Open access e-Journal
Earth Science India, eISSN: 0974 – 8350 Vol. 5(I), January, 2012, pp. 1- 11
http://www.earthscienceindia.info/
1
Engineering Geological Investigations of Rock Mass from the
Excavated North Wall Face in the Pump House Area of
Mahatma Gandhi Lift Irrigation Scheme-III, District
Mahboobnagar, Andhra Pradesh, India
A. K. Naithani1, Manoj Kumar
1, Rabi Bhusan
1 and P.C. Nawani
2
1National Institute of Rock Mechanics, Kolar Gold Fields, 563 117, Karnataka, India
2Nirvana Country, Sector 49-50, Gurgaon, 122 001, India
Email: [email protected]
Abstract
Vertical wall and foundation floor geological mapping of the important structures is
essential to provide data input for geological interpretations during construction and also it
forms valuable documentation for post-construction stage. For important structures like
deep surge pool and pump house of lift irrigation, the supporting wall and foundation strata
have to be well studied and documented for credible geologic interpretations. MGLIS-III is
being constructed for the irrigation of drought prone upland areas of Mahboobnagar
District, Andhra Pradesh. In order to evaluate the basic design parameters for pump house
of Mahatma Gandhi Lift Irrigation Scheme-III, engineering geological mapping on 1:200
scale of north wall was carried out. All the lithological variance and the structural
discontinuities in rock mass of the wall were identified and mapped. Classification of rock
mass using Tunnelling Quality Index ‘Q’ of Barton et al. (1974, 1980) has been done.
Based on investigations geotechnical problems were identified and remedial measures were
suggested for the vertical wall.
Keywords: Lift irrigation, Tunnelling quality index, Consolidation grouting, Rock bolt
Introduction
The Mahatma Gandhi Lift Irrigation Scheme (MGLIS) is being constructed having
the three stages (I, II & III) for lifting the Krishna water from Srisailam reservoir to
Gudipallygattu balancing reservoir through channels and tunnels to cater the needs of
irrigation in the drought prone upland areas of Mahboobnagar District, Andhra Pradesh. The
project envisage to irrigate about 3,40,000 acres of uplands in Mahboobnagar District. The
present investigations were carried out in the north wall of the pump house area of Mahatma
Gandhi Lift Irrigation Scheme-III (MGLIS-III). This scheme is being constructed near village
Gouridevipalli, Mahboobnagar District, Andhra Pradesh, located 165 km away from
Hyderabad city. The latitude and longitude of the pump house are: 16o23’10” and 78
o18’42”
respectively and fall in SOI toposheet no. 56 L/7. The ground elevation of the area varies
from RL+470.0 m to RL+530.0 m. The major components of the MGLIS-III are: i) 6.0 km
long gravity canal, ii) 6.156 km long and 6.85 m finished diameter horseshoe shaped tunnel,
iii) surge pool (80m long x 20m width x 110m height), 55 m long five numbers of draft tube
tunnels, iv) pump house (80m long X 20m width X 116m height) and v) five numbers 15 m
long horizontal & 163 m long inclined having 2.6 m finished diameter delivery main tunnels
(Fig.1; Anon, 2011). Due to the intersection of joint plane and shear zone, slip had occurred
on the northern wall of pump house on 20th
April 2008 during the excavation. For the
Engineering Geological Investigations of Rock Mass from the Excavated North Wall Face in the Pump House Area of
Mahatma Gandhi Lift Irrigation Scheme-III, District Mahboobnagar, Andhra Pradesh, India: A. K. Naithani et al.
2
remedial measures of support in slippage of rock mass from the excavated face of the north
wall in the Pump House area of Lift-III engineering, geological investigations were carried
out. The ground level of pump house is at R.L. +482m while the foundation level is at R.L.
+364m. All the four sides of the pump house will be lined with 300mm RCC filling from the
bed line and floor with 800mm thick raft foundation to distribute the load as per design
specification. In this study permanent engineering support measures have been recommended
for the treatment of north vertical wall in the Pump House area of MGLIS-III based on
detailed engineering geological investigations.
Methodology
Geological mapping on 1:200 scale of the north wall of pump house was carried out
using the Crane, because mapping was carried out after the total design excavation of pump
house from R.L. 449m up to R.L. 364m. Grids of 2m x 2m, dimension were prepared for
mapping of the wall, decided based on the mapping accuracy and resolution required for such
investigations. Elevations and chainages were also marked on the wall face using the Total
Station surveying equipment. ISRM (1978), classifications for weathered mass was used to
characterize the rock mass into different grade (Table-1). The assessment of Tunneling
Quality Index ‘Q’ (Barton et al., 1974, 1980) for granite rock masses, based on the rock joints
characteristics has been done. Total 6445 m2
area was mapped.
Engineering Geological Assessment
The vertical north wall of pump house was excavated from RL+449.00 m to
RL+364.00 m. This wall is aligned along the N355o direction. On the top of the wall at
RL+449.00 m three storied Annexure building will be constructed (Fig. 2). The average
height of the wall is 85.0m from existing foundation level at RL+364.00m to the top of the
wall which is at RL+449.00m and the total length of wall is 80.0m.
Rock type exposed on the wall section and the foundation level is fine to coarse
grained, hard compact and jointed granite. Its colour varies from pink to grayish and its
colour variation is due to varying in the amount of orthoclase. Granite is generally fresh to
moderately weathered (WI – WIII) in nature. The granite of this area belongs to Eastern
Dharwar Craton of Late Archaean age (Ramakrishnan, 1994; Ramam and Murty, 1997). The
rock mass is characterized by six number of joints, which are continuous and persistent,
rough and irregular to slickensided and undulating to planar with unaltered joint walls.
Staining has been recorded along the joint surfaces where the joints are tight and where
opening is up to 10.0 cm, soft clay mineral filling has been recorded. In general, the rock
mass is characterized by dry condition or minor inflow i.e. <5.0 l/min. Crack/fractures
developed due to excavation / blasting were also recorded during geological mapping. Some
of the cracks are tight while some are open and the size of the opening varying from 1 mm to
5 cm. The rock types of north vertical wall of pump house is intersected by a vertical dolerite
dyke (N115o/85
o) and shear zone (N030
o-028
o/85
o-80
o) containing clay gauge material and
disintegrated rock fragments. The details of the joint characteristics of north wall of pump
house are given in Table-2.
Open access e-Journal
Earth Science India, eISSN: 0974 – 8350 Vol. 5(I), January, 2012, pp. 1- 11
http://www.earthscienceindia.info/
3
Fig
.1:
Pla
n m
ap o
f th
e M
GL
IS-I
II a
nd
lo
cati
on
of
no
rth
wal
l is
als
o s
ho
wn
.
Engineering Geological Investigations of Rock Mass from the Excavated North Wall Face in the Pump House Area of
Mahatma Gandhi Lift Irrigation Scheme-III, District Mahboobnagar, Andhra Pradesh, India: A. K. Naithani et al.
4
Table- 1: Description of Weathering Grade (ISRM, 1978)
Term Description Grade
Fresh No visible sign of rock material weathering; perhaps slight discolouration on major
discontinuity surfaces. I
Slightly
weathered
Discolouration surfaces. All the rock material may be discoloured by weathering and
may be somewhat weaker extremely than its fresh condition. II
Moderately
weathered
Less than half of the rock material is decomposed and / or disintegrated to a soil.
Fresh or discoloured rock is present either as a continuous framework or as
corestones.
III
Highly
weathered
More than half of the rock material is decomposed and / or disintegrated to a soil.
Fresh or discoloured rock is present either as a continuous framework or as
corestones.
IV
Completely
weathered
All rock material is decomposed and / or disintegrated to soil. The original mass
structure is largely intact. V
Residual
soil
All rock material is converted to soil. The mass structure and material fabric are
destroyed. There is a large change in volume, but the soil has not been significantly
transported.
VI
Fig.2: View of north vertical wall of pump house of MGLIS-III, part of Annexure Building is
also shown.
Open access e-Journal
Earth Science India, eISSN: 0974 – 8350 Vol. 5(I), January, 2012, pp. 1- 11
http://www.earthscienceindia.info/
5
Table- 2: Prominent joint sets developed in granite at the face of vertical north wall of pump
house. Joint Set Dip
Direction
Dip
amount
Spacing
(m)
Persistence
(m)
Roughness Infilling Ground
Water
Remark
Shear
Zone
N030o-028
o 85
o - >100m Slickensided-
Undulating
Gaugy
Material
Dry Subvertical
and thickness
varies from
0.6m to 5m
J1
Subvertical
N125o 75
o - >20m Slickensided-
Undulating
Gaugy
Material
Dry Dipping
towards east
wall side
J2
Subvertical
N025o -
035o
75o –
80o
1 – 2 3 – 8 Rough-
Planar
Tight Dry Dipping inside
slope
J3
Inclined
N240o -
245o
65o –
70o
1 – 2 2 – 5 Rough –
Undulating
Clay
filling
Dry Dipping
towards west
wall side
J4
Subvertical
N110o –
130o
75o –
80o
0.6 – 2 3 – 5 Rough-
Planar,
Undulating
Tight Dry Dipping
towards east
wall side
J5
Inclined
N105o -
110o
20o –
25o
1 – 2 4 – 12 Rough-
Planar,
Undulating
Crushed
rock
material,
opening
from 50
to 150
mm
Dry Dipping
towards east
wall side
J6
Inclined
N210o -
230o
40o -
45o
0.6 – 2 4 – 10 Rough,
Undulating
Clay
and
crushed
rock
filling
up to 10
mm
Dry Dipping
towards west
wall side
The dolerite dyke trending in N115o direction with a dip amount of 85
o, and a strike
length of more than 100m has been mapped on the western side of the wall, i.e., between RD-
28m on the top of the wall and RD-19m on the bottom of the wall. The width of the dyke
varies from 1.2m to 2.6m. The prominent joint set intersecting the dyke are: N095o (dip
direction)/ 30o (dip amount), N245
o /65
o, N015
o -020
o /15
o -22
o and N350
o /85
o. Dolerite is
fine grained, fresh, hard, compact and massive in nature and dark gray in colour. The contact
between granite and dolerite dyke is unweathered (Fig. 3). No displacement has been
recorded along this feature.
A shear zone trending in N030
o-028
o direction with a dip amount of 80
o-85
o, and a
strike length of more than 100m, has been mapped on the central face of the wall i.e. between
RD+2 to -3 m on the top of the wall and RD+10.4m on the bottom of the wall. The width of
shear zone varies from 0.6m to 5m and its thickness is generally increasing towards top. The
prominent joint set intersecting the shear zone are: N125o /75
o, N230
o /45
o, N290
o /75
o and
Engineering Geological Investigations of Rock Mass from the Excavated North Wall Face in the Pump House Area of
Mahatma Gandhi Lift Irrigation Scheme-III, District Mahboobnagar, Andhra Pradesh, India: A. K. Naithani et al.
6
Fig.3: An intrusive dolerite dyke trending in N115o direction and its width is varying from
1.2m to 2.6m.
Fig.4: View of major shear zone along the north vertical wall of pump house, at foundation
level lining work was in progress.
Open access e-Journal
Earth Science India, eISSN: 0974 – 8350 Vol. 5(I), January, 2012, pp. 1- 11
http://www.earthscienceindia.info/
7
Fig.5: Views of portals of Delivery Main Tunnels 3 & 4, lying on the either side of major
shear zone.
N095
o /30
o. As reported by the project engineers, during excavation, a huge slide occurred in
pump house along this vertical wall between RL +453m to RL+375m. Rock mass failure was
due to structural wedge formation between the shear zone (Sh N030o /85
o) and joint (J N125
o
/75o) and extended to 2.0 to 7.4 m depth in to excavated line of face (Fig. 4). Wedge was
formed because line of intersection of these discontinuities (N098o) is towards pump house
pit and plunge (75o) is less than the cut slope. No displacement has been recorded along this
feature. This shear zone has also been mapped inside the Delivery Main Tunnels number 1, 2
and 3 at 16.15m, 10.20m and 5.97m respectively from the slope face (Fig. 5). The width of
this zone measured inside the Delivery Main Tunnels number 1, 2 and 3 are 1.9m, 3.14m and
2.82m respectively.
Based on the engineering geological mapping carried out in the north vertical wall of
pump house and the details collected including lithology, joint patterns measured in the field,
the geological map was compiled on scale 1:200 (Fig. 6). Longitudinal sections at the
different RDs of slide area have also been developed and given in Fig. 7. The rock mass
classification is very poor to fair rock mass (Q 0.11 to 4.56) in the entire vertical wall area as
per Barton`s classification. The details of the Q values of north wall of pump house are given
in Table- 3.
Recommendations
On the basis of geological and structural data input from the north vertical wall (pump
house) the following recommendations have been made.
Engineering Geological Investigations of Rock Mass from the Excavated North Wall Face in the Pump House Area of
Mahatma Gandhi Lift Irrigation Scheme-III, District Mahboobnagar, Andhra Pradesh, India: A. K. Naithani et al.
8
a. The stability of the cut slopes/ vertical walls depends upon the geometry, frequency
and orientation of joint sets, dip of slope and its plane of weakness. The site condition
is not favourable for slope stability, particularly along the shear zone due to its
interplay with a joint set (Sh N030o /85
o and J N125
o /75
o) forming a wedge. Other
major joint sets are subvertical, dipping towards the east and west sides of the wall do
not tend to cause unfavourable condition. Generally the rocks are fresh to moderately
weathered, hard and compact. But the top level is fractured/jointed and joints are
open, due to blasting, may require proper treatment either by removal of loose
material or consolidation grouting once the lining of wall is provided.
Table- 3: Rock mass classification using ‘Q’ of the face of vertical north wall of pump
house.
From RD 0.00 to +40.00m From RD 0.00 to +40.00m
Elevation Q Description Elevation Q Description
From To From To
450.0 440.0 0.11-0.21 Very Poor 450.0 440.0 0.41-0.82 Very Poor
440.0 430.0 0.33 Very Poor 440.0 430.0 0.41 Very Poor
430.0 420.0 0.28 Very Poor 430.0 420.0 0.44 Very Poor
420.0 410.0 0.30 Very Poor 420.0 410.0 0.90 Very Poor
410.0 400.0 0.41 Very Poor 410.0 400.0 3.14 Poor
400.0 390.0 1.53 Poor 400.0 390.0 3.42 Poor
390.0 380.0 1.43 Poor 390.0 380.0 3.42 Poor
380.0 375.0 1.63 Poor 380.0 375.0 3.55 Poor
375.0 370.0 0.61-1.84 Very Poor
to Poor
375.0 370.0 1.23-3.69 Poor
370.0 364.0 2.73 Poor
364.0 358.7.0 4.56 Fair
b. Loose, fractured, detached protruded rock mass in the wall section (feature marked as
A in the Fig. 6) need to be removed before final treatment.
c. Due to collapse of rock mass occurred due to failing of wedge formed due to the
intersection of joint plane and shear zone, a large opening has been formed extending
2.0m to 7.40m depth in to wall between RL+453m and RL+379m. The joint planes
present on either side of the failed wedge are to be properly stitched from chainage -
18m to +10m by providing rock bolts (28mm dia.) across the joint planes at an
average spacing of 3 m and length of the rock bolt should not be less then 10m in
staggered fashion. After installing rock bolts, wire mesh shotcrete of 100 mm
thickness be applied in this failed zone i.e. from chainage -10m to +6m. Cross
sections (Fig. 7) indicating that the entire area below EL+394m is in normal condition
except between chainage +5 and +10m, so rock bolt and shotcrete is not required
other than these chainages from EL 364m to EL 394m.
d. There in a need to property scale off the loosened rock fragments all along the vertical
north wall of the pump house pit. After proper scaling, 50 mm thick wire mesh
shotcrete be applied all along the face of the excavated surface of the pit. Rock bolts
(28mm dia.) should be horizontally driven in to vertical side wall up to a depth of 5m
at an average spacing of 4m c.c. The areas which will be concrete lined need not by
shotcreted. Further drainage holes may be provided in to this vertical side wall.
Open access e-Journal
Earth Science India, eISSN: 0974 – 8350 Vol. 5(I), January, 2012, pp. 1- 11
http://www.earthscienceindia.info/
9
Fig.6: Geological map of the north vertical wall of pump house.
Engineering Geological Investigations of Rock Mass from the Excavated North Wall Face in the Pump House Area of
Mahatma Gandhi Lift Irrigation Scheme-III, District Mahboobnagar, Andhra Pradesh, India: A. K. Naithani et al.
10
Fig. 7: Longitudinal section along the slippage of north wall of pump house.
e. All portals of Delivery Main Tunnel opening in to the pump house pit are to be claded
with RCC lining. Shear zone which is exposed on this vertical wall is extending to
downstream side face and was observed and mapped in 1, 2, and 3 Delivery Main
Tunnel, which need to be strengthened with rock bolts.
f. Concrete lining be done from foundation up to the level of five units of pump house
i.e. 385m and above this level lining be done following the cut slope.
g. In the design three storied Annexure Building has been provided on the top of this
wall at RL+453m and some portion of the building has already been constructed. Just
on the top of this wall, where shear zone is passing building has to be constructed. As
the rock mass here on the edge of collapsed wall is not competent to bear the load of
this building it is recommended that the load should be transferred towards the
opposite side of the pump house wall. Up to 1.5 m horizontal distance from the failed
rock edge, load should not be transfered. Beyond 1.5 m, rock mass is competent on
Open access e-Journal
Earth Science India, eISSN: 0974 – 8350 Vol. 5(I), January, 2012, pp. 1- 11
http://www.earthscienceindia.info/
11
the surface and below the surface and suitable for the building foundation and Crane
Loads.
h. After providing lining in the area, consolidation grouting (with 2.5 to 3.5 kg/cm2
pressure) up to maximum 20 m depth be done from the top surface (from RL +453m)
using primary , secondary and tertiary holes so that the opening created due to
blasting are filled and area behaves as monolithic or single rock mass. 6m spacing for
the primary, 3m for secondary and 1.5 m for tertiary holes, is recommended.
Acknowledgements: This paper is prepared from the report of MGLIS-III, which was sponsored by Gammon
India Limited, Hyderabad. We sincerely thank the Management of Gammon India Limited for the same. We
also sincerely acknowledge the support extended by Mr. K.N.M. Rao, Vice-President, M/S Deepika Infratech
Pvt. Ltd and Mr. Srinivas Rao, Deputy Manager, M/S Gammon India Limited, during the field investigations at
the MGLIS-III site. We also sincerely acknowledge the co-ordination and support rendered by Mr. Srinivas
Reddy, Project Manager, M/S Deepika Infratech Pvt. Ltd and Mr. R. Ravindar, Deputy Executive Engineer,
Irrigation and Cad Department, Andhra Pradesh. We are thankful to Director NIRM for his permission to send
the manuscript for publication. We thank to Dr. G.R. Adhikari, Head, TC & PMD, NIRM, for encouragement
during the preparation of this manuscript.
References
Anon (2011) Report on slippage of rock mass from the excavated north wall face in the pump house area of
Mahatma Gandhi Lift Irrigation Scheme-III, Mahboobnagar District, Andhra Pradesh. NIRM Report
No. EG-11-01 (unpublished).
Barton, N., Lien, R. and Lunde, J. (1974) Engineering classification of rock masses for the design of tunnel
support. Rock Mechanics, v. 6(4), pp. 189-236.
Barton, N., Loset, F. and Lien, R. and Lunde, J. (1980) Application of the Q-system in design decisions
concerning dimensions and appropriate support for underground installations. Inter. Conf. on Sub-
surface Space, Rock store, Stockholm. Sub-Surface Space, v.2, pp. 553-561.
ISRM (1978) Suggested methods for the quantitative description of discontinuities in rock mass. International
Journal Rock Mech. Sci. & Geomech. (Abstract), Pergamon, v. 15(6), pp. 319-368.
Ramakrishnan, M. (1994) Stratigraphic evolution of Dharwar craton. GeoKarnataka (MGD Centenary Volume),
Karnataka Asst. Geol. Assoc., Dept. of Mines and Geology, Govt. of Karnataka, Bangalore, pp. 6-35.
Ramam, P.K. and V.N. Murty (1997) Geology of Andhra Pradesh. Geological Society of India, 245p.