an evaluation of slope stability classification - xs4all madeira... · an evaluation of slope...
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 1
Engineering Geology
An evaluation of slope stability classification
Eurock’2002, Madeira, 25 November 2002
Robert HackSection Engineering Geology, International Institute for Geoinformation Sciences and Earth Observation
(ITC), Delft, The Netherlands
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 2
Engineering Geology
Slopes in The Netherlands?
Jan van Goyen, View at Leiden, 1650 – Museum Lakenhal, Leiden
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 3
Engineering Geology
Dykes have slopes!
(Brouwersdam, The Netherlands)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 4
Engineering Geology
Dyke with basalt cover may be modelled with discontinuous rock
mechanics
(seadyk with basalt cover: photo: Sytske Dijksen; http://www.waddenzee.nl/)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 5
Engineering Geology
Also real rock slopes in the Southern part of The Netherlands!
(ENCI quarry; photo: http://www.beeldexpressie.be/film/)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 6
Engineering Geology
Other reasons to study slopes even if coming from a flat country
Slopes are an ideal study object for soil and rock mechanics in general because:
Soil or rock in tunnels and foundations often not visible
Failures in tunnels or foundations not or difficult to study
Slopes often easily accessibleOften many slopes in a relatively small area
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 7
Engineering Geology
and not very scientific, but highly important:
many Dutch civil engineering companies work worldwide with soil and rock slopes
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 8
Engineering Geology
Slope stability
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 9
Engineering Geology
What is required to analyse the stability of a slope ?
soil and rock mass propertiespresent and future geometrypresent and future geotechnical
behaviour of soil or rock massexternal influences such as earthquakes
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 10
Engineering Geology
Slope stability analyses done per geotechnical unit in a
geometrically uniform slope geometry,
e.g. a slope analyses is done for a uniform material with uniform
geometryIs that possible ?
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 11
Engineering Geology
VariationHeterogeneity of mass causes:
variation in mass propertiesHeterogeneity of slope geometry causesVariation in geometry
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 12
Engineering Geology
Mass versus geotechnical unitMass is split in units such that
homogenous geotechnical units are created that can be analysed with assumed uniform properties for the unit
However, a certain variation in properties will always be present
How to define a unit?
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 13
Engineering Geology
Example of geotechnical units
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 14
Engineering Geology
Definition of a geotechnical unit is based on economical or
environmental impact or the hazard the project forms for human live
the more different units, the better the uniformity per unit and the better the analyses, but the higher the costs
costs are balanced against the economical and environmental value of a project, and the potential hazard a project may impose on human live
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 15
Engineering Geology
But no unit will be absolutely uniform
Hence, a certain variation will always be present in any
geotechnical unit, causing an uncertainty in properties used for
the analyses
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 16
Engineering Geology
UncertaintyUncertainty in propertiesUncertainty (error) in measurements
of propertiesUncertainties in geometryUncertainty (error) in measurements
of geometry (often small)Uncertainty in failure mechanisms
applicable
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 17
Engineering Geology
Options for analysing slope stability
AnalyticalNumerical
Classification
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 18
Engineering Geology
Analysing slope stability
analytical: only in relatively simple cases possible for a discontinuous rock mass
numerical: difficult and often cumbersome, however, possible with discontinuous numerical rock mechanics programs such as UDECHence, classification systems may be a good and simple alternative
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 19
Engineering Geology
What options from existing classification
systems?
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 20
Engineering Geology
Classification systems are empirical relations that relate rock mass properties either directly or
via a rating system to an engineering application, e.g. a
slope
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 21
Engineering Geology
For underground:Bieniawski (RMR)
Barton (Q)Laubscher (MRMR)
etc.For slopes:
SelbyBieniawski (RMR)
VecchiaRobertson (RMR)Romana (SMR)
Hainesetc.
Existing classification systems:
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 22
Engineering Geology
Development of existing rock mass classification systems
First developed for underground excavationsMost slope systems are based on underground systems adjusted to be used for slopes
Therefore a legacy in properties and parameters from underground systems
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 23
Engineering Geology
Development of existing rock mass classification systems
Most systems that are used at present are based on systems developed some 30 years ago
At that time “state-of-the-art” and new, but this is no reason not to investigate whether the systems are still as applicable or that new methodologies (for example, with the use of computers) allow for better systems
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 24
Engineering Geology
Existing rock mass classification systems
Wide variation in rating systems, methodologies, parameters, calculation methods, boundaries, etc.Addition, multiplication, logarithmic, etc.Wide variation in the influence of parameters on the final resultIn some un-understandable ratings and relations
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 25
Engineering Geology
Strange influence parameters in some systems
For example:
A slope in a rock mass with a high intact rock strength and one thick clay filled (gauge type) discontinuity set that will lead to sliding failure.
In some systems the intact rock strength will partially determine the stability rating, while the slope will be unstable due to the presence of the thick clay filled discontinuity and not at all be influenced by the intact rock strength.
How valid is such a system?
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 26
Engineering Geology
very
goo
d
extremelpoor very poor poor fair good very
goodext.
goodexc.good
fair
poor
very
poo
r
exceptionallpoor
100
80
60
40
20
00.001 0.01 0.1 1 10 100 1000
Bie
niaw
ski (
RMR)
Barton (Q-value)
RMR = 9 ln Q + 44
good
(after Bieniawski, 1989)
Correlation between RMR and Q ?
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 27
Engineering Geology
Rock mass parameters of interest for engineering structures in or
on rock
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 28
Engineering Geology
intact rock strength
orientation (with respect to engineering structure)
amount of disc. sets
spacing per disc. set
persistence per disc. set
material frictionroughness (dilatancy)strengthdeformation
infill material
susceptibility to weathering
deformation parameters of intact rock/rock mass
engineering structure
geometry of engineering structure (size and orientation of a tunnel, height and orientation of a slope, etc.)
water pressure/flow, snow and ice, stress relief, external stress, etc.external influences type of excavation
surface characteristics of discontinuity wall
shear strength along discontinuity(condition of discontinuity)
rock block size and form
discon-tinuitiesgeotechnical
unit
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 29
Engineering Geology
Existing classification systems• The absence of the intact rock strength (except for a
low intact rock strength/environment stress ratio), in the Barton system.
• The absence of discontinuity spacing as quantitative parameter in the Barton system.
• The strong reduction in influence of the water parameter in the Laubscher and Haines systems as compared to the systems of Bieniawski and Barton.
• The absence of a water/water pressure parameter in the Robertson modification for slopes of the Bieniawski system and in the slope stability system of Vecchia.
• The strong influence of the susceptibility to weathering in the Laubscher system.
• The strong increase in influence of orientation of discontinuities in relation to the orientation of the walls and roof of underground excavations in the Laubscher system compared to the Bieniawski system.
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 30
Engineering Geology
Influenceof intact
rock strength and
RQD
MAXIMUM NEGATIVE INFLUENCE OF PARAMETERS (in percentage from final maximum rating)(1)(2)
classification system(2) rating range intact rock
strength RQD
EARLY SYSTEMS (for underground excavations) Deere (RQD) 0 - 100 100 Wickham (RSR) 19 - 120 RECENT SYSTEMS (for underground excavations)
15 20 Bieniawski (RMR) 0 - 100
0.00006 - 2666
with rock load
parame-ter(3)
Barton(3) (Q)
0 - 120 17 13(5) Laubscher (no change of class)
SLOPE SYSTEMS Selby 0 - 100 20 Bieniawski (RMR) 0 - 100 15 20
Vecchia 0 - 100 Robertson (RMR)(10) 0 - 100 30 20
Romana (SMR) 0 - 115 13 17 Haines 0 - 100 17 13(5)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 31
Engineering Geology
Influenceof water and method of excavation
MAXIMUM NEGATIVE INFLUENCE OF PARAMETERS (in percentage from final maximum rating)
classification system water excavation methods
EARLY SYSTEMS (for underground excavations) Deere (RQD) Wickham (RSR) 7 17 RECENT SYSTEMS (for underground excavations)
Bieniawski (RMR) 15
Barton(3) (Q) 95
Laubscher 3 20
SLOPE SYSTEMS Selby Bieniawski (RMR) 15 Vecchia Robertson (RMR)(10) Romana (SMR) 13 13 Haines 3 20
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 32
Engineering Geology
Classification systems:Problems with Intact rock strength
If intact rock is defined as Unconfined Compressive Strength (UCS):
1. Inclusion of discontinuities within 10 cm length
2. Samples tested in the laboratory tend to be of better quality (or of lower quality if rock is very strong)
3. The intact rock strength measured depends on the sample orientation if the intact rock exhibits anisotropy.
4. UCS is not a valid parameter because, in reality, most rock will be stressed under circumstances resembling conditions of triaxial tests rather than UCS test conditions
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 33
Engineering Geology
Classification systems:Problems with RQD (1)
1. Arbitrary length of 10 cm
2/3. Orientation of borehole in relation with discontinuity spacing
spacing discontinuities 0.09 m
vertical borehole RQD = 0 %
horizontal borehole
RQD = 100 %
horizontalborehole RQD = 0 %
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 34
Engineering Geology
Classification systems:Problems with RQD (2)
4. Weak rock pieces (weathered pieces of rock or infill material) that are not sound should not be considered for determining the RQD (Deere et al., 1967, 1988). To exclude infill material will usually not be too difficult; however, excluding pieces of weathered, not sound rock is fairly arbitrary.
5. The RQD value is influenced by drilling equipment, drilling operators and core handling. Especially RQD values of weak rocks can be considerably reduced due to inexperienced operators or poor drilling equipment.
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 35
Engineering Geology
Classification systems:Problems with RQD (3)
6. No standard core barrel - single, double, or triple barrel ?
7. Diameter of boreholes
8. Drilling fractures should be re-fitted, but what are drilling fractures?
9. RQD should be determined per lithology, but where is the lithology boundary if washed away?
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 36
Engineering Geology
Classification systems:Problems with RQD (5)
Some systems allow for replacing RQD by fracture frequency or equivalent
or use a relation to calculate an RQD value from discontinuity measurements on an exposure
Why should then the RQD be used as parameter?
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 37
Engineering Geology
Many classification systems allow for only one rating for discontinuity
set spacing and shear strength;this then to be the spacing and
shear strength of the most unfavourable discontinuity set
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 38
Engineering Geology
discontinuity set with good condition; e.g. high shear strength discontinuity set with very poor condition; e.g. low shear strength
What is the most unfavourable discontinuity set ?
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 39
Engineering Geology
Classification systems problem:(1)
In many systems the following parameters are absent:Anisotropic roughness of discontinuitiesDiscontinuity karst featuresSusceptibility to weatheringDeformation of intact rock and rock mass, stress reliefRelative orientation of slope and discontinuitiesSlope heightWater, influence of ice and snow
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 40
Engineering Geology
Classification systems problem: Water (1)
If water parameter defined on amount of water:1 Amount of water depending on intersected
number of discontinuities, hence, on the size of the excavation
2 The amount of water is not the pressure of water (which is the important parameter)
3 Amount and pressure not constant throughout the slope; e.g. lower in the slope higher pressure than high in the slope
4 Difference in underground excavations and slopes for pressure regime
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 41
Engineering Geology
Classification systems problem: Water (2)
5 Water transport in discontinuities mainly via channels: if also applicable to pressure: resulting pressure on a discontinuity considerably less than pressure over full discontinuity surface
6 Run-off water over the slope face degrades slope face and may lead to instability
7 Not constant over time - wait for maximum rainfall?
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 42
Engineering Geology
Classification systems problem: Water (3)
Practical problems with determining water:1 How to differentiate between run-off water over
the slope face and water under pressure out of a discontinuity?
2 How to measure the quantity of water out of a slope (tunnel with weir) and differentiate with surface run-off
3 Terminology often subjective: dripping <> wet
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 43
Engineering Geology
No clear differentiation “as is”and “as will be”
External influences as weathering and method of excavation will have influenced the site characterized but will also (and likely differently) influence the new slope in the future
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 44
Engineering Geology
Bias and familiarization
Often not clear how many different persons developed a system and whether designer bias may be presentThose using a system and being satisfied with the system may be so familiarized that they do not see the flows anymore
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 45
Engineering Geology
Slope Stability probability Classification (SSPC)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 46
Engineering Geology
SSPC
• three step classification system• based on probabilities• independent failure mechanism
assessment
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 47
Engineering Geology
Three step classification system (1)
riverold road
proposed new road cut slightly
weathered
moderately weathered
1
2
3
Reference Rock Mass
fresh
1: natural exposure made by scouring of river, moderately weathered; 2: old road, made by excavator, slightly weathered; 3: new to develop road cut, made by blasting, moderately weathered to fresh.
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 48
Engineering Geology
Three step classification system (2)EXPOSURE ROCK MASS (ERM)
Exposure rock mass parameters significant for slope stability: • Material properties: strength, susceptibility to weathering • Discontinuities: orientation and sets (spacing) or single • Discontinuity properties: roughness, infill, karst
REFERENCE ROCK MASS (RRM) Reference rock mass parameters significant for slope stability:• Material properties: strength, susceptibility to weathering • Discontinuities: orientation and sets (spacing) or single • Discontinuity properties: roughness, infill, karst
SLOPE ROCK MASS (SRM) Slope rock mass parameters significant for slope stability: • Material properties: strength, susceptibility to weathering • Discontinuities: orientation and sets (spacing) or single • Discontinuity properties: roughness, infill, karst
Exposure specific parameters:• Method of excavation • Degree of weathering
Slope specific parameters: • Method of excavation to be used • Expected degree of weathering at
end of engineering life-time of slope
SLOPE GEOMETRYOrientation
Height
SLOPE STABILITY ASSESSMENT
Factor used to remove the influence of the method excavation and degree of weathering
Factor used to assess the influence of the method excavation and future weathering
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 49
Engineering Geology
Excavation specific parameters for the excavation which is used to
characterize the rock mass
• Degree of weathering• Method of excavation
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 50
Engineering Geology
Rock mass Parameters
Intact rock strengthSpacing and persistence discontinuitiesShear strength along discontinuity
- Roughness - large scale- small scale- tactile roughness
- Infill- Karst
Susceptibility to weathering
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 51
Engineering Geology
Slope specific parameters for the new slope to be made
• Expected degree of weathering at end of lifetime of the slope
• Method of excavation to be used for the new slope
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 52
Engineering Geology
Intact rock strength
By simple means test - hammer blows, crushing by hand, etc.
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 53
Engineering Geology
Spacing and persistence of discontinuities
Based on the block size and block form by first visual assessment and then quantification of the characteristic spacing and orientation
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 54
Engineering Geology
Shear strength -roughness large scale
slightly wavy
curved slightly curved
straight (i-angles and dimensions only approximate)
amplitude roughness:wavy
i = 14 - 20°
i = 9 - 14°
i = 2 - 4°
i = 4 - 8°
≈ 5 – 9 cm
≈ 5 – 9 cm
≈ 3.5 – 7 cm
≈ 1.5 – 3.5 cm
≈ 1 m
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 55
Engineering Geology
Shear strength -roughness small scale
stepped
undulating
planar
≈ 0.20 m
amplitude roughness > 2 - 3 mm
(dimensions only approximate)
amplitude roughness > 2 - 3 mm
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 56
Engineering Geology
Shear strength -roughness
tactile
Three classes:
rough
smooth
polished
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 57
Engineering Geology
Shear strength
- Infill
Infill:
- cemented
- no infill
- non-softening (3 grain sizes)
- softening (3 grain sizes)
- gauge type (larger or smaller than roughness amplitude)
- flowing material
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 58
Engineering Geology
Shear strength - karst
Karst or no karst
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 59
Engineering Geology
Shear strength - condition factor
Discontinuity condition factor (TC) is a multiplication of the rating for small- and large scale roughness, infill and karst (similar to method used by Laubscher)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 60
Engineering Geology
Orientation dependent stability
Stability depending on relation between slope and discontinuity orientation
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 61
Engineering Geology
How did we develop it? - sliding criterion:
AP (= apparent discontinuity dip in direction slope dip) (deg)
TC (=
disc
ontin
uity
cond
ition
par
amet
er) (
-)
0 20 40 60 800
0.2
0.4
0.6
0.8
1
stableunstable
TC = 0.0113 * AP (AP in deg)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 62
Engineering Geology
Sliding criterion
APTC *0113.0:ifoccurssliding
<
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 63
Engineering Geology
Sliding probability
AP (deg)
TC (c
ondi
tion
of d
iscon
tinui
ty)
1.00
0.80
0.60
0.40
0.20
0.000 10 20 30 40 50 60 70 80 90
5 %30 %discontinuity stable
with respect to sliding
discontinuity unstable with respect to sliding
70 %50 %
95 %
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 64
Engineering Geology
Toppling criterion
( )itydiscontinudipAPTC +−°−< 90*0087.0
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 65
Engineering Geology
Toppling probability
Fig. 9. Toppling criterion.
- 90 - AP + slope dip (deg)
TC (c
ondi
tion
of d
iscon
tinui
ty) (
-)
0 10 20 30 40 50 60 70 80 90
1.00
0.80
0.60
0.40
0.20
0.00
70 %
5 %
95 %
discontinuity stable with respect to toppling
discontinuity unstable with respect to toppling
50 %30 %
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 66
Engineering Geology
Orientation independent stability
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 67
Engineering Geology
Overall spacing of discontinuity setsBlock size and form relations from Taylor
0.1 1 10 100 10000.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
discontinuity spacing (cm)
fact
or
1 discontinuity set
2 discontinuity setsminimum spacingmaximum spacing
factor1
factor3
joint2
factor2
3 discontinuity sets minimum spacing intermediate spacingmaximum spacing
bedding1&
joint3
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 68
Engineering Geology
Overall condition of discontinuity sets
3 2, 1, setsity discontinu of spacings theare and condition, theare
111
3,2,13,2,1 DSTCDSDSDS
DSTC
DSTC
DSTC
CD
321
3
3
2
2
1
1
++
++=
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 69
Engineering Geology
Shear plane failure following Mohr-Coulomb for rock mass
( ) ( )( )’ - dip -
’ * dip *’ * coh * . = H
H
:’ dip
massslope
massslope
mass-
max
massslope
ϕϕ
ϕ
cos1cossin
1061else
infinite is )(height slope maximum the
theIf
4max
≤
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 70
Engineering Geology
1
0.1
10
0.0 0.2 0.4 0.6 0.8 1.0
5 % 10 % 30 % 50 %
95 % 90 %
70 % probability to be stable > 95 %
probability to be stable < 5 %
(example)
ϕ ’mass / slope dip
Hm
ax /
Hsl
ope
Das hed pr obabilit y lines indi c ate that the number of sl opes us ed for the devel opment o f the SS PC s ys tem for thes e s ec tions of the graph is limited and the pr obability lines may not be as c ertai n as the pr obability lines dr awn with a conti nuous line.
Probability orientation independent failure
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 71
Engineering Geology
How did we do this?
∑=
⎪⎪⎪
⎩
⎪⎪⎪
⎨
⎧
⎪⎪⎩
⎪⎪⎨
⎧
=→>
=→≤<
=→≥
=
⎪⎪⎪
⎩
⎪⎪⎪
⎨
⎧
⎪⎪⎩
⎪⎪⎨
⎧
=→<
=→≥
<
=→≥
=
jj
slope
max
slope
max
slope
max
slope
mass
slope
mass
slope
mass
max
slope
slope
max
slope
max
slope
mass
slope
mass
erER
HHerstable
HH
erunstableHH
dip
diperstable
dip
HH
erunstableHH
erstableHH
dip
erstabledip
j
)(1
1)(11
)(1
3or 2 classstability estimatedvisaually
)(1
1)(11
1)(1
1 classstability estimatedvisually
: slope eachFor
ϕ
ϕϕ
ϕ
ϕ
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 72
Engineering Geology
How did we do this?
0 0.2 0.4 0.6 0.8 1 1.2 1.40.01
0.1
1
10
100
visually estimated stabilitystable (class 1)unstable with small problems (class 2)unstable with large problems (class 3)
Hm
ax /
Hsl
ope
ϕmass / slope dip
shear plane model:stable
shear plane model:unstable
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 73
Engineering Geology
SSPC stability probability (%)
num
ber o
f slo
pes (
%)
< 5 7.5 15 25 35 45 55 65 75 85 92.5 > 950
20
40
60
80 visually estimated stability
stable (class 1)unstable (class 2)unstable (class 3)
Romana's SMR (points)
num
ber o
f slo
pes (
%)
5 15 25 35 45 55 65 75 85 950
20
40
60
80 visually estimated stability
stable (class 1)unstable (class 2)unstable (class 3)
Haines' slope dip - existing slope dip (deg)
num
ber o
f slo
pes (
%)
-45 -35 -25 -10 -5 5 15 25 35 45 0
20
40
60
80visually estimated stability
stable (class 1)unstable (class 2)unstable (class 3)
Percentages are from total number of slopesper visually estimated stability class.
visually estimated stability:
class 1 : stable; no signs of present or future slopefailures (number of slopes: 109)class 2 : small problems; the slope presently showssigns of active small failures and has the potential forfuture small failures (number of slopes: 20)class 3 : large problems; The slope presently showssigns of active large failures and has the potential forfuture large failures (number of slopes: 55)
unstable stable stable unstable
a: SSPC b: Haines
c: SMR
Haines safety factor: 1.2
completelyunstable
completelystable
partiallystableunstable stable
'tentative' describtion of SMR classes: Comparison
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 74
Engineering Geology
Poorly blasted slope
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 75
Engineering Geology
General impression: extremely poor. The stability of the new road cut with a height of 13.8 m, with a degree of rock mass weathering of 'moderately' and 'dislodged blocks' due to blasting, results in a stability assessment of about 8 % for a slope dip of 70° in 1996. This is in agreement with the visual observed stability at that time. The rock mass is clearly not able to support a slope with a dip of 70°. According to the SSPC system, stability will be achieved if the slope dip is decreased to about 45°. In 2002 the slope dip had been reduced to about 55° and visually assessed the slope is still unstable.
OLD ROAD CUTS (> 40 years old) in same thin bedded limestone: SSPC system probability to be stable of > 95 % with a slope dip of 70° and a height of 5 m. The same rock mass characteristics are used for the new slope. Hence, both slopes are assumed to have been made in the same 'reference' rock mass as far as the thin-bedded units are considered.
Poorly blasted slope
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 76
Engineering Geology
Plane sliding failure 40 year old road cut, Spain
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 77
Engineering Geology
road
9 m15 m
37°
bedding planes
162°
Fig. 108. Geometrical cross section of the slope.
Plane sliding failure (2)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 78
Engineering Geology
Plane sliding failure (3)
Laboratory test: φ=45°SSPC: φ≈35°Stability assessed using:
SSPC – 55% stability probability, failure imminent (φ≈35°)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 79
Engineering Geology
Slope Stability probability Classification (SSPC)
Saba case - Dutch Antilles
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 80
Engineering Geology
Landslide in harbour
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 81
Engineering Geology
Geotechnical zoning
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 82
Engineering Geology
SSPC results
P y r o c l a s t ic d e p o s it s C a lc u l a t e d S S P C L a b o r a t o r y / f i e l d R o c k m a s s f r ic t io n 3 5 ° 2 7 ° ( m e a s u r e d )
R o c k m a s s c o h e s i o n 3 9 k P a 4 0 k P a ( m e a s u r e d ) C a lc u la t e d m a x i m u m p o s s ib l e h e i g h t o n t h e
s lo p e
1 3 m 1 5 m ( o b s e r v e d )
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 83
Engineering Geology
Failing slope in Manila, Philippines
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 84
Engineering Geology
Failing slope in Manila (2)
tuff layers with near horizontal weathering horizons (about every 2-3 m)slope height is about 5 mSSPC non-orientation dependent stability about 50% for 7 m slope heightunfavourable stress configuration due to corner
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 85
Engineering Geology
Earthquake influence on rock slopes
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 86
Engineering Geology
During an earthquake may occur either together or subsequently:
reduction normal stress and consequently also shear strengthbreaking of cementation in discontinuitiesbreaking of asperities on discontinuity planesdisplacement of discontinuities - leading to non-fitting of discontinuity roughnessresonance effects - increasing accelerations and displacements(breaking of intact rock - generally only if intact rock strength is very weak)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 87
Engineering Geology
The results of an earthquake
• permanent reduction of shear and tensile strength (if present) along discontinuities
• opening of discontinuities; allowing water influx, etc.
• (increase in number of discontinuities because of fracturing of intact rock)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 88
Engineering Geology
Stability calculation -pseudo-static analysis (1)
u
v
W
Fh
Fv
ψ
tension crack
a
c
b
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 89
Engineering Geology
Stability calculation - pseudostaticanalyses (2)
( )( )( )
onaccelerati eathquake todue force verticaland horizontal itiesdiscontinu in the forces water the
block ofweight Witydiscontinu along
frictionly respectivi force,cohesion ,coscossin
tan*sincosforce drivingforce resisting
==
=
=++−
−−−+=
==
Fv, Fh,vu
cohvFhFvW
uFhFvWcoh
F
bcab
ab
bc
abab
ϕψψψ
ϕψψ
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 90
Engineering Geology
Stability calculation - pseudostaticanalyses (3)
onsaccelerati a , block ofweight W
v ==
===
h
vh
a
gWaFv
gWaFh
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 91
Engineering Geology
Stability calculation - pseudostaticanalyses (4)
choice of ah and av- difficult- no clear rules what to use- Terzaghi (1950): ah = 0.1 g for severe, = 0.2 g for
violent, and = 0.5 g for catastrophic earthquakes- Marcuson (1981): ah and av about 1/3 to 1/2 of
apeak- Franklin (1980): ah = 0.5 apeak (to avoid
“dangerously large deformations”)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 92
Engineering Geology
Drawbacks of a pseudo-static analyses
Reduction shear strength during the earthquake only due to reduction in normal stressesNo breaking of cementation or asperitiesNo displacement effects and subsequent reduction in shear strengthNo deformation or rotation of blocksNo resonance effects(no breaking of intact rock)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 93
Engineering Geology
Stability analysis - Newmark (1)Criterion of displacement rather than stress equilibriumDisplacement of a ridged block over a surfaceDisplacement depends on
- Frequency (number of pulses in which yield acceleration is exceeded)
- Maximum acceleration per peak
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 94
Engineering Geology
Stability analysis - Newmark (3)
Possible to include “strain hardening” or “strain softening” constitutive models for the sliding plane (later may be very applicable to rock slopes - permanent reduction shear strength, etc.)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 95
Engineering Geology
Drawbacks of Newmark -displacement methodologies
Only plane slidingNo deformation or rotation of blocksNo resonance effects(no breaking of intact rock)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 96
Engineering Geology
Simple empirical relationsUmbria-Marche earthquake of 26
September 1997
EE
E
26 September 0:33 GMT26 September 9:40 GMT
14 October 15:23 GMT
ANCONA
PERUGIA
8
8
(after Lucia Luzi in Hack, 2002)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 97
Engineering Geology
Simple empirical relations (2)Umbria-Marche earthquake of 26
September 1997
(after Lucia Luzi in Hack, 2002)
constants failure; lity tosusceptibi landslide the parameter seismic the nt;displaceme landslide the
)()()(
====
+⋅+⋅=
A, B, Ch(k)g(s)D
CkhBsgADf
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 98
Engineering Geology
Simple empirical
relations (3)
(after Lucia Luzi in Hack, 2002)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 99
Engineering Geology
Numerical crocodile tail effect
Surface acceleration, from light to dark increasing surface acceleration (lightest 3 m/s2 and darkest 17 m/s2)
Armenia earthquake of January 1999
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 100
Engineering Geology
Discussion earthquakes
slope stability analyses with earthquake influence far more difficult than withoutsimplifications in accepted calculation methods such that it is questionable whether they make sensewhy are there no classification system for earthquake prone areas?
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 101
Engineering Geology
Heterogeneityeven if uncertainty is included this is only up to a certain extend – what extend is to the discretion of the engineercan heterogeneity be defined by an automatic procedure , e.g. for example Lidar
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 102
Engineering Geology
Heterogeneity (2)
unit 1
unit 2
unit 3
(modified after Slob et al, 2002)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 103
Engineering Geology
Future degradation of soil or rock due to weathering, ravelling, etc.
no reliable quantitative relations exist to forecast the future geotechnical properties of soil or rock mass
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 104
Engineering Geology
Future degradation (2)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 105
Engineering Geology
Future degradation (3)
1.0
1.5
2.0
2.5
3.0
3.5
7.0 7.5 8.0 8.5 9.0 9.5
y [m]
z [m
]
Excavated 1999 May 2001 May 2002
Reduction in slope angle due to weathering, erosion and ravelling (after Huisman)
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 106
Engineering Geology
Conclusionsclassification works for slope stabilityclassification can incorporate uncertaintyclassification can be improved by using more elaborate relationscomputers can be used to optimise complicated relationsbe not afraid to abandon inherited methodologies and parameters
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25 November 2002 Eurock'2002 - keynote class.systems slopes - Robert Hack 107
Engineering Geology
Future
definition of heterogeneityexpressions for quantification of future geotechnical propertiesclassification systems for earthquake areasinfluence of snow and icesubmersed marine slopes ?