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Earth Science India, eISSN: 0974 – 8350 Vol. 5(I), January, 2012, pp. 1- 11

http://www.earthscienceindia.info/

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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.

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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.




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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

.



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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.




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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



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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.




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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.



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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



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.




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Fig.6: Geological map of the north vertical wall of pump house.



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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




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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.

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