monograph on rock mass classification systems and applications

Monograph

On

Rock Mass Classification Systems and Applications

2011

Hari Dev, Scientist ‘C’

S.K. Sharma, Chief Research Officer (Retd.) Publication-2

Central Soil and Materials Research Station, New Delhi

Monograph on Rock Mass Classification Systems and Applications

Monograph

On

Rock Mass Classification Systems and Applications

2011

By

Hari Dev, Scientist ‘C’

&

S.K. Sharma, Chief Research Officer (Retd.)

Central Soil and Materials Research Station Olof Palme Marg, Outer Ring Road, Hauz Khas, New Delhi-110016


i

FOREWORD

The Central Soil and Materials Research station (CSMRS), an attached office of the Ministry of

Water Resources, is a premier institute in the country at New Delhi which deals with field and

laboratory investigations, basic and applied research in problems on geomechanics, concrete

technology, construction materials and associated environment issues, having direct bearing on the

development of irrigation and power in the country and functions as an adviser and consultant in

the above fields to various projects and organisations in India and abroad.

So far in India, the excavation of large cavities has been restricted to underground power houses.

The first underground power house was constructed at Maithen for Damodar Valley Corporation,

way back in 1953, followed by Koyna in Maharashtra. Since then, a number of underground

excavations for hydropower development are in progress. Recently, road and rail tunnels have also

been successfully executed. Delhi Metro Rail Corporation (DMRC) bored tunnels with the help of

Tunnel Boring Machines (TBM). Rail link between Jammu and Srinagar has also become a reality

with many tunnels in between. Border Roads Organisation (BRO) has also taken up the task of

connecting the Lahaul and Spiti valley with Kullu-Manali through 9 km long all weather road

tunnel at Rohtang Pass to connect Leh and Ladakh area of Jammu and Kashmir. Scores of

underground excavations for hydropower development are either coming up or are in final stages of

execution.

Though lot of innovations have taken place in the field of rock engineering, still rock classification

and support systems are based on empirical calculations. The first engineering approach was

developed by the great genius Karl Terzaghi in 1946 followed by some other engineers. Deere gave

his concept of rock quality criteria on the basis of the drill core recovery. Later on, in 1970's some

development took place with the evolution of classification systems like Rock Structure Rating

(RSR) by Wickham, Rock Mass Rating (RMR) by Bieniawski and Q system by Nick Barton. RMR

and Q systems were immediately adopted by professionals working in the field of rock mechanics.

This monograph contains information about the developments in the field of rock classification

systems and their applications. Case studies of various underground structures viz. power houses

and water conveyance tunnels have also been included. The rock mass has been classified using

various classification methods. Support pressures have also been worked out. Attempt has been

made to compile the actual support systems adopted in underground excavations and correlate with

rock classification systems. Support pressures accommodated by the actual supports have also been

worked out. Observed support pressures for different projects from the instrumentation data have

been provided wherever available. Relative utilities of classification systems have been discussed.

This monograph is therefore informative and will be useful to the engineers and geologists working

in the field of rock mechanics dealing with underground structures in particular.

(Murari Ratnam)

Dated August 16, 2011 Director, CSMRS


ii

CONTENTS

Page No. 1. INTRODUCTION 1

2. UTILITIES OF ROCK MASS CLASSIFICATIONS 2

3. ROCK MASS CLASSIFICATION SYSTEMS 2

3.1. Terzaghi’s Rock Load Classification System 4

3.2. Classification System of Stini and Lauffer 7

3.3. Deere’s Rock Quality Designation (RQD) Classification System 8

3.3.1. Rock Quality Designation, RQD 8

3.4. Rock Structure Rating Classification System 11

3.5. Geomechanics Classification System of rock masses, Rock Mass Rating 14

(RMR)

3.6. NGI Tunnelling Quality Index Classification System or Q-System 21

3.6.1. Correlation between RMR and Q Values 28

4. APPLICATIONS OF ROCK MASS CLASSIFICATION SYSTEMS FOR 29

DESIGN OF SUPPORTS FOR UNDERGROUND EXCAVATIONS

4.1. Nathpa Jhakri H. E. Project, H.P. 30

4.1.1. Geology 30

4.1.2. Rock Mass Classification and Rock Pressures 30

4.1.3. Supports Actually Provided 31

4.2. Sardar Sarovar Project, Gujarat 32

4.2.1. Geology 32



4.3. Sanjay Vidyut Pariyojna, H.P. 35

4.3.1. Geology 35



4.4. Baspa H.E. Project, H.P. 36

4.4.1. Geology 36



4.5. Yamuna Hydroelectric Scheme Stage II (Chhibro Power House), Uttrakhand 37

4.5.1. Geology 37

4.5.2. Rock Mass Classification and Rock Pressure 38



iii

4.6. Lakhwar H.E. Project, Uttrakhand 40

4.6.1. Geology 40



4.7. Chamera H.E. Project, H.P. 43

4.7.1. Geology 43



4.8. Kadamparai Pumped Storage H.E. Project, Tamilnadu 45

4.8.1. Geology 45



4.9. Chukha H.E. Project, Bhutan 46

4.9.1. Geology 46



4.10. Tala H.E. Project, Bhutan 47

4.10.1. Power House 48

4.10.1.1 Geology 48

4.10.1.2 Rock Mass Classification and Rock Pressures 49

4.10.1.3 Supports Actually Provided 49

4.10.2 Head Race Tunnel 50

4.10.2.1 Geology 51

4.10.2.2 Rock Mass Classification and Rock Pressures 51

4.10.2.3 Supports Actually Provided 52

4.11. Ramganga Project Tunnels, U.P. 53

4.11.1. Geology 54



4.12. Narmada Sagar Project, M.P. 56

4.12.1. Geology 56



4.13. Giri Project Head Race Tunnel, H.P. 57

4.13.1. Geology 58



4.14. Uri Project, J & K 59

4.14.1. Geology 60




iv

4.15. Loktak H.E. Project, Manipur 61

4.15.1. Geology 61



4.16. Salal H.E. Project, J & K 63

4.16.1. Geology 64



4.17. Yamuna Hydroelectric Scheme, Stage II, Part I 65

4.17.1. Geology 66



4.18. Yamuna Hydroelectric Scheme, Stage II, Part II 67

4.18.1. Geology 67



4.19. Maneri Bhali Hydel Project, Stage I, U.P. 69

4.19.1. Geology 69



4.20. Khara Hydel Project, U.P. 71

4.20.1. Geology 71



4.21. Tehri Hydroelectric Project, U.P. 73

4.21.1. Geology 73



4.22. Bodhghat Hydel Project, M.P. 74

4.22.1. Geology 75


5. OBSERVED SUPPORT PRESSURES 77

6. COMPARISON OF ROCK CLASSIFICATION METHODS 78

RECOMMENDATIONS 79

REFERENCES 80


1

ROCK MASS CLASSIFICATION SYSTEMS AND APPLICATIONS

1.0 INTRODUCTION

In rock mechanics, the designer deals with complex rock masses and specific properties

of rock mass cannot be determined to meet design requirements. The forces resulting

from the redistribution of the virgin stresses existing before the excavation was made, are

more important than the applied loads in rock masses. An underground excavation is an

extremely complex structure and it is seldom possible, theoretically, to determine the

influence and interaction of various parameters (structural discontinuities, in-situ stresses

and weathering profile etc.) which control the stability of the excavation.

Analytical design methods utilize the analysis of stresses and deformations around

openings. They include such techniques as closed form solutions, numerical methods

(finite elements, finite difference and boundary elements etc.), analog simulations

(electrical and photo elastic) and physical modelling.

The design methods which are available for assessing the stability of underground

structures are analytical, observational and empirical methods i.e. to base the design on

precedent practice and experience.

Observational design methods rely on actual monitoring of ground movement during

excavation to detect measurable instability and on analysis of ground-support interaction.

Empirical design methods assess the stability by the use of statistical analysis of

underground observations. Engineering classifications of rock masses constitute the best

known empirical approach for assessing the stability of openings in rock. Empirical

design approach is recognized still as a primary approach to a wide range rock

engineering design problems. The continued reliance of the rock engineering designer on

this approach is a function of the difficulty in predicting or modelling the behaviour of a

complex system of fractured rock in response to, for example, the excavation of a large

cavern or series of caverns. Thus, all currently available forms of analysis generally

require the application of engineering judgement in one form or another and many

designers prefer to exercise this judgement via the recommendations of a rock mass

classification system rather than to apply their own judgement directly to the geological

data available to them.

Rock mass classifications have provided the systematic approach in an otherwise

haphazard trial and error procedure on many underground construction projects.

However, modern rock mass classifications have never been intended as the ultimate

solution to design problems, but only a device toward this end. Rock mass classifications

were developed to create some order out of the chaos in site investigation procedures and

to provide the desperately needed design approaches. They were not intended to replace

analytical studies, field observations and measurements.


2

There are various classifications of rock masses developed and adopted through out the

world. The aims and objectives of classifications along with description of the most

popular classifications, their merits and demerits and solution of a practical problem have

been presented in this monograph. Summaries of some important classification systems

are presented in this monograph, and although every attempt has been made to present all

of the pertinent data from original texts, there are numerous texts and comments which

can not be included. The interested reader should make every effort to read the cited

reference for a full appreciation of the use, applicability and limitations of each system.

2.0 UTILITIES OF ROCK MASS CLASSIFICATIONS

A rock mass classification system has the following utilities in an engineering application

(Bieniawski, 1989):

1. To divide a particular rock mass into groups of similar behaviour;

2. To provide a good basis for understanding the characteristics of each group;

3. To identify the most significant parameter influencing the behaviour of a rock mass;

4. To relate the experience of rock conditions at one site to the conditions and

experience encountered at other sites;

5. To facilitate the planning and design of structures in rock by yielding quantitative

data required for the solution of real engineering problems; and

6. To provide a common basis for communication among the engineering geologists,

rock mechanicians, design engineers and contractors.

These utilities can be fulfilled by ensuring that a classification system has the following

characteristics:

1. It is simple, easily remembered and understandable;

2. Each term is clear and the terminology used is widely accepted by engineers and

geologists;

3. The most significant properties of rock mass are included;

4. It is based on measurable parameters which can be determined by relevant tests

quickly and cheaply in the field;

5. It is based on rating system that can weigh the relative importance of the

classification parameters; and

6. It is functional by providing quantitative data for the design of rock support.

3.0 ROCK MASS CLASSIFICATION SYSTEMS

Rock mass classification schemes have been developing for over 100 years since Ritter

(1879) attempted to formalise an empirical approach to tunnel design, in particular for

determining support requirements. While the classification schemes are appropriate for

their original application, especially if used within the bounds of the case histories from


3

which they were developed, considerable caution must be exercised in applying rock

mass classification to other rock engineering problems.

Rock mass classifications have been successfully applied throughout the world: United

States (Deere et al., 1967; Wickham et al., 1972; Bieniawski, 1979), Canada (Coates,

1963; Franklin, 1975), Western Europe (Lauffer, 1958; Pacher et al., 1974; Barton et al.,

1974), South Africa (Bieniawski, 1973; Laubscher, 1977; Olivier, 1979), Australia

(Baczynski, 1980), New Zealand (Rutledge, 1978), Japan (Nakao, 1983), India (Ghose

and Raju, 1981), USSR (Protodyakonov, 1974), and in Poland (Kidybinski, 1979).

Some of the characterisation and classification systems have been summarised in Table 1.

Table 1: Characterisation and classification systems

Name of the classification Form and Type

*) Main application Reference

Terzaghi's rock load

classification

Descriptive and

behaviouristic form

Functional type

For design of steel support in

tunnels

Terzaghi, 1946

Lauffer's stand-up time

classification

Descriptive and

general type

For input in tunnelling design Lauffer, 1958

New Austrian Tunnelling

Method (NATM)

Descriptive and

behaviouristic form

Tunnelling concept

For excavation and design in

incompetent (overstressed) ground

Rabcewicz,

Muller and

Pacher, 1958-64

Rock Classification for

rock mechanical purposes

Descriptive form

General type

For input in rock mechanics Patching and

Coates, 1968

Unified classification of

soils and rocks

Descriptive form

General type

Based on particles and blocks for

communication

Deere et al, 1969

Rock quality designation

(RQD)

Numerical and

general type

Based on core logging; used in

other classification systems

Deere et al, 1967

Size strength

classification

Numerical Form

Function type

Based on rock strength and block

diameter; used mainly in mining

Franklin, 1975

Rock structure rating

(RSR) classification

Numerical Form

Function type

For design of (steel) support in

tunnels

Wickham et al,

1972

Rock mass rating (RMR)

classification

Numerical Form

Function type

For use in tunnel, mine and

foundation design

Bieniawski, 1973

Q classification system Numerical Form

Function type

For design of support in

underground excavations

Barton et al,

1974

Typological classification Descriptive form

General type

For use in communication Matula and

Holzer, 1978

Unified rock classification

system

Descriptive form

General type

For use in communication Williamson,

1980

Basic geotechnical

classification (BGD)

Descriptive form

General type

For general use ISRM, 1981

Geological Strength Index

(GSI)

Numerical Form

Function type

For design of support in

underground excavations

Hoek, 1994

Rock Mass Index (RMi)

system

Numerical Form

Function type

For general characterisation,

design of support, TBM progress

Palmstrom, 1995

*) Definition of the following expressions:

Descriptive form: the input to the system based on descriptions


4

Numerical form: the input parameters are given numerical ratings according to their

character

Behaviouristic form: the input is based on the behaviour of the rock mass in a tunnel

General type: the system is worked out to serve as a general characterisation

Functional type: the system is structured for a special application (for example for

rock support)

Of many rock mass classification systems in existence, six require special attention

because they are most common, namely Terzaghi (1946), Lauffer (1958), Deere et al.

(1967), Wickham et al. (1972), Bieniawski (1973), and Barton et al. (1974).

The concept of rock structure rating (RSR), developed in the United States by Wickham

et al. (1972,1974), was the first system featuring classification ratings for weighing the

relative importance of classification parameters. The Geo-mechanics Classification

(RMR System), proposed by Bieniawski (1973), and the Q-System, proposed by Barton

et al. (1974), were developed independently and both provide quantitative data for the

selection of modern tunnel reinforcement measures such as rock bolts and shotcrete.

The Q-system has been developed specifically for tunnels and chambers, whereas the

Geo-mechanics Classification, although also initially developed for tunnels, has been

applied to rock slopes and foundations, ground rippability assessment, and mining

problems (Laubscher, 1977; Ghose and Raju, 1981; Kendorski et al. 1983).

3.1 Terzaghi’s Rock Load Classification System

In 1946, Terzaghi proposed a simple rock classification system for use in estimating the

loads to be supported by steel arches in tunnels. He described various types of ground

and, based upon his experience in steel-supported rail and road tunnels in them Alps, he

assigned ranges of rock loads for various ground conditions.

Terzaghi stresses the importance of the geological survey which should be carried out

before a tunnel design is completed and particularly the importance of obtaining

information on the defects in the rock mass. To quote from his original classification:

“From an engineering point of view, knowledge of the type and intensity of the rock

defects may be much more important than the type of rock which will be encountered.

Therefore, during the survey, rock defects should receive special consideration. The

geological report should contain a detailed description of the observed defects in

geological terms. It should also contain a tentative classification of the defective rock in

the tunnel man’s terms, such as blocky and seamy, squeezing or swelling rock.”

He then defined these tunnelling terms as follows:

Intact rock contains neither joints nor hair cracks. Hence, if it breaks, it breaks across

sound rock. On account of the injury to the rock due to blasting, spalls may drop off the

roof several hours or days after blasting. This is known as a spalling condition. Hard,


5

intact rock may also be encountered in the popping condition involving the spontaneous

and violent detachment of rock slabs from the sides or roof.

Stratified rock consists of individual strata with little or no resistance against separation

along the boundaries between strata. The strata may or may not be weakened by

transverse joints. In such rock, the spalling condition is quite common.

Moderately jointed rock contains joints and hair cracks, but the blocks between joints

are locally grown together or so intimately interlocked that vertical walls do not require

lateral support. In rocks of this type, both spalling and popping conditions may be

encountered.

Blocky and seamy rock consists of chemically intact or almost intact rock fragments

which are entirely separated from each other and imperfectly interlocked. In such rock,

vertical walls may require lateral support.

Crushed but chemically intact rock has the character of a crusher run. If most or all of

the fragments are as small as fine sand grains and no recementation has taken place,

crushed rock below the water table exhibits the properties of water-bearing sand.

Squeezing rock slowly advances into the tunnel without perceptible volume increase. A

pre-requisite for squeeze is a high percentage of microscopic and sub-microscopic

particles of micaceous minerals or of clay minerals with a low swelling capacity.

Swelling rock advances into the tunnel chiefly on account of expansion. The capacity to

swell seems to be limited to those rocks which contain clay minerals such as

montmorillonite, with a high swelling capacity.

The rock load classification of Terzaghi (1946) was the first practical classification

system introduced and has been dominant in the United States for over 40 years, proving

very successful for tunnelling with steel supports.

A liner has to support the entire weight of overlying rock and soil only in extreme case of

shallow tunnel where the rock contains smooth vertical joints and where a little or no

horizontal stress acts to enhance friction. Stresses are redistributed around opening by

dilation and mobilization of strength along the joints in a mechanism known as arching

(Terzaghi 1946). The liner has to support only these stresses not carried by rock arch.

Terzaghi’s rock load concept has been explained in Fig. 1.

Terzaghi carried out numerous model tests using cohesion less sand to study the shape of

what he termed the “ground arch” above the tunnel. On the basis of these tests and on his

experience in steel –supported tunnels, he proposed the range of rock load values listed in

Table 2. The footnotes which accompanied this table in the original paper are included

for completeness. However, Cecil found that Terzaghi’s classification was too general to

permit an objective evaluation of rock quality and that it provides no quantitative


6

information on the properties of the rock mass. He recommended that its use be limited

to estimating rock loads for steel arch-supported tunnels.

Fig. 1: Terzaghi’s ground arch concept

Table 2 – Terzaghi’s rock load classification for steel arch-supported tunnels

{Rock load Hp in feet of rock on roof of support in tunnel with width B (feet) and height

Ht (feet) at a depth of more than 1.5 (B+Ht)*}

Rock condition Rock load Hp in feet Remarks

1. Hard and intact. Zero Light lining required only if

spalling or popping occurs

2. Hard stratified or

schistose**

.

0 to 0.25 B Light support, mainly for protection

against spalls.

Load may change erratically from

point to point. 3. Massive, moderately

jointed.

0 to 0.5 B

4. Moderately blocky and

seamy.

0.25 B to 0.35 (B+Ht) No side pressure

5. Very blocky and seamy 0.35 to 1.10(B+Ht) Little or no side pressure

6. Completely crushed but

chemically intact.

1.10(B+Ht) Considerable side pressure.

Softening effects of seepage

towards bottom of tunnel requires

either continuous support for lower

ends of ribs or circular ribs.

7. Squeezing rock, moderate

depth

1.10 to 2.10(B+Ht) Heavy side pressure, invert struts

required. Circular ribs are

recommended 8. Squeezing rock, great depth. 2.10 to 4.50(B+Ht)

9. Swelling rock Up to 250 feet,

irrespective of the value

of (B+Ht)

Circular ribs are required. In

extreme cases use yielding support.


7

*The roof of the tunnel is assumed to be located below the water table. If it is located

permanently above the water table, the values given for types 4 to 6 can be reduced by

fifty percent.

**Some of the most common rock formations contain layers of shale. In an unweathered

state, real shales are no worse than other stratified rocks. However, the term shale is often

applied to firmly compacted clay sediments which have not yet acquired the properties of

rock. Such so-called shale may behave in a tunnel like squeezing or even swelling rock.

If a rock formation consists of a sequence of horizontal layers of sandstone or limestone

and of immature shale, the excavation of the tunnel is commonly associated with a

gradual compression of the rock on both sides of the tunnel, involving a downward

movement of the roof. Furthermore, the relatively low resistance against slippage at the

boundaries between the so-called shale and the rock is likely to reduce very considerably

the capacity of the rock located above the roof to bridge. Hence, in such formations, the

roof pressure may be as in very blocky and seamy rock.

3.2 Classification System of Stini and Lauffer

Lauffer’s classification (1958) was based on the work of Stini (1950) and was a

considerable step forward in the art of tunnelling since it introduced the concept of stand-

up time of the active span in a tunnel, which is highly relevant in determining the type

and amount of tunnel support.

Lauffer suggested that the stand-up time for any given active span is related to the rock

mass characteristics in the manner illustrated in Fig. 2. Stand-up time is the length of time

which an underground opening will stand unsupported after excavation and barring down

while active span is the largest unsupported span in tunnel section between the face and

supports. In a tunnel, the unsupported span is defined as the span of the tunnel or the

distance between the face and the nearest support, if this is greater than the tunnel span.

Fig. 2: Relation between active span and stand-up time for different classes of rock mass

(After Lauffer 1958)


8

In this figure, the letters refer to the rock class. A is very good rock, corresponding to

Terzaghi’s hard and intact rock, while G is very poor rock which corresponds roughly to

Terzaghi’s squeezing or swelling rock.

Lauffer's original classification has since been modified by a number of authors, notably

Pacher et al (1974), and now forms part of the general tunnelling approach known as the

New Austrian Tunnelling Method (NATM).

3.3 Deere’s Rock Quality Designation (RQD) Classification System

The classification of Deere et al. (1967) introduced the rock quality designation (RQD)

index, which is a simple and practical method of describing the quality of rock core from

boreholes.

A proposal for providing uniform terminology for the description of joints was made by

Deere as given in Table 3.

Table 3: Descriptive terminology for joint spacing

Descriptive term Spacing of joints

English Metric

Very Close Less than 2 in Less than 5 cm

Close 2 in-1 ft 5 cm-30 cm

Moderately Close 1 ft-3 ft 30 cm-1 m

Wide 3 ft-10 ft 1 m-3 m

Very wide Greater than 10 ft Greater than 3 m

For RQD values greater than 60, they recommended support consisting of rock bolts,

mesh and strapping whereas for RQD values less than 40, steel sets or ribs were

specified. RQD values between 40 and 60, called for linear interpolation of support

requirements. RQD method is of interest as it can be used for the preliminary choice of

support as well as a constitutive parameter for more elaborate systems.

The following is general method of obtaining the quality of the rock at a site based on the

relative amount of fracturing and alteration.

3.3.1 Rock Quality Designation, RQD

The rock quality designation (RQD) is based on a modified core recovery procedure

which, in turn, is based indirectly on the number of fractures and the amount of softening

or alteration in the rock mass as observed in the rock cores from a drill hole.

Total length of core is summed up by counting only those pieces of core which are 10 cm

in length or longer and which are hard and sound. RQD is defined as the percentage of

intact core pieces longer than 100 mm (4 inches) in the total length of core. The core


9

should be at least NW size (54.7 mm or 2.15 inches in diameter) and should be drilled

with double tube core barrel. The correct procedure for measurement of the length of core

pieces and the calculation of RQD are summarised in Fig. 3.

Fig. 3: Procedure for measurement and calculation of RQD (After Deere, 1989)

Palmstrom (1982) suggested that, when no core is available but discontinuity traces are

visible in surface exposures or exploration adits, the RQD may be estimated from the

number of discontinuities per unit volume. The suggested relationship for clay-free rock

masses is:

RQD = 115 - 3.3 Jv …… (1)

Where Jv is the sum of number of joints per unit length for all joint (discontinuity) known

as volumetric joint count.

RQD is directionally dependent parameter and its value may change significantly,

depending upon the borehole orientation. The use of the volumetric joint count can be

quite useful in reducing this directional dependence.

RQD is intended to represent the rock mass quality in situ. When using diamond drill

core, care must be taken to ensure that fractures, which have been caused by handling or

the drilling process, are identified and ignored while determining the value of RQD.

While using Palmstrom's relationship for exposure mapping, blast induced fractures

should not be included for estimation of Jv.


10

It has been found that there is a reasonably good relation between the numerical values of

the RQD and general quality of the rock for engineering purposes. Table 4 can be

referred for Deere's rock classification and support requirements for tunnels.

Table 4: Support recommendations for tunnels in rock (6-12 m in diameter), Deere 1969

Rock

Quality

Tunnelling

Method

Alternate Support System

Steel Setsa Rock Bolts

b Shotcrete

c

Excellanta

RQD>90

A Boring

Machine

None to occasional light set

Rock load 0 to 0.2Bd

None to

occasional

None to occasional

local application

B. Conventional None to occasional light set

Rock load 0 to 0.3B

None to

occasional

None to occasional

local application 50 to

75 mm

Gooda

75<RQD<90

A Boring

Machine

Occasional light sets to

pattern on 1.5 to 1.8 m

centre. Rock load 0 to 0.4B

Occasional to

pattern 1.5 to

1.8 m centre.

None to occasional

local application 50 to

75 mm

B. Conventional Light sets at 1.5 to 1.8 m

centre, Rock load 0.3 to

0.6B

Pattern 1.5 to

1.8 m centre

Occasional local

application 50 to 75

mm

Fair

50<RQD<75

A Boring

Machine

Light to medium sets, 1.5 to

1.8 m centre, Rock load 0.4

to 1.0B

Pattern 1.5 to

1.8 m centre

50 to 100 mm on crown

B. Conventional Light to medium sets, 1.5 to

1.8 m centre, Rock load 0.4

to 1.3B

Pattern 1.5 to

1.8 m centre

100 mm or more in

crown and sides

Poorb

75<RQD<90

A Boring

Machine

Medium circular sets on 0.9

to 1.2 m centre, Rock load

1.0 to 1.6B

Pattern 1.5 to

1.8 m centre

100 mm to 150 mm on

crown and sides,

combine with bolts.

B. Conventional Medium to heavy sets on

0.6 to 1.2 m centre, Rock

load 1.3 to 2.0B

Pattern 1.5 to

1.8 m centre

150 or more on crown

and sides, combine with

bolts

Very Poorb

RQD<25

(Excluding

squeezing or

swelling

grounds)

A Boring

Machine

Medium to heavy circular

sets on 0.6 centre, Rock

load 1.6 to 2.2B

Pattern 0.6 to

1.2 m centre

150 mm or more on

whole section, combine

with medium sets.

B. Conventional Heavy circular sets on 0.6

centre, Rock load 2.0 to

2.8B

Pattern 0.9 m

centre

150 mm or more on


medium to heavy sets.

Very Poorb

RQD<25

(Squeezing

and

swelling)

A Boring

Machine

Very heavy circular sets on

0.6 m centre. Rock load

upto 75 m.

Pattern 0.6 to

0.9 m

150 mm or more on


with heavy sets.

B. Conventional Very heavy circular sets on

2 foot m centre. Rock load

upto 75 m.

Pattern 0.6 to

0.9 m

150 mm or more on


with heavy sets. a In good and excellent rock, the support requirement in general be minimal but will be

dependent on joint geometry, tunnel diameter and relative orientation of joints and

tunnel. b Lagging requirements will usually be zero in excellent rock and will range from upto

25% in good rock to 100% in very good rock. c Mesh requirement usually will be zero in excellent rock and will range from

occasional mesh (or straps) in good rock to 100% mesh in very poor rock. d B = width of tunnel in m.


11

Deere's RQD was widely used, particularly in North America, after its introduction.

Deere and Deere (1972), Meritt (1972) and Deere and Deere (1988) attempted to relate

RQD to Terzaghi's rock load factors and to rock bolt requirements in tunnels. The most

important use of RQD is as a component of the RMR and Q classifications.

3.4 Rock Structure Rating Classification System

The Rock Structure Rating (RSR) concept developed in the USA by Wickham, Tideman

and Skinner presents a quantitative method for describing the quality of a rock mass for

selecting the appropriate ground support (Tables 5, 6 and 7). It was the first complete

rock mass classification system proposed after being introduced by Terzaghi in 1946. The

main contribution of the RSR concept was that it introduced a rating system for rock

masses and classification system gives both input and output.

The RSR concept considered two general categories of factors influencing rock mass

behaviour in tunnelling; geological parameters and construction parameters. These

parameters grouped as A, B, & C are explained as follows:

Parameter A (General appraisal of rock structure) includes:

• Rock type origin ( igneous, sedimentary or metamorphic)

• Rock hardness (Hard, Medium, Soft, Decomposed)

• Geological Structure (Massive, slightly faulted/folded, moderately faulted/folded,

intensely faulted/folded)

Parameter B (Effect of discontinuity pattern with respect to the direction of tunnel drive)

includes:

• Joint spacing

• Joint orientation (strike & dip)

• Direction of tunnel drive

Parameter C (Effect of groundwater inflow) includes:

• Overall rock mass quality due to parameters A & B combined

• Joint condition (good, fair)

• Amount of water inflow

Table 5: Rock structure rating-parameter A, geological condition

*Basic

Rock Type

Massive

RQD>75

Slightly

folded or faulted

RQD 50-75

Moderately folded

or faulted

RQD 25-50

Intensely

folded or faulted

RQD<25

Type I 30 22 15 9

Type II 27 20 13 8

Type III 24 18 12 7

Type IV 17 15 10 6


12

*Basic Rock Type

Basic Rock Rock Condition

Hard Medium Soft Decomposed

Igneous I II III IV

Metamorphic I II III IV

Sedimentary II III IV IV

Table 6: Rock structure rating-parameter B, joint spacing condition

Average Joint

Spacing

Strike Perpendicular to Axis Strike parallel to Axis

Direction of Drive Direction of Drive

Both With Dip Against Dip Both

Dip of Prominent Joints Dip of Prominent Joints

Flat Dipping Vertical Dipping Vertical Flat Dipping Vertical

Very closely

Jointed< 2’’

9 11 13 10 12 9 9 7

Closely Jointed

2’’-6

’’ 13 16 19 15 17 14 14 11

Moderately

Jointed 6’’-1’

23 24 28 19 22 23 23 19

Moderate to

Blocky 1’-2

’ 30 32 36 25 28 30 28 24

Blocky to

Massive 2’-4’ 36 38 40 33 35 36 34 28

Massive > 4’ 40 43 45 37 40 40 38 34

Flat 0°-20° Dipping 20°-50° Vertical 50°-90°

Table 7: Rock structure rating-parameter C, ground water joint condition

Anticipated water inflow

Gallons/min/1 m

Sum of Parameters A & B

13-44 45-75

Joint condition

Good Fair Poor Good Fair Poor

None 22 18 12 25 22 18

Slight< 200 gpm 19 15 9 23 19 14

Moderate 200-1000 gpm 15 11 7 21 16 12

Heavy >1000 gpm 10 8 6 18 14 10

Good-Tight or cemented, Fair-Slightly weathered, Poor-Severely weathered or open

The RSR value of any tunnel section is obtained by summing the weighted numerical

values determined for each parameter. This reflects the quality rock mass with respect to

its need for support. Since a lesser amount of support was expected for machine bored

tunnels than those excavated by drill and blast methods, it was suggested that RSR values

be adjusted for machine bored tunnels.


13

Note that the RSR classification used Imperial units and that these units have been

retained in this discussion.

Three tables from Wickham et al's 1972 paper can be used to evaluate the rating of each

of these parameters to arrive at the RSR value (maximum 100).

For example, a hard metamorphic rock which is slightly folded or faulted has a rating of

A = 22 (from Table 5). The rock mass is moderately jointed, with joints striking

perpendicular to the tunnel axis which is being driven east-west, and dipping at between

20o to 50

o.

Table 6 gives the rating for B = 24 for driving with dip. (defined below)

The values of A + B = 46 and this means that, for joints of fair condition (slightly

weathered and altered) and a moderate water inflow of between 200 and 1000 gallons per

minute, Table 7 gives the rating for C = 16. Hence, the final value of the rock structure

rating RSR = A + B + C = 62.

A typical set of curves for a 24 foot diameter tunnel are given in Fig. 4 which shows that,

for the RSR value of 62 derived above, the predicted support would be 2 inches of

shotcrete and 1 inch diameter rock bolts spaced at 5 foot centres. As indicated in the

figure, steel sets would be spaced at more than 7 feet apart and would not be considered a

practical solution for the support of this tunnel.

Fig. 4: RSR support estimates for a 24 ft. (7.3 m) diameter circular tunnel. Note that rock

bolts and shotcrete are generally used together. (After Wickham et al 1972)


14

For the same size tunnel in a rock mass with RSR = 30, the support could be provided by

8 WF 31 steel sets (8 inch deep wide flange I section weighing 31 lb per foot) spaced 3

feet apart, or by 5 inches of shotcrete and 1 inch diameter rock bolts spaced at 2.5 feet

centres. In this case it is probable that the steel sets solution would be cheaper and more

effective than the use of rock bolts and shotcrete.

Although, the RSR classification system is not widely used today, Wickham et al's work

played a significant role in the development of the classification schemes discussed in the

following pages.

3.5 Geomechanics Classification System of Rock Masses, Rock Mass Rating (RMR)

Bieniawski (1974) developed a rock mass rating system based on the following five

parameters:

1) Uniaxial compressive strength of intact rock,

2) Rock quality designation,

3) Spacing of joints,

4) Condition of discontinuities, and

5) Ground water conditions.

In addition, the strike and dip orientations of joints were removed from the list of basic

classification parameters and their effects allowed for by a rating adjustment made after

the basic parameters had been considered. RMR rating on the basis of various influencing

parameters is given in Table 8. The Effect of Joint Strike and Dip Orientations in

Tunnelling have been presented in Table 9. Average stand-up time of underground

openings of various sizes with varying rock classes and the effect of joint strike and dip

orientation in tunnelling are given in Tables 10 and 11.

He assigned numerical rating values to all these parameters. The rock mass rating is the

summation of the individual ratings of the five parameters and correction for orientation

of joints made after the basic parameters had been considered. Based on the value of the

rock mass rating designated as RMR value, Bieniawski divides the whole universe of

rock mass into five classes, I through V. The five basic classification parameters are:

1. Strength of intact rock material

Bieniawski uses the classification of the uniaxial compressive strength of intact rock

proposed by Deere and Miller. Alternatively, for all but very low strength rocks the point

load index may be used as a measure of intact rock material strength.

2. Rock Quality Designation

Deere’s RQD is used as a measure of drill core quality.


15

3. Spacing of Joints

Here, the term joint is used to mean all discontinuities which may be joints, faults,

bedding planes and other surfaces of weakness. Here again, Bieniawski uses a

classification proposed by Deere.

4. Condition of joints

This parameter takes into account the separation or aperture of joints, their continuity, the

surface roughness, the wall condition (hard or soft), and the presence of infilling

materials in the joints.

5. Ground Water conditions

An effort is made to account for the influence of ground water flow on the stability of

underground excavations in terms of the observed rate of flow into the excavation, the

ratio of joint water pressure to major principal stress or by some general qualitative

observation of ground water conditions.

Bieniawski told that each parameter does not necessarily contribute equally to the

behaviour of the rock mass. For example, an RQD of 90 and a uniaxial compressive

strength of intact rock material of 200 MPa would suggest that the rock mass is of

excellent quality, but heavy inflow of water into the same rock mass could change this

assessment. Bieniawski, therefore applied a series of important ratings to his parameters

following the concept used by Wickham, Tiedemann and Skinner. A number of points or

a rating is allocated to each range of values for each parameter and an overall rating for

the rock mass is arrived at by adding the ratings for each of the parameters. This overall

rating must be adjusted for joint orientation by applying the corrections.

Table 8: CSIR Geomechanics classification of jointed rock masses

A Classification Parameters and their Ratings Sl.

No

Parameter Range of values

1 Strength

of Intact

Rock

Material

Point load

strength Index

>8 MPa 4-8 MPa 2-4 MPa 1-2 MPa For this low range-

uniaxial compressive

test is preferred

Uniaxial

compressive

strength

>200 MPa 100-200

MPa

50-100 MPa 25-50 MPa 10-25

MPa

3-10

MPa

1-3

MPa

Rating 15 12 7 4 2 1 0

2 Drill Core Quality (Rock

Quality Designation ),

RQD

90-100% 75-90% 50-75% 25-50% <25%

Rating 20 17 13 8 3

3 Spacing of joints >3 m 1-3 m 0.3-1 m 50-300 mm <50 mm

Rating 30 25 20 10 5


16

4 Condition of joints Very rough

surfaces

Not

continuous

No

separation

Hard joint

wall rock

Slightly rough

surfaces

Separation

< 1m

Hard joint

wall rock

Slightly rough

surfaces

Separation

< 1mm

Soft joint wall

rock

Slickensided

surfaces or

Gouge< 5mm

thick or joints

open 1-5 mm

Continuous

joints

Soft gouge >5mm

thick or Joints open >

5mm

Continuous joints

Rating 25 20 12 6 0

5. Ground

water

Inflow per

10 m

tunnel

length

None

OR

<25

liters/min

25-125

liters/min

>125 liters/min

Ratio of

Joint

water

pressure

to

major

principal

stress

0

OR

0.0-0.2

OR

0.2-0.5

OR

>0.5

General

conditions

Completely

dry

Moist only

(interstitial

water)

Water under

moderate

pressure

Severe water

problems

Rating 10 7 4 0

B Rating adjustment for joint orientations Strike and dip

orientations of joints

Very

favourable

Favourable Fair Unfavourable Very

unfavourable

Ratings Tunnels 0 -2 -5 -10 -12

Foundations 0 -2 -7 -15 -25

Slopes 0 -5 -25 -50 -60

C Rock mass classes determined from total ratings Rating 100-81 80-61 60-41 40-21 <20

Class No I II III IV V

Description Very good

rock

Good rock Fair rock Poor rock Very poor

rock

D Meaning of rock mass classes Class No. I II III IV V

Average

stand-up time

10 years for

5m span

6 months for

4m span

1 week for 3

m span

5hours for

15m span

10m in. for

0.5m span

Cohesion of

the rock mass

>300kPa 200-300kPa 150-200kPa 100-150kPa <100kPa

Friction

angle of the

rock mass

>45° 40°-45° 35°-40° 30°-35° <30°


17

Table 9: Effect of joint strike and dip orientations in tunnelling

Strike perpendicular to tunnel axis Strike parallel to tunnel axis Dip

0°-20°

irrespective

of strike

Drive with dip Drive against dip

Dip 45°-

90°

Dip

20°-45°

Dip

45°-90°

Dip 20°-45° Dip 45°-90

° Dip

20°-45

°

Favourable Fair Unfavourable Very unfavourable Fair Unfavourable

Table 10: Stand-up time of underground openings

Rock Class I II III IV V

Unsupported

Span, m

5 4 3 1.5 0.5

Average

Stand-Up

Times

10 Years 6 Months 1 Week 5 Hours 10 Minutes

Table 11: The effect of joint strike and dip orientation in tunnelling

Strike Perpendicular to Tunnel Axis Strike Parallel to Tunnel

Axis Drive With Dip Drive Against Dip

Dip Dip Dip Dip Dip Dip

45o-90o 20o -45o 45o -90o 20o -45o 45o -90o 20o -45o

Very

Favourable

Favourable Fair Unfavourable Very

Favourable

Fair

Dipo 0

oto 20

o: Unfavourable, irrespective of strike

To apply the geo-mechanics classification, the rock mass along the tunnel route is divided

into a number of structural regions, i.e. zones in which certain geological features are

more or less uniform within each region. The above six classification parameters are

determined for each structural region from measurements in the field and entered into the

standard input data sheet.

The first five parameters are grouped into five ranges of values. Since the various

parameters are not equally important for the overall classification of a rock mass,

important ratings are allocated to the different value ranges of the parameters, a higher

rating indicating better rock mass conditions.

Once the classification parameters are determined, the important ratings are assigned to

each parameter. In this respect, the typical rather than the worst conditions are evaluated.

Furthermore, it should be noted that the important ratings, which are given for

discontinuity spacings, apply to rock masses having three sets of discontinuities. Thus,

when only two sets of discontinuities are present, a conservative assessment is obtained.


18

After the important ratings of the classification parameters are established, the ratings for

the five parameters are summed to yield the basic rock mass rating for the structural

region under consideration.

At this stage, the influence of the strike and dip of discontinuities is included by adjusting

the basic rock mass rating. This step is treated separately because the influence of

discontinuity orientation depends upon engineering application, e.g. tunnel (mine), slope,

or foundation. It will be noted that the ‘value’ of the parameter ‘discontinuity orientation’

is not given in quantitative terms but by quantitative descriptions such as ‘favourable’. To

facilitate a decision whether strike and dip orientations are favourable or not, reference

should be made to studies by Wickham et al. (1972). In the case of civil engineering

projects, an adjustment for discontinuity orientations will suffice. For mining

applications, other adjustments may be called for such as the stress at depth or a change

in stress.

After the adjustment for discontinuity orientations, the rock mass is classified and

grouped in the final (adjusted) rock mass ratings (RMR) into five rock mass classes, the

full range of the possible RMR values varying from 0 to 100. Note that the rock mass

classes are in groups of twenty ratings each.

A tunnel is to be driven through slightly weathered granite with a dominant joint set

dipping at 60o against the direction of the drive. Index testing and logging of diamond

drilled core give typical Point-load strength index values of 8 MPa and average RQD

values of 70%. The slightly rough and slightly weathered joints with a separation of <1

mm are spaced at 300 mm. Tunnelling conditions are anticipated to be wet. The RMR

value for the example under consideration is determined as follows:

Table Item Value Rating

5, A.1 Point load index 8 MPa 12

5, A.2 RQD 70% 13

5, A.3 Spacing of

discontinuities

300 mm 10

5, E.4 Condition of

discontinuities

Note 1 22

5, A.5 Ground water Wet 7

5, B Adjustment for joint

orientation

Note 2 -5

Total 59

Note 1: For slightly rough and altered discontinuity surfaces with a separation of <1 mm,

Table 5.A.4 gives a rating of 25. When more detailed information is available, Table 5.E

can be used to obtain a more refined rating. Hence, in this case, the rating is the sum of: 4

(1-3 m discontinuity length), 4 (separation 0.1-1.0 mm), 3 (slightly rough), 6 (no filling)

and 5 (slightly weathered0 = 22


19

Note 2. Table 5.F gives a description of 'Fair' for the conditions assumed where the tunnel

is to be driven against the dip of a set of joints dipping at 60o. Using this description for

'Tunnels and Mines' in Table 5.B gives an adjustment rating of -5.

The value of 59 indicates that the rock mass is on the boundary between the 'Fair rock'

and 'Good rock' categories.

In the case of tunnels and chambers, the output from the Geo-mechanics Classification is

the stand up time and the maximum stable rock span for a given rock mass ratings.

Bieniawski has related his rock mass rating (or total rating score for the rock mass) to the

stand-up time of an active unsupported span as originally proposed by Lauffer. Average

stand-up time v/s unsupported span is shown in Fig. 5.

Fig 5: Average Stand-up time v/s Unsupported Span

Support load can be determined from the Geomechanics classification as:

P= {(100-RMR)/100}γB} …… (2)

Where, P is the support load, RMR is the rock mass ratings; and γ is the density of the

rock Kg/m3.

The Geomechanics Classification provides guidelines for the selection of roof support to

ensure long-term stability of various rock mass classes. These guidelines depend on such


20

factors as the depth below surface (in-situ stress), tunnel size and shape, and the method

of excavation.

Bieniawski (1989) published a set of guidelines for the selection of support in tunnels in

rock for which the value of RMR has been determined. The guidelines are reproduced in

Table 12.

Table 12: Guidelines for excavation and support of 10 m span rock tunnels in accordance

with the RMR system (After Bieniawski 1989)

Rock mass

class

Excavation Rock bolts (20 mm

diameter, fully

grouted)

Shotcrete Steel sets

I-Very good

rock

RMR: 81-100

Full face

3 m advance

Generally no support required except spot bolting

II- Good rock

RMR: 61-80

Full face

1-1.5 m advance. Complete

support 20 m from face

Locally, bolts in

crown 3 m long,

spaced 2.5 m with

occasional wire

mesh

50 mm in

crown where

required

None

III- Fair rock

RMR: 41-60

Top heading and bench

1.5-3 m advance in top

heading

Commence support after

blast

Complete support 10 m

from heading

Systematic bolts 4

m long, spaced

1.5-2 m in crown

and walls with

wire mesh in

crown.

50-100 mm

in crown and

30 mm in

sides

None

IV- Poor rock

RMR: 21-40

Top heading and bench

1.0-1.5 m advance in top

heading

Install support concurrently

with excavation, 10 m from

face

Systematic bolts 4-

5 m long, spaced

1-1.5 m in crown

and walls with

wire mesh.

100-150 mm

in crown and

100 mm in

sides

Light to medium

ribs spaced 1.5 m,

where required

V- Very poor

rock

RMR: <20

Multiple drifts 0.5-1.5 m

advance in top heading.

Install support concurrently

with excavation. Shotcrete

as soon as possible after

blasting.

Systematic bolts 5-

6 m long, spaced

1-1.5 m in crown

and walls with

wire mesh. Bolt

invert

150-200 mm

in crown,

150 mm in

sides and 50

mm face.

Medium to heavy

ribs spaced 0.75

m with steel

lagging and

forepoling if

required. Close

invert.

Table 12 has not had any major revision, hence in mining and civil engineering

applications, steel fibre reinforced shotcrete (SFRS) may be considered in place of wire

mesh and shotcrete.

The Geomechanics Classification is also applicable to rock foundation and slopes. This is

a useful feature that can assist with the design of slopes near the tunnel portals as well as

allow estimates of deformability of foundations for such structures as bridges and dams.


21

In the case of rock foundation, the following correlation was obtained:

Em = 2xRMR – 100 …… (3)

Where Em is the in-situ modulus of deformation in GPa and RMR> 50.

Most recently, Serafim and Pereira (1983) provided many results in the range RMR< 50

and proposed a new correlation:

Em = 10[(RMR-10)/40]

…… (4)

Hoek and Brown (1980) proposed a method for estimating rock mass strength which also

makes use of RMR classification. The RMR system is very simple to use and the

classification parameters are easily obtained from either drill hole data or underground

mapping. This classification is applicable and adaptable to many different situations

including coal mining, hard rock mining, slope stability, foundation stability and

tunnelling.

The output from the RMR classification method tends to be rather conservative, which

can lead to overdesign of support system (Beiniawski 1989). This aspect is best overcome

by monitoring rock behaviour during tunnel construction and adjusting RMR ratings to

local conditions. An example of this approach is the work of Kaiser et al. (1986), who

found that the no support limit was too conservative and proposed the following

correction to adjust RMR (no support) at the no support limit for opening size effect:

RM (NS) = 22 ln ED + 25 …… (5)

Where ED is the equivalent dimension as defined by Barton et al. (1974).

3.6 NGI Tunnelling Quality Index Classification System or Q-System

The Q–system of rock mass classification was developed in Norway by Barton, Lien and

Lunde (1974), all of the Norwegian Geotechnical Institute (NGI). Its development

represented a major contribution to the subject of rock mass classification for a number of

reasons; the system was proposed on the basis of an analysis of some 212 tunnel case

histories from Scandinavia. It is quantitative classification system, and it is an

engineering system enabling the design of tunnel supports.

The Q-system is based on a numerical assessment of the rock mass quality using six

different parameters:

Block Sizes

!. Rock Quality Designation (RQD);

2. Number of joint sets;


22

Shear Strength

3. Roughness of the most unfavourable joint or discontinuity;

4. Degree of alteration or filling along the weakest joint;

Active Stresses 5. Water inflow; and

6. Stress condition.

The above six parameters are grouped into three quotients to give the overall rock mass

quality Q as follows:

SRF

Jx

J

Jx

J

RQDQ w

a

r

n

= …… (6)

Where,

RQD = Deere’s rock quality designation;

Jn = joint set number;

Jr = joint roughness number;

Ja = joint alteration number;

Jw = joint water reduction factor;

SRF = stress reduction factor .

The numerical values of each of the above parameters are interpreted as follows:

The first two parameters represent the overall structure of the rock mass and their

quotient (RQD/Jn) is a relative measure of the block size.

The quotient of the third and the fourth parameters (Jr/Ja) represents the roughness and

frictional characteristics of the joint walls or filling materials and is said to be an

indicator of the inter-block shear strength (of the joints). This quotient is weighted in

favour of rough, unaltered joints in direct contact. It is to be expected that such surfaces

will be close to peak strength, that they will therefore be especially favourable to tunnel

stability.

When rock joints have thin clay mineral coatings and fillings, the strength is reduced

significantly. Nevertheless, rock wall contact after small shear displacement has occurred

may be a very important factor for preserving the excavation from ultimate failure.

Where no rock wall contact exists, the conditions are extremely unfavourable to tunnel

stability. The friction angles are a little below the residual strength values for most clays,

and are possibly downgraded by the fact that these clay bands or fillings may tend to

consolidate during shear, at least if normally consolidated or if softening and swelling has

occurred. The swelling pressure of montmorillonite may also be a factor here.

The fifth parameter is a measure of water pressure, which has an adverse effect on the

shear strength of joints due to a reduction in effective normal stress. Water may, in


23

addition, cause softening and possible outwash in the case of clay-filled joints. The sixth

parameter is a measure of: a) loosening load in the case of shear zones and clay bearing

rock b) rock stress in competent rock, and c) squeezing and swelling loads in plastic

incompetent rock. The sixth parameter is regarded as the ‘total stress’ parameter. The

quotient of the fifth and sixth parameters (Jw/SRF) is a complicated empirical factor

describing the ‘active stresses’.

Barton et al. (1974) consider the parameters, Jn, Jr and Ja as playing a more important

role than joint orientation, and if joint orientation had been included, the classification

would have been less general. However, orientation is implicit in parameters, Jr and Ja

because they apply to the most unfavourable joints.

Q values ranges from 0.001 to 1000 as per modified Q charts. The Q value is related to

tunnel support requirements by defining the equivalent dimension (ED), which is a

function of both the size and the purpose of the excavation, is obtained by dividing the

span, diameter, or the wall height of the excavation by a quantity called the excavation

support ratio (ESR), thus:

ED = (Excavation Span, Diameter or Height (m))/ESR (7)

The ESR is related to the use for which the excavation is intended and the degree of

safety demanded as shown below.

Excavation Category ESR No. of cases

A. Temporary mine openings 3-5 2

B. Vertical shafts:

Circular section 2.5 --

rectangular/square section 2.0 --

C. Permanent mine openings, 1.6 83

D. Storage rooms, water treatment 1.3 25

Plants, minor highway and rail road tunnels,

Surge chambers access tunnels.

E. Power stations, major highway rail /road 1.0 73

Tunnels, civil/defence chambers, portals,

Intersections.

F. Underground nuclear power stations 0.8 2

The relationship between the index Q and the equivalent dimensions (ED) of an

excavation determines the appropriate support measures. Barton et al. (1974) provide 38

support categories which give estimates of permanent support. For temporary support

determination either Q is increased to 5Q or ESR is increased to 1.5 ESR. For selection of

the support measures using the Q-system, the reader should consult the original paper.

The maximum span (unsupported) =2(ESR) Q0.4

…… (8)


24

The classification of individual parameters used to obtain the Tunnelling Index Q for a

rock mass has been given in Table 13.

Table 13: Q-logging ratings for RQD, Jn , Jr , Ja , Jw and SRF (Barton, 2002)

1. Rock Quality Designation RQD (%)

A Very poor 0-25

B Poor 25-50

C Fair 50-75

D Good 75-90

E Excellent 90-100

Notes: i) Where RQD is reported or measured as ≤ 10 (including 0), a nominal value of 10 is used

to evaluate Q.

ii) RQD intervals of 5, i.e., 100, 95, 90, etc., are sufficiently accurate.

2. Joint set number Jn

A Massive, no or few joints 0.5-1

B One joint set 2

C One joint set plus random joints 3

D Two joint sets 4

E Two joint sets plus random joints 6

F Three joint sets 9

G Three joint sets plus random joints 12

H Four or more joint sets, random, heavily jointed, ‘sugar-cube’, etc. 15

J Crushed rock, earthlike 20

Notes i) For tunnel intersections, use (3.0 × Jn).

ii) For portals use (2.0 × Jn).

3. Joint roughness number Jr

a) Rock-wall contact, and b) Rock-wall contact before 10 cm shear

A Discontinuous joints 4

B Rough or irregular, undulating 3

C Smooth, undulating 2 D Slickensided, undulating 1.5

E Rough or irregular, planar 1.5

F Smooth, planar 1.0

G Slickensided, planar 0.5

Notes: i) Descriptions refer to small-scale features and intermediate scale features, in that order.

b) No rock-wall contact when sheared

H Zone containing clay minerals thick enough to prevent rock-wall contact.

1.0

J Sandy, gravely or crushed zone thick enough to prevent rock-wall contact

1.0

Notes: ii) Add 1.0 if the mean spacing of the relevant joint set is greater than 3 m.


25

iii) Jr = 0.5 can be used for planar, slickensided joints having lineations, provided the lineations are oriented for minimum strength. Jr and Ja classification is applied to the joint set or discontinuity that is least favourable for stability both from the point of view of orientation and shear resistance,

τ (where τ ≈ σn tan-1 (Jr /Ja ).

4. Joint alteration number Φr

approx. Ja

a) Rock-wall contact (no mineral fillings, only coatings)

A Tightly healed, hard, non-softening, impermeable filling, i.e., quartz or epidote.

-- 0.75

B Unaltered joint walls, surface staining only. 25-35° 1.0

C Slightly altered joint walls. Non-softening mineral coatings, sandy particles, clay-free disintegrated rock, etc.

25-30° 2.0

D Silty- or sandy-clay coatings, small clay fraction (non-softening).

20-25° 3.0

E Softening or low friction clay mineral coatings, i.e., kaolinite or mica. Also chlorite, talc, gypsum, graphite, etc., and small quantities of swelling clays.

8-16° 4.0

b) Rock-wall contact before 10 cm shear (thin mineral fillings).

F Sandy particles, clay-free disintegrated rock, etc. 25-30° 4.0

G Strongly over-consolidated non-softening clay mineral fillings (continuous, but < 5 mm thickness).

16-24° 6.0

H Medium or low over-consolidation, softening, clay mineral fillings (continuous, but < 5 mm thickness).

12-16° 8.0

J Swelling-clay fillings, i.e., montmorillonite (continuous, but < 5 mm thickness). Value of Ja depends on per cent of swelling clay-size particles, and access to water, etc.

6-12° 8-12

c) No rock-wall contact when sheared (thick mineral fillings)

K,L& M

Zones or bands of disintegrated or crushed rock and clay (see G, H, J for description of clay condition).

6-24° 6, 8, or 8-12

N Zones or bands of silty- or sandy-clay, small clay fraction (non-softening).

-- 5.0

O,P & R

Thick, continuous zones or bands of clay (see G, H, J for description of clay condition).

6-24° 10, 13, or

13-20

5. Joint water reduction factor approx.

water pres. (kg/cm

2)

Jw

A Dry excavations or minor inflow, i.e., < 5 l/min locally. < 1 1.0

B Medium inflow or pressure, occasional outwash of joint fillings.

1-2.5 0.66

C Large inflow or high pressure in competent rock with unfilled joints.

2.5-10 0.5

D Large inflow or high pressure, considerable outwash of joint fillings.

2.5-10 0.33

E Exceptionally high inflow or water pressure at blasting, decaying with time.

> 10 0.2-0.1

F Exceptionally high inflow or water pressure continuing without noticeable decay.

> 10 0.1-0.05

Notes: i) Factors C to F are crude estimates. Increase Jw if drainage measures are installed.

ii) Special problems caused by ice formation are not considered. iii) For general characterization of rock masses distant from excavation influences, the use of Jw = 1.0, 0.66, 0.5, 0.33 etc. as depth increases from say 0-5m, 5-25m, 25-250m to >250m is


26

recommended, assuming that RQD /Jn is low enough (e.g. 0.5-25) for good hydraulic connectivity. This will help to adjust Q for some of the effective stress and water softening effects, in combination with appropriate characterization values of SRF. Correlations with depth-dependent static deformation modulus and seismic velocity will then follow the practice used when these were developed.

6. Stress Reduction Factor SRF

a) Weakness zones intersecting excavation, which may cause loosening of rock mass when tunnel is excavated

A Multiple occurrences of weakness zones containing clay or chemically disintegrated rock, very loose surrounding rock (any depth).

10

B Single weakness zones containing clay or chemically disintegrated

rock (depth of excavation ≤ 50 m). 5

C Single weakness zones containing clay or chemically disintegrated rock (depth of excavation > 50 m).

2.5

D Multiple shear zones in competent rock (clay-free), loose surrounding rock (any depth).

7.5

E Single shear zones in competent rock (clay-free), (depth of excavation

≤ 50 m). 5.0

F Single shear zones in competent rock (clay-free), (depth of excavation > 50 m).

2.5

G Loose, open joints, heavily jointed or ‘sugar cube’, etc. (any depth) 5.0 Notes: i) Reduce these values of SRF by 25-50% if the relevant shear zones only influence but do not

intersect the excavation. This will also be relevant for characterization.

b) Competent rock, rock stress problems σσσσc /σσσσ1 σσσσφ /σσσσc SRF

H Low stress, near surface, open joints. > 200 < 0.01 2.5

J Medium stress, favourable stress condition. 200-10 0.01-0.3 1

K High stress, very tight structure. Usually favourable to stability, may be unfavourable for wall stability.

10-5 0.3-0.4 0.5-2

L Moderate slabbing after > 1 hour in massive rock. 5-3 0.5-0.65 5-50

M Slabbing and rock burst after a few minutes in massive rock.

3-2 0.65-1 50-200

N Heavy rock burst (strain-burst) and immediate dynamic deformations in massive rock.

< 2 > 1 200-400

Notes: ii) For strongly anisotropic virgin stress field (if measured): When 5 ≤ σ1 /σ3 ≤ 10, reduce σc to

0.75 σc. When σ1 /σ3 > 10, reduce σc to 0.5 σc, where σc = unconfined compression strength,

σ1 and σ3 are the major and minor principal stresses, and σθ = maximum tangential stress (estimated from elastic theory).

iii) Few case records available where depth of crown below surface is less than span width.

Suggest an SRF increase from 2.5 to 5 for such cases (see H). iv) Cases L, M, and N are usually most relevant for support design of deep tunnel excavations in

hard massive rock masses, with RQD /Jn ratios from about 50 to 200. v) For general characterization of rock masses distant from excavation influences, the use of

SRF = 5, 2.5, 1.0, and 0.5 is recommended as depth increases from say 0-5m, 5-25m, 25-250m to >250m. This will help to adjust Q for some of the effective stress effects, in combination with appropriate characterization values of Jw. Correlations with depth - dependent static deformation modulus and seismic velocity will then follow the practice used when these were developed.


27

c) Squeezing rock: plastic flow of incompetent rock under the influence of high rock pressure

σσσσφ /σσσσc SRF

O Mild squeezing rock pressure 1-5 5-10

P Heavy squeezing rock pressure > 5 10-20 Notes: vi) Cases of squeezing rock may occur for depth H > 350 Q

1/3 according to Singh 1993. Rock

mass compression strength can be estimated from SIGMA cm ≈ 5 γ Qc1/ 3

(MPa) where γ = rock

density in t /m3, and Qc = Q x σc /100, Barton, 2000.

d) Swelling rock: chemical swelling activity depending on presence of water

SRF

R Mild swelling rock pressure 5-10

S Heavy swelling rock pressure 10-15

NOTES ON Q-METHOD OF ROCK MASS CLASSIFICATION 1) These tables contain all the ratings necessary for classifying the Q-value of a rock mass. The ratings form the basis for the Q, Qc and Qo estimates of rock mass quality (Qc needing only

multiplication by σc /100, and Qo the use of a specifically oriented RQD, termed RQDo relevant to a loading or measurement direction). All the classification ratings needed for tunnel and cavern design are given in the six tables, where Q only would usually apply.

2) For correlation to engineering parameters as described in this paper, use Qc (multiplication of

Q by σc / 100). For specific loading or measurement directions in anisotropically jointed rock masses use RQDo in place of RQD in the Q estimate. This means that an oriented Qc value should contain a correctly oriented RQDo for better correlation to oriented engineering parameters.

3) Q-parameters are most conveniently collected using histogram logging. Besides space for

recording the usual variability of parameters, for structural domain 1, domain 2 etc., it contains reminders of the tabulated ratings at the base of each histogram. Space for presentation of results for selected (or all ) domains at the top of the diagram, includes typical range, weighted mean and most frequent (Q-parameters, and Q-values). 4) During field logging, allocate running numbers to the structural domains, or core boxes, or

tunnel sections, e.g. 1 = D1, 2 = D2 etc. and write the numbers in the allotted histogram columns, using a regular spacing for each observation such as 11, 113, 2245, 6689 etc. In this way the histograms will give the correct visual frequency of all the assembled observations, in each histogram column. Besides this, it will be easy to find the relevant Q-parameters for a particular domain, core box or section of tunnel, for separate analysis and reporting. Overall frequencies of observations of each rating (or selected sets of data) can be given as numbers on separate logging sheets. Large data sets can be computerised when returning from the field. 5) It is convenient and correct to record rock mass variability. Therefore allow as many as five observations of each parameter, for instance in a 10m length of tunnel. If all observations are the same, great uniformity of character is implied, if variable – this is important information. At ‘the end of the day’ the histograms will give a correct record of variability, or otherwise. 6) Remember that logged RQD of < 10, including 0, are set to a nominal 10 when calculating Q. In view of the log scale of Q, the histograms of RQD in the logging sheet will be sufficiently accurate if given mean values, from left to right, of 10, 15, 25, 35……85, 95, 100. The log scale of Q also suggests that decimal places should be used sparingly. The following is considered realistic 0.004, 0.07, 0.3, 6.7, 27, 240. Never report that Q = 6.73 or similar, since a false sense of accuracy will be given.


28

7) Footnotes below the tables that follow, also give advice for site characterization ratings for the case of Jw and SRF, which must not be set to 1.0 and 1.0, as some authors have suggested. This destroys the intended multi-purposes of the Q-system, which has an entirely different structure compared to RMR. Important: Use all appropriate footnotes under the six tables. Some have been updated or added since the minor 1993/1994 updating of three SRF values for highly stressed massive rock, which were changed due to ‘new’ support techniques, namely B+S(fr).

The relationship between the Q and the permanent support pressure Proof is calculated

from the following equations:

r

roofJ

QP

3/12 −

= for three or more set of joints …… (9)

r

n

roofJ

QJP

3

2 3/12/1 −

= for less than three joint sets …… (10)

Use Q' instead of Q for wall support pressure

Where Q' = 5Q for Q>10

Q' = 2.5Q for 0.1<Q<10

Q' = Q for Q<0.1

Although the Q-system involves 9 rock mass classes and 38 support categories, it is not

necessarily too complicated. Some users of the Q-system have pointed out that the open

logarithmic scale of Q varying from 0.001 to 1000 can be source of difficulty; it is easier

to get a feeling for a quoted rock mass quality using a linear scale of upto 100. The

support chart for Q values ranging from 0.001 to 1000 is given in Fig. 6.

3.6.1 Correlation between RMR and Q Values

A correlation has been provided between the RMR and Q-values (Bieniawski-1976). The

plotted results indicate the following relationship:

RMR = 9 ln Q + 44 …… (11)

Jethwa et al. (1982) further substantiated the correlation by Bieniawski (1976) on the

basis of 12 projects in India. Rutledge (1978) determined in New Zealand, the following

correlations between the three classification systems.

RMR =13.5 log Q + 43 (Standard deviation = 9.4) …... (12)

RSR = 0.77 RMR + 12.4 (Standard deviation = 8.9) …... (13)

RSR = 13.3 log Q + 46.4 (Standard deviation = 7.0) …... (14)


29

Fig. 6: Rock support as per Q system

A comparison of the stand up time and the maximum unsupported span reveals that geo-

mechanics classification is more conservative than the Q-system.

4.0 APPLICATIONS OF ROCK MASS CLASSIFICATION SYSTEMS FOR

DESIGN OF SUPPORTS FOR UNDERGROUND EXCAVATIONS

A number of underground excavations in rock mass relating to water resources projects

were taken up for the calculation of rock loads or support pressures using different

methods. The methods widely applied have been used to work out the support

requirements for underground openings. These methods widely applied have been used to

workout the support pressures also. These methods include the following:

• Terzaghi’s Method (1946)

• Deere’s Rock Quality Designation (1963 and 1967)

• Wickham’sRock Structure Rating (1972)

• Bieniawski’s Rock Mass Rating System (1974 and 1979)

• Barton’s Q System (1974 and 1993)

Also, the actual supports provided to reinforce the cavities were compiled and supports

pressures were worked out using various methods after classification of rock mass. The


30

observed support pressures in various underground structures were also collected for

comparison with accommodated support pressures.

4.1 Nathpa Jhakri H. E. Project, H.P.

Nathpa Jhakri H.E. Project envisages the utilization of about 488 m drop in river Sutlej

between Nathpa and Jhakri in Himachal Pradesh on the Indo-Tibet National Highway

about 150 km from Shimla. The fully underground project consists of concrete gravity

dam, four underground desilting chambers, 10.15 m diameter and 27.3 km long head race

tunnel, 301 m deep underground surge tank, three pressure shafts, underground

powerhouse 222 m (L) x 20 m (W) x 49 m (H), an underground transformer hall and

10.15 m diameter and 960 m long tail race tunnel with a downstream surge gallery.

4.1.1 Geology

The pre-cambrian rocks belong to the Wangtu-Jeory Gneissic Complex in the eastern

margin of Rampur window. They are surrounded by Jutog series of carbonaceous slates,

limestones, quartzites and schist separated by Main Central Thrust (MCT) which is

prominent and well known shear zone in the Himalayan region. The weaker rocks

(mainly schists) are folded with more than two generations of folds and are intersected by

steeply dipping faults and shear zones.

The area encompassing the power house site contains essentially quartz –mica schist.

These rocks are moderately jointed and at places slightly to moderately weathered. Rocks

are intruded by quartzite veins of varying thickness often forming boundaries which

follow the foliation trend. Geological map of Nathpa Jhakri Project is shown in Fig. 7.

4.1.2 Rock Mass Classification and Rock Pressures

Depending upon the geological and engineering properties of the rock, RMR and RSR

have been calculated. The rock loads have been presented in Table 14. For details of

tunnel supports refer Bhasin et. al. (1996a).

Table 14: Rock class and support pressures at Nathpa Jhakri Power House

Method of Rock Classification Rock Type : Quartz Mica schist

Rock Class by Terzaghi

Support Pr. (kg/cm2)

Massive Moderately Jointed (Class 4)

1.35 to 6.5

Wickham’s RSR


52

5.07

Bieniawski’s RMR


60 (Fair)

2.16

Barton’s Q value

Support Pr. (kg/cm2), Proof

Pwall

2.7 (Fair)

0.42

0.31


31

Fig. 7: Geological map of Nathpa Jhakri Project

4.1.3 Support Actually Provided

Roof Arch

Crown Portion: 6 m long, 25mm diameter rock bolts both ways with

8m long, 32mm diameter bolts at 2m spacing

Remaining part: 32mm diameter, 6m & 8m long bolts at 3 m spacing

Walls:

Below springing Level: Rock Bolts of 32 mm diameter, 7.5 m and 9 m long, at 3m

spacing.

Central Portion: 32 mm diameter, 11 m and 9 m long, at 3 m spacing

Lower Portion : 32 mm diameter, 7.5 m and 9 m long, at 3 m spacing

In addition to the rock bolts, two layers of shotcrete of 5 cm thickness with welded wire

mesh in between have also been provided. Rock supports adopted in Nathpa Jhakri Power

House is shown in Fig. 8.


32

Fig. 8: Rock supports adopted in Nathpa Jhakri Power House

4.2 Sardar Sarovar Project, Gujarat

The multipurpose Sardar Sarovar Project, was constructed on river Narmada in the state

of Gujarat with 1450 MW installed capacity (including river bed and canal bed

powerhouses). The fully underground powerhouse 212 m (L) x 23 m (W) x 58 m (H)

cavern houses six turbines of 200 MW each working under a head of 100 m and is

situated immediately downstream of the 128 m high and 1210 m long concrete gravity

dam across river Narmada.

4.2.1 Geology

The bed rock within the area around the powerhouse consists of sub-horizontal lava flows

of basalt with intrusive dolerite sills and lenses of agglomerates. Mainly three joint sets

have been identified along with some randomly oriented joints. Bedding is sub-

horizontal. The orientations of the joints are as follows.

1) NNW/60-80 SE, SW

2) ENE/60-80 SE/NW

3) ENE/30-45 NW


33

Joints striking ENE have been found to contain thin fillings of calcite and chlorite. In

general the joints can be described as having a rough surface, very narrow aperture and

having medium persistence. These Characteristics have been found to be favourable for

constructing a cavern of such dimension.

A shear zone of 1 to 2 m wide dipping 60

o to 65

o south was noticed across the cavern

along the contact of a dolerite dyke at the southern end. It consists of rock fragments of

dolerite with little clay and is calcified. The porphyritic basalt which covers 85% of the

cavern roof is traversed by two shear zone 0.1 to 0.8 m thick running across the cavern

roof.

4.2.2 Rock Mass classification and Rock Pressures

The rock pressures have been presented in Table 15.

Table 15: Rock class and support pressures at Sardar Sarovar Power House

Method of rock

classification

Rock Type

Basalt Dolerite Sheared rock mass

Rock Class By

Terzaghi

Support Pr., kg/cm2

Very Blocky &

Seamy, Class 4

Very Blocky &

Seamy, Class 4

Completely crushed but

chemically inert, Class 5

1.6 to 4.4 1.6 to 4.4 2.2 to 6.8

Bieniawski’s RMR

Support Pr., kg/cm2 63 (Good) 72 (Good) 40-21 say 30 (Poor)

2.26 1.71 4.57

Barton’s Q values

(Bhasin et al, 1996b)

Support Pr., kg/cm2

Proof

9.2 to 14.4

(Av. 11.8)

14.4 to 18.5

(Av. 16.45)

0.33

0.63-0.73 0.58 =-0.63 1.1

4.2.3 Supports Actually Provided

The roof of the underground powerhouse, located within the basaltic rocks, have been

stabilized with William's hollow core, mechanically anchored grouted bolts, 6-7 m long

bolts at 1.75 m staggered spacing, with two layers of 7.5 cm thick shotcrete wire

mesh. Across shear zone, three rows of 8-10 m long inclined bolts were installed with

minimum 1.5 m length grouted in sound rock.

It was learnt from the extensometer observations that, in the roof where a 4 to 5 m thick

conglomerate band was present, one of the contacts with basalt was opening up. Hence,

after installing 9 m long anchor bolts, the roof became stable. Across the shear zone,

three rows of 8 to 10 m long inclined bolts were installed with minimum 1.5 m length

grouted in sound rock. An additional layer of 38 mm thick shotcrete and wire mesh were

also used. The side walls of Powerhouse were initially reinforced using 6 m long bolts @

2 x 2 m pattern, pre-tensioned to 14 T and grouted.


34

The side walls of the power house posed problems of instability due to the presence of

shear zones. The walls were reinforced using 6 m long bolts at 2 x 2 m pattern, (pre

tensioned to 120 kN in case of 25 mm diameter bolts and to 180 kN in case of 32 mm

diameter bolts) and grouted. In the upstream wall, the intersection of two shear zones

formed a wedge block which moved inside the cavern developing wide fractures in the

wall. The distressed area was reinforced with 40 tendons, pre-tensioned to 500 to 800 kN.

The tendons were made of 25 wires, each of 7 mm diameter. Numerical studies showed

stress concentration around the junction which was strengthened using 32 mm diameter,

10 m long pre-tensioned grouted bolts.

While these recommendations were under implementation, fractures developed around

the shear zone A in the downstream wall at the vicinity of bus galleries 2 and 3.

Numerical analysis indicated that the tensile zones extended 15 to 20 m inside the

downstream wall in the vicinity of shear zones and bus galleries1 and 2. As the fractures

extended inside the wall upto 15 m depth, it was decided to provide additional cable

anchors of 20 to 25 m long with a total bearing capacity of 500 kN. These anchors

consisted of three steel strands of 12.7 mm diameter, provided with spacers and grips at

regular intervals. Down stream wall was reinforced with two strands of 16 mm diameter.

Rock reinforcements pattern in roof and side walls of Sardar Sarovar power house is

shown in Fig. 9.

Fig. 9: Rock reinforcement pattern in Sardar Sarovar power house

Roof and Side Walls

Roof reinforcement Support in shear zone


35

4.3 Sanjay Vidyut Pariyojna, H.P.

Sanjay Vidyut Pariyojna is located underground in a hill which runs nearly east-west in

Sungra in Kinnaur district of Himachal Pradesh. Hill is flanked by the river Sutlej in the

South and Bhaba in the North. The size of the powerhouse is 71 m (L) x 20.5 m (W) x

12.25 m (H). The powerhouse capacity is 3x40 MW (Pelton Turbines) operating under a

head of 988 m.

4.3.1 Geology

The site of power house lies on the crystalline rocks belonging to the Jutog Group. The

Jutog formation comprises phylites, carbonaceous schists, sericite mica schists with tiny

garnets, quartz – biotite schists and amphibolites. The site has been explored by a drift

200 m long with its axis running between N35oE and N40

oE cuts across the rocks

belonging to the Jutogs.


The rock pressures have been worked out using various methods and are presented in

Table 16.

Table 16: Rock class and support pressures at Sanjay Vidyut Pariyojna Power House

Method of Classification Augen Gneiss Rock



Very blocky and Seamy(Class 5)

5.34 to 16.8

Bieniawski’s RMR value (Agarwal et. al. 1985)


Stand-up time

44(Poor)

3.03

Immediate Support is required

Barton’s Q value

(Agarwal et. al. 1985)


Pwall

13 (Good Rock)

0.16

0.09


The power house roof was systematically supported using rock bolts and shotcrete in

conjunction with chain link wire mesh. Grouted rock bolts of 25 mm diameter and 6.5 m

in length were installed in the roof arch at 2 x 2 m spacing, with 5 m long bolts in

between these bolts (i.e. again at 2 x 2 m spacing). Based on stereo plotting of joint sets,

critical wedges were identified in the upstream wall. Where such wedge formation was

anticipated, additional bolts of 9 m length were provided at 3 m spacing, and 6 m in

length bolts at 1.5 m spacing.


36

4.4 Baspa H.E. Project, H.P.

Underground power house complex of Baspa Hydro-electric project is located on the left

bank of river Sutlej about 800 m u/s confluence of river Sutlej with Baspa. The power

house cavity of Baspa is 92 m (L) x 18 m (W) x 39.75 m (H). Three pelton turbines and

generating units of 100 MW each have been installed in the underground power house.

Spherical inlet valves of 1.5 m diameter, service bay at one end and control block on the

other end. Transformer Hall cavity 75 m (L) x 13 m (W) x 20.4 m (H) is aligned parallel

to the power house cavity at a distance of 31 m in the downstream direction.

4.4.1 Geology

One central adit has been excavated along the full length (92 m) of the power house

cavity N82oW - S82

oE direction. The rock show a general strike of N10

oE - S10

oW to

N20oE - S20

oW and dip of 45

o in S70

oE - S80

oE direction, whereas in the exposed cliff

face the general strike ranges from N-S to N10oE to S10

oW and dip varies from 45

o to

50o in easterly direction. In the adit quartzite has been met from chainage 0-37 m and 51-

53 m (42.4% length) while quartzite mica schist from 37-51 m and 53-92 m (57.6 %

length). Average Q values are above 4 (Singh et al 1995b) except in the reaches between

17-50 m where average value of Q is 3. Geological section along centre line of Baspa

Power House is shown in Fig. 10.

Fig. 10: Geological section along centre line of Baspa Power House


37


The rock parameters and the rock quality have been presented in Table 17.

Table 17: Rock class and support pressures at Baspa Power House

Method of Rock Classification Description



Massive Rock (Class 3)

0 to 2.39

Wickham’s RSR


78

0.2

Bieniawski’s RMR


Stand-up Time

54-62 (Fair Rock)

1.74 to 2.1


Barton’s Q value (Singh et al, 1995

b)


Pwall

3 to 8 (Fair Rock)

0.66 to 0.92

0.49 to 0.68


Design of excavation was based on two-dimensional finite element analysis, rock support

interaction analysis and wedge stability analysis. Based on these, the roof support system

consisting of 25 mm diameter mechanical anchored, grouted rock bolts at 1.5 x 1.5 m

pattern and 100 to 150 mm thick shotcrete and wire mesh, was provided. Length of rock

bolts was 5 to 6 m in power house and 4.5 m in transformer cavern.

4.5 Yamuna Hydroelectric Scheme Stage II (Chhibro Power House), Uttrakhand

Yamuna Hydroelectric Scheme Stage II in Dehradun district of Uttrakhand, envisages

development of the power potential of river Tons, a tributary of river Yamuna at Ichhari

and its outfall at Dakpathar. The total available drop of 186 m is utilised for power

generation in two stages. Part I utilises a drop of 124 m by the construction of dam at

Ichhari, for diverting water through a 6.3 m long tunnel to an underground power house

at Chhibro (first underground power house) with installed capacity of 4 x 60 MW.

The underground power house at Chhibro comprises a network of cavities for housing the

machines, transformers, turbine inlet valves, control room and to serve as various

operating galleries water conductor system to feed the part II of the project. The main

cavity is 113.2 m long x 18.35 m wide and 32.5 m high and has a circular roof and

vertical sides.

4.5.1 Geology

The power house cavity is located in a stratified limestone band 25 m thick and 200 m

horizontal thickness with minor or thinly bedded slate bands. The rock is closely jointed


38

with numerous shear zones ranging from 2 to 50 cm thick and nearly parallel to the

bedding. A major shear zone lies at a minimum depth of 10 m below the lowest draft tube

level in the power house cavity. The formations dip at about 45o towards N15oW to

N29oW. The cavity is aligned parallel to the strike of rock formations. Geological section

of Chhibro Power House is shown in Fig. 11.


The rock at the site may be classified as stratified limestone closely jointed. The support

pressure as per Terzaghi's classification works out to 4.8-5.1 kg/cm2 (very blocky and

seamy rocks, class 5) and 1-2.0 kg/cm2

(Singh et al 1995)


The roof of the power house has been supported by steel arches and the walls have been

supported by 350 pre-stressed anchors of average length 23.5 m of 600 KN capacity at 2-

5 m spacing and reinforced shotcrete 7.5 cm thick has been used where found necessary.

In the roof R.S. Joists of 250 x 125 mm with cover plates of 250 x 20 mm at top and 150

x 20 mm at the bottom spaced at 25 cm centres have been used as rock support. Backfill

concrete of M150 strength has been used.

Fig. 11: Geological section of Chhibro Power House


39

The side walls of the power house were reinforced by multiple strand pre-stressed,

sheathed cable anchors. Each anchor was made of 16 high tension steel wires (7 mm

diameter), provided with spacers at 1.5 m intervals. The anchor capacity was 450 to 600

kN. Anchors of 35 to 40 m length were installed in 75 mm diameter holes. The spacing

was 4.6 m in horizontal plane and 2.75 m in vertical plane. The steel bearing plates

provided were 150 x 150 x 35 mm at the loading nut end, and 750 x 750 x 16 mm at the

tensioning end, with additional 750 x 750 mm pads made of 75 mm thick shotcrete on

both sides of the anchor. These cable anchors were installed from draft tube operating

gallery (w 5 m) on the downstream side (25 m from power house) and from anchor drift

gallery (w 4 m) and adit to expansion chamber on the upstream side. This is a "single

wire" system where individual wires are stressed to 700 kN load , held for two minutes,

fully released and again stressed, and locked at 500 to 550 kN after 6 months. A total of

445 cables were installed in this way (231 on u/s side and 214 on d/s side). Over the

anchors, 75 mm thick shotcrete was applied, supplemented with chain link mesh and

perfo bolts. Roof and wall supports in Chhibro Power House are shown in Fig. 12.

Fig. 12: Roof and wall supports in Chhibro Power House


40

4.6 Lakhwar H.E. Project, Uttrakhand

Originally, Lakhwar project was planned to envisage the construction of 204 m high

concrete gravity dam across river Yamuna and an underground power house located

inside right abutment of the dam near village Lakhwar about 80 km from Dehradun in

Uttar Pradesh. The power house will have an installed capacity of 3 x 100 MW and shall

utilise a drop of 166 m. Power house cavity of 130 m (L) x 20 m (W) x 43.5 m (H) size

comes almost in line of dam axis. Layout of Lakhwar Power House is shown in Fig. 13.

4.6.1 Geology

At the power house location, the rock types were phylites, slates, shales, quartzites and

limestones of Jaunsar group with moderate to highly jointed basic intrusions of

dolerite/hornblende, and fine to coarse grained rhyolite/trap rock. Nine sets of joints have

been identified in the power house cavern formations. Some joints were slickensided, but

tight: some have mylonite or gouge infilling, or open with 10 mm aperture: dipping water

was present. The rock was traversed at places by quartz or calcite veins. A few shear

zones of 10 cm thickness were present.


The rock pressures and rock classes are presented in Table 18:

Table 18: Rock class and support pressures at Lakhwar Power House



Support Pr. (kg/cm2) Massive to moderately jointed rock (Class 3)

0-2.65

Bieniawski’s RMR


Stand-up Time

63 (Good Rock)

2.09


Barton’s Q value (Singh et al, 1995

b)


8.5 (Fair Rock)

0.35


The power house cavity has been supported on ISMB 250 x 125 mm sets at 0.9 m

spacing (Fig. 14). Supplementary reinforcement was with 20 mm diameter, 3 to 5 m long,

mild steel rock bolts installed at 1.8 m spacing. The bolts were grouted in 40 mm

diameter holes using 1:1 sand-cement slurry, and tensioned (Singh et al 1988). In

addition, 70 mm thick shotcrete was applied in two layers over welded wire mesh (size

100 x 100 x 3 mm diameter wires). For the wedge blocks with safety factor less than 1.5,

additional rock bolting, shotcrete (using M-100 grade) and weld mesh were carried out.


41

Fig. 13: Layout of Lakhwar Power House


42

Fig. 14: Section of steel rib supported arch of Lakhwar Power House


43

For the side walls of the power house, 36 mm diameter, 8 to 9 m long grouted tensioned

bolts were used at 1.5 m spacing, plus 10 cm thick shotcrete over 100 x 100 x 4.2 mm

welded wire mesh. The east face wall was reinforced with 25 mm diameter, 8 m long

expansion shell bolts, post grouted and tightened to 100 kN tension. The bolts were fixed

at an inclination of 15o downwards from horizontal, using bevel washers.

4.7 Chamera H.E. Project, H.P.

Chamera Power Station Stage-I (540 MW) is a run-of-the-river scheme built on river

Ravi, which is a major river of the Indus Basin, originating in the Himalayas from the

Baira Bhanghal branch of the Dhaula Dhar Range. The project utilises the Hydro Power

potential available after the confluence of the river Siul with Ravi. The project was

commissioned in April 1994. The project comprise of a 140 m high, 295 m long concrete

arch gravity dam, a 6.4 km long & 9.5 m dia head race tunnel and Underground Power

House containing 3 units of 180 MW each.

4.7.1 Geology

The powerhouse complex comprising of two caverns viz. the machine hall and

transformer hall and other ancillary components have been excavated in granite gneiss,

carbonaceous phylite, graphitic phylite, limestone, metavolcanics, sandstone, and shale.

The rock formations were intensely folded, with three major thrust zones present. The

power house was located under a cover of 230 m in fine grained metamorphosed andesite

basalt (metavolcanics), blocky to foliated and intersected by five sets of discontinuities of

different orientations. The rock mass was generally 'fair', but poor in foliated crushed

zone. Foliation joints were continuous and undulating and generally moderate to closely

spaced. Most of the joint sets have low persistence. Water seepage in caverns during

excavation was negligible. Geological section of Chamera Project is shown in Fig. 15.


The rock mass classification and support pressures are given in Table 19.

Table 19: Rock class and support pressures at Chamera Power House

Method of classification Description



Blocky to foliated Rock Mass (Class 4)

1.65-5.87

Bieniawski’s RMR


50 (Fair Rock)

3.3

Barton’s Q value (Sharma et al 1994)


Pwall

1.95

1.07

0.62


44

Fig. 15: Geological section of Chamera Project


Flexible support system consisting of combination of rock bolts, anchors and shotcrete

with wire mesh was considered prudent with regular monitoring of excavated section by

instrumentation. Depth of anchors was sufficient to ensure formation of the required zone

of compression. Rock reinforcement in Chamera Power House is shown in Fig. 16.

Fig. 16: Rock reinforcement in Chamera Power House

Rock Bolts 6 m long, 2 x 2 m spacing


45

Based on this design approach, the following support systems were adopted.

• 7.5 m long and 25 mm diameter rock bolts (yield strength 267 KN) on 1.5 m

square grid.

• 6.0 m long and 25 mm diameter rock bolts (yield strength 204 KN), on a 1.5 m

square grid as primary support and longer , 51 mm diameter hollow core anchors,

10.5 m long of 843 KN on a 4.5 m square grid as the secondary support.

4.8 Kadamparai Pumped Storage H.E. Project, Tamilnadu

The project constructed by Tamilnadu Electricity Board in South India has been designed

to meet the peaking requirements of Tamilnadu grid. The project envisages construction

of a dam across the Kadamparai River for forming the upper reservoir and utilisation of

the existing Upper Aliyar Reservoir as a tail pool. The project has an underground

powerhouse of 128.5 m (L) x 20.9 m (W) x 38.0 m (H) size of 400 MW installed

capacity.

4.8.1 Geology

The area encomapssing the Kadamparai scheme is occupied by biotite gneiss intruded by

pegmatites. The gneisses are folded but the folds are generally tight along the water

conductor system. From the Kadamparai dam to the tail race tunnel outlet, granite gneiss

with veins of pegmatite are met with. General foliation of the gneisses varies from NNE -

SSW direction, with dips ranging from 60o to 80

o in the easterly direction. There are three

sets of joints in gneisses.

Set No. Strike of Joint Set Dip

Set 1 N25oW - S25oE 10o-20o in S65o

Set 2 N75oE - S75oW Vertical

Set 3 NE - SW 70o towards SE


Rocks have been classified by Terzaghi's method as moderately jointed (Class 3) with

rock pressure varying from 0-2.84 kg/cm2. By Singh et al 1995, the support pressures

should be 0.7-1.0 kg/cm2.


The arch portion of the roof has been reinforced with 20 mm diameter, 5 to 7 m long

expansion shell mechanically anchored grouted bolts at a spacing of 2 x 2 m,

subsequently grouted to full length using thick cement grout. Additionally 7.5 cm thick

guniting has been carried out over chain link fabric. In view of the occurrence of minor

cracks both in the upstream and downstream walls, the side walls were also reinforced

with similar bolts of 5 - 7 m length supplemented with 7.5 cm thick guniting and chain

link mesh. Rock reinforcement in Kadamparai Power House is shown in Fig. 17.


46

Fig. 17: Rock reinforcement in Kadamparai Power House

4.9 Chukha H.E Project, Bhutan

Chukha hydroelectric project was constructed during 1973 to 1986 across river Wangchu

making use of 468 m head near Chimakothi in Bhutan. It is a run of the river project. The

336 MW power house (4 x 84 MW) located under 230 m rock cover and 40 m laterally

inside the hill, was excavated in granitic rocks.

4.9.1 Geology

The rock mass encountered around the underground power house was granite gneiss and

migmatite with intervening bands and lenses of mica schist, quartzite and amphibolites of

Thimpu series. With and RMR of 70, this rock was expected to be competent and self

supporting for a 25 m span. However, because of the highly jointed and fractured nature

and the occurrence of minor schist bands, the excavations did not stand beyond 6 m.

4.9.2 Rock Classifications and Support Pressures

RMR value of granite gneiss rock mass has been calculated as 70 which correspond to

good class. For this RMR, the support pressure works out to be 0.3 kg/cm2.


47


The roof of the power house 141 m (L) x 24.5 m (W) x 38 m (H) was supported by 4 to 9

m long bolts at 3 to 4 m spacing (Fig. 18). For the walls, wedge analysis was carried out

using three dimensional stereographic method considering the six joint sets, and the

results indicated that the downstream side has a potential unstable blocks. For this, 9 m

and 13.5 m long pre-tensioned grouted rock bolts were used in two rows to prevent

wedge formation (Char et al 1988). Perfo bolts of 25 mm diameter were grouted in 38

mm holes using 1:2 cement mortar. Shotcrete of 100 mm thickness was applied over

chain link wire mesh or hard drawn steel wire mesh. Where practical problems were

experienced for bolt installation in sheared zones, and stand-up time was short, RSJ's of

300 x 140 and 250 x 125 were used at 0.25 to 0.5 m intervals. Wagon drill with auto feed

arrangement were used in the bolting operations. Reinforcement of the power house

cavern at Chukha project is shown in Fig. 18.

4.10 Tala H.E. Project, Bhutan

Tala hydroelectric project has been constructed on river Wangchu in Bhutan. The main

structures include a 92 m high concrete gravity dam, three underground desilting

chambers, a 23 km long & 6.8 m diameter modified horse shoe shaped HRT, a 184 m

high & 15/12 m diameter restricted orifice type surge shaft, two 4 m diameter &1.1 km

long pressure shafts, underground power house to house 6 pelton wheel turbine units of

170 MW capacity each, an underground transformer cavern to accommodate 19

transformers and a 7.75 m diameter & 3.1 km long tail race tunnel to carry the water back

into the river.

Fig. 18: Reinforcement of the power house cavern at Chukha project


48

4.10.1 Power House

The underground power house of 206 m x 44.5 m x 20.4 m size was constructed to house

6 pelton wheel turbine units of 170 MW capacity each and a total installed capacity of

1020 MW. The transformer cavern of 191 m x 26.5 m x 16 m size was constructed

parallel to power house cavern to accommodate 19 transformers.

4.10.1.1 Geology

The geological mapping has indicated that the ridge which houses the machine hall and

the transformer hall cavern, is occupied by fresh and hard, inter banded sequence of

quartzite, phyllitic quartzite, phyllitic with quartzite boudins and amphibolite schist

partings. These rocks are highly puckered and folded into synform and antiform. The

general foliation trend varies from N65oE-S65

oW to N70

oW-S70

oE with 35

o to 60

o

N25oW to N20

oE dips. The plunge of the folds recorded at RD 16m (25

o/270

o), RD 93 m

(18o/56

o), RD 128m (10

o/90

o), RD 143 m (15

o/130

o) and at RD 183m (10

o/88

o). The

joints recorded in the central gullet excavation are given in Table 20.

The long axis of the powerhouse in N37oW-S37oE direction is across the strike of

foliation. Due to folding, the angle between the long axis of powerhouse and the strike of

formation varies from 15o to 55o.

Table 20: Major Discontinuities in Machine Hall Cavern

Sl. No. Strike

Dip Spacing

cm

Continuity

cm

Nature

Foliation N65oE-S65

oW

to N70oW-S70

oE

35o-60

o:

N25oW to N20

oE

10-300 500-1200 Rough

Undulating

J1

N20oW-S70

oE

to N15oW-S75

oE

40o-80

o:

N7oE to N75

oE

100-200 200-500 Rough

Undulating

J2 N-S

to N30oE-S30

oW

25-80:

W to N60oW

5-200 200-1000 Rough

Undulating

J3 N30oE-S30oW

to N20o E-S20

oW

30-50o:

S60oE to S70

oE

6-20 200 Rough

Planner

J4 N50oW-S50E

o

To N30oW-S60

oE

60o-70

o:

S40oW-S60

oW

10-200 200-500 Smooth

Planner

J5 N80oE-S80W

o

to N70oW-S20

oE

40o-70

o:

S10oE to S20

oW

20-200 200-500 Rough

Planner

The rock mass in the first bench has been mostly in class IV with Q values (Grimstad and

Barton 1993) varying from 2.5 to 4 mainly due to bottom effect while rock mass

conditions in the second bench had shown improvement and has been classified mostly in

class III with Q values varying from 4.2 to 10.5. Excavation for third bench (trench) in

progress had shown considerable improvement in rock mass conditions and is in class III.

Collapse of the drill holes in first bench between RD 120-125 m has been observed due to

the presence of quartz veins in the holes.


49

4.10.1.2 Rock Mass Classification and Rock Pressures

During pre-construction stage, the detailed mapping of the drift parallel to the alignment

of machine hall crown matching with its crown revealed maximum stretch falling in fair

category of rock mass though the Q values varied from 0.24 (very poor) to 13.2 (very

good). The geological strength index was computed as 50.

4.10.1.3 Support Actually Provided

Excavation of powerhouse cavern was taken up in conventional drill and blast method

starting with excavation of 7 m wide and 7.5m height central gullet with its invert level at

El 531 m, suiting to the final profile of the cavern. The gullet was supported with 32 mm

dia and 6 m long rock bolts with expansion shell end anchorage at 3 m by 1.5m pattern.

SFRS of 100mm thickness was applied after installation of rock bolts. After the roof

support of central gullet, its widening was taken up first on downstream side followed by

upstream side by keeping a distance of about 20 m between faces of semi-widened

sections. Concurrent supporting in the widened portion was completed with 6 m and 8 m

(6 m + 2 m) long and 32 mm dia rock bolts (alternative) both ways staggered @ 1500

mm c/c along with SFRS of 75 mm-100 mm thick. Sequence and period of excavation in

power house cavern are shown in Fig.19.

Many problems were encountered during crown excavation and finally it was supported

with conventional support system of steel ribs of ISMB 350x140 with 12 mm thick plates

on both the flanges @ 0.6 m c/c in conjunction with 32 mm dia and 8 m/10 m long rock

bolts @ 3 m c/c staggered after collapse of portion of the crown. Having faced collapse

during crown widening, methodology of excavation and support system for benching

operation was reviewed through investigations by a borehole camera, testing for physical

properties of the rock mass and on review 3-D numerical analysis so as to have proper

and smooth benching down of the cavern. Support system review comprises 3 shotcrete

layers of 50mm each and 12m long and 26.5 mm/32 mm diameter Dywidag rock bolts

(with tensile strength equal to 57 tons) @ 1.5 m c/c with 100 mm x 100 mm x 5 mm wire

mesh.

The systematic rock mass excavation with controlled blasting and concurrent support

system during benching down in powerhouse cavern was adopted. Bench depths have

been fixed between 2.5 m to 3.5 m depending upon rock mass conditions. In the first

bench, the rock mass has been excavated by providing central gullet of 6 m width.

Adopting safe blast design in staggered manner, sides through nitches of 3 m sizes were

excavated. As the rock parameters improved with every bench, width of central gullet

was increased to 8 m and opening of sides was done with 6 m long nitches in the second

bench. The lengths of nitches were increased subsequently to 9 m in third bench onwards

to enhance the pace of excavation. During the bench excavation wall support system was

ensured within 48 hours after the excavation except for 5% of the events such as in initial

nitches.


50

EL 538.5

EL 531

EL 528.5

EL 525

EL 521.5

EL 518.5

EL 515.5

EL 513

7m

11-Dec-00 to 23-Mar-01

102 Days

D/s U/s

I II III

05-Apr-01 to 25-Dec-01

264 Days

07-Apr-01 to 15-Dec-01

252 Days

IV

6.5m 7.1m 7.1m

28-May-02 to 17-Oct-02

142 Days

11-May-02 to 30-May-02

19 Days 23-May-02 to 08-Oct-02

138 Days

10m 5.2m 5.2m

19-Aug-02 to 27-Nov-02

100 Days

V

19-Oct-02 to 06-Dec-02

81 Days

12-Sep-02 to 27-Oct-02

45 Days

6.35m 6.35m 8m

07-Oct-02 to 10-Nov-02

34 Days 21-Oct-02 to 18-Nov-02

28 Days

09-Sep-02 to 29-Nov-02

VI

VII

VIII

IX

X

XI

XII

XIII

First Bench

Second Bench

Third Bench

Fourth Bench

Fifth Bench

Sixth Bench

Seventh Bench

Eighth Bench

Ninth Bench

Tenth Bench

11-Dec-02 to 29-Dec-02

18 Days

48 Days

14-Nov-02 to 04-Dec-02

20 Days

07-Nov-02 to 26-Dec-02

49 Days

20-Dec-02 to 17-Jan-03

28 Days

02-Jan-03 to 09-Feb-03

38 Days

31-Dec-02 to 17-Jan-03

17 Days

6.85m 7.0m 6.85m

25-Jan-03 to 24-Feb-03

30 Days

19-Jan-03 to 11-Jan-03

23 Days

26-Jan-03 to 26-Feb-03

31 Days

07-Mar-03 to 23-Mar-

16 Days

23-Feb-03 to 1-Mar-03

6 Days

26-Feb-03 to 28-Mar-03

30 Days

EL 510

EL 507


8 Days

16-Mar-03 to 23-Mar-03

7 Days


8 Days

EL 504

EL 501

(11-May-02 to 17-Oct-02) 159 days

(19-Aug-02 to 29-Nov-02) 102 days

(07-Oct-02 to 06-Dec-02) 60 days

(07-Nov-02 to 29-Dec-02) 52 days

(20-Dec-02 to 09-Feb-03) 51 days

(19-Jan-03 to 26-Feb-03) 38 days

(23-Feb-03 to 28-Mar-03) 33 days

(16-Mar-03 to 31-Mar-03) 15 days

Under Extraction

Under Extraction

Based on investigations by borehole camera, physical properties of the rock mass, and 3-

D numerical analysis for upstream and downstream walls of the cavern, the support

system comprising 12 m long Dywidag rockbolts @ 1.5 m c/c staggered both ways with

wire mesh and 150mm thick shotcrete on the walls has been contemplated for the walls.

Fig. 19: Date wise sequence of excavation of Machine hall.

4.10.2 Head Race Tunnel

The water conductor system of Tala hydroelectric project in Bhutan consist of 6.8 m

diameter modified horse shoe shaped HRT terminating into a 184 m high surge shaft and

then two pressure shafts of 4 m diameter and 1.1 km long each. The entire HRT was

divided into four packages.


51

The total length of HRT has been divided into four packages. Package C-1 comprise of

6.4 km length of HRT from inlet end. Package C-2 consists of 5.0 km length from C-1 to

C-3 packages. Package C-3 comprise of 4.4 km length of HRT between C-2 and C-4

packages. Package C-4 with a length of 7.2 km is the most typical package with regard to

the difficult tunnelling conditions. Because of the poor rock strata, tunnel had to be

diverted from Kalikhola U/S side.

4.10.2.1 Geology

The entire HRT has been excavated through medium to high metamorphic rocks of

Central Crystalline Group (designated as Thimphu formation) of pre-cambrian age in

Eastern Himalayas. The entire head race tunnel was excavated through 11 faces and was

divided into four packages viz. C1, C2, C3 and C-4.

In contract package C-1, hard and massive high grade metamorphic rocks such as biotite-

gneiss, augen gneiss and quartzo-felspathic gneiss have been encountered Excavation

through Padechu adit in contract package C-2 (4997 m), severe geological problems were

faced through highly sheared , weathered and water charged schists and gneisses. The

rock mass in this reach consist of slightly to moderately weathered , highly sheared,

folded, jointed, wet and thinly foliated quartz-biotite-schist with occasional bands of

quartzite and thinly to moderately foliated biotite-gneiss.Excavation in Contract package

C-3 (4430 m), progressed mainly through folded and warped quartz-biotite-schist, biotite-

schist with frequent interbands of biotite gneiss, quartzitic-gneiss and quartzite, dissected

by shears and joints. Stretch between Mirchingchu and surge shaft (Contract package C-4

- 7110 m) faced most difficult geology because of low rock cover, gentle hill slope, deep

cross drainages and almost total absence of rock exposures. Out of 23.2 km length 337 m

length was excavated through extremely poor geological conditions termed as adverse

geological occurrence (AGO) in beyond class VI category. Highly shattered, moderate to

highly weathered, folded interbands of quartzite, amphibolites and biotite schist with 10-

20 cm thick foliation shears water charged strata was encountered which was tackled

with DRESS (Drainage, Reinforcement, Excavation and Support Solution) technique.

4.10.2.2 Rock Mass Classification and Rock Pressures

A 23 km long and 6.8 m diameter HRT at Tala Hydroelectric Project passes through

various rocks classified by Q system developed by Barton et. al. (1974) and further

modified by Grimstad and Barton (1993). The rock classes in all the four contract

packages (Tripathi et al 2003) are given in Table 21.


52

Table 21: Rock classification and support pressures in Tala HRT

Rock Type Method of Rock

Classification

Q Value Class Support

Pressure,

kg/cm2

Contract Package C-1

Massive, very hard

widely jointed

gneisses

Terzaghi's

Classification

Class 3 0-0.93

Barton' Q

Classification

17.5-40 Good to Very

Good

0.39-0.51

5.8-8.7 Fair 0.58-0.87


Hard massive and

moderately jointed

gneisses

Terzaghi'

classification

Class 3 0-0.93

Barton' Q

Classification

1.16-7.0 Fair 1.05-1.9

Squeezing rock Terzaghi'

classification

Class 7

Barton' Q

Classification

Between 0.1

and 0.01

Very Poor to

Extremely poor

2.8-5.7


Moderately blocky

gneisses and schists

Terzaghi'

classification

Class 4 0.88-1.23

Barton' Q

Classification

1.16-6.0 Fair 1.1-1.9


Dry moist gently to

moderately dipping

quartz biotite schist

Terzaghi'

classification

Class 5 1.23-3.85

Barton' Q

Classification

0.8-2.6 Very poor to

poor

1.45-2.17

Squeezing rock

(highly shattered

moderate to highly

weathered folded

interbands of

quartzite,

amphibolite and

biotite 10 -50 cm

thick shears water

charged strata)

Terzaghi'

classification

Class 8 7.35-

15.75

Barton' Q

Classification

0.055-

0.00625

Extremely poor

to exceptionally

poor

5.26-

10.75

4.10.2.3 Support Actually Provided

Resin grouted rock bolts, steel fibre reinforced shotcrete (SFRS) and steel ribs were

provided to support the rock in HRT based on the rock class. The rock support system


53

adopted to support the HRT at Tala hydroelectric project in Bhutan is presented in Table

22.

Table 22: Rock classification and support system for Tala HRT

Rock mass class Designed support Alternate support

Class-I (Very good

rock mass with

Q>40)

Spot bolting (25 φ, 3500 mm long) or

local application of 50 mm SFRS (as

required)

-

Class-II (Good rock

mass with Q=10-40)

Rock bolt (25 φ, 3500 mm long) @ 1750

mm c/c both ways staggered or 50 mm

SFRS from haunch to haunch plus spot

bolting (25 φ, 3500 mm long)

-

Class-III (Fair rock

mass with Q=4-10)

Pattern bolting (25 φ, 3500 mm long),

1750 c/c both ways staggered along with

50 mm SFRS upto spring level.

-

Class-IV (Poor rock

mass with Q=1-4)



100 mm SFRS upto invert level.

Steel ribs ISMB-250 @

750 mm c/c, 50 mm

SFRS and backfill

concrete

Class-V (Very poor

rock mass with

Q=0.1-1)



150 mm SFRS upto invert level.

Steel ribs ISMB-250 @

600 mm c/c, 75 mm

SFRS and backfill

concrete

Class-VI (Extremely

poor rock mass with

Q=0.01-0.1

- Steel ribs ISMB-250 @

500 mm c/c, 100 mm

SFRS and backfill

concrete

Steel ribs of ISMB 250 x 125 @ 0.5 m spacing with bottom struts were installed for

supporting the excavated tunnel in the highly squeezing and extremely poor geological

section termed as adverse geological occurrence (AGO) zone. However, upheaval of the

invert also took place in course of time in this squeezing zone. Because of this upheaval,

bending/cracking of bottom struts also took place (Fig. 20). These struts were replaced

before start of reinforced concrete lining in this zone to avoid any additional loads on

R.C.C. Lining.

4.11 Ramganga Project Tunnels, U.P.

Ramganga dam, 126 m high earth and boulder fill dam has been constructed across river

Ramganga, a tributary of river Ganga. Based upon economical studies and feasibility of

construction of the 1st stage dam for diversion of floods, two tunnels of 9.45 m internal

diameter are constructed in the right abutment of the dam. In order to make maximum

utilisation of the tunnels as permanent works after construction of dam, is over, eastern

tunnel (No. 1) was converted to power tunnel and western tunnel (No. 2) was utilised as

outlet works for releasing water for irrigation requirements when power house is closed

or for emergency dewatering of the reservoir in case of damage to the power house.


54

Fig. 20: Broken bottom strut during upheaval and Repairs

4.11.1 Geology

Tunnels pass through alternate bands of sand rock and clayshales, the latter covering

about one forth of entire length. Tunnels were excavated in favourable geological set up.

Rocks are mostly massive and closely jointed. The bands are highly micaceous and

included thin layers and lenses of hard calcified sandstones. Clayshales are green or

chocolate coulored with thickness varying from 1.5 m to 2.0 m. Rocks are soft and

concretionary in nature. Geological L-section of Ramganga tunnels (1 and 2) is shown in

Fig. 21.


The rocks have been classified under category 5 of Terzaghi's classification with rock

pressures varying between 1.75 and 6.74 kg/cm2 (Gupta et al 1968). As per modified

classification (Singh et al 1995), the support pressure comes out to be 1.0-2.0 kg/cm2.


Full circle ribs of 10.993 m outer diameter made from R.S. Joists 300 mm x 140 mm

were used to support the rock mass. The spacing of ribs varies from 0.61 to 1.2 m

depending upon rock conditions. In tunnel no. 1 which was to be converted to power

tunnel, spacing of ribs were kept as 0.61 m in all reaches except portals. In tunnel no. 2,

rib spacing is 0.61 m to 1.2 m except in reaches near portal having inadequate cover and

the plug and valve chamber reaches where it has been reduced to 0.305 m. Rock

reinforcement in Ramganga tunnels is shown in Fig. 22.

450 mm


55

Fig. 21: Geological L-section of Ramganga tunnels

Fig. 22: Rock reinforcement in Ramganga tunnels


56

4.12 Narmada Sagar Project, M.P.

Narmada Sagar Project near Punasa comprise of 92 m high concrete gravity dam across

river Narmada to divert 2040 cusec of water through 40 to 55 m deep, 450 m long head

race tunnel to feed pressure shafts of 8 m finished diameter to generate 1000 MW (8 x

125 MW) of power in a 55 m deep pit power house and release the tail water back into

the Narmada river through 25-48 m deep 865 m long tail channel.

4.12.1 Geology

The tunnelling media is quartz arenites (quartzites) and ferruginous fine grained

sandstones with the intercalated layers of silt/clay stones. The pressure shafts are aligned

parallel to the general trend of the rocks in N50oE to S50

oW direction. The beds dip by

20o to 35

o towards NNW i.e. towards right abutment with occasional dips of 40o due to

local warping between pressure shafts No. 5 and 8. L-section of pressure tunnels of

Narmada Sagar Project is shown in Fig. 23.

The rock mass has been characterised in three categories as follows:

Category 1 - Quartz Arenites (Quartzites)

Category 2 - Ferruginous Sand Stones

Category 3 - Ferruginous Silt/Clay Stones

Fig. 23: L-section of pressure tunnels of Narmada Sagar Project


The rock mass has been classified as per the available methods and the support pressures

are as per Table 23.


57

Table 23: Rock class and support pressures in pressure shafts of Nadmada Sagar Project

(Mohd. J. Ahmad, 1996)

Method of Rock

Classification

Rock type

Quartz Arenites

(Quartzites), Cat. 1

Ferruginous Sand

Stones, Cat. 2

Ferruginous

Silt/Clay Stones,

Cat. 3

Joint Spacing (m) 0.1 to 0.7 0.1 to 0.3 0.1 to 0.2

Joint Volume Count Between 2 & 8 Between 15 & 20 >40

Compressive strength,

kg/cm2

622-143 496-762 126-203

Tensile Strength,

kg/cm2

99-148 30-73 43-64


Support Pr., kg/cm2

Widely to Moderately

Jointed (Class 3)

Closely to

Moderately Jointed

(Class 4)

Closely to Very

Closely Jointed

(Class 5)

0-1.2 0.9-6-1.7 1.7-5.2

Deere's Method, RQD

Support Pr., kg/cm2

95 (Excellent) 57 (Fair) <25 (Very Poor)

0-0.7 1.43-3.1 4.77-6.68

Bieniawski's RMR

Support Pr., kg/cm2

75 Good to Very

Good

47 (Fair Rock) 20-26, Poor Rock

0.6 1.25 1.83

Barton's Q Values

Support Pr., kg/cm2,

Proof

Pwall

21.1 9.5 0.83

0.42 0.54 1.64

0.25 0.40 1.21


Rock bolts of 20 mm diameter expansion shell type 4 to 5 m long at 2 m spacing of

variable depths restricting the bottom level of about 0.5 m above crown level have been

used to support the rock. Bolts are grouted and tensioned to 60% of yield strength i.e.

about 8 to 10 tonnes. Permanent steel half supports (ISMB 300) at 1 m spacing in the

crown portion by cutting haunches at the spring level backfill concrete. Section showing

actual class of rock and support system is shown in Fig. 24.

4.13 Giri Project Head Race Tunnel, H.P.

Giri hydel project is situated in Himachal Pradesh across rive Giri having an installed

capacity of 60 MW (2 x 30 MW). Besides this, there is 160 m long barrage and an intake

regulator. The water conductor system of the project comprise of a concrete lined tunnel

7.12 km long with a circular finished diameter of 3.6 m and passes under the ridge

separating the Giri and Bata Valleys.


58

Fig. 24: Section showing actual class of rock and support system

4.13.1 Geology

The tunnel passes through various types of rocks namely slate/phyllites interbedded with

quartzites, shales of various shades, limestone conglomerates and sandstones of various

grades. The most important feature from the engineering geology view point was the

occurrence of three thrusts lying in the close proximity to one another. Tunnel crosses

two major regional thrusts (Viz. Krol and Nahan) which were considered most

problematic zones for tunnelling operations.

Along the tunnel alignment, the strata changes to claystones and siltstones which are

highly jointed and deteriorate on saturation with water. The material in vicinity of faults

is highly saturated, soft and plastic. However, near the outlet of the tunnel, the strata

generally comprise of sandstones and siltstones. Geological L-section of Giri Project

HRT is shown in Fig. 25.

Fig. 25: Geological L-section of Giri Project HRT


59


The rock mass has been classified as per the available methods and the support pressures

are as per Table 24.

Table 24: Rock class and support pressures in Giri HRT

Method of Rock Classification Rock type

Slates Phyllites


Support Pr., kg/cm2

Very Blocky and Seamy

(Mild Squeezing), Class 7

Crushed Phyllites (Highly

Squeezing), Class 8

2.4-4.6 6.1-11.6

Deere's Method, RQD

Support Pr., kg/cm2

5-25 5-25

1.88-3.12 60.75 (Upto 75 m rock)

Bieniawski's RMR

Support Pr., kg/cm2

38, Very Poor 25, Very Poor

0.7 0.84

Barton's Q Values (Jethwa et al 1982)

Support Pr., kg/cm2

0.51 0.12

2.4 3.4


Horse shoe shaped steel sets with bottom struts were used to support the rock. Two steel

sections viz. 150 x 80 mm and 150 x 150 mm have been used with varying spacing given

in Table 25.

Table 25: Rib support systems in Giri HRT

Rib Section Spacing Capacity in Tonnes (Fibre Stress = 2500 kg/cm2)

150 x 80 1.0 65

150 x 80 0.5 65

150 x 80 0.33 65

150 x 150 1.0 100

150 x 150 0.5 100

4.14 Uri Project, J & K

Uri hydroelectric project is situated 75 km west of Srinagar in Baramullah district. The

project is run of the river scheme with 20 m high barrage across Jhelum River near

Village Bunyar. Project comprise of 8.4 m finished diameter & 10.5 km long horse shoe

shaped HRT; 22 m diameter & 75 m high underground surge tank; 5 m diameter twin

vertical pressure shafts; an underground powerhouse of 4 x 120 MW capacity operating

under a gross head of 260 m and finally a 2 km long tail race tunnel for discharging the

water back to the river Jhelum near Uri town.


60

4.14.1 Geology

The overall rock mass is fairly hard but intensely folded, faulted/sheared leading to

various degree of fracturisation. The general foliation trend varies from N60oE - S60oW

to EW with 70o to 90o dips mostly in northerly direction. Quartzitic schist was found to

be hard, compact with some softer and very closely foliated phylitic zones in between.

On other hand, Panjal Volcanoes found in the rest part of tunnel are greenish grey and

well foliated with more frequency of schistose zones. Bieniawski's rock mass

classification has been slightly modified to categorise the prevailing rocks (Sharma et al

1995). Geological section along HRT and TRT of Uri Project is shown in Fig. 26.

Fig. 26: Geological section along HRT and TRT of Uri Project


The rock mass classification and support pressures are presented in Tables 26 and 27.

Table 26: Rock classification at Uri Project HRT (Sharma et al, 1995)

Rock

Type

Tunnel

Length, %

Rock Mass RMR

Value

Description

I 1.8 Good Rock >61 Massive blocky, partly foliated competent hard

rock

IIA 17.8 Fair Rock 51-60 Jointed, fractured, thinly foliated, competent and

hard. Foliation perpendicular to tunnel

IIB 60 Fair Rock 41-50 Rock Mass as that of IIA but foliation parallel to

tunnel

IIB 6.6 Fair Rock

(High Stress)

41-50 As that of IIB with high stress

III 13 Poor rock 21-40 Fractured or thinly foliated of low to medium

strength

IV 0.8 Very Poor

rock

<20 Crushed or shattered with clay & gauge material or

weathered rock


61

Table 27: Rock class and support Pressures in Uri Project HRT

Method of Rock Classification Rock type

Cat. I Cat. II


Support Pr., kg/cm2

Moderately blocky and

seamy, Class 4

Completely crushed but

chemically inert, Class 6

0.6-1.7 5.2

Bieniawski's RMR

Support Pr., kg/cm2

41-60, Class III, Fair Rock 21-40, Class IV, Poor Rock

0.95-1.4 1.43-1.90

Barton's Q Values

Support Pr., kg/cm2

2.0 0.21

1.06 2.24


The support system provided in the head race tunnel corresponds to both the RMR and Q

systems. The supports provided in the HRT are as follows:

Cat. I - 3-4 m long bolts (grouted) at 2 m spacing + fibre reinforced shotcrete 6 cm thick

Cat. II - 4 m long bolts at 1.5 m spacing and 10 cm thick fibre reinforced shotcrete.

Special support measures by shotcrete arches in crushed or graphic zones in Uri Project

HRT are shown in Fig. 27.

4.15 Loktak H.E. Project, Manipur

Loktak hydroelectric project in the eastern Himalayas is situated 39 km south of Imphal,

the capital city of Manipur state. It envisages diversion of 42 cumecs of water from

Loktak lake formed due to construction of a barrage across Manipur river with a gross

head of 312 m for generation of 105 MW (3 x 35 MW) of power. The water conductor

system is 10.27 km long and consists of 2.27 km long open channel, a 1.22 km long &

5.0 m diameter horse shoe shaped cut and cover section and a 6.5 km long & 3.81 m

diameter horse shoe shaped HRT.

4.15.1 Geology

The head race tunnel passes through lake sediments, terrace deposits and rock units of

Disang group. The lake sediment is constituted by silt, sand and pebbles of variable

proportions. The terrace material contains broken rock fragments and large size boulders

in addition to silt and sand fractions. The rocks are mainly sandstones, shale and

siltstones. The sandstone is predominant rock and more abundantly exposed.

Along the tunnel, the rock shows three generation folding. The ground water in the hilly

area has been observed to circulate within the weathered mantle and open fractures in

rock and emerges out as springs. The majority of these springs emerge much above the


62

tunnel grade and are principal source of water for streams draining the hill slopes.

Geological section of Loktak Hydel tunnel is shown in Fig. 28.

Fig. 27: Special support measures by shotcrete arches in crushed

or graphic zones in Uri Project Head Race Tunnel

Fig. 28: Geological section of Loktak Hydel tunnel


63


The rock pressures and rock mass classes are presented in Table 28.

Table 28: Rock class and support pressures in Loktak HRT



Support Pr., kg/cm2

Highly Squeezing (Class 8)

6.1-11.6

Deere's Method, RQD

Support Pr., kg/cm2

5-25 (Highly Squeezing)

Very Very High, Upto 75 m of rock

Bieniawski's RMR

Support Pr., kg/cm2

Stand-up Time

10 (Very Poor)

1.17

Immediate Collapse

Barton's Q Values (Jethwa et al 1982)

Support Pr., kg/cm2, Proof

Pwall

0.023 (Very Poor Rock)

4.7

4.7


The following supports have been provided in the head race tunnel:

• 3 m long bolts with a flexible shotcrete lining with wire mesh is provided as

temporary or immediate support

• Finally steel sets of 150 x150 mm size embedded in 30 cm thick M250 cement

concrete lining was provided as permanent support.

In this case no gap was left between shotcrete lining and steel supports. The steel

supports were designed to take entire squeezing rock pressure. Details of rock support in

Loktak Hydel tunnel are shown in Fig. 29.

4.16 Salal H.E. Project, J & K

Salal hydroelectric project is situated around 120 km south of Jammu in J & K state. The

tail race tunnel of the project consists of 12 m diameter & 2.6 km long horse shoe shaped.

TRT passes through various grades of dolomites of Lower Himalayas. While tunnelling,

no frequent tunnelling problems were encountered except a major collapse with water

inrush and gougy material. Tunnel was monitored by installation of load cells and closure

studs for evaluating steel supports.


64

Fig. 29: Details of rock support in Loktak Hydel tunnel

4.16.1 Geology

The tunnel is aligned through single litho-unit of dolomite rocks. Since the site is located

in the close proximity of the Main Boundary Thrust (MBT), the dolomites are highly

jointed. The geological cross section shows the anticlinal fold with its axis trending

NNW-SSE. At inlet side, the dolomites generally strike N80oE - S80

oW with dip 50

o-60

o

towards NNW-North and at outlet side strike NE-NW with dip of 45o-60

o. The

orientation axis of the tunnel is N20o. The dolomites exposed in the area have been

divided in various categories based on their physical behaviour, extent of crushing,

shearing, number of joints and their spacing (Goel et al 1996). Geological L-section

along TRT II of Salal Hydel Project is shown in Fig. 30.

Fig. 30: Geological L-section along TRT II of Salal Hydel Project


65


The rock pressures and rock mass classes are presented in Table 29.

Table 29: Rock class and support pressures in Salal TRT

Method of Rock

Classification

Rock Type

Blocky & cherty

dolomites

Highly jointed

dolomites

Crumbly and sheared

dolomites


Support Pr., kg/cm2

Massive moderately

jointed (Class 3)

Very Blocky and

seamy (Class 5)

Squeezing at moderate

depth (Class 7)

0-1.59 2.23-7.0 7-13.4

Bieniawski's RMR

Support Pr., kg/cm2

47 (Fair) 32 (Poor) 15 (Very Poor)

1.7 2.2 2.7

Barton's Q Values (Goel et

al 1996)


1-2.3

0.17-0.22 0.02

1.1 2.3 4.4


For grade II and III rock masses, steel supports with concrete backfill has been used ass

the primary support, whereas in grade I rocks, no support or spot bolting as primary

support has been used. Mainly four sections of steel have been used in the tunnel.

Capacity of these sections in case of TRT II with varying spacing of steel ribs are given

in Table 30. Capacities of steel rib support can be increased or decreased by changing the

spacing of steel ribs. ISMB 300 x 140 mm has been used in grade III rocks with their

spacing as 0.5 m. Section of Salal Hydel Project TRT showing rib support is shown in

Fig. 31.

Table 30. Supports provided in Salal TRT

Steel Rib Section Cross- Sectional

Area, cm2

Support Capacity for Spacing, MPa

0.5 m 0.7 m 1.0 m 1.3 m

ISMB 200 x 200 47.54 0.39 0.28 0.19 0.15

ISMB 300 x 140 56.26 0.47 0.33 0.23 0.18

ISMB 250 x 125 42.02 0.35 0.25 0.17 0.13

ISMB 300 x 150 48.08 0.399 0.285 0.199 0.15

4.17 Yamuna Hydroelectric Scheme, Stage II, Part I

Yamuna hydroelectric stage II, part I comprise of a diversion dam at Ichhari, a head race

tunnel and an underground power house at Chhibro. The head race tunnel of circular

section comprise of 7.0 m finished diameter and 6.1 km long.


66

Fig. 31: Section of Salal Hydel Project TRT showing rib support

4.17.1 Geology

The rock type comprise of slates interbedded with limestones. The limestones belonging

to Bansa stage of Chandpur are hard and tough, whereas the limestones of Dhaira stage of

the Mandhalis are relatively sift and interbedded with slates. The alignment of the tunnel

is N60oW to S60

oE direction, which is almost at right angle to the regional strike of local

variations. Geological L-section of Ichhari-Chhibro HRT is shown in Fig. 32.

Fig. 32: Geological L-section of Ichhari-Chhibro HRT


67


The rock load varies between 0.25 B to 0.5 B as per Terzaghi's rock classification. A rock

load of 0.375 B (0.7 kg/cm2) has been taken for the design of supports. The rock

pressures by modified classification by Singh come out to be between 0.4 to 0.7 kg/cm2.


For supporting the rock load, steel supports of ISMB 250 x 125 mm size at a spacing of

1.5 m have been provided. In greater part of the tunnel, the support was not required.

Rock bolts have been provided for jointed rocks. Adopted rock support for Ichhari -

Chhibro HRT is shown in Fig. 33.

4.18 Yamuna Hydroelectric Scheme, Stage II, Part II

Yamuna hydroelectric stage II, part II in Outer Himalayas envisages utilisation of 64 m

drop available between tail race of Chhibro underground power house and power house

of Khodri. Chhibro-Khodri tunnel 5.6 km long and 7.5 m finished diameter is constructed

to carry water from Chhibro power house for generation of 120 MW of power.

Fig. 33: Adopted rock support for Ichhari - Chhibro HRT

4.18.1 Geology

Chhibro-Khodri head race tunnel passes through Nahans constituted of bands of

sandstones, siltstones and claystones from Khodri end in about 3.0 km length. From

Chhibro end, the tunnel passes through Mandhalis consisting of quartzites and slates in a

length of about 2.3 km. In between these two formations about 300 m, length thrust zone

bounded by Krol and Nahan thrusts and comprising of crushed, sheared and highly


68

brecciated red shales and subathu clay has been met along the tunnel alignment.

Geological L-section of Chhibro Khodri HRT is shown in Fig. 34.

Fig. 34: Geological L-section of Chhibro Khodri HRT through Intra-Thrust Zone of

Kalawar


The rock mass classification and the support pressures are as given in Table 28.

Table 31: Rock class and support pressures in Chhibro-Khodri HRT

Method of Rock

Classification

Rock type

Red Shales Black clays


Support Pr., kg/cm2

Moderately squeezing, Class 7 Moderately squeezing, Class 7

4.08-7.79 4.08-7.79

Deere's Method, RQD

Support Pr., kg/cm2

<25 (Very Poor) <25 (very poor)

3.71-5.19 3.71-5.19

Bieniawski's RMR

Support Pr., kg/cm2

17, Very Poor 7, Very Poor

1.54 1.73

Barton's Q Values

(Jethwa et al 1982)


Pwall

0.05 (Extremely Poor)

0.022 (Extremely Poor)

3.5 7.0

3.5 7.0


Heavy steel supports of size 300 x 140 mm RS joists with cover plates of size 250 x 20

mm welded in the outer and inner flange of RS joist placed at 0.35 m centres and rigid

backfill has been used to support the tunnel. Sequence of excavation and support for

Chhibro - Khodri HRT through Intra-Thrust Zone of Kalawar is shown in Fig. 35.


69

Fig. 35: Sequence of excavation and support for

Chhibro - Khodri HRT

4.19 Maneri Bhali Hydel Project, Stage I, U.P.

Maneri Bhali hydroelectric project stage I has been constructed across the river

Bhagirathi. Maneri Bhali stage I project in the middle Himalayas has 8.36 km long &

4.75 m finished diameter circular HRT. In case of Maneri Bhali, Stage II, the tunnel is 16

km long and 6.0 m finished diameter horse shaped.

4.19.1 Geology

The tunnel passes through heterogeneous rock formations represented by the

metavolcanoes, basic intrusives (epidiorites), quatrzites, slates, phyllites, limestones,

sandstones, shales and even consolidated sand, soil clay siltstones and bed material

deposit. The gneisses and granites exhibit sheared and weathered phyllites at thrust

contacts. Apart from this, squeezing ground was encountered for a length of about 350 m.

Geological L-section along Maneri Bhali Hydel Scheme Stage I - HRT is shown in Fig.

36.


70

Fig. 36: Geological L-section along Maneri Bhali Hydel Scheme Stage I - HRT



Table 32: Rock class and support pressures in Maneri Bhali Stage I, HRT

Method of Rock

Classification

Rock type

Moderately

fractured quartzites

Foliated

metabasics

Sheared

metabasics

Highly fractured

quartzites


Support Pr., kg/cm2

Rock Class 4 Rock Class 4 Rock Class 6 Rock Class 7

0.3-0.8 0.3-0.8 2.77 2.77-5.29

Deere's Method, RQD

Support Pr., kg/cm2

75 (Fair to Good) 82, Good Rock 60, Fair Rock 60, Fair Rock

0.48 0.36-0.72 0.72-1.56 0.72-1.56

Bieniawski's RMR

Support Pr., kg/cm2

58 (Fair rock) 59, Fair rock 49, Fair rock 38, Poor rock

0.61 0.60 0.74 0.90

Barton's Q Values

(Jethwa et al 1982)

Support Pr., kg/cm2,

Proof

Pwall

3.0-6.0

3.4-6.8 0.3-3.3 0.5

0.5-0.7 0.5-0.7 0.7-1.8 1.6

0.1-0.2 0.1-0.2 0.2-1.2 1.1


Maneri Bhali HRT has been provided with ISMB 250 x 125 steel rib supports.

Depending upon the type of rock quality, the rib spacing has been varied from 50 cm to

120 cm. Steel rib supports of 150 x 150 mm has also been used at a spacing of 120 cm for

rock load of 0.375 B and 80 cm for rock load 1.0 B, respectively. Rock support system

adopted in Maneri Bhali Hydel Scheme Stage I - HRT is shown in Fig. 37.


71

Fig. 37: Rock support system adopted in

Maneri Bhali Hydel Scheme Stage I - HRT

4.20 Khara Hydel Project, U.P.

The project lies within Shivalik formation of tertiary ages. However, the tunnelling is

confined to Upper Shivaliks. Two twin tunnels of 6 m diameter and 1.2 km long each are

located on the left bank of Yamuna river near Paonta Sahib.

4.20.1 Geology

The tunnels pass through weakly compacted and erratically distributed calcareous and

argillaceous boulder conglomerates of Shivalik formation. The conglomerates in the area

are represented by boulder to granular size fragments of various shapes of quartzite,

sandstone, schist and gneisses. Two types of conglomerates have been identified within

the tunnels site namely calcareous and argillaceous. Geological section along Khara

project tunnels is shown in Fig. 38.

Fig. 38: Geological section along Khara project tunnels


72



Table 33: Rock class and support pressures at Khara Hydel HRT

Method of Rock

Classification

Moderately fractured

quartzites

Foliated metabasics Sheared metabasics


Support Pr., kg/cm2

Massive to distinctly

jointed (Class 2)

Moderately

squeezing (Class 7)

Moderately Blocky

(Class 4)

0.92 3.5-6.8 0.5-1.3 (Saini et al 1985)

Deere's Method, RQD

Support Pr., kg/cm2

75 (Good rock)

1.48

Bieniawski's RMR

Support Pr., kg/cm2

67 (Good rock)

1.22

Barton's Q Values (Saini

et al 1985)


5 (Fair rock)

0.022 (Extremely

poor)

0.05 (Extremely poor)

0.4 3-3.5 0.7-1.7


In Khara HRT, ISMB 250 x 125 mm size steel rib support have been provided at varying

spacing from 375 mm to 750 mm where the rock cover is less than 3D and in reaches

where the rock cover is more than 3D, the same ribs have been used at 500 mm spacing.

Tie rods of 20 mm diameter bars have also been used. Steel rib supports adopted in Khara

project tunnels are shown in Fig. 39.

Fig. 39: Steel rib supports adopted in Khara project tunnels


73

4.21 Tehri Hydroelectric Project, U.P.

Tehri dam project, across river Bhagirathi, has been constructed with a 260 m high

rockfill dam and underground power house in two stages. The underground works mainly

comprise of diversion tunnels, two on each bank, four HRT's and underground

powerhouse complex. The diversion tunnels of 11.0 m diameter horse shoe shaped are

designed to pass a routed construction stage flow of nearly 7500 cumecs.

4.21.1 Geology

The rock type in tunnels T1 and T2 comprise of grade II and II whereas in tunnels T3 and

T4, phyllites of grade I, grade II and grade III in about 30%, 60% and 10% of the tunnel

length, respectively, have been encountered. Geological sections along left bank and right

bank Tehri dam diversion tunnels are shown in Figs. 40 and 41.

Fig. 40: Geological section along left bank Tehri dam diversion tunnels

Fig. 41: Geological section along right bank Tehri dam diversion tunnels


74



Table 34: Rock class and support pressures in Tehri Dam Diversion Tunnels

Method of Rock

Classification

Description of rock

Phyllites grade I Phyllites grade II Phyllites grade III


(Singh et al 1995)

Support Pr., kg/cm2

Massive Phyllites

(Class 3)

Moderately Blocky

phyllites (Class 4)

Phyllites with argillaceous

material bands (Class 5)

0-1.8 0.73-2.04 2.22-7.00

Deere's Method, RQD

Support Pr., kg/cm2

50-75 (Fair rock) 50

0.95-1.90 4.13-6.36

Barton's Q Values

(Jethwa et al 1982)


--

0.8

0.25-2.00 1.2


The supports actually provided for various classes of rock are summarised in Table 35.

Rock support and construction sequence in Tehri dam diversion tunnels is shown in Fig.

42.

Table 35: Actual support systems provided in Tehri Diversion Tunnels

Rock Type

Grade I Grade II Grade III

Alternate I Alternate II

25 mm diameter

bolts 3 m deep at 90

cm centres with 10

cm thick shotcrete

15 cm thick

shotcrete

without rock

bolts

ISMB 150 x

150 (34.6

kg/m) at 50-

75 cm centres

Steel supports of ISMB

300 x 140 (44.2 kg/m) at a

spacing of 95 mm centres

with plates of 250 x 10 mm

on both flanges

4.22 Bodhghat Hydel project, M.P.

The water conductor system of Bodhghat hydel project in Madhya Pradesh consists of a

13 m diameter and 2.8 km long HRT, 450 m long penstocks. The HRT cuts the transverse

hills within the loop of Indravati River and it intersects high ridges and saddles trending

along NW-SE direction. The penstocks are located in south western slopes of the hill

ranges with the power house pit away from the toe of the hill in a gently undulating

terrace.


75

Fig. 42: Rock support and construction sequence in Tehri dam diversion tunnels

4.22.1 Geology

The area is occupied by tightly folded sequence of metamorphic rocks - phyllites and

quartzites. The joints are spaced at 15-30 cm apart and their surfaces are plane, smooth

and coated. Rough surfaces are rare. Some incipient planes of weaknesses along which

movement of the rock masses have taken place, occur in the form of axial shear stresses

and faults. The tunnelling media have been classified into four categories for the purpose

of support system as follows:

• Blocky structure in quartzite, metabasics (40% which include schistose quartzite

and massive variety of approximately 10%.

• Layered structure in phyllite, schist (35%) which includes their variants as

quartzitic phyllite, quartz sericiteschist.

• Fractured structure in weathered zone and closed jointed reaches (10%).

• Loosened structure along shear zones (15%).

Geological plan and section of water conductor system of Bodhghat project is shown in

Fig. 43.


76

Fig. 43: Geological plan and section of water conductor system of Bodhghat project


The rock mass has been classified as RMR and Q systems (Ghosh et al 1985) and support

pressures have been presented in Table 36.

Table 36: Rock class and support pressures in Bodhghat Hydel Tunnel

Method of Rock

Classification

Rock type

Metabasics Quartzite Phyllites


Support Pr., kg/cm2

Blocky and seamy zones, Class 4 Layered structure Class 5

0.8-2.4 2.4-7.4

Deere's Method, RQD

Support Pr., kg/cm2

Av. RQD>50, fair rock

2.1-4.56

Bieniawski's RMR

Support Pr., kg/cm2

96, Class I, Very good rock 69, Class II, Good rock

0.14 1.1

Barton's Q Values


Pwall

19.8 (Good) 8.8 (Fair)

0.25 0.65

0.15 0.48


77

5.0 OBSERVED SUPPORT PRESSURES

The case studies of tunnels for which the actual supports provided were available, support

pressures accommodated were determined using the following equations:

lc

bf

sbmxSS

TP = for rock bolts ….. (15)

( )

−−= −

2

2

. 12

i

ciconcc

scmxr

trP

σ for shotcrete ….. (16)

( )

−

+−+

=

θθ

σ

cos12

32

3

xtrxAISr

IAP

bissi

ysss

ssmx

for steel supports ….. (17)

Where

Psbmx = Maximum support pressure accommodated by rock bolts.

Tbf = Ultimate load of bolts from pull out tests

Sc = Circumferential rock bolt spacing

Sl = Longitudinal rock bolt spacing

Pscmx = Maximum support pressure accommodated by shotcrete

σc-conc = Uniaxial compressive strength of concrete or shotcrete

ri = Internal radius of opening

tc = Thickness of shotcrete

Pssbmx = Maximum support pressure accommodated by steel supports

x = Depth of section of steel set

As = Cross sectional area of steel set

Is = Moment of inertia of steel section

σys = Yield strength of steel

S = Steel set spacing along tunnel axis

θ = Half angle between blocking points

tb = Thickness of block

Instrumented data for support pressures or rock loads was available in some of the

tunnels. These observed support pressures have also been presented in Table 36 along

with the accommodated support pressures.


78

Table 36: Support pressures accommodated by actual supports and observed by

instrumentation

Sl.

No.

Name of the project Rock type Accommodated

support pressure by

actual supports,

kg/cm2

Observed

support

pressure,

kg/cm2

1 Ramganga Project -

Tunnels

Sand rock & clay shale 3.41-6.71 -

2 Narmada Sagar Project -

Pressure shafts

Quartzite 4.59 -

3 Giri Project - HRT Slates (Squeezing) 5.29-16.04 2.0

Phyllites (Squeezing) 1.7

4 Loktak Project - HRT Sandstone, shale and siltstone - 5.4

5 Uri project - HRT Quartzitic schist 2.70 -

Panjal volcanoes 4.54 -

6 Salal Project - TRT Sheared dolomite 4.71 1.1

7 Yamuna Stage I, Part I -

HRT

Shales with bands of quartzite

& limestones

3.24 -

8 Yamuna Stage II, Part II -

Chhibro Khodri HRT

Red shales 17.17 10.8

Black clays 3.2

9 Maneri Bhali Project -

HRT

Moderately fractured

quartzites

11.30 0.6

Foliated metabasics 8.48 0.8

Sheared metabasics 6.59 2.0

Highly fractured quartzites 15.82 -

10 Khara Project - HRT Phyllites 7.89 -

Argillaceous conglomerates 15.77 0.75-3.0

Calcareous conglomerates 11.83 -

11 Tehri Project, diversion

tunnels

Phyllite Grade I 4.83 0.25

Phyllite Grade II 5.38 0.52

Phyllite Grade III 3.51 1.24

12 Tala Project - HRT Highly shattered, moderate to

highly weathered, folded

interbands of quartzite,

amphibolites and biotite

schist (highly squeezing)

6.0-7.0 upto 17.08

6.0 COMPARISON OF ROCK CLASSIFICATION METHODS

Various rock mass classification methods have been used to classify rock mass and at

various hydro power projects in India and Bhutan. In old projects rock classification and

supports in these projects were based upon Terzaghi’s method of rock classification

which recommends steel rib arch supports. This method is too much conservative as it

anticipates high rock loads which results to heavy supports leading to wastage of time,

material and funds. With advancement in developments, systematic rock classifications

came into existence.


79

Deere’s method was the first systematic approach in this direction. Wickham’s RSR

concept was the first complete rock mass classification system with introduction of rating

system. The classification systems developed by Bieniawski (RMR) and Barton (Q

System) takes into account various rock mass parameters. These classification systems

have been adopted world wide including India. Although these methods contain a few

case histories of Himalayan Rocks, these systems have been successfully applied in

various projects in India. Sometimes these methods need a slight modification as RMR

method was adopted in Uri Project in Jammu and Kashmir. It would be better to combine

experience and techniques for better results. As visual observations are applied in

evaluation of Q and RMR, therefore field experience plays as a key role in classification

of rock mass as well as in selection of supports.

With regard to support pressures, RMR and Q systems seem to be in close agreement

with observed support pressures whereas all the other methods give high anticipated

support pressures. Though correlations between different rock classifications i.e. RSR,

RMR and Q in particular exist for calculating the support pressures, but actual support

pressures from instrumentation is advisable.

Apart from rock classification, Q system provides thumb rules for selection and the

extent of supports and charts are available. These supports can be simulated with

numerical methods. In view of the wide range of case histories and subsequent

modifications in Q system since its inception, it can be used with more confidence. Q

system incorporates the latest developments in construction of underground structures

such as tunnelling methods whether boring or TBM tunnels, recent rock support concepts

such as flexible reinforced shotcrete arches in place of conventional heavy and rigid steel

supports etc.

RECOMMENDATIONS

Even though the developments have taken place in the field of rock engineering, the rock

support classification approach as well as the support system design is empirical. Hence,

the available classification systems need to be dealt carefully. These classifications were

not intended to replace analytical studies, field observations and measurements. The

judgement of the field geologists and the engineers is more significant. Although

guidelines for support systems exist, but the final decision should be taken by the site in-

charge regarding the nature and extent of support systems. Himalayan rocks are posing

different problems which need to be dealt with experience. Exploration during the

detailed project report (DPR) stage helps in assessment of geological strata to be

encountered. Therefore, holes should be drilled at regular intervals along the tunnel

alignment and at critical locations so that detailed geological information can be

gathered. Instrumentation should be made an essential part in underground excavations.

Instrumented data can be used to study the behaviour of structures in and on rock. In the

light of the above, RMR and Q systems seems to have some advantages over other


80

methods for use in rock classifications, but rock supports determined recommended by

these methods should be validated through numerical modelling methods also.

REFERENCES

Agarwal K.B., Singh Bhawani, Swami Saran, Jain P.K., Chandra S., Awasthi A.K. and

Prem Dayal (1985), "A case study with reference to Geotechnical Aspects for an

underground power house of Sanjay Vidyut Pariyojna - Bhaba", University of Roorkee,

Roorkee

Ahmad, M.J. (1996), "Rock mass improvement and support systems for pressure tunnels

- Narmada Sagar project, Distt. Khandwa, M.P.", Recent Advances in Tunnelling

technology, New Delhi, pp 275-280

Barton, N, Lien, R. And Lunde, J. (1974). Engineering classification of Rock Masses for

the Design of Tunnel Support, Rock Mech. Vol. 6, No. 4, pp. 189-236.

Barton, N. (1988). Rock mass classification and tunnel reinforcement selection using Q-

system”, Proc. Symp. Rock Class. Eng. Purp., ASTM 984, Philadelphia, pp. 59-88.

Baczynski, N. (1980) “Rock mass characterization and its application to Assessment of

unsupported underground Openings”, Ph.D. thesis, University of Melbourne, pp.233.

Bhasin R., Barton N., Grimstad E. and Chryssanthakis P. (1996a), "Engineering

geological characterisation of low strength anisotropic rocks in Himalayan Region for

assessment of tunnel support", Recent Advances in Tunnelling technology, New Delhi,

pp 157-181.

Bhasin R.K., Singh R.B., Dhawan A.K. and Sharma V.M. (1996b), "Geotechnical

evaluation and review of remedial measures in limiting deformations in distressed zones

in a power house cavern", Conference on design and construction of underground

structures, New Delhi, pp 145-161.

Bieniawski, Z. T. (1973), “Engineering classification of jointed rock masses

transactions”, South African Institution of Carl Engineers, Vol. 15, No. 12, pp. 335-344.

Bieniawski, Z.T. (1976), "Rock mass classification in rock engineering", Proceeding

Symposium on Exploration for Rock Engineering, ed. Z.T. Bieniawski, A.A. Balkema

Rotterdam, pp. 97-106.

Bieniawski, Z.T. (1979), "The geomechanics classification in rock engineering

applications", Proc. 4th Int. Congress Rock Mech. , ISRM, Montreaux, A.A. Balkema ,

Rotterdam , Vol. 2 , pp. 51-58.


81

Bieniawski, Z.T. (1989), "Engineering rock mass classifications", John Wiley and Sons,

New York, 251p.

Char S.A., Menon K.K. and Sood P.K. (1988), "Geotechnical aspects affecting the design

and construction of underground structure for Chukha hydroelectric project", Proc. ISRM

Symp. Rock Mech. & Power Plants, Madrid, 1, pp 299-308.

Coates D.F. (1963), "Rock mechanics applied to the design of underground installations

to resist ground shock from Nuclear blasts", Proc. 5th

Symp. on Rock Mechanics,

Minneapolis, 1962, pp 525-562.

Deere D.U. (1963), "Technical description of rock cores for engineering purposes",

Felsmechanik and Ingenienrgeologic, Vol. 1, No. 1, pp 16-22.

Deere D.U., Hendron A.J., Patton F.D. and Cording E.J. (1967), " Design of sorface and

near surface construction in rock", Failure and breakage of rock, Proc. 8th

U.S. Symp.

Rock mech., (Ed. A. Fairhurst), New York: Soc. Min. Engs., Am. Inst. Min. Metall.,

petrolm. Engs., pp 237-302.

Deere D.U., Peck R.B., Monsees J.E. and Schmidt (1969), "Design of tunnel; liners and

support systems", Report prepared by University of Illinois Urbana, for the office of High

Speed Ground Transportation, NTIS Publication PB 183-799.

Deere D.U. and Deere, D.W. (1988), "The RQD index in practice", Proc. Symp. Rock

Classif. Eng. Purp., ASTM 984, ), Philadelphia, pp. 91-100.

Deere D.U. (1989), "Rock quality designation (RQD) after 20 years", U.S. Army Corps

Engs. Contract Report GL-89-1, Vicksburg, MS: Waterways Experimental Station.

Dube A.K., Singh B. and Singh Bhawani (1986), "Study of squeezing pressure

phenomenon in a tunnel - I and II", Tunnelling and Underground Space Technology, 1,

pp 35-48.

Franklin J.A. (1975), "Safety and economic of tunnelling", Proc. 10th Canadian Rock

Mech. Symp., Kingstone, pp 27-53.

Ghose A.K. and Raju N.M. (1981), "Characterisation of rock mass vis-a-vis application

of rock bolting in Indian coal measires, Proc. 22nd

U.S. Symp. on Rock Mech., MIT,

Cambridge MA, pp 422-427.

Ghosh D.K. and Ahmad M.J. (1985), "Geotechnical consideration in forecasting

tunnelling conditions for the water conductor system of Bodhghat Hydel project", IIIrd

Symp. on Rock Mech., Roorkee, pp 36-41.


82

Goel R.K, Swarup S.K., Dube A.K. and Kumar P. (1996), "Tunnelling through blocky

rock masses of Lower Himalayas - A case study", Recent Advances in Tunnelling

Technology, New Delhi, pp 241-247.

Grimstad E. and Barton N. (1988), "Design and methods of rock support", Norwegian

Tunnelling Today, Norwegian Soil and Rock Engg. Association, Pub. 5, pp 59-64.

Grimstad E. and Barton N. (1993), "Updating of Q system for NMT", Proc. Int. Symp. on

Sprayed Conc., Fargenes, Norway, Norwegian Concrete Association, Oslo.

Gupta O.P. (1968), "Evaluation of rock loads for design of steel supports for tunnels",

Indian Journal of Power and River Valley Development, March Edition.

Hari Dev (1997), "Design Criteria for supports and lining of underground structures for

water resources projects - some case studies", M.E. Dissertation, WRDTC, University of

Roorkee.

Hoek E. and Brown E.T. (1980), "Underground excavations in rock", Institution of

Mining and Metallurgy, London, 527 pp.

ISRM (1981), "Basic Technical Description of Rock Masses", Int. J. Rock Mech. Min.

Sci., Vol. 18, pp. 85-110.

Jethwa J.L., Dube A.K., Singh B. and Mithal R.S. (1982), "Evaluation of methods for

tunnel support design in squeezing rock conditions", Proc. 4th

Int. Cong. Assn. Eng. Geol.

Delhi, pp.125-134.

Kaisar P.K., Mackay C. and Gale A.D. (1986), "Evaluation of rock classifications at B.C.

rail tumbler ridge tunnel", Rock Mech. Rock Engg. 19, pp 205-234.

Kendorski F., Comminger R., Bieniawski Z.T. and Slommer E. (1983), "Rock mass

clasification for Block Caving mine drift support", Proc. 5th

Int. Congr. Rock Mech. ISR,

Melbourne, pp B51-B63.

Kindybinski (1979), "Experience with rock penetrometers for mine rock stability

predictions", Proc. 4th Int. Congr. Rock mech., ISRM, Montreux, pp 293-301.

Laubscher, D.H. (1977), "Geomechanics classifications of jointed rock masses - mining

applications", Trans. Inst. Min. Metall.Sect. A 86, pp.A1-A7.

Lauffer H. (1958), "Gebirgsklassifizeirung fur den stollenbau", Geologie and Bauwesen,

Vol. 24, No. 1, pp 46-51.

Merritt A.H. (1972), "Geologic prediction for underground excavations", Proc. North

American Rapid Excav. Tunnelling Conf., Chicago, (Eds. K.S. Lane and L.A. garfield) 1,

New York: Soc. Min. Engs., Am. Inst. Min. Metall., petrolm. Engs., 115-132.


83

Nakao K., Gihoshi S. and Koyama S. (1983), "Statistical reconsiderations on the

parameters for the geomechanics classification", Proc. 5th Int. Congr. Rock Mech., ISRM,

Melbourne, pp B13-16.

Oliver H.J. (1979), "Applicability of the geomechanics classification to the Orange - Fish

tunnel rock masses", Civ. Engg. S. Africa 21, pp 179-185.

Pacher F., Rabcewicz L. and Golser J. (1974), "Zum der seitigen Stand der

Gebirgsklassifizierung in Stollen-und Tunnelbau”, Proc. XXII Geomech. Colloq.,

Salzburg, pp 51-58.

Palmstrom A. (1982), "The volumetric joint count - a useful and simple measure of the

degree of rock jointing", Proc. 4th

Congr. Int. Assn. Engg. Geol., Delhi 5, 221-228.

Protodyakonov M.M. (1974), "Klassifikacija gornych porod", Tunnels Ouvrages

Souterrains 1, pp 31-34.

Ritter, W (1879), "Die Statik der Tunnelgewolbe", Berlin: Springer.

Rutledge J.C. and Preston R.L. (1978), "Experience with engineering classifications of

rock", Proc. Int. Tunnelling Symp., Tokyo, pp A3 1-37.

Saini G.S., Goel R.K. and Dube A.K. (1985), "Geotechnical assessment and behaviour of

tunnelling media at Khara project tunnels", IIIrd

Symp. on Rock Mech., Roorkee, pp 69-

77.

Serafim J.L. and Pereira J.P. (1983), "Considerations for geomechanics classification of

Bieniawski", Proc. Int. Symp. Engineering Geology and Underground Construction,

Lisbon, Vol 1, pp II.33-42, LNEC, Lisbon.

Sharma Brijendra and Sethi Rajeev (1994a), "Design of water conductor system of

Chamera Project", Indian Journal of Power and River Valley Development, May-June

Edition, pp 138-147.

Sharma Brijendra and Sethi Rajeev (1994b), "Design and excavation of underground

power house complex - some special features", Indian Journal of Power and River Valley

Development, May-June Edition, pp 148-158.

Sharma Kultar, hegde U.V. and Sayeed Imran (1995), "Tunnelling and adopted support

measures in fair to poor rock conditions of Kashmir Himalayas", Conference on design

and construction of underground structures, New Delhi, pp 495-508.

Singh Bhawani, Jethwa J.L. and Dube A.K. (1985a), "A Classification for support

pressure in tunnels and caverns", Jour. of Rock Mechanics and Tunnelling Technology

(India), Vol. 1, No. 1, pp 13-24.


84

Singh Bhawani, Jethwa J.L, Dube A.K. and Singh B. (1992), "Correlation between

observed support pressure and rock mass quality", Tunnelling and Underground Space

Technology, Vol. 7, No. 1, pp 59-74.

Singh Narinder and Agarwal Sanjay (1995b), "FEM analysis and design of roof support

for power house and transformer cavities of Baspa II project", Conference on design and

construction of underground structures, New Delhi, pp 323-336.

Singh Narendra, Agarwal D.K. and Bhatia P.K. (1988), "Design of cavity for

underground power house of Lakhwar project", Proc. Symp. Underground Engg., Delhi,

pp 237-242.

Stini I. (1950), "Tunnul baugeologie", Springet-Verlag, Vienna, pp 336.

Terzaghi K. (1946), "Rock defects and loads on tunnel supports", Rock tunnelling with

Steel Supports, (Eds. R.V. proctor and T.L. White) 1, 17-99, Youngstown, OH:

Commercial Shearing and Stamping Company.

Terzaghi K (1973), "Introduction to Tunnel Geology", Rock Tunnelling with Steel

Supports, Edited by Proctor and White, Commercial Shearing and Stamping Co.,

Youngstown, Ohio.

Tripathi S.K., Chowdhary A.K., Sengupta C.K. and Yadava V.S. (2003), "Geological

appraisal and rock mass classification of 23 km long head race tunnel, Tala hydroelectric

project, Bhutan", International conf. on Accelerated Construction of Hydropower

Projects, Gedu, Bhutan, Vol. 2, pp II/30-41.

Wickham G.E., Tiedmann H.R. and Skinner E.H. (1972), "Support determination based

on geologic predictions", Proc. 1st Rapid Excavation and Tunn. Conf., Chicago, Vol. 1,

pp 43-64.

Wickham G.E. and Tiedmann H.R. (1974), "Ground support prediction model - RSR

Concept", Proc. 2nd Rapid Excavation and Tunnelling Conf., Chicago, Vol. 1, pp 691-

707.

monograph on rock mass classification systems and applications

Documents