 1.27 1.30 1.28 1.32 1.35 1.32 1.32 1.29 1.33 1.29 1.32 1.31 1.29 1.27 1.28 1.30 1.27 1.38 1.35 1.35 1.34 1.36 1.34 1.29 1.28 1.28 1.30 1.32 1.29 1.29
159 066 267 031 122 172 206 159 119 071 242 297 208 171 240 082 172 120 165 116 071 032 147 021 058 107 102 193 151 060 128 217 066 173 187 116 158 068 071 125 041 315 006 090 025 191 069 126 088 341 184 035 093 333 055 124 094
372
298
299
300
301
302
303
304
305
306
6071 6072 6073 6074 6075 6076 6077 6078 6079 6080 6081 6082 6083 6084 6085 6086 6087 6088 6089 6090 6091 6092 6093 6094 6095 6096 6097 6098 6099 6100 6101 6102 6103 6104 6105 6106 6107 6108 6109 6110 6111 6112 6113 6114 6115 6116 6117 6118 6119 6120 6121 6122 6123 6124 6125 6126 6127
1211413.
283298. 1211446.
283222. 1211462.
283339. 1211487.
283328. 1211442.
283324. 1211424.
283330. 1211406.
283342. 1211372.
283343. 1211402.
283356. 1211435.
1.31 1,30 1.30 1.32 1.28 1.29 1,29 1.33 1.32 1.32 1.33 1,31 1.33 1.32 1.35 1.32 1.31 1.30 1.29 1.31 1.31 1.32 1.29 1.31 1.27 1.26 1.29 1.30 1.29 1.27 1.26 1.27 1.28 1.28 1.26 1.29 1.31 1.32 1.31 1.32 1.31 1.21 1.21 1.23 1.20 1.24 1.17 1.30 1.30 1.31 1.28 1.30 1.30 1.33 1.33 1.34 1.35
158 066 034 120 358 162 072 097 013 139 049 139 359 031 088 117 061 100 012 060 122 149 041 214 293 149 180 234 275 052 063 136 091 026 170 108 133 161 017 046 066 080 199 054 115 169 140 013 106 076 044 130 342 346 008 075 139
373
307
308
287
288
289
290
291
293
309
310
6128 6129 6130 6131 6132 6133 6134 6135 6136 6137 6138 6139 6140 6141 6016 6017 6018 6019 6020 6021 6022 6023 6024 6025 6026 6027 6028 6029 6030 6031 6032 6033 6034 6035 6036 6037 6038 6039 6040 6041 6042 6043 6044 6045 6046 6047 6048 6049 6050 6051 6142 6143 6144 6145 6146 6147 6148
283366. 1211480.
283382. 1211552.
283389. 1211743.
283386. 1211744.
283373. 1211746.
283341. 1211757.
283305. 1211770.
283276. 1211799.
283358. 1211677.
283375.
1.34 1.31 1.35 1.35 1.36 1.36 1.38 1.35 1.35 1.35 1.34 1.32 1.35 1.35 1.34 1.32 1.30 1.30 1.33 1.32 1.31 1.30 1.32 1.30 1.30 1.30 1.31 1.31 1.30 1.30 1.31 1.30 1.30 1.32 1.31 1.30 1.30 1.31 1.27 1.30 1.31 1.30 1.31 1.28 1.33 1.34 1.35 1.33 1.34 1.34 1.29 1.30 1.33 1.32 1.30 1.33 1.33
050 099 046 012 098 026 120 134 104 026 340 048 059 152 230 107 078 142 180 203 024 137 050 075 167 117 052 155 018 119 093 181 359 078 128 222 101 341 111 020 063 128 154 045-069 358 333 075 059 028 083 046 025 001 120 135 067
374
311
312
313
314
315
273
274
275
276
6149 6150 6151 6152 6153 6154 6155 6156 6157 6158 6159 6160 6161 6162 6163 6164 6165 6166 6167 6168 6169 6170 6171 6172 6173 6174 6175 6176 6177 6178 6179 6180 6181 6182 6183 5932 5933 5934 5935 5936 5937 5938 5939 5940 5941 5942 5943 5944 5945 5946 5947 5948 5949 5950 5951 5952 5953
1211673.
283394. 1211669.
283423. 1211663.
283278. 1211805.
283283. 1211830.
283288. 1211849.
282604. 1212329.
282668. 1212359.
282664. 1212425.
282560. 1212379.
1.33 1.33 1.33 1.34 1.32 1.31 1.32 1.33 1.33 1.32 1.33 1.36 1.36 1.35 1.36 1.37 1.35 1.36 1.36 1.35 1.36 1.34 1.36 1.33 1.33 1.30 1.34 1.34 1.29 1.36 1.36 1.35 1.36 1.35 1.34 1.36 1.33 1.33 1.35 1.36 1.33 1.36 1.34 1.35 1.36 1.34 1.36 1.34 1.36 1.35 1.35 1.37 1.33 1.37 1.35 1.35 1.35
161 055 026 114 145 090 119 062 002 329 031 034 129 019 110 075 160 106 165 141 049 025 075 325 234 035 291 082 187 105 115 158 015 024 068 099 017 308 043 071 340 079 108 015 037 129 177 091 019 042 076 129 357 076 120 029 164
375
277
278
279
280
283
284
175
135
137
182
138
5954 5955 5956 5957 5958 5959 5960 5961 5962 5963 5964 5965 5966 5967 5968 5969 5970 5971 5972 5973 5974 5975 5976 5977 5978 5979 5992 5993 5994 5995 5996 5997 5998 5999 6000 6001 6002 6003 4860 4861 4862 4863 4768 4769 4770 4771 4772 4773 4774 4775 4898 4899 4900 4901 4875 4876 4877
282678. 1212402.
282676. 1212397.
282676. 1212390.
282565. 1212354.
282342. 1212406.
282401. 1212392.
283817. 1212677.
283811. 1212651.
283799. 1212604.
283798. 1212582.
283801. 1212581.
1.36 1.35 1.38 1.32 1.38 1.35 1.36 1.35 1.38 1.39 1.38 1.37 1.38 1.38 1.35 1.39 1.35 1.37 1.37 1.38 1.25 1.26 1.26 1.25 1.26 1.25 1.35 1.36 1.35 1.31 1.35 1.36 1.37 1.37 1.38 1.38 1.35 1.38 1.28 1.30 1.32 1.29 1.32 1.37 1.30 1.35 1.36 1.35 1.38 1.35 1.31 1.33 1.31 1.30 1.29 1.27 1.27
092 001 075 110 023 350 331 120 158 068 044 125 105 197 055 094 027 144 124 010 130 078 030 190 099 171 135 070 112 160 046 015 094 015 164 133 078 043 010 312 042 278 161 067 123 000 161 076 026 109 096 231 182 142 098 136 178
376
228
139
180
181
183
184
185
186
142
143
144
192
191
190
4878 5293 5292 5291 5294 4879 4880 4881 4882 4890 4891 4892 4893 4894 4895 4896 4897 4902 4903 4904 4905 4906 4907 4908 4909 4910 4911 4912 4913 4914 4915 4916 4917 4776 4777 4778 4779 4781 4782 4783 4950 4784 4785 4786 4787 4938 4939 4940 4941 4934 4937 4951 4952 4930 4931 4932 4933
283792. 121256.7.
283793. 1212571.
283790. 1212566.
283790. 1212562.
283789. 1212558.
283787. 1212554.
283787. 1212548.
283785. 1212540.
283778. 1212525.
283772. 1212496.
283760. 1212445.
283832. 1212638.
283828. 1212592.
283816. 1212573.
1.27 1.36 1.36 1.34 1.35 1.34 1.39 1.40 1.37 1.31 1.31 1.32 1.32 1.40 1.35 1.38 1.38 1.32 1.38 1.38 1.36 1.40 1.37 1.39 1.35 1.38 1.38 1.39 1.41 1.34 1.31 1.33 1.34 1.26 1.30 1.28 1.29 1.25 1.30 1.29 1.37 1.30 1.33 1.27 1.27 1.29 1.35 1.31 1.29 1.34 1.36 1.34 1.35 1.33 1.33 1.33 1.40
053 327 181 269 247 164 255 319 226 180 320 226 281 308 043 086 177 218 127 258 183 066 024 309 351 254 112 219 168 137 049 104 198 079 024 112 164 311 078 220 161 110 148 092 060 038 303 162 072 332 241 109 021 041 278 189 131
377
189
187
188
193
194
258
259
260
261
262
263
264
4926 4927 4928 4929 4918 4919 4920 4921 4922 4923 4924 4925 4942 4943 4944 4945 4946 4947 4948 4949 5854 5855 5856 5857 5858 5859 5860 5861 5862 5863 5864 5865 5866 5867 5868 5869 5870 5871 5872 5873 5874 5875 5876 5877 5878 5879 5880 5881 5882 5883 5884 5885 5886 5887 5888 5889 5890
283815. 1212567.
283811. 1212555.
283810. 1212546.
283807. 1212529.
283791. 1212477.
281433. 1196469.
281441. 1196472.
281443. 1196477.
281450. 1196479.
281405. 1196451.
281417. 1196460.
281411.
1.38 1.38 1.37 1.36 1.36 1.37 1.34 1.35 1.39 1.41 1.36 1.41 1.34 1.35 1.34 1.34 1.31 1.35 1.36 1.39 1.22 1.18 1.20 1.22 1.24 1.24 1.21 1.23 1.20 1.19 1.20 1.21 1.21 1.22 1.20 1.22 1.21 1.22 1.19 1.19 1.23 1.21 1.22 1.26 1.17 1.16 1.18 1.19 1.20 1.20 1.19 1.19 1.19 1.20 1.18 1.21 1.22
176 134 206 265 081 122 169 032 117 162 267 026 354 045 314 087 154 008 243 274 179 118 162 149 082 211 128 050 193 085 019 352 048 009 096 075 153 136 073 102 040 014 132 150 098 345 063 010 334 080 129 064 095 358 033 335 197
378
265
266
267
B 3
B 4
NNl
NN3
NN4
NN5
5891 5892 5893 5894 5895 5896 5897 5898 5899 5900 5901 5902 5903 5904 5905 5906 5907 5908 5909 5910 5911 5912 5913 145 146 147 148 149 150 163 164 166 167 168 049 050 051 052 053 054 055 056 057 058 059 060 103 104 105 106 107 108 127 128 129 130 131
1196453.
281484. 1196504.
281534. 1196539.
281624. 1196601.
252093. 1234574.
253313. 1236213.
250599. 1234076.
250582. 1234095.
250557. 1234093.
250478. 1234111.
1.23 1.21 1.19 1.22 1.23 1.19 1.16 1.25 1.24 1.20 1.23 1.22 1.21 1.20 1.20 1.22 1.22 1.18 1.16 1.17 1.18 1.18 1.18 1.12 1.11 1.09 1.12 1.12 1.12 1.09 1.10 1.08 1.08 1.09 1.03 0.98 1.02 1.03 1.03 1.04 1.05 1.04 1.05 1.05 1.06 1.05 1.04 1.02 0.97 1.02 1.02 1.03 1.14 1.12 1.12 1.12 1.13
349 136 082 053 102 097 009 064 041 312 332 159 122 068 356 092 024 080 039 155 086 127 173 028 172 119 051 074 145 058 121 031 092 178 047 177 140 020 105 089 178 018 133 107 086 052 052 004 021 109 137 090 154 049 112 063 138
379
NN9
NNIO
NNll
NN12
QA 1
OA 2
OA 3
OA 5
OA 6
OA 7
132 121 122 123 124 125 126 169 170 171 172 173 174 133 134 135 136 137 138 061 062 063 064 065 066 025 026 027 028 029 030 031 032 033 034 035 037 038 039 040 041 042 091 092 093 094 095 096 115 116 117 118 119 120 097 098 099
25173. 123138.3.
25131. 1231745.
25171. 1231782.
25015. 1231708.
253204. 1230886.
252963. 1231747.
252124. 1232587,
253249. 1230974.
251963. 1232015.
252247. 1230801.
1.13 1.07 1.06 1.06 1.06 1.07 1.07 1.06 1.04 1.05 1.02 1.05 1.08 1.10 1.09 1.11 1.12 1.11 1.10 1.04 1.03 1.05 1.04 1.05 1.04 1.09 1.01 1.05 1.05 1.05 1.04 1.02 1.01 1.04 1.01 1.02 1.05 1.06 1.06 1.06 1.07 1.08 1.13 1.12 1.14 1.13 1.14 1.11 1.11 1.13 1.14 1.12 1.14 1.12 1.10 1.10 1.05
022 036 175 084 010 127 102 189 047 062 113 151 104 094 007 033 059 120 152 108 016 124 039 063 151 003 062 109 149 021 084 091 059 009 126 028 018 044 114 150 138 062 252 131 005 163 278 041 060 021 091 113 000 148 207 178 237
380
NB 2
NB 3
NB 5
NB 6
NBll
NB12
TI
T2
T5
T15
100 101 102 067 068 069 070 071 072 073 074 075 076 077 078 085 086 087 088 089 090 151 152 153 154 155 156 187 188 189 190 191 192 193 194 196 197 198 001 002 003 004 005 006 007 008 009 010 Oil 012 181 182 183 184 185 186 217
253438'. 1229040.
252654. 1229112.
252067. 1229324.
254146. 1229005.
251741. 1229370.
251685. 1229370.
262000. 1209750.
262080. 1209920.
262125. 1209730.
261515.
1.07 1.08 1.09 1.11 1.14 1.13 1.12 1.14 1.14 1.06 1.08 1.06 1.06 1.06 1.06 1.07 1.09 1.09 1.08 1.05 1.07 1.12 1.10 1.09 1.13 1.10 1.11 1.09 1.09 1.10 1.10 1.07 1.09 1.11 1.12 1.07 1.09 1.12 1.09 1.06 1.09 1.07 1.09 1.09 1.14 1.13 1.14 1.12 1.14 1.14 1.16 1.15 1.15 1.15 1.15 1.15 1,12
141 115 086 052 125 162 095 008 032 074 023 143 113 167 049 046 022 131 105 156 068 050 110 165 021 073 139 127 179 106 018 088 043 049 167 098 010 145 135 196 105 094 182 048 083 097 007 167 123 039 047 083 352 138 033 116 183
3 8 1
T20
T21
218 219 220 221 222 247 248 249 250 251 252 253 254 255 256 257 258
1210815.
„
261600. 1209105.
262530. 1209680.
1.13 1.13 1.16 1.13 1.12 1.04 1.05 1.06 1.04 1.06 1.05 1.15 1.12 1.12 1.14 1.13 1.10
094 055 148 220 311 282 188 133 259 154 217 238 268 118 148 178 208
382
APPENDIX IV-1
Order of
Drivage
(Heading)
(a)
1(A)
1(A)
1(A)
1(A)
1(A)
1(A)
1(A)
1(A)
1(A)
1(C)
1(C)
1(C)
1(A)
SIRESS ORIENTATICN AND LONG TE3?M DEPORMATICN
Location
(b)
0-1 CT.
1-2 C.T.
2-3 C.T.
3-4 C.T.
4-5 C.T.
5-6 C.T.
6-7 C.T.
7-8 C.T.
8-9 C.T.
9-10 C.T.
10-11 C.T
11-12 C.T.
12-13 C.T.
NW PANEL- TAHMXR MINE
FIRST DRIVEN HEADING
Aziiraith
of
^1
(c)
001
001
003
006
009
014
016
014
013
019
027
019
027
Gsr
(d)
35
35
37
40
43
48
50
48
47
53
61
53
61
Long Term Roof (Condition
(Proportion per m)
(Gcxxi Sag
(e)
100
100
81
95
73
63
37
25
0
71
7
0
35
(f)
0.
0.
19.
5.
14.
8.
21.
13.
100.
28.
48.
22.
18.
Cantilever
(g)
0.
0.
0.
0.
4.
20.
18.
24.
13.
10.
83.
83.
47.
(Gut
(h)
0.
0.
0.
0.
7.
17.
41.
45.
0.
8.
0.
0.
7.
383
APPENDIX IV-2
(a)
2(B)
2(B)
2(B)
2(B)
2(B)
2(B)
2(B)
2(B)
2(B)
2(D)
2(D)
2(D)
2(B)
STRESS ORIBWTAnCN AND lONG TERM DEPCRMATICN
(b)
0-1 C.T.
1-2 C.T.
2-3 C.T.
3-4 C.T.
4-5 C.T.
5-6 C.T.
6-7 C.T.
7-8 CT.
8-9 CT.
9-10 C.T.
10-11 C.T.
11-12 C.T.
12-13 C.T.
NW PANEL
SBOGND DRIVEN HEADINS
(C)
001
001
003
006
009
014
016
014
013
019
027
019
027
(d)
35
35
37
40
43
48
50
48
47 '
53
61
61
61
(e)
100.
96.
100.
96.
100.
96.
93.
33.
53.
5.
3.
12.
38.
(f)
0.
4.
0.
4.
0.
4.
4.
45.
12.
70.
53.
32.
29.
(g)
0.
0.
0.
0.
0.
0.
0.
13.
0.
33.
44.
65.
33.
(h)
0.
0.
0.
0.
0.
0.
3.
17.
19.
10.
45.
7.
0.
384
APPHOIX I V - 3
STRESS ORIBITATICK AND LONG TERM DEPORMATIOW
NW PANEL - TAHMOCR MINE
THIRD DRIVEN HEADING
(a)
3(C)
3(C)
3(C)
3(C)
3(C)
3(C)
3(C)
3(C)
3(C)
3(A)
3(A)
3(A)
3(C)
(b)
0-1 C.T.
1-2 C.T,
2-3 C.T.
3-4 C.T.
4-5 C.T.
5-6 C.T.
6-7 C.T.
7-8 C.T.
8-9 CT.
9-10 C.T.
10-11 CT.
11-12 C.T.
12-13 C.T.
(c)
001
001
003
006
009
014
016
014
013
019
027
019
027
(d)
35
35
37
40
43
48
50
48
47
53
61
46
61
(e)
90.
96.
91.
91.
96.
90.
90.
94.
53.
8.
4.
6.
64.
(f)
10.
4.
10.
7.
4.
4.
4.
4.
47.
58.
45.
15.
36.
(g)
0.
0.
0.
0.
0.
0.
0.
0.
0.
61.
70.
36.
0.
(h)
0.
0.
0.
0.
0.
6.
3.
6.
0.
18.
0.
53.
0,
385
(a)
4(D)
4(D)
4(D)
4(D)
4(D)
4(D)
4(D)
4(D)
4(D)
4(D)
4(B)
4(B)
4(D)
APPENDIX IV-4
STRESS CRIENTATICH AND l O G TERM DEPCRMATICN
(b)
0-1 C.T.
1-2 C.T.
2-3 C.T.
3-4 C T .
4-5 C.T.
5-6 C.T.
6-7 C.T.
7-8 C T .
8-9 C.T.
9-10 C.T.
10-11 C T .
11-12 C T .
12-13 C.T.
NW PANEL -
(c)
001
001
003
006
009
014
016
014
013
019
027
019
027
TAHMOCR Onr.T.TERY
PCXKIH DRIVEN HEADINS
(d)
35
35
37
40
43
48
50
48
47
53
61
50
61
(e) (
100.
100.
100.
100.
100.
100.
53 .
19.
16.
93 .
85 .
75 .
77 .
f )
0 .
0.
0.
0.
0 .
0.
23 .
47.
66.
4 .
0.
9.
1 1 .
(g)
0.
0.
0.
0.
0 .
0.
5 .
0.
0 .
0.
14.
13 .
5 .
(h)
0 .
0.
0.
0 .
0 .
0.
19.
44.
4 1 .
3 .
0.
3 .
6 .
386
APPENDIX IV-5
SIRESS CRIENTATIQN AND LCHG TERM DEPCRMATICN
N-W PANEL - TAHMOCR
CUT-THROUGHS 1 TO 13
(a)
not
applic
able for
cut-
throughs
(b)
1 C.T.
2 C.T.
3 C.T.
4 C.T.
5 C.T.
6 C.T.
7 C.T.
8 C.T.
9 C.T.
10 C.T.
11 CT.
12 C.T.
13 C.T.
(c)
001
002
005
008
012
015
015
014
016
023
023
023
027
(d)
55
54
51
88
44
41
41
42
40
33
33
33
29
(e)
62.
10.
33.
8.
0.
0.
0.
0.
0.
0.
0.
0.
46.
(f)
38.
90.
66.
88.
100.
88.
90.
100(ARCH)
100.
90.
82.
52.
42.
(g)
0.
0.
10.
0.
16.
16.
12.
. 9.
0.
18.
34.
62.
44.
(h)
0.
0.
5.
5.
0.
0.
0.
0.
0.
0.
0.
25.
10.
Note: C is calculated frcm the average of adjacent ^unit' stress
ciirecrtions.