Pir Panjal Railway Tunnel - A dream realized

7/23/2019 Pir Panjal Railway Tunnel - A dream realized

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PIR PANJAL RAILWAY TUNNEL

A DREAM REALIZED


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PIR PANJAL RAILWAY TUNNEL

A DREAM REALIZED

Concept

V. K. Gupta

Project Initiation & Co-ordination

B. D. Garg

Working Group

Achal JainVijyant Bhardwaj

Kumar Ravi Shankar

NORTHERN RAILWAY


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Published by

Northern Railway

Concept

V. K. Gupta General Manager, Northern Railway

Project Initiation & Co-ordination

B.D. GARG Chief Administrative Officer/USBRL Project, Northern Railway

Working Group

Achal Jain Chief Engineer/USBRL Project, Northern Railway

Vijyant Bhardwaj Ex. DGM/GC-Rites

Kumar Ravi Shankar DGM/IRCON

Contributors

R.S. Poonia Chief Engineer/SECRly

Dr. F. Prinzl GeoConsult Austria

P.C.Pardhan Asstt. Engineer/IRCON

Sharanappa Yalal Project Manager HCC

Vikas Goyal XEN/ USBRL Project, Northern Railway

Manuscript Typing

Santosh Kumar USBRL Project, Northern Railway

Manjit Singh USBRL Project, Northern Railway

Printed At

KOJO Press, New Delhi

Designed By

Arpit Printographers

Copyright@2013

Northern Railway

Presented by


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Contents

Preface xiii

1. Udhampur-Srinagar-Baramulla Rail Link (USBRL) Project A Historical Perspective 1

1.1 Background 1

1.2 Selection of The Alignment of The Railway Line 3

1.3 Geology and Terrain 5

1.4 Pir Panjal Railway Tunnel (T-80) 8

1.5 Construction of the Banihal Road Tunnel in Kashmir 8

2. Tunnelling Philosophy An Engineering Perspective 16

2.1 Background 16

2.2 Evaluation/Description of different Tunnelling methods 16

2.3 NATM : Detail & Design 33

2.4 Appointment of the Detailed Design and Construction Supervision Consultant (DDC)

A New Initiative 50

2.5 Main Deliverables Required from DDC 50

2.6 Salient Features of Pir Panjal Tunnel 52

3. Exploring The Unknown 54

3.1 Geological And Geotechnical Investigations 543.2 Importance of Investigations Required for The Construction of Tunnel 55

3.3 Why these Investigations are Necessary? 56

3.4 Classification of Investigations 56

3.5 Approach to Carrying out the Investigations 58

3.6 Investigation During Planning and Design Stage 58

3.7 Investigation During Construction Stage 61

3.8 Geological Overview 65

4. Putting The Dream On Paper (DESIGN) 89

4.1 Introduction 89

4.2 Collection of Data/Information 91

4.3 Site Topography 93

4.4 Alignment and Layout 94

4.5 Tunnel Drainage and Waterproofing 104

4.6 Geotechnical Design 106

4.7 Geotechnical Instrumentation and Monitoring 111

4.8 Design of Outer Lining 112

4.9 Design of Inner Lining 114

4.10 Tunnel Safety 115


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5. Dream in Motion (Tendering) 116

5.1 General 116

5.2 Need for Strategizing the Construction 116

5.3 Early works 118

5.4 Main Tunnel Contracts 120

6. Bringing The Dream To Reality (Construction) 139

6.1 Construction of Pir Panjal Tunnel 139

6.2 Construction Materials and Their Quality Aspects 139

6.3 Detail of Construction Materials 140

6.4 Waterproofing and Permanent Groundwater Drainage 162

6.5 Drives (Mining and Lining) 168

6.6 The Access Tunnel 170

6.7 Shaft and Cross Passage 171

6.8 Construction of Cavern at Junction of Access Tunnel and Main Tunnel 175

6.9 Soft Ground Tunneling at the North and South Ends 176

6.10 Portal Development 176

6.11 Construction Methodology of Main Tunnel 179

6.12 Permanent Lining 190

6.13 Year wise Progress of Lining Work 195

6.14 Problems Faced During Construction 196

6.15 Anticipated Rock Class v/s Actually Encountered 203

6.16 Second Stage Concreting 204

6.17 Ballast-less Track (BLT) 205

7. Breathing Life into The Tunnel (Ventilation) 212

7.1 Need of Ventilation System 212

7.2 Design Basics/Fundamentals 215

7.3 Boundary Conditions for Ventilation Design against Emissions and Fire 216

7.4 Layout of Ventilation System 223

7.5 Smoke Behaviour 226

7.6 Waiting Time 227

7.7 Specifications of Machinery 228

7.8 Summary of the Final Longitudinal Ventilation System 229

8. Livening The Tunnel (Electrical & Mechanical Systems) 231

8.1 General 231

8.2 Compliance with the UIC 779-9 R provisions 231

8.3 A Short Description of the System 233

8.4 Electrical and Mechanical Installations: 234

9. Safety (Operational Concepts) 246

9.1 Safety Concept 246

9.2 Main Scenarios And Required Measures 246

10. Through The Eyes of a Camera 256

Appendix A : Geodetic Survey 301

Appendix B : The Role of The Roadheader 310

Appendix C : Instrumentation & Monitoring of Tunnel - Section 314


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Preface

The engineering work on a large tunnel project is so complex that number of

engineers and specialists in many areas are required to be involved in design and

construction. The decisions, of which there may be several, call for a vast amount of

technical knowhow and sound judgement based on many years of experience.

The 11 km. long tunnel the Pir Panjal Railway Tunnel represents a culmination of a

tremendous effort on the part of myriads of engineers who were involved in its

planning, design and construction engineers from Northern Railway, the Contractor

IRCON and their various Subcontractors/consultants.

Northern Railways engineers felt it worthwhile to pen down and put on paper for

the benefit of posterity the multitude of the involved technical details and the lessons

that were learnt during design and construction of Pir Panjal Railway Tunnel the

longest transportation tunnel in india.These notes, stated in the format of a book,give discrete steps to decision making and undoubtedly provide a comprehensive

coverage of the subject for both the designer and the constructor. At its heart lies

the Capacity for Development which then is the ability to solve problems, and make

informed choices, and plan for future.The material in the Book is presented in the

vein of a comprehensive yet concise compendium. The presentationshave a flow

that moves from the individual to the organization,with practical skills and

theory woventogether, offering real-life engineering experience, from problem

formulation through to implementation.

This would educate thefuture creatorsin understanding the subject of tunnelling,thus enabling them to employ their grounding in engineering to become workman-

like partners in future in such type of project.


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FIRSTTR

AIN

THROUGH

TUNNEL


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Chapter

1Udhampur-Srinagar-Baramulla Rail Link

(USBRL) Project A Historical Perspective

1.1 Background

1.1.1 With a view to provide a reliable alternative transportation system to the Kashmir Valley, the Government

of India sanctioned the construction of a 326 Km long railway line to the States Summer Capital, Srinagar, taking off

from its Winter Capital, Jammu.

1.1.2 Terminating at Baramulla, near Srinagar, the railway line connects Jammu with Udhampur, then Katra,

Reasi, Banihal, Qazigund and Srinagar en route (Fig 1.1). It is one of the largest and toughest mountain - railway

project undertaken in the country since independence. The railway line traverses the young Himalayas, which is

tectonically very active and dotted with many Thrusts and Faults. Work on the Jammu Udhampur section (53 Km)

was completed and commissioned in April, 2005. Then the section from Baramulla to Qazigund (119 Km) was

completed and opened to traffic in October, 2009. Work in the remaining stretch from Udhampur to Qazigund,

totalling 154 Km, is in various stages of construction. The Udhampur-Srinagar-Baramulla rail link (USBRL-273Km)was declared as a Project of National Importance. Some of the important salient features of USBRL Project are as

follows:

Item Udhampur Katra Qazigund Total

Katra Section Qazigund Section Baramulla Section

Route length 25Km 129Km 119Km 273

Ruling gradient 1 in 100 1in 80 1in 100

Sharpest in - plan Curvature 2.75o 4o 2.75o -

No. of Bridges 38 62 811 911

Max. height of Bridge 85 m 359 m 22 m -

Longest individual span length 154m Steel Girder, 467 m Steel Arch, 45 m -

over river Jhajjar over river ChenabAggregate Bridge Length 1488m 7310m 4210m 13008m

No. of Tunnels 10 36 - 46

Aggregate Tunnel Length 10.90 Km 105.00 Km 0 115.90Km

Aggregate Tunnel length as % of

section length 43.60 81.40 0 -

Longest Tunnel length 3.15 Km. 11.27 Km - -

Max Depth of Cutting 20 m 40 m 12 m -

Rly. Stations 3 10+1 15 28+1


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2 Pir Panjal Railway Tunnel

Fig. 1.1: Alignment Plan


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1.3.4 Other geomorphic processes that are related to the meteorological conditions have also lead to continuous

modification of the shapes of the Himalayan ranges. Some of these changes in the slopes of mountains and drainage

basins have occurred within the experience of an average life span of humans. Emergence of the Himalayas is

considered to have caused the onset of the Indian Summer Monsoon some time in the geological past (about 8

million years ago, according to one school). The Indian Monsoon has since become more intense and well diversified

in terms of regional variations in annual rain fall. The Himalayas have also shown themselves as an ideal case forcoupled effects of tectonics and climate. Whereas the tectonics have lead to the rise of the Himalayas, high

precipitation and high relief have been responsible for faster rates of erosion. Higher rates of erosion, in turn, lead

to an increase in the rate of uplift of the mountains, and thus the tectonics-climate coupling continues to modify

the shape of the Himalayan ranges. Understanding these processes of tectonics and erosion has a great bearing on

designing, executing and maintaining the civil structures, such as rail-roads.

1.3.5 The rail alignment from Katra to Banihal traverses the most difficult terrains of the Lesser Himalayas

characterized by steep hills and deep valleys. The Main Boundary Fault (MBF) that marks the boundary between

the Outer and Lesser Himalayas is located near the Katra end of the alignment. Along the MBF, rocks of Shiwalik

Group are thrust by the Late Precambrian carbonate sequence named Sirban Limestone. Whereas the Shiwalik

Group is made up of alternate bands of claystone, siltstone and sandstone, the overlying carbonate sequence

comprises predominantly of limestone and dolomite with some arenaceous beds in the upper parts of the succession.The limestones and dolomites of the Sirban Limestone are highly jointed and sheared in the vicinity of the MBF.

1.3.6 The Sirban Limestone is overlain by coaliferous shales and limestones named Subathu Formation of Eocene

age. These are overlain by the Jungalgali Formation that is made up of limestone, chert, quartzite, shale, sandstone,

clay bands and bauxite at a few places. Both, the Subathu Formation and the Jungalgali Formation, are exposed

along the rail alignment in relatively thinner bands of outcrops on the northern bank of the Chenab river. These, in

turn, are overlain by a thick succession of shale, siltstone and sand stone comprising Murree Formation. While the

Subathu Formation represents a marine facies, the rocks of younger Murree Formation were deposited in fluvial

and lacustrine basins.

1.3.7 The Subathu Formation and Sirban Limestone are again exposed in the upper reaches along the alignment

where they are separated by the Murree Formation by a series of strike faults. The Murree rocks continue till they

are separated by yet another important thrust named as Murree Thrust. This structure has lead the Late Proferozoicsequence of phylhtis slates and quartzites, named Ramban Formation, to lie over Late Tertiary sequence (Murree

Formation).

1.3.8 The Ramban Formation is truncated in the north by Panjal Thrust that brings a sequence of Late Precambrian

Salkala Formation of Tethyan Himalayas to lie over the rocks of Ramban Formation. The Salkhala Formation contains

large bodies of granitic rocks that are foliated and highly jointed. These, in turn, are overlain by rocks of Ramsu

Formation that are made up of slate phylhtis, quartzite, schist and limestone. The Ramsu Formation is unconformably

overlain by a sequence of agglomeratic shales, slates and phylhtis with interbeds of fossiliferous limestone. This

sequence is overlain by a thick sequence of volcanic rocks known as Panjal Volcanics that are exposed in the higher

reaches of the Pir Panjal Range beyond Banihal.

The above sequence of Late Precambrian to Tertiary ages have undergone folding and faulting during the Himalayan

orogeny. Quarternary sediments comprising fluvial, lacustrine, eluvial and glacial sediments occur in small packetsat different places in the Himalayas. These are unconsolidated sediments of variable thicknesses, met with at a few

places along the alignment (Fig. 1.4).


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Fig. 1.4

Udhampur-Srinagar-Baramulla Rail Link (USBRL) Project A Historical Perspective 7


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the final tunnel design. In respect of earthquakes no experience at the Banihal area was available, however, on

various other points in the Kashmir Valley, between 1909 and 1946 observations were made as shown in table I:

TABLE-I

Rossi Forel Scale Acceleration in mm s StationsSrinagar Gurez Gulmarg Dras

I Upto 2.5 6 1

II 2.5 to 5.0 6 1 1

III 5 to 10 14 4 1

IV 10 to 25 54 3 1 2

V/VI 25 to 50 113 15 46 6

VII 50 to 100 34 5 18 4

VIII 100 to 250 3 3 18 4

IX 250 to 1000 1 1

X More than 1000

Noted, intensity

not known 1 1 2

Total number of

earthquakes 1909- 1946 231 29 90 19

During the construction period of the tunnel a number of earthquakes were noted in Banihal of which only two on

two subsequent days in spring 1956 must be considered as heavier earthquakes which may have been in the order

VIII of the Rossi Forel scale. As the above table shows the heaviest earthquakes observed in Kashmir were of the

grade IX of the scale. Since Kashmir is located in the seismological area of the Himalaya, the government decided on

an acceleration of 0.1 g for the statical computation of tunnel vault which equivalent to the intensity X of the Rossi

Forel scale.

At the time of construction commencement available meteorogical values with respect to temperature, precipitation,

atmospheric pressure, relative humidity and wind velocities for stations in the Kashmir Valley and in the areas of

the Chenab and Tavi rivers could not be taken into consideration for the design of the Banihal tunnel since the Pir

Panjal range follows own weather and natural laws which show very abrupt differencies which in many respects

deviate from those measured in the Kashmir Valley.

In order to collect information for the tunnel ventilation and water supply the Central Public Works Department

installed on the north and south portal of the Banihal tunnel, meteorological stations. With respect to the avalanche

problem, the Joint Venture could only rely on oral information of the local Public Works Department and their

observations and experiences in the past.

1.5.5 Cross-section of the Tunnel

For both tunnel tubes a contractual clearance area in form of a horseshoe was fixed as shown in picture 4, with a

semi-circle of 2.72 m radius and a trapezoidal lower part of 5.44 m width at top at 5.03 m at about road level.


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The clearance height in the center is 5.54 m, the maximum width at the spring of calotte 5.44 m. The one-lane road

pavement has a slope of 1:70 and is normally 3.20 m wide, on by-passes it widens to 5.64 m, the one-sided walkway

has a railing at 1.25 width, the curbstone on the other side has a width of 0.58 m, both have been executed with arounded-off curb as usually used in this country. The clearance height is for Indian circumstances unusually high

and even sufficiently high for particular army vehicles. The design of the cross-section particularly took care of the

possibility, in case of necessity, to allow the installation of a channel for ventilating and fresh air supply. If one

compares this cross- section e.g. with the Lammerbuckel tunnel of the highway Stuttgart-Ulm, which is also used in

one-directional traffic only, the cross-section of the Banihal with about 30 m is not even half as big as the highway

tunnel with approx. 70 m.

The lining of the tunnel in the earlier projects was to be done in stone-masonry with a thickness of 1" per 1

clearance width. For the execution, however, instead of stone-masonry concrete and reinforced concrete was chosen

with a mixing ratio of 1:2:4 and thickness fixed at 12", 15" and 18" respectively, whereby the latter, wherever

required was to be reinforced and even provided with an invert. The Indian government was not satisfied with the

empiric formula of thickness as above mentioned, but insisted on a statical computation of the vault in accordance

with the geological charting and the resulting loadings onto the vaults.

Therefore, a calculation with a pressure ellipse according to O. Kommerell of h = 100a/p was taken into account

whereas the deformation of the tunnel top a and the permanent loosening of the rock p in percent were

estimated according to the local conditions of the rock. For the 21" profile with earthquake reinforcement and

reinforced concrete invert selected for the area of clay and debris at the tunnel ends, the calculation showed a

maximum eccentricity of the pressure resultant with the Kommerell load as indicated of only 15 kg/cm, as against

a permissible value of 52.7 kg/cm according to the Indian standard code IS-456-1953 for a mix of 1:2:4, and even

the pressure in the concrete/rock interface joint of the invert was within marginal limits.



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Chapter

2Tunnelling Philosophy

An Engineering Perspective

2.1 Background

Tunnelling is both a Science and An art that over-arches the many disciplines of engineering - civil, structural,

geological, mechanical, electrical and computer as well as the ecological and environmental constraints. Apart from

being a highly expensive engineering enterprise, tunnels can present very difficult problems in their construction.

As more and more tunnels are built, it calls for continued improvement in tunnelling technology. Tunnel as an

alternative, has to be a cost-effective engineering solution with minimal impact on the ambient environment and

ecology. Although significant innovations have been made over the years in tunnel construction, the substantial

growth in passenger traffic and the consequent need for more efficient rapid transit systems in urban areas

necessitates more and more improvement in tunnel construction practices.

Here an attempt has been made to examine and evaluate the currently practised construction technologies i.e.

Tunnel Boring Machine (TBM) method, Conventional Indian Method of Tunnelling and New Austrian TunnellingMethod (NATM) for tunnelling through different medium i.e. through soil and rock.

2.2 Evaluation/Description of Different Tunnelling Methods

First a short overview of different construction Technologies is attempted (for better evaluation):

2.2.1 TBM Technology

i. Tunnelling by boring, using a Tunnel Boring Machine (TBM) is often adopted for long tunnels. An effective TBM

method requires the selection of appropriate equipment for different types of rock mass and geological conditions.

The TBM may be suitable for excavating those tunnels which contain competent rocks that can provide adequate

geological stability when boring through a long section without structural supports. However, extremely hard rock

can cause significant wear of the TBM rock cutter and may slow down the progress of the tunnelling to the point

where TBM becomes inefficient and hence uneconomical and may take longer time than the drill-and-blast tunnelling

method in such a case. The detail of TBMs commonly use in rock are as under:-

a. Gripper TBM (Open TBM)- For use in solid rock. The machine is locked at the rock using two or four gripper

plates. Then, hydraulic cylinders push the cutter head into the tunnel face at high pressure, grinding it with

cutter rings (Fig. 2.1).


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Fig. 2.1

b. Single Shield TBM-For use in brittle or soft rock. The tunnel is lined with concrete segments. To tunnel

forward, the hydraulic thrust cylinders of the Single Shield TBM push against the last installed lining ring

(Fig. 2.2) .

Fig. 2.2

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c. Double Shield TBM-These combine the principles of the Gripper and the Single Shield TBM, enabling fast

excavation even in varying rock formations (Fig. 2.3) .

Fig. 2.3

There are two major shield machines available for tunnelling in soft ground in urban areas i.e the earth pressure

balanced (EPB) and the slurry type shield machines. Selection of the appropriate shield machine depends on the

ground conditions, surface conditions, dimensions of the tunnel section, the boring distance, the tunnel alignment

and the construction period available. Both are closed-face type shield machines, meaning the head part of

machine is closed and separated from the rear part of machine. The head has a working chamber filled with soi lor slurry between the cutting face and bulkhead to stabilize the cutting face under soil pressure. The EPB type

shield machine turns the excavated soil into mud pressure and holds it under soil pressure to stabilize the cutting

face. It has an excavation system to cut the soil, a mixing system to mix the excavated soil into mud pressure, a soil

discharge system to discharge the soil and a control system to keep the soil pressure uniform. Therefore, EPBM may

not be applicable for the rocky strata that where it is difficult to turn the excavated soil into slurry. It can be used at

ground which is predominated by clayey soil. The slurry type shield machine, on the other hand, uses the external


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pressurized slurry to stabilize the cutting face, similar to bored piles or diaphragm walls using Bentonite to hold

back the trench wall. The slurry is circulated to transport the excavated soil by fluid conveyance. Besides having an

excavation system, the slurry type shield machine has slurry feed and discharge equipment to circulate and pressurize

the slurry and a slurry processing equipment on the ground to adjust the slurry properties.

ii. The sequential steps for construction of tunnel by TBM:

Schematic construction sequence for working by TBM

iii) Schematic representation of EPBM ( See Fig.2.4,Fig.2.5)

Fig. 2.4



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Fig. 2.5

iv) Types of cutting face of EPBM ( See Fig. 2.6)

??

Fig. 2.6


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x) Types of cutting face of slurry type shield ( See Fig. 2.12)

Fig. 2.12

xi) Slurry type TBM : Slurry circulation system ( Representative) (See Fig. 2.13)

Fig. 2.13

xii) Slurry type TBM : Slurry circulation system ( Line Diagram) (See Fig. 2.14)

Fig. 2.14



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xiii) Slurry type TBM : Slurry Circulation system ( See Fig. 2.15)

Fig. 2.15

xiv) Slurry treatment plant. ( See Fig. 2.16)

Fig. 2.16


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xv) Typical site utilization plan for working with slurry type TBM including working shaft, gantry crane, segment

stock yard, tanks, etc. ( See Fig. 2.17)

Fig. 2.17

xvi) Section view of the site utilization for working with the slurry type TBM (See Fig.2.18)

Fig. 2.18



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2.2.2 Shaft Construction

i) Shaft construction using diaphragm wall method (See Fig. 2.19,Fig.2.20)

Fig. 2.19

Fig. 2.20


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ii) Shaft construction using diaphragm wall method - Access stairs, ventilation and passenger hoist are provided (

See Fig. 2.21)

Fig. 2.21



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iii) A receiving shaft to accommodate dismantling ( right) and assembling (left) TBM at the same time (See Fig. 2.24)

Fig. 2.24

iv) The shield machine at work ( See Fig. 2.25)

Fig. 2.25



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v) The functioning part of TBM ( back up) at the rear (See Fig. 2.26)

Fig. 2.26

2.2.4 Conventional Indian Method Of Tunnelling

In conventional Indian method of tunnelling, the excavation is done by Drill and blast method and thereafter steel

ribs with backfilling by tunnel muck or lean concrete is used as an almost automatic first step in tunnel support.

This being a passives support system, a considerable damage is done to the rock mass before the ribs interact with

it. The combination of the drill-and-blast method of excavation and steel rib support system delays the supporting

action, allows opening of the existing joints, creates new fractures, permits loosening of the rock mass in the roof,

mobilizes higher tunnel closures and greater rock loads which require larger excavation and thicker support. All

these problems result in increased cost and completion period. The steel ribs invite unwanted loosening, and a

potential weakening-because-of-loosening (Fig.2.27,2.28).The tunnel construction that is based on extensive use

of steel ribs the conventional Indian Method (Fig. 2.29) is unfortunately slow in most of the rock classes.

Fig. 2.27 Fig. 2.28


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b) Maintain strength of the rock mass and avoid detrimental loosening by careful excavation and by

immediate application of support and strengthening means.Shotcrete and rock bolts applied close to the

excavation face help to maintain the integrity of the rock mass.

c) Rounded tunnel shape:avoid stress concentrations in corners where progressive failure mechanisms

commence.

d) Flexible thin lining:The primary support shall be thin-walled in order to minimize bending moments and to

facilitate the stress rearrangement process without exposing the lining to unfavorable sectional forces.

Additional support requirement shall not be added by increasing lining thickness but by rock bolting. The

lining shall be in full contact with the exposed rock. Shotcrete fulfils this requirement.

e) Statically the tunnel is considered a thick-walled tube consisting of the rock and the lining. The closing of

the ring is therefore important, i.e. the total periphery including the invert must be shotcreted.

f) In situ measurements: Observation of tunnel behavior during construction is an integral part of NATM.

With the monitoring and interpretation of deformations, it is possible to optimize the working procedures

and the support requirements.

2.2.6 Why the TBM Method was not adopted for construction of Pir panjal Tunnel

Because of Likelihood of encountering-Mixed Geology (non-uniform medium)

Heavily Faulted and/or Wide Fault Zones

High Squeezing Effected Anticipated in the middle portion, with High Overburden almost 1100 to 1200 m.

Heavy Water Flows in the Lime Stone Zones with High overburden

Ground Movement that could easily trap the TBM.

The TBM technology is suitable for excavating through nearly uniform medium with no serious obstacles.

The TBM method with shield is also used for tunnels in pervious ground below water level.

2.2.7 Why Conventional Indian method of tunnelling was not adopted in

construction of Pir panjal Tunnel

This method of construction is not flexible enough to accommodate required changes to suit ground

conditions/encountered geology like :

o Vary the support system as per requirement

o Splitting of the excavation face to tackle varied geological conditions

o To carry out Ground treatment

o Tackle heavy ingress of water

2.2.8 Why NATM was adopted for construction of Pir panjal Tunnel

NATM provides for more cost effective, flexible and safe tunnelling methodology without the long mobilization

process endemic with TBM procurement. NATM is well suited for tunnelling in ground with varying geology. As

such, the New Austrian Tunnelling Method (NATM), was the appropriate alternative.


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2.3 NATM : Detail & Design

2.3.1 Development of Natm

i) The name NATM (New Austrian Tunnelling Method) was introduced by Prof.Rabcewicz in 1962 to

differentiate this new method from the then old Austrian Tunnelling Method which was one of several

tunnelling methods that were developed during the first half of the 20thcentury. Typical for these old

European methods were small headings with temporary timber support, which were systematically widened

to the full cross section. During the installation of the final lining, usually made of bricks and stone masonry,

the timber strutting was removed but timber lagging often was left in place. Another characteristic was the

use of heavy side walls and foundation beams but no invert (no ring closure), Figure 2.30

Fig. 2.30 : Karawanken Railway Tunnel, Cracking due to missing ring closure

ii) Rabcewicz initiated a new and entirely different tunnel construction procedure and disregarded completely

the generally used state-of-the-art techniques. He also introduced newly developed construction

technologies into tunnelling.

iii) Rabcewicz had collected a profound tunnelling experience between the two world wars when he was

working on hydropower and railway projects in Persia and Turkey. He summarized his knowledge and

understanding of tunnelling in a systematic way in his book Rock Mass Pressure and Tunnelling which

was published in 1944. The books title is characteristic for some of the important topics which he described.

iv) He differentiated very clearly between the pressure fromrock mass loosening, real rock (squeezing) pressure

and swelling pressure. He recognized that the development of the loosening pressure is related to the



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shortcomings of the construction procedure and the temporary support with timber struts and lagging,

which could not prevent material loss, loosening and excessive movements even at low pressure. He stated

time factorand rock mass structureas important parameters for control of loosening and the necessity to

maintain a three dimensional stress distribution throughout the procedure of excavation and support

installation. On the other side he explained that real rock mass pressure can be observed when the

stressesat the side walls exceed therock mass strength. If this happens the stresses will be redistributed,away from the opening, deeper into the rock mass where confined stress conditionsexist and the so called

protective shell is developed. Rabcewiecz also distinguished the different behavior of the various rock

types under high pressure with spalling appearances in hard rock and large plastic deformation in soft

rock. He stated that in the latter case even strongest support can not withstand the pressure if installed too

early. In this respect he criticized the practice of lining design of that time, as being only suitable to support

the loosening pressure. He introduced and insisted in the importance of monitoringas a compulsory

requirement for his new tunnelling method.

v) Other tunnel engineers to be mentioned for their contributions during the very early stage of the

development of the NATM are Dr.Lauffer who introduced the rock mass classification system in 1962,

Prof.Pacherwho described the rock mass behavior in the Fenner-Pacher characteristic curve and Prof.Mller

who was a leading member of the Salzburg Circle a group of tunnel engineers who met regularly inSalzburg for exchange of experiences and new ideas.

vi) Important break through eventswere the successful application of the NATM in the Massenberg Tunnel in

Austria and in the Schweikheim Tunnelin Germany in 1964 which were both tunnels with shallow cover. At

the Massenberg Tunnel, Figure 2.31, the design and construction method was changed after great difficulties

were encountered during construction.

Fig. 2.31: Original and New Design (after stand still) of the Massenberg Tunnel

vii) With the Tauerntunnel, which started in 1970, the method was applied for the first time in a tunnel with

high overburden and real rock mass pressure. It was also used in the talus section at the portal zones where


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soft ground with large boulders had to be tunnelled. The 6.5 km long main tunnel section with more than

1000 m overburden consisted of various rock types including long sections of highly stressed Phyllites. For

the stabilization of the heavy rock mass pressure with large deformations, longitudinal slots in the shotcrete

were used for the first time. In combination with long rock bolts this section was also successfully completed

and the tunnel was a technical and economical success.

2.3.2 Basic Principles of NATM

i) It is important to understand that NATM is a construction procedure and the excavation and support have

to be seen always in cross sectional and longitudinal direction. It has been always avoided to limit the

application of NATM by the definition of particular and distinct guide lines. The application depends widely

on the particular conditions of each tunnel project and a generalization and simple copying may lead to an

inadequate design in other conditions. For better understanding some of the basic principles of the method

are summarized below:.

a) The major load bearing member is the rock mass.

b) The primary support shall help to:

maintain the integrity and strength of the rock mass around the opening, shall be slim but shall have a good contact with the rock mass and shall cover the whole area of the

rock face (shotcrete),

shall strengthen the rock mass (bolts, grout)

shall provide immediate protection to workers (steel ribs, wiremesh) and

shall be installed as quickly as possible

c) Effective ring closure shall be achieved fast. This is provided by the rock or by the installation of an invert,

if the rock strength is too low.

d) Two dimensional stress conditions shall be avoided.

e) The excavation area shall be as large as possible and if possible full face excavation shall be used. Small

partial excavations shall be avoided.

f) Tunnel cross section should have a smooth and rounded shape.

g) The Rock mass and support interaction (system behavior) must be continuously controlled by monitoring.

h) The inner lining should increase the factor of safety of the permanent support and shall be installed only

after complete balance of the stresses when deformations have stopped.

ii) Rock Mass Classification of Lauffer (1962)

a) In 1962 a rock mass classification system was introduced by Dr.Lauffer.

b) The Lauffer diagram (Fig. 2.32) shows the relation between the unsupported effective span (m) and

the standing time (h) in relation to seven Rock Mass Classes which he separated in accordance with the

rock mass behavior. As such, classes A to G represent rock mass behavior types. He also indicated the

characteristic range of application. He proposed that the rock mass classification shall accompany the

project from the design to the final documentation. This system has been used with some modifications

until recently and still provides the basis for the Rock Mass Behavior types which are described later.



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Fig. 2.32: Rock Mass Classification system of Lauffer

X-axis: Stand Time (h), Y-axis: Effective

Span (m), Rock mass classes A to G

Shaded area presents characteristic range of application

iii) Characteristic Curve of Pacher (1963)

The characteristic curve, Fig. 2.33 generally called the Fenner Pacher curve, shows the relation between

deformation (X-axis) and load/support development (Y-axis - up) and deformation and time of support

development (Y-axis - down). It represents the interaction of the rock mass and the support system with

time. In non stable rock mass the decrease of the radial stresses with deformation will have a low point

after which the loosening pressure and the required support increase. The point of pressure balance of the

rock mass and the support should be always on the downward curve of the radial stress.

Fig. 2.33: Fenner Pacher Curve

X-axis: Deformation, Y-axis: up: Load/Support

Development down: Time


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2.3.3. Geotechnical Tunnel design

i) Basic Procedure of the Geotechnical Design

The present status of tunnel design in accordance to NATM has been described in

The Austrian Draft of CONVENTIONAL TUNNELLING

these are guidelines published by the Austrian Society of Geomechanics. The guidelines were recently republished

still as a draft as Guideline for Geotechnical Design of Underground Structures with Conventional Excavation.

These guidelines have been developed by a working group of engineers from clients, contractors and consultants in

Austria using the experience gained in many projects constructed in accordance with NATM over several decades.

In Austria the guidelines serve as a supplement to the Standard OENORM B-2203-1, Regulation of the Construction

Contract for Mined Tunnelling.

The following sections, limited to the Design Phase, are partly an extract of the Austrian Draft, and provides a

better understanding of the design process. The Geotechnical and Tender Design as used for the Pir Panjal Railway

Tunnel follows widely the Austrian Draft.

ii) Purpose Scope of Work

The intended purpose of the Austrian Draft is to summarize the state of the art for conventional tunnelling inAustria. The design, contractual applications and construction management are described in detail.

Fundamental requirements for conventional tunnelling projects in Austria are:

Evaluation and classification of the ground conditions with respect to particular project requirements

Design subdivided in phases, staged with the project (and construction) development, which provides the

framework for a range of potential applications

Construction methods suitable for standard plant, equipment and materials

Back-checking of the predictions by geotechnical monitoring and adjustment to the conditions encountered

Flexible contractual models for fair remuneration

iii) Geological Geotechnical Evaluation

a) The main task of the geotechnical design is the economic optimization of the construction considering the

rock mass conditions as well as safety, stability, and environmental requirements.

b) The variability of the geological architecture including the local rock mass structure, rock mass and soil

parameters, stress and ground water conditions requires that a consistent and specific procedure be used

during the design process. The key influences governing the geotechnical design are the ground conditions

and behavior.

c) Existing schematic rating systems and their recommendations for excavation and support have been

developed from experience under specific conditions. A generalization for other rock mass and boundary

conditions frequently leads to inadequate design. Consequently a technically sound and economical design

and construction can be achieved only by applying a project specific and rock-mass-specific procedure.

d) In spite of all uncertainties in the description of the rock mass conditions, underground engineering needsa strategy, allowing a consistent and coherent design procedure that is traceable throughout the entire

project. The procedure outlined in this guideline consists of several phases.

e) There are two basic phases:



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A. Phase-1-Design

Basic Procedure

The geotechnical design, as part of the tunnel design, serves as a basis for approval procedures, the tender documents

(determination of excavation classes and their distribution), and the determination of the excavation and support

methods used on site .

The flow chart (Fig.. 2.3) shows the basic procedure, consisting of 5 general steps, to develop the geotechnical

design, beginning with the determination of the rock mass types and ending with the definition of excavation classes.

The five steps, which have to be followed, include:

Step 1 Determination of Rock Mass Types

The first step starts with a description of the basic geologic architecture and proceeds by defining geotechnically

relevant key parameters for each ground type. The key parameters, values and distributions are determined from

available information and/or estimated with engineering and geological judgment; values are constantly updated

as pertinent information is obtained. Rock Mass Types (RMT) are then defined according to their key parameters.

The number of Rock Mass Types elaborated depends on the project specific geological conditions and on the stage

of the design process.

Step 2 Determination of Rock Mass Behavior Types (BT)

The second step involves evaluating the potential rock mass behaviors considering each rock mass type and local

influencing factors, including the relative orientation of relevant discontinuities to the excavation, ground water

conditions, stress situation, etc. This process results in the definition of project specificBehavior Types.

The rock mass behavior has to be evaluated for the full cross sectionalarea without considering any modifications

including the excavationmethod or sequence and supportor other auxiliary measures.

The rock mass behavior types form the basisfor determining the excavation and supportmethods as well as assist

in evaluating monitoring data during the excavation.

Step 3 Determination of the excavation and support

Based on the defined project specific behavior types, different excavation and support measures are evaluated and

acceptable methods determined.

The System Behavior is a result of the interactionbetween the rock mass behaviorand the selected excavation

and supportschemes. The evaluated System Behavior has to be compared with the defined requirements. If the

system behavior does not comply with the requirements, the excavation and/or support scheme has to be modified

until compliance is obtained.

Once the acceptable excavation and support methods have been determined, both risk and economic analyses

should be performed to allow appropriate assessments during the tender process.



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This is the final step in the geotechnical design process. All possible geological conditionsshould be addressed with

a defined rangeof excavation and supportmethods as well as the probability or likely hood of occurrence.

Step 5 Determination of excavation classes

In the final step of the design process the geotechnical design must be transformed into a costand time estimate

for the tender process. Excavation Classes are defined based on the evaluation of the excavation and support

measures. The excavation classes form a basis for compensation clauses in the tender documents. In Austria the

evaluation of excavation classes is based on the regulations in ONORM B2203-1. At other places the local or agreed

regulations should be used.

The distributionof the expected behavior types and the excavation classes along the alignment of the underground

structure provides the basisfor establishing the bid priceduring tender and the bill of quantitiesduring project

execution.

iv) Detailed Assessment

a) Determination of Rock Mass Types

A Rock Mass Type is defined as a geotechnically relevant rock mass volume, including discontinuities and

tectonic structures, which is similar with respect to following properties

- in rock: rock type, mineral composition, strength (intact rock rock mass), rock- and rock mass conditions,

types of discontinuities, discontinuity properties, hydraulic properties

- in soil: grain size distribution, density, mineral composition, parameters of the soil components, matrix

parameters, water content and hydraulic properties

See Table 2.1 for key Parameters in Basic Rock Types.

Different Rock Mass Types have different characteristic parameters that influence their mechanical behavior.

To determine different rock mass types relevant key parameters have to be evaluated and defined. Rock

masses with similar combinations of relevant parameters are distinguished as one Rock Mass Type.

The definitions of the Rock Mass Types have to be based on the current knowledge in each project stage,

considering their importance for the successful completion of the project. The numberof defined Rock

Mass Typesisproject specificand depends on the design phase as well as on the complexity of the geologicalconditions in the project area. In general, in early design phases, a rough discrimination will be sufficient,

with increased information in subsequent design phases the distinction between the single Rock Mass Types

will be, and has to be more precise.

The final task in this step is to assignthe Rock Mass Typesalong the alignment.

Method

- Selected key parameters describe the geotechnically relevant properties of the rock mass. Table 2.1 is

intended to provide assistance for the selection of the relevant parameters for different rock types.

Depending on project specific boundary conditions, weighting of the parameters may be required. In

any case it has to be checked if the selected parameters are sufficient to adequately describe the rock

mass properties.

- The determination of the various parameters shall be based on local standards and regulations. The

reasons for the use of other standards or procedures have to be clearly explained.

- Identical lithological types with significantly different discontinuity and/or intact rock properties have to

be specified as different Rock Mass Types if this difference results in a different behavior type when

considering the variation in influencing parameters.



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Table 2.1: Example of selected key parameters for different general rock types

- Different key parameters may be required depending on the type and use of the underground structure.

The number of parameters used for the definition of the Rock Mass Types and their mode of classification

can change as the project progresses.


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- Collection of the relevant geotechnical parameters and influencing factors is done preferably during the

preliminary design. Investigations during the tender design should concentrate on reducing the uncertainty

or risk in geotechnically critical areas.

- Simple rating methods can be used in early project phases (feasibility study, preliminary design). Frequently

in these phases parameters from literature or previous experience have to be used due to lack of data

from the project area.

- Empirical and numerical methods, as well as in situ tests may be used in later project phases (project

approval, tender design) for the determination of the properties of a representative rock mass volume.

- Rock mass strength, deformation characteristics, hydraulic properties, as well as specific properties (for

example pronounced anisotropy, low friction of discontinuities, time dependent behavior, intercalation

of other rock types, etc.) have to be evaluated and shown in the documents.

b) Determination of Rock Mass Behavior Types

The rock mass behavior is determined for each rock mass type by evaluating the effect of the influencing

factors on the response of the rock mass with the full excavation geometry. First the orientation of relevant

discontinuity sets relative to the axis of the underground structure must be determined; the appropriatestress conditions defined, as well as the local ground water conditions for single homogeneous sections

along the alignment. After assigning all relevant properties and influencing factors to each section, the rock

mass behavior (reaction to the excavation) can be evaluated for each section of the underground structure.

The expected rock mass behavior is then categorized into the general types listed in Table 2.2, and the

distribution along the alignment determined.

The Rock Mass Behavior Types form the basis for the design of the excavation sequence and appropriate

support.

Method

- An unsupported and indefinitely long cavity has to be assumed When considering long underground

structures (tunnels). Sequential excavation steps are not considered in this phase. All construction

measures (excavation and support, as well as auxiliary measures) shall be derived from the determinedrock mass behavior determined in a consistent manner.

- For underground structures with a limited length (portals, caverns, lay-bys, etc.) the evaluation should

consider the entire length and geometry.

- The following influencing factors are usually considered for the evaluation of the Rock Mass Behavior:

a) Rock Mass Type (RMT)

b) Virgin stress conditions

c) Shape, size, and location of the underground structure

d) Excavation method

e) Relative orientation of the underground structure and discontinuities as a basis for kinematical

analyses, and the influence of the rock mass structure on the stress redistribution

f) Ground water, seepage force, hydraulic head

For the determination of the rock mass behavior the following evaluations are recommended:

g) Kinematics: Kinematical analyses for the determination of discontinuity controlled overbreak and

sliding of wedges



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Methods: Key Block Theory , analyses using stereographic projection

h) Rock mass utilization: evaluation of the ratio between the strength of the rock mass and the spatial

and transient stress situation in the vicinity of the underground opening.

Methods: analytical and numerical methods

i) Time dependent effects: evaluation of creeping, swellingj) Failure mechanisms: possible failure mechanisms of the rock mass have to be analyzed and described

at least qualitatively (for example: spalling, shearing along discontinuities as result of stress release,

shear failure, etc.)

Methods: model tests, analytical analyses, numerical analyses, which allow the modeling of discrete

failure planes, case histories, which are backed up by measurement results.

- Analytical and/or numerical methods are to be used, which provide appropriate modeling methods for

the characteristics of the rock mass types under evaluation under the given boundary conditions.

- The Rock Mass Behavior Types resulting from the analyses have to be assigned to one of the general

categories listed in Table 2.2. In case more than one Behavior Type is identified in one of the general

categories, sub types have to be assigned (for example 2/1, 2/2 for a rock mass with a different potential

for overbreak with different combinations of joint sets or orientations)

Behavior Type (BT) Description of potential failure modes/mechanisms during excavation of the

unsupported rock mass

1 Stable Stable rock mass with the potential of small local gravity induced falling or sliding

of blocks

2 Stable with the potential of Deep reaching. discontinuity controlled, gravity induced falling and sliding of

discontinuity controlled blocks, occasional local shear failure

block fall

3 Shallow shear failure Shallow stress induced shear failures in combination with discontinuity and gravity

controlled failure of the rock mass.

4 Deep seated shear failure Deep seated stress induced shear failures and large deformation

5 Rock burst Sudden and violent failure of the rock mass, caused by highly stressed brittle

rocks and the rapid release of accumulated strain energy

6 Buckling failure Buckling of rocks with a narrowly spaced discontinuity set, frequently associated

with shear failure

7 Shear failure under low Potential for excessive overbreak and progressive shear failure with the

confining pressure development chimney type failure, caused mainly by a deficiency of side pressure

8 Ravelling ground Flow of cohesionless dry or moist, intensely fractured rocks or soil

9 Flowing ground Flow of intensely fractured rocks or soi l with high water content

10 Swelling Time dependent volume increase of the rock mass caused by physical-chemicalreaction of rock and water in combination with stress relief, leading to inward

movement of the tunnel perimeter

11 Heterogeneous rock mass Rapid variations of stresses and deformations, caused by block-in-matrix rock

with frequently changing situation of a tectonic mlange (brittle fault zone)

deformation characteristics

Table 1.2: General categories of Rock Mass Behavior Types


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c) Records

Each Rock Mass Behavior Type has to be described sufficiently. The following list represents the minimum

requirements:

- Sketch of the expected rock mass structure

- Rock Mass Type(s)

- Orientation of relevant discontinuities relative to the underground structure

- Rock mass strength/utilization

- Ground water, both quantities and influence on rock mass behavior

- Rock mass behavior (behavior during excavation, face stability, type of failure mechanism, long term

behavior) with sketches of expected failure mechanisms

- Displacements, estimate of magnitude, orientation, and development over time

In case more than one Behavior Type is determined in one general category, the delimiting criteria for the

sub types can be:

- Rock Mass Type- Rock mass structure

- Ground water

- Kinematics, failure mode

- Magnitude and time dependent development of displacements

d) Determination of excavation and support

After the Rock Mass Types and the Behavior Types have been determined, appropriate construction methods

(excavation sequence, separation of faces, support methods, and auxiliary measures if required) are

determined. The following step evaluates the System Behavior (representing the interaction between the

rock mass behavior and construction measures), which is then compared to the design requirements. Influencing factors for the System Behavior are:

- Rock Mass Behavior Type

- Shape and size of underground opening, considering intermediate construction steps

- Spatial and timely construction sequence

- Time dependent properties of the rock mass and support elements, if relevant

- Support elements, their place and time of installation

Method

- The analysis methods depend on the boundary conditions of the underground structure investigated.

Basically the following methods for analysis of the System Behavior are applicable:

a) Analytical methods

b) Numerical methods

c) Comparative studies, based on experience from previous similar projects

- The variability of the influencing factors, as well as the influence of the construction on the environment

has to be considered.



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- Analysis and Proofs: The system behavior shall be confirmed by analyses and compared with the design

requirements. The analysis of the system behavior shall decide:

a) The stability of all construction stages.

b) The compliance with environmental requirements (surface settlements, vibrations ground water

disturbance, etc.)

c) that displacements are within defined limits (critical strain, serviceability, compatibility)

e) Determination of excavation classes

After the final determination of all construction related measures related to the rock mass behavior,

excavation classes must be determined. In Austria this is according to ONORM B2203-1. The excavation

classes by definition are required to specify the underground work, enable a cost estimate, and provide the

basis for compensation. The two parameters, the round length and a support rating (normalized support

quantity value) define the excavation classes.

An excavation class may be assigned to more than one Behavior Type, as the same measures can be

appropriate for different rock mass behavior types. On the other hand it may be required to design more

than one excavation class for one Behavior Type, in case the variation of properties requires a wider rangeof support measures. Preferably in such cases separate Behavior Types should be defined, with clear limiting

criteria (for example range of displacements, volume of expected overbreak, etc.). However, if one Behavior

type requires different excavation classes depending on local influencing factors then the criteria should be

reevaluated and new behavior type determined with clear limiting criteria (for example the expected range

of displacements, volume or location of expected overbreak, etc.

To establish the bill of quantities a prediction of the distribution of excavation classes is required. This

distribution has to be established for the most probable distribution of Behavior Types, and should also

show the likely variations of excavation classes resulting from the distribution (variation, spread) of

influencing factors. When establishing the distribution of excavation classes along the alignment the

heterogeneity of the rock mass has to be considered. In very heterogeneous ground, frequently changing

the excavation and support methods in many cases will be technically and economically unfeasible.

f) Geotechnical Report

The results of the geotechnical design have to be summarized in a Geotechnical Report. In this report, the

single steps outlined in this guideline have to be shown in a way to allow a review of the decisions taken.

The individual reports submitted by the various expert teams involved in the project form the basis for the

Geotechnical Report. Experts, geotechnical engineers and the tunnel designer should prepare the report in

a joint effort.

Contents of the Geotechnical Report

- A summary of the results of geological and geotechnical investigations, and the interpretation of the

results.

- A description of the Rock Mass Types and the associated key parameters

- A description of the Rock Mass Behavior Types, the relevant influencing factors, the analyses performed,

and the geotechnical model on which the BT is based

- A report on the determination of excavation and support, relevant scenarios considered, analyses applied,

and results


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- The baseline construction plan

- Detailed specifications to the Baseline construction plan (system behavior, measures to be determined

on site, warning criteria and limits, etc.)

- Report on the determination of excavation classes, their distribution along the alignment

Contents of the Baseline Construction PlanThe baseline construction plan summarizes the geotechnical design and should contain following information:

- Geological model with distribution of Rock Mass Types and Behavior Types in a longitudinal section

- Sections, where specific requirements for construction have to be observed

- Fixed excavation and support types (round length, excavation sequence, overexcavation, invert distance,

support quality and quantity, ground improvements, etc.)

- List of measures to be determined on site (support ahead of the face, face support, ground improvement,

drainage, etc.)

- Description of System Behavior (behavior during excavation, deformation characteristics, utilization of

supports, etc.)

- Warning criteria and levels, as well as remedial measures according to the safety management plan

2.3.4 NATM Process on site

The simplified steps of an underground transition created with NATM are shown below.

Step #1

Cutting a length of tunnel,with a roadheader/

Excavator/Drill &Blast



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Step#2

Applying layer of shotcrete on reinforcementmesh and thereafter Rockblt


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Step#3

Primary lining applied to whole cavity, which

remains under observation.

Step#4

Final lining applied.

Step#5

Completed Tunnel



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2.4 Appointment of the Detailed Design and Construction Supervision Consultant (DDC)

A New Initiative:

2.4.1 The detailed design and construction of the new Rail line project in Pir Panjal range of the Himalayas (a

relatively young Geological Formation) was a big challenge for Engineers. It is well known that Himalayan

geology is complex full of frequently changing formation and surprises. Folds, thrust zones and Faults arecommon. The strata comprises Fluvioglacial deposits, Limestone , Quartzite , Slate and Tuff , Volcanic traps

and bands of Shale, Sandstone and Limestone. The geology along the chosen alignment comprises rocks

with unconfined compressive strength ranging between 60MPa to 140 MPa, and at places laden with

considerable amount of trapped water.

2.4.2 All Underground works are prone to unforeseen problems. Geological and Geotechnical investigations can

only provide some clues to these problem but their gravity can best understood only when encountered. In

Pir-Panjal tunnel the defined alignment shows it commencing in soft ground with low overburden at each

end. This low cover was due to the nallahs flowing over the tunnel alignment. Both nallahs are perennial in

nature and are situated at tunnel meters 220 and 442 at its North and South ends respectively. The tunnel

alignment passes under populated villages, NH-1A, and an Aquifer with considerable charge of water. These

make the construction more difficult.2.4.3 It is also to be noted that the region falls in seismic Zone-V of the country ,which experiences severe tectonic

movement and seismicity.

2.4.4 Besides the unpredictable geology, the terrain, the mode of communication and the climatic conditions

impose further challenges in the construction of the countrys longest railway/transportation tunnel. It was

almost a dream to construct this Tunnel which would be open a marvel of civil engineering. National Highway

NH 1A is the only link between Jammu and Srinagar, the winter and summer capitals of the state of Jammu

& Kashmir. Landslides close this Highway frequently during the snows and also the rainy season. This cuts off

road communication the only available economical mode of communication between the two capitals.

2.4.5 The clear objective of the Indian Railways is to establish a dependable all weather rail transportation in the

state of Jammu and Kashmir and connect it with the rail network in the rest of the country.

2.4.6 The in house knowledge and expertise available in this field within the Railways was very limited and

inadequate to meet the requirements of design of the tunnel of this magnitude. The tunnel had to be designed

and constructed catering for ventilation and disaster safety aspects. Considering these factors, it was desirable

to engage the services of a consultant who would design the tunnel system as a whole, together with the

construction methodology, also rendering the technical know-how during the process of construction through

the variable strata conditions.

2.4.7 Keeping the above requirements in view, the notice for expression of interest for design of this tunnel was

issued, inviting applications from different firms agencies, who were interested in associating themselves

with the design and construction supervision of this tunnel.

2.4.8 In response of NIT for this work, 25 firms/consultants showed interest, evaluation and selection of Consultant

for this complex and highly specialized assignment was done on QCBS method (quality and cost based system).

In the evaluation, 80% weight age was given to the technical competence of the consultant.

2.5 Main Deliverables Required from DDC

2.5.1 The detailed design and construction supervision consultant (DDC) required to prepare detailed engineering

documentation required for actual implementation of work In summary, the DDC had to :


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(i) Develop design criteria: The consultant shall prepare comprehensive design criteria that achieve the

objectives of the Project which had to deal with the vagaries of the varying geology coupled with soft

ground and high overburden and trapped water formations.

. The design criteria was to be prepared and presented in such a way that these could be readily applied by

the DDC and any other design consultant (such as the one that was to be engaged under a design and

construct contract). The design criteria has to include all requisite and incumbent assumptions regardingloads imposed, deformations expected and to be accounted for in the design in a way that the proposed

method could deal with the varying geology and other existing conditions.

(ii) Prepare schematic designs for all elements of the Project, Notwithstanding any earlier feasibility studies,

the DDC was required to develop the relevant outline designs for a number of different options for the

main Tunnel, the Access drive inside the tunnel, the Shaft, the approach roads and, if appropriate, the

slope protection works to enable options to be objectively compared against each other. Each option had

to developed in sufficient detail to demonstrate that the project objectives and design criteria had been

complied with and to enable estimate the preliminary construction costs to enable prepare the construction

program. The DDC had then to formulate an objective method for comparing the options in order to select

the design of the preferred scheme.

(iii) Formulate the construction methodology, construction sequences and the construction program.

(iv) Design the Tunnel ventilation system during construction and during subsequent service

(v) Design the Drainage system as appropriate during and after construction

(vi) Define the scope and requirement of safety and disaster management

(vii) Detailed planning;-The DDC was required to prepare a program for all aspects of the project implementation,

including for the activities within the DDCs scope of services and those that were to be undertaken by

others concerned. This was to be referred to as the project program. This program had to reflect the agreed

procurement strategy and Scheme Designs for all elements of the Project. It had to be achievable and

accompanied by a commentary which had to identify options and alternative scenarios where ever

appropriate.

(viii) Define requirements for any further investigations or tests, Additional studies prior to and during the detaileddesign phase (expected to be needed) to provide important information that would reduce any uncertainty

that would be associated with the technical, and commercial aspects of the Project. The DDC had to identify

the extent of the above studies and any other studies considered appropriate which would lead to the

overall objective of reducing all risks to acceptable levels. As part of this undertaking the DDC had to define

in detail where and if appropriate how the additional studies would be executed and what the objectives of

the studies would be.

(ix) Prepare tender documents for all elements of the Project. The DDC was required to prepare comprehensive

detailed technical specifications, setting out the objectives of the requisite studies, the required deliverables

and the information that would be provided by the DDC to form part of the studies. These technical

specifications, where appropriate, had to set out the minimum requirements for tests e.g. scale, duration,

sample type, etc.(x) Assist with the prequalification and appointment of contractors who would be responsible for the

construction of this long Tunnel forming part of the Construction of Udhampur Srinagar Baramulla

Broad Gauge Rail Link



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2.6 Salient Features of Pir Panjal Tunnel

GENERAL FEATURES

CLIENT NORTHEN RAILWAY

PRIME CONTRACTOR IRCON INTERNATIONAL LIMITEDSUB CONTRACTORS M/S HCC LTD, FOR PACKAGE V-A & V-B &BUMI DEVELOPERS

FOR SOFT GROUND TUNNELLING

CONSULTANT M/S GEO CONSULT RITES JV

TOTAL LENGTH OF TUNNEL 10.960 Km

TOTAL LENGTH OF TUNNEL INCLUDING CUT

AND COVER PART 11.215 Km

WORK AT SOUTH PORTAL COMMENCED ON 10Aug 2005

WORK AT NORTH PORTAL COMMENCED ON 30 July 2005

WIDTH OF TUNNEL AT 2.167 M above rail level 8.394 m

FINISHED WIDTH At rail level 7.331 m

FINISHED HIGHT Above rail Level 6.629 m

FINISHED CROSS SECTIONAL AREA OF TUNNEL 48 m2

FINISHED PERIMETER OF TUNNEL 26 m

EXCAVATED CROSS SECTIONAL AREA OF TUNNEL 59 m2TO 80 m2

DIFFRENCE BETWEEN C/L OF TUNNEL AND

C/L OF TRACK 1.196m

TYPE OF CONSTRUCTION SINGLE LINE TRACK WITH 3 M WIDE RESCUE ROAD ON ONE SIDE

METHOD OF CONSTRUCTION NEW AUSTRIAN TUNNELLING METHOD (NATM)FINAL INNER LINING CONCRETE M30

OUTER LINING SHOTCRETE M25

2.TECHINAL PARAMETERS

FORMATION LEVEL AT SOUTH END 1713.15 m

FORMATION LEVEL AT NORTH END 1756.22 m

TUNNEL HIGH POINT (altitude) 1771.479 m at CH 159+124

DESIGN SPEED 100 KmPh

TUNNEL CURVATURE (in plan) STRAIGHT (INFINITY)

RULING GRADIENT 1 IN 100

GEOLOGICAL FEATURE / ROCK TYPE FAULTED MOUNTAIN RANGE WITH SILTY CLAY SOIL, SHALE, LIMESTONE,

QUARTZITE, AGGLOMERATIC SHALE, ANDESITE/BASALT

RAIL GAUGE 1676 mm

TRACK 60KG HH ,RHEDA 2000 BLT WITH VOSSLOH 300-1U FASTENING SYSTEM

VENTILATION BY JET FANS


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Chapter 3

Exploring The Unknown

3.1 Geological And Geotechnical Investigations

3.1.1 These investigations are the key to tunneling with comprehensiveness that urges well for reliability and

simplicity that permit convenient repetition of procedures and support-systems during construction.

Knowledge of ground conditions plays a key role in choosing the optimized construction technique which

ultimately leads to successful completion of the Project. It is important to realize that the ability to influence

the project outcome (in terms of cost and schedule) is easier only through proper site investigations.

3.1.2 However, it is worth mentioning here that no matter how much of the ground we test in the preliminary site

investigation, how many bore hole cores we test in the laboratory, even then we can test only a small portion

of the total strata affected by the construction of the Tunnel.

3.1.3 Preliminary site investigations only help in making merely an informed decision but investigations conducted

during construction and the continuous measurements made during construction are essential to compare

the actual with the data anticipated from the preliminary site investigations. It is important to realize thatthe preliminary site investigations only help in closing-in on the ground model that develops and evolves as

the project progresses.

3.1.4 Site investigation is defined as the overall investigation of sites associated with tunnel construction including

the overhead and subsurface strata investigation. The aim of site investigation is to produce a full three

dimensional model of the site including the overhead and the subsurface strata. This can assist in guessing

the associated risk involved in the tunneling work. The risk can then be assessed and its mitigation attempted

using the appropriate construction technique.

3.1.5 The cost involved in carrying out appropriate site investigation can range between 1% to 3% of total the cost

of the Tunnel Project. It is important to use this money wisely to enable encounter the risks likely to be faced

during the actual construction.

3.1.6 In the subsurface works pre- and post-construction investigations play important roles in planning, designing,

and in the actual construction work. Tunnel construction is governed by the ground through which it is to

penetrate and hence overhead and subsurface site investigations are vital to obtain the requisite ground

characteristics the geotechnical and hydrological parameters. Hidden Geology and Hydrology not only

influence the cost of the project but also the completion time, the potential in service behavior of the

structure and in deciding the long term maintenance strategies and procedures. The Geology of the area can

affect the alignment of the railway line in hilly terrain. Hence a serious combined effort is necessary from all

parties that are involved in planning, designing and construction.


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Exploring The Unknown 55

3.1.7 Geology of the strata to be tunneled through plays significant role in the planning and construction of the

tunnel. Subsurface work can pose formidable, if not impossible challenges to the geotechnical design and

construction teams.

3.1.8 In this chapter an attempt is made to explain the importance of geological and geotechnical investigations

that were required in planning, designing and constructing the Pir-Panjal Railway Tunnel. It emphasizes on

overall approach and the flexible rules set out for investigation in the complex geological conditions. Great

care had to be taken in the geological and geotechnical investigations called for in the construction of this

10.960 Km long Pir-Panjal tunnel. The Tunnel construction schedule necessitated construction of an Access

Tunnel and Shaft for creating additional faces (fronts) for taking up the Tunnel excavation. This tunnel is for

a single track Broad Gauge Railway line with approximately 3m wide side service road in the west side of the

tunnel. It is a straight tunnel aligned nearly in N-S direction. It has a maximum overburden of 1.2 Km and

minimum overburden as low as 10m.

3.2 Importance of Investigations Required for The Construction of Tunnel

3.2.1 Geology of the area affects almost every major decision that must be taken in the planning, design, andconstruction of a tunnel. Geology dictates the cost of the project and behavior of the structure. Indeed

geology and hydrology of the area in the tunnel construction dominantly effects nearly all aspects of planning,

design, construction and even the subsequent maintenance work.

3.2.2 In view of rather complex geology and surface conditions in the Pir-Panjal range, our approach had to be

very flexible and yet elaborate. This definitely helped in deciding the support systems in a way that lead to

limited over-breaks in the excavation, less risk of collapse and ultimately prevented any major incidents. This

helped in optimizing construction time and cost. Geological and geotechnical investigations in complex

geological ambience can be divided in three phases, namely:- 1) investigations required during fixing of

alignment, 2) investigations required before detailed design and tendering and 3) investigations required

during construction.

3.2.3 Himalayas present a rather young folded mountain range whose geology is complex and rapidly changing.Detailed geological and geotechnical investigations of the project area were carried out and a surface map of

the project area 500m either side of the alignment was developed together with tectonic and drainage map.

On the basis of these maps limited seismic surveys were conducted in the soft ground near the portals to

know more about the effects of the low overburden strata there.

3.2.4 Due to steep slopes, accessibility along the tunnel alignment was severely limited to allow extensive

geotechnical investigations along the alignment. Geo-technical explorations were carried out by drilling 76mm

dia cores and testing them. More deep bore geotechnical investigations were done in an attempt to understand

the medium to be tunneled through, to establish various bedding planes and to verify the geological profile

based on the captured surface geological data. M/s RITES and M/s Mineral Exploration Corporation Limited

(MECL) were engaged for drilling bore holes varying in depth from 30m to 640m. Majority of these extended

below the formation level of the tunnel. Deep bore holes were drilled by wire line method hence weresusceptible to deviate from direction and some times the results could well be misleading. Despite these

limitations, a fairly good knowledge of the rocks that were likely to be encountered, was obtained from

initial investigation. A total of 14 bore holes were drilled in all.

3.2.5 A significant variation was expected between the predicted geology and the actual geology owing to presence

of weathering in the rock under low rock cover and presence of deep seated faults and folds. Probe holes

were drilled during the progress of the Tunnel work in entire length. These proves very useful in obtaining

the required Geological and Geotechnical inputs. Based on the results of these probe holes and the geology

actually encountered, geological predictions were made for the approaching face. This helped in deciding


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the support system in advance. In addition to probe holes, Seismic prediction method at the face was also

used to know the geology ahead, but this method was not found very useful on account of rapidly changing

geology.

3.3 Why these Investigations are Necessary?

These are necessary in order to:

3.3.1 Establish at least the general nature, the pattern and some properties and behavior of the rock/soil mass,

3.3.2 Assess the the most probable conditions and the most unfavourable conceivable deviations from these

conditions which play a major role in the assessment of geology.

3.3.3 Establish a design based on a workable hypothesis regarding the behavior anticipated under the most probable

of conditions.

3.3.4 Estimate the quantities likely to be executed on the basis of the working hypothesis as construction proceeds.

3.3.5 Estimate the quantities under the most unfavourable conditions.

3.3.6 Selection in advance of any action on or modification of the design for every foreseeable (significant) deviation

of the observable findings vis--vis those predicted on the basis of the working hypothesis.

3.3.7 Modify design to suit actual site conditions.

3.4 Classification of Investigations

3.4.1 The required investigations can be classified as follows:

i) Preliminary investigations,

ii) Design investigations and

iii) Control investigations.

i) Preliminary Investigations

Investigations needed to access general suitability of the site and compare different alignments with due consideration

of third party.

ii) Design Investigations

Investigations needed to provide information required for design of tunnel including its construction methodology.

iii) Control Investigations

Investigations required during construction or execution of the project for checking and alerting against the ground

characteristics and ground water condition.

3.4.2 A typical site investigation comprises following four key el

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Pir Panjal Railway Tunnel - A dream realized