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TRANSPORT and ROAD RESEARCH LABORATORY

Department o f the ~ n v i r o n m e n t Department o f Transport

SUPPLEMENTARY REPORT 335

A REVIEW OF TUNNEL LINING PRACTICE I N T H E U N I T E D KINGDOM

by

R N Craig and A M Mui r Wood

(Sir William Halcrow and Partners)

The work described in this Report was sponsored by the T R R L

A n y views expressed in this Report are no t necessarily those of the Transport and Road Research Laboratory or o f any other division of

either the Department o f the Environment o r the Department o f Transport

Prepared for the Tunnels Division Structures Department

Transport and Road Research Laboratory Crowthorne, Berkshire

1978


CONTENTS

Abstract

1. Introduction

2. Investigation methods

3. Purpose and methods of lining tunnels

3.1 General

3.2 Market for tunnel linings (1970-76)

3.3 Previous forms of tunnel linings

3.3.1 Timber

3.3.2 Brickwork

3.3.3 Masonry

4. Cast iron and steel tunnel linings

4.1 Cast iron tunnel linings

4.1.1 Bolted grey iron tunnel linings

4.1.2 Bolted spheroidal graphite iron tunnel linings

4.1.3 Expanded grey iron tunnel linings

4.1.4 Expanded spheroidal graphite iron tunnel linings

4.2 Steel tunnel linings

4.2.1 Bolted steel tunnel linings

4.2.2 Expanded steel tunnel linings

4.2.3 Liner plates

5. Precast concrete tunnel linings

5.1 Moulds

5.2 Steel reinforcement

5.3 Joints

5.3.1 Plane or helical joints

5.3:2 ~oncave/convex and convex/convex joints

5.3.3 Tongue and groove joints

5.4 Bolted and dowelled tunnel linings

5.5 Expanded concrete tunnel linings

5.6 Grouted smooth bore concrete tunnel linings

5.7 Expanded grouted concrete tunnel linings

5 .8 Pipe jacking with concrete pipes

6. Cast in-situ concrete tunnel linings and temporary ground support

6.1 Cast in-situ concrete tunnel linings

6.2 Rock bolting

6.3 Sprayed concrete tunnel linings

6.4 Temporary arch and lagging supports

7. Instrumentation, monitoring, research and development

7.1 General

7.2 Deformation of tunnel linings

7.3 Sub-surface n ~ o v e n ~ e n t s and porewater pressure changes

7.3.1 Horizontal sub-surface movements transvers to tunnels

7.3.2 Horizontal movements parallel to the centre line of tunnels

7.3.3 Vertical ground movements

7.3.4 Porewater pressure changes


Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on 1'' April 1996.

This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.


7.4 Surface settlement 7.4.1 Development of settlement profile and trough

7.4.2 Extent of settlement

7.4.3 Discussion on ground movements and settlement

7.4.4 Settlement above multiple tunnels

7.4.5 Settlement above tunnels constructed using pipe jacking methods

7.5 Stresses and hoop loads in linings

7.6 Recent instrumentation and monitoring of tunnels

7.7 Research

7.8 Development

8. Design 8.1 Designmethods

8.1.1 Soft ground tunnels 8.1.2 Rock tunnels

8.2 Joints in linings

8.3 Openings in preformed linings 8.4 Linings in mining areas

9. Waterproofing 9.1 Grouting

9.2 Lead caulking 9.3 Cement based caulking compounds 9.4 Flexible caulking compounds

9.5 Sealing strips

9.6 Grummets 10. Tunnel construction

10.1 Rates of Progress 10.2 Suggested tunnel lining methods

10.2.1 Bolted cast iron linings

10.2.2 Expanded cast iron linings 10.2.3 Bolted concrete linings

10.2.4 Grouted smooth bore concrete linings

10.2.5 Expanded concrete linings

10.2.6 Expanded grouted concrete linings 10.2.7 Steel liner plate linings

10.2.8 Steel circular membranes

10.2.9 Bolted and expanded steel linings

10.2.10 Cast in-situ concrete linings 10.2.1 1 Sprayed concrete or gunite linings

10.2.12 Rock bolting ' 10.2.13 Pipe jacking

10.3 Special ground conditions 10.3.1 Aggressive ground conditions 10.3.2 Mining areas

11. Costs 1 1.1 Unit cost of linings

11.1.1 Precast concrete linings

1 1 .1.2 Cast iron linings 1 1.1.3 Secondary linings


12. Maintenance

12.1 Road tunnels

12.2 Railway tunnels

12.3 Small diameter tunnels

13. Recommendations

13.1 Standardisation

13.2 Specifications

13.3 Developinent of linings

13.4 Waterproofing

13.5 Instrumentation, monitoring and research

Acknowledgenlents

14. Appendix 1 List of organisations consulted 15. Appendix 2 Primary and secondary linings - General

15.1 Tunnel lining demand, 1970-76 15.1.1 Collection of data

15.1.2 Total length of tunnels constructed

15 .I .3 Total excavated volume of tunnels constructed

15.1.4 Average external diameters of tunnels

15.1.5 Tunnelling in 1976-1980

15.1.6 Tunnelusage

15.2 Secondary linings

15.2.1 Brick lining

15.2.2 Cast in-situ concrete linings

15.2.3 Infill panels

15.2.4 Thin cement mortar linings

15.2.5 Sprayedmortarorgunitelinings

1 5.2.6 Steel linings

15.2.7 Glass reinforced linings

15.2.8 Other forms of secondary linings

15.3 Developments overseas

15.3.1 Concrete linings

15.3.2 Cast iron linings

15.3.3 Steel linings

15.3.4 Other forms of lining

16. Appendix 3 Cast iron and steel tunnel linings

16.1 Grey iron

16.2 Spheroidal graphite iron 16.3 Manufacture of cast iron linings

16.4 Steel linings

16.5 Bolted grey iron linings

16.6 Bolted spheroidal graphite iron

16.7 Bolted steel linings

16.8 Expanded grey iron lining

1 6.8.1 Articulated grey iron lining

16.8.2 Expanded bolted grey iron lining

16.9 Expanded steel linings

16.1 0Steel liner plates

16.10.1 Armco liner plates

16.10.2 Com~nercial Hydraulics liner plates


17. Appendix 4 Precast concrete tunnel linings

17.1 General 17.2 Manufacture

17.3 Moulds 1 7.4 Reinforcement

1 7.5 Joints 17.6 Bolted and dowelled concrete linings

17.6.1 LTE - Central Line extension 17.6.2 Deep tunnel air raid shelters in London 17.6.3 Defence installation - Dorset Coast

17.6.4 Standard bolted concrete linings 17.7 Expanded concrete linings

17.7.1 Don-Seg lining 17.7.2 Wedge Block lining

17.7.3 Greenwood to Potters Bar tunnels

17.7.4 LTE running tunnels 17.7.5 Heathrow Cargo tunnel

17.7.6 Collins lining 17.8 Grouted smooth bore tunnel lining

17.8.1 McAlpine lining

17.8.2 Spun Concrete Flexilok lining 17.8.3 Spun Concrete Extra Flex lining 17.8.4 Charcon Tunnels Rapid lining 17.8.5 Charcon Tunnels Universal lining

17.8.6 Rees Mini tunnel 17.8.7 Mersey Kingsway and Dartford Duplication tunnels

17.9 Expanded grouted concrete tunnel linings 18. Appendix 5 Cast in-situ concrete tunnel linings and temprary ground support

18.1 Cast in-situ concrete tunnel linings 18.1.1 Roadtunnels

18.1.2 Railway tunnels 18.1.3 Water tunnels 18.1.4 Sewer tunnels

18.2 Rock bolting 18.2.1 Mechanical anchored bolts 18.2.2 Resin anchored bolts 18.2.3 Other forms of anchor

18.3 Sprayed concrete tunnel linings

18.4 Temporary arch and lagging supports 18.4.1 Steel arches

18.4.2 Bernold system 19. Appendix 6 Instrumentation, monitoring research and development

19.1 Instrumentation and monitoring

19.1.1 LTE Central Line extension to Ilford (1942) 19.1.2 MWB Ashford Common tunnel (1952)

19.1.3 LTE underground tunnels (1952-5 6) 19.1.4 River Clyde water tunnel (1953-55) 19.1.5 Shell building 1957

19.1.6 MWB tunnels (1955-75)


19.1.7 Clyde vehicular tunnel (1954-1961)

19.1.8 CEGB, Sizewell Power Station cooling water tunnels (1962-1963)

19.1.9 LTE Victoria Line (1960-1968)

19.1.10 Elephant and Castle shopping centre (1963-1965)

19.1.1 1 BAA - Heathrow cargo tunnel (1968) 19.1.12 Mersey Kingsway tunnels 2A and 2B (1968-1972) 19.1.13 Ely-Ouse water tunnel (1969-1973)

19.1.14 LTE Fleet Line at Green Park (1972-1973)

19.1.1 5 CEGB Severn-Wye cable tunnel (1972-1973) 19.1 .I 6 Cleveland Potash: Boulby Shaft (1973-1975) 19.1.1 7 BR Liverpool Loop-Moorfields Station (1 973-1975)

19.1.1 8 LTE - Fleet Line at New Cross (1973) 19.1.19 LTE - Fleet Line at Regents Park (1973-1974)

19.1.20 NWA Tyneside sewerage scheme - Hebburn contract (1973-1974)

19.1.21 NWA Tyneside sewerage scheme - Tyne Syphon (1974)

19.1.22 NWA Tyneside sewerage scheme - Willington Gut (1974-1975)

19.1.23 Kings Lynn mini tunnel (1974)

19.1.24 NWA Kielder scheme (1974)

19.1.25 TRRL Chinnor trials (1974)

19i1.26 Warrington sewer (1975-1976)

19.1.27 Channel Tunnel Stage 2 (1974-1975)

19.1.28 Tunnels crossing at right angles or on the skew

19.1.29 Settlement at the surface

19.2 Research 19.3 Development

20. Appendix 7 Design methods

20.1 Bull's Method

20.2 Morgan's ~ e t h o d ~ '

20.3 Muir Wood's Method

20.4 Schulze and Duddeck Methods 20.5 Peck's Method

20.6 Temporary design conditions

20.7 Terzaghi's Method

2 1. References

0 CROWN COPYRIGHT I978 Extracts from the text may be reproduced except for

commercial pulposes provided the source is acknowledged


A REVIEW OF TUNNEL LINING PRACTICE I N THE UNITED KINGDOM

ABSTRACT

This Report outlines the several methods used in the United Kingdom for

lining tunnels and gives brief details of some of the more recent tunnels

constructed with each form of lining. The different methods available for

lining tunnels are discussed taking into account the tunnel usage and the

ground conditions. Methods of waterproofing tunnels, use of secondary

linings and cost data are included.

The approximate annual length and volume of tunnels constructed

for the period 1970-76 are given, broken down into different types of

lining and tunnel usage.

The instrumentation of tunnel linings and of ground movements

during the construction of tunnels have been examined and the design

methods are discussed. Recommendations are given for research and

development of tunnel linings.

1. INTRODUCTION

Following the Organisation for Economic Co-operation and Development (OECD) Advisory Conference on 1 Tunnelling held in Washington, U.S.A. in 1970 , theTransportand Road Research Laboratory's Research

2 Committee on Tunnels, on the advice of the Panel on Tunnel Linings, recohmended that a review be carried out of tunnel lining ,practice in the United Kingdom. After discussion with Sir William Halcrow and Partners,

Consulting Engineers, the senior author was seconded to the Transport and Road Research Laboratory to carry out the survey.

This Report is divided into two parts with details of tunnel linings, research, design and recommendations

in the main text which is supplemented with more detailed data, including brief details of some of the more

recent tunnels, in the Appendices. The Report is aimed to give comprehensive information on tunnelling practice

and research on tunnel linings in the United Kingdom which will be useful not only t o those who have a wide

knowledge but also to those with little or no knowledge of tunnelling who may be considering the use of tunnels

for future schemes. It covers the whole field of tunnels from the 1 .Om diameter to the largest road tunnels.

There is a predominant use in the United Kingdom of preformed linings since the localities for much of the

recent tunnelling are found in soft ground, weak rock or shattered or heavily jointed rock.

The several methods of lining are discussed in Chapters 3, 4,s and 6 with additional data in Appendices 2, 3 ,4 and 5. The ground conditions in which each lining has been constructed are given together with tunnel usage. However, in some instances the choice of lining may not necessarily have been that most suited t o the ground

conditions. Tumellers, like most groups of engineers, are seldom unanimous on the best lining to use in given

circumstances. In addition, the ground conditions likely to be encountered may not have been accurately known

or may be so variable as to require a highly tolerant scheme. There is great skill in knowing when t o specify the


types of linings and methods which have been well tried and proven over the last 2 0 to 100 years and when to

pioneer the new tunnel linings and/or construction methods which have greatly contributed to reduce the overall

cost of tunnelling. In each instance there will be a choice and the final decision must be an engineering judgement

after weighing up the technical and economic considerations. This Report attempts to distinguish between fact

and opinion, pointing to the factors which should be considered in selecting a tunnelling system. The recommen-

dations for the methods of lining tunnels, given in Chapter 10, take into account tunnel usage and ground

conditions and have therefore, t o some extent, to cover both extremes of the tolerant and the specific types of

lining. When making suggestions for future research and development, however, some new ideas have been put

forward as a basis for discussion.

The market for tunnel linings in the United Kingdom is briefly discussed in Chapter 3 with more detailed information in Appendix 2 , where statistics are given of the approxiinate annual length and volume of tunnels

constructed, broken down into the several forms of tunnel linings and tunnel usage.


2. INVESTIGATION METHODS

The survey has been carried out by reference to published literature on design and construction of recent tunnels and by discussions with interested and experienced organisations. At the outset of the survey, the importance of

personal discussions and visits t o tunnelling sites was seen as far more fruitful than the circulation of questionnaires.

It was clearly impossible to cover more than a small percentage of those organisations concerned in tunnelling, bu t

this has to be seen in the knowledge that a wider investigation would entail diminishing returns. A list of

organisations was drawn up consisting of the larger local authorities, a selection of the larger tunnelling consulting

engineers and contractors, manufacturers of linings, shields and waterproofing materials, research organisations

and universities working on tunnelling problems. Some fifty such organisations were visited, many on several

occasions, a list of which is given in Appendix 1. In almost every case there was good co-operation, assistance and

free discussion with disclosure of much valuable and sometimes confidential material. In particular, from this

material and with the consent of the organisations concerned, it has been possible to draw up the histograms and

graphs of lengths of tunnels constructed and of related costs. The authors and the Transport and Road Research

Laboratory are very grateful to all these organisations for their co-operation in this survey.


3. PURPOSE AND METHODS OF LINING TUNNELS

3.1 General

The size of tunnels constructed in the United Kingdom may be classed in three categories.

a) Small diameter tunnels, up to 3 m internal diameter, for sewers, water and cable tunnels.

b) Medium diameter tunnels, 3 ni to 6 m internal diameter, for underground railways and associated

tunnels and for the larger sewer and water tunnels.

c) Large diameter tunnels, 6 m upwards internal diameter, for road and main line railway tunnels,

underground chambers and larger tunnels associated with underground railways.

These tunnels are constructed through a large variety of ground types, which may be classified under the

headings given in Table I , predominantly in soft ground* or weak to moderately strong rock.

TABLE 1

Ground classification

This classification is based on the rock strengths and terminology given in the Geological Society 3 Engineering Group, Working Party Report and on the new British Standards Institution draft code of practice

4 on site investigations . The rock groupings have been reduced to three, for convenience for tunnelling methods

and techniques. The classification of rock masses should also include the structure of the rock, the discontinuity

characteristics and the amount of eath her in^.^'^?^ A method commonly used for indicating the intensity of discontinuities is that of Rock Quality Designation ( R Q D ) ~ , which is the proportion of a borehole core that

* The Geologist would describe 'soft ground' as 'unconsolidated deposits' but this designation would be confusing in the engineering context.

Ground type

(a) Recent alluvium and glacial drift

deposits including waterbearing sands,

gravels, silts and clays and boulder clay.

(b) Eocene, Cretaceous and Jurassic stiff

fissured clays.

Low strength rocks including shales,

Cretaceous Chalk, Triassic (Keupar) Marl

and Jurassic rock formations.

Many Triassic and Permian rock formations,

sandstones and medium strength Carbonifer-

ous coal measures.

The hard Carboniferous and older rocks,

the limestones and harder rocks.

Classification

Soft ground

Very weak to moderately

strong rock

Strong rock

Very strong and extremely strong rock

Compressive strength

M N / ~ ~

-

-

up to 50

5 0 to 100

above 100


7 consists of intact lengths longer than O.lm. This was later used t o classify the stronger rocks . Priest and Hudson 8

have shown that the conventional RQD based on 0.1 m lengths is insensitive to variations in rock quality when the

mean discontinuity spacing is greater than 0.3 m. They advocated presenting rock quality information in terms of

average fracture spacing or frequency.

Rock classification by strength and discontinuity spacing has been used t o indicate preferred methods of

excavation?*10 However, for the design of tunnel support systems more complicated designations are necessary as discussed in Chapter 8.'

Three forms of lining may be used during the construction of a tunnel:

a) Temporary ground support

b) Primary lining

c) Secondary lining

In rock tunnels where the ground is not fully self supporting and where the primary lining is not erected or

cast as the excavation proceeds, a "temporary ground support" may be necessary t o support the ground until the primary lining is complete. Steel arches, shotcrete and rock bolts are commonly used for temporary ground support.

All tunnels, except in sound unjointed rock, where the ground is self supporting are lined with a "primary lining" which is designed to support the ground loads and t o sustain such deformations of the lining which may

occur in the temporary conditions and for the design life of the structure.

The most severe stress conditions for many preformed linings may occur during handling of the segments or

from thrust from the shield rams. The primary lining should also exclude or control the ingress of water into the

tunnel. Several forms of primary lining are commonly used ranging from the monolithic cast in-situ concrete

linings to the flexible types of articulated linings which have a number of segments allowing the lining to deform

to reach an equilibrium state with the forces acting on the lining. In between these extremes there are linings of

different degrees of stiffness, such as the bolted linings which are not usually designed to take full bending moments

across the joints.

A 'secondary lining' may be required to convert the primary lining to a form suitable for the tunnel use. The secondary lining will provide a smooth bore finish to the tunnel and may be necessary to prevent erosion of the

primary lining or to act as an anti-corrosion barrier. A secondary lining may also be used as a waterproof umbrella, as insulation or to provide an aesthetic finish. Table 2 gives details of the types of primary lining in relation to the usage of the tunnels and the need for a secondary lining. Secondary linings are briefly included in Appendix 2 in order that cost comparisons can be made concerning the different forms of primary linings, only some of which require secondary linings.

The primary lining for a tunnel may be one of several forms of lining, as illustrated in Fig. 1:

a) a bolted grouted lining

b) an expanded lining

c) a smooth bore grouted lining

d) a cast in-situ lining


TABLE 2

Need for secondary lining related t o type of tunnel usage

The 'bolted' lining is made up of a number of segments cast with a skin or web curved to the radius of the

tunnel with flanges along each of the four sides. The segments are bolted together along the longitudinal flanges

t o form rings and along the circumferential flanges for erection purposes and for continuity in the longitudinal

direction. The rings are made up of three types of segments - 'ordinary' segments, a smaller 'key' segment and

adjacent 'top' segments.

Usage

Sewer

Water

Cable

Underground

railways

High speed

railways

Road and

Pedestrian

Passages

The lining is erected and bolted to the previous ring and the void between the external periphery of the

lining and the excavation filled with a grout or with pea gravel and grout. This form of lining has been

manufactured in concrete, cast iron and steel.

The 'expanded' lining is made up of a number of segments which are erected without bolts in the longi-

tudinal joints and are expanded to fit the profile of the excavation (see Fig. 1). The present form of this lining is

used with a tailless shield in self supporting ground in which a true circular profile can be cut. The lining may be

expanded in the crown or a t or near the axis level (see Section 5 . 5 ) . The longitudinal joints may be plane or articulated (see Section 5.3). The plane joint gives a flat contact surface between segments while the articulated

joint gives theoretically a line or point contact. The articulated joint may be of a convex/convex or concave/

convex profile, which allows the line of contact to rotate from the designed position without overstressing the

joint. This form of lining has been manufactured in concrete, cast iron and steel.

Type of primary preformed lining

The 'smooth bore' lining is made up of a number of solid segments with plane or articulated joints. The

linings are normally erected either on a former ring or with reinforcement in the joint (or in the centre of the ring)

or each ring may be bolted to the previous ring. After erection the void behind the lining is grouted or alternatively

filled with pea gravel and then grouted. These linings have been manufactured only in concrete.

Bolted linings

Smooth bore finish

required

Smooth bore finish

required

Smooth bore linings

Generally no secondary lining



unless for waterproofing reasons


unless for waterproofing or acoustic reasons

Smooth bore finish

probably required

Secondary, water-

proof, aesthetic

lining required


unless for waterproofing

reasons

Secondary, waterproof,

aesthetic lining required if not

incorporated in primary lining


The 'cast in-situ' lining is generally used in rock where only temporary ground support is required during the excavation for the tunnel. The lining is then cast as a separate operation.

In Chapters 4 , s and 6 the type of primary linings used in the United Kingdom are briefly discussed with additional data in Appendices 3 ,4 and 5. These chapters give a general background to the individual linings with

information on where and in what ground conditions they have been used. In Chapter 10 general recommendations are given on the types of lining to be used for particular tunnels, taking into account the type of tunnel usage and the ground conditions.

3.2 Market for tunnel linings (1970-76)

During the course of the latter part of the survey it was possible, with the co-operation of the lining manufacturers, to obtain data on the production and delivery of tunnel linings. In order t o obtain a realistic figure for the length of tunnels constructed the total number of rings of each diameter delivered t o the sites for each calendar year was abstracted from the records of each manufacturer. The lengths of tunnels lined with segments cast on site, or with cast in-situ concrete or left unlined were estimated from site data.

These statistics are included in Appendix 2 and a summary of the combined data is given in Table 3. These data represent the first compilation of such information in a comprehensive manner and should form a reliable datum for future tabulation and predictions.

TABLE 3

Tunnel statistics

* Includes the Mersey Kingsway 2B Tunnel

Year

1970 1971

1972 1973 1974 1975 1976

3.3 Previous forms of tunnel linings

Many of the tunnels in service today have been in use for up to 150 years and were constructed with forms of linings which have not been used for new tunnels for many years. This is due mainly to the introduction of new

materials and tunnelling techniques which have enabled the construction of tunnels to be carried out at rates of progress many times those previously attained. The three main forms of lining which fall into this category are timber, brickwork and masonry.

Length

constructed

km

65 62 83

122 77 8 1 8 1

Average

Total volume of excavation

100,000 m3

4.5

6.1 * 5.3 8.9

5.6 5 .O

6.2

Average

external

diameter

m

3 .O 3.6 2.9 3.1

3.1 2.8 3.1

3.1

Percentage of total length

sewer

%

68 67 7 1 7 1 75 88

80

74

Percentage of total volume

water

%

2 7 24 20 13 15

5 15

18

sewer

%

46 28 5 8

49 53 72 48

49

water

%

32 42 2 1 14

16 5

3 3

24


3.3.1 Timber: Timber is a traditional building material and has been used on a limited scale in the United States as a structural lining in-conjunction with an internal skin of brickwork or concrete. In the United Kingdom

where soft ground tunnelling predominates, timber has normally been used only as a temporary ground support

until the final structural lining is constructed. Timber has a limited life except for pitch pine and elm in the fully

saturated state, and has normally to be imported to this country. Economics dictate that timber is used today as a

temporary ground support in conjunction with steel arches for rock tunnels, for temporary ground support in

timber headings or at special locations such as junctions, breakups for enlargements and openings. The use of

timber headings, which was once common for small diameter pipes or cable ducts in built up areas has reduced

during the last decade. This is mainly due to the introduction of new smaller-diameter tunnelling techniques,

coupled with the increased cost of timber and of skilled workmen with the accon~panying decline in timbering

skills.

3.3.2 Brickwork: Brickwork linings have been used for a considerable length of tunnel in the United Kingdom. The great majority of railway tunnels, over 1000 in number, on British Railways (BR) routes are brick lined and

were constructed 75 to 125 years ago. There is little standardisation in the cross-section profile of these tunnels though they are usually a horseshoe shape, the largest probably being those built for the deep level station on the

Mersey Railway at Hamilton Square and James Street which are 15 m wide, 1 0 m high and 120 rn long.13 The

majority of railway tunnels are twin track tunnels with up to 100 metres of overburden. Several of these old

tunnels, such as the Thames (Wapping) Tunnel, Mersey Railway Tunnel and the Severn Railway Tunnel are

beneath rivers. Many millions of bricks were required for the longer tunnels, for example 36 million were used for the Kilsby Tunnel in the 1820's and 38 n~illion for the Mersey Railway Tunnel in the 1880's.13 For some tunnels

the bricks were made in the vicinity of the construction and often from the excavated material. The thickness of

the brickwork varied from tunnel to tunnel but was normally between four and eight rings. In stiff clays, brick

railway tunnels were often constructed without a structural invert, such that subsequently the clay softened and

the invert support was lost often aided by inadequate or blocked drainage. For shallow and medium depth tunnels

many faces were worked simultaneously to speed construction. Many of these tunnels were constructed using the

'English Method' of tunnelling. This method incorporated a bottom haulage heading which was constructed ahead

of the main tunnel. A top heading was then excavated 3 m to 6 m ahead supported by crown bars extended from the section previously constructed. The enlargement for the top half of the tunnel was then excavated, followed

by the bottom half. The brickwork was built up or the in-situ concrete cast from the invert upwards until the

whole section, supported by timber formwork in the crown, had been constructed. The system of crown bars

may be seen as a forerunner of the tunnel shield.

For underground railways, brickwork was often used for the cut and cover section and for tunnels and

station walls constructed in headings. For deep tunnels, however, brickwork linings have seldom been built except

for special sections at junction openings or overbridge passages. In deep road tunnels the use of brickwork has been

confined to internal architectural finishes. Brickwork has been used extensively for canal and river tunnels.

For sewers, brickwork has been used for many hundreds of kilometres of tunnel and was the main form of

lining for sewers constructed until the 1930's except for sections in difficult ground where cast iron linings were

installed. The majority of these brick sewers are now about 100 years old and many of these may well require

considerable repairs or replacement during the next two decades. Brickwork has advantages for sewers in that the

sectional profile may readily be altered to suit junctions, enlargements and the economic shape of the sewer. The

egg-shaped sewer is one such profile. Great cost and effort was given to the quality and precision of the brickwork.

The thickness of the brickwork varied from 2 rings of bricks for the smaller diameter sewers in clay to 4 rings for larger tunnels. In poor ground, additional thicknesses were often necessary. Apart from the use of brickwork as a

secondary lining inside a precast concrete primary lining (see Section 15.2), very few brick-lined sewers have been constructed during the last 2 0 years.


Disadvantages of brick tunnels include the large quantity of timber work and centering which is required and

the consequent congestion at the face. Progress was bound to be slow due to the delay in erecting the brickwork lining after the excavation and timbering for a length of tunnel. The use of multiple faces compensated for this t o

some degree by allowing the alternation of excavation and brickwork gangs between faces. Although brick linings have been used in conjunction with a shield, precautions are necessary to avoid the thrust loads causing damage to the newly erected brickwork.

3.3.3 Masonry: There are few tunnels in Britain lined with masonry, most of these being water or railway tunnels. For railway tunnels this form of lining was only economic when used in place of a thick brick lining

where heavy loads were anticipated. Local stone was used in the interest of economy and was not always resistant to severe atmospheric conditions associated with steam driven engines. The old Woodhead Twin Tunnels provide an example where severe deterioration of the mortar in the joints between the stones resulted in falls during the last years of the railway life. These tunnels which were replaced by the new Woodhead Tunnel have been relined and now carry Central Electricity Generating Board (CEGB) cables.

The repair of brickwork and masonry tunnels is briefly discussed in Chapter 12 on maintenance.


4. CAST IRON AND STEEL TUNNEL LININGS

Cast iron linings have traditionally been manufactured from grey iron which derives its name from the grey

crystalline appearance of its fractured structure on account of the presence of free flake graphite. During the last

decade successful experiments have been carried out with tunnel linings cast in spheroidal graphite iron which has

a chemical composition similar t o grey iron except that the impurities of manganese, sulphur and phosphorus are

reduced. The flake graphite is changed to spheroidalgraphite by the addition of very small proportions of cerium

or magnesium.

Spheroidal graphite iron is more expensive than grey iron but, on account of its higher tensile strength,

thinner and wider sections can be designed which may be more economical. Thus in the larger diameter tunnels,

rings of widths up to 1.2 m, with fewer circumferential bolts and thus reduced erection times, have been

competitive with the conventional grey iron linings. In the future, spheroidal graphite iron is likely to be more

economical for most diameters of tunnels.

Cast iron linings, generally, have been of the bolted type and have usually been used with a shield for long

drives, although, in good cohesive ground with long stand up time, short lengths of tunnel have been excavated

and the lining erected by hand without a shield. When a shield is used in non-cohesive ground the lining is erected

within the shield tail skin, which overlaps a short length of the previously erected ring; the grouting of the void

between the ground and the external surface of the lining is carried out after the shield has been shoved forward

for the next ring. Alternatively pea gravel may be injected in the void as the shield is shoved forward and the

grouting carried out at a later date. This latter method, however, has seldom been used in the United Kingdom

(see Sections 5.6 and 9.1).

In the early 1960's an expanded form of grey iron lining was developed for the experimental tunnel for the

London Transport Executive (LTE) Victoria Line. This lining was used in good cohesive ground in conjunction

with a tailless shield and was later used for sections of the Victoria Line. The lining was erected without bolts in

the longitudinal joints and with fewer bolts in the circumferential joints than for the conventional bolted lining.

The bolted form of cast iron lining,now rarely used for tunnels in good ground apart from step plate

junctions between tunnels, is mainly adopted for special sections or for tunnels in waterbearing ground where a

cast iron lining can be made more watertight than a concrete lining. Cast iron linings have been used for a

relatively small number of large projects which have been influenced in their timing by financial constraints.

During the last decade the use of this type of lining has reduced as a percentage of the total length of tunnel

constructed.

Fig. 2 shows the annual production, in tonnes, of cast iron segments in the United Kingdom for the period

1963-74 broken down into the weights of grey iron and spheroidal graphite iron used both in the United 1 4 Kingdom and exported for use abroad .

The peak of production during the period 1963-67 is mainly due to the LTE Victoria Line, for which

120,000 tonnes were cast at an annual production rate of approximately 45,000 tonnes, the Blackwall Road

Tunnel (25,000 tonnes) and the Tyne Road Tunnel (45,000 tonnes). The smaller peak 1967-70 included the

LTE Victoria Line extension to Brixton (37,500 tonnes), and the early stages of the first Mersey Kingsway

Road Tunnel. The 197 1-74 peak included part of the lining for the second Mersey Kingsway Road Tunnel, the

LTE Fleet Line (Stage l ) , the BR Liverpool Loop Railway, the San Paulo Metro, for which approximately

12,000 tonnes of spheroidal graphite iron were exported to South America, the Washington Metro and part of

the lining for the early stages of the Dartford Duplication Road Tunnel.


The majority of schemes using cast iron linings require a production of less than 45,000 tonnes and for the twelve year period under review only the production for the LTE Victoria Line has been above this figure. The. average production of cast iron segments for the period 1963-74 excluding the Victoria Line was approximately

21,000 tonnes per annum with a peak of over 36,000 tonnes and a trough of 6,000 tonnes. During the period an average of 10 per cent of the production was for export with a peak of over 35 per cent in 1973. The average

production for use in the United Kingdom during this period was therefore approximately 18,000 tonnes with a correspondingly reduced peak of 33,000 tonnes and a trough of 6,000 tonnes.

Large differences in production requirements from year to year lead to considerable problems for the foundries in forecasting future demands and for budgeting for their investment on research and new casting plant.

Fortunately the foundries can often be turned over to casting other products during these lean periods. The production of cast iron segments, however, represents less than one per cent of all cast iron production in the

United Kingdom. During the peak period of 1964, the percentage by weight of cast iron segments was only 1.5 per cent of the total production. During the last two decades the number of foundries casting segments has gradually

reduced to two, Stanton and Staveley (a subsidiary of the British Steel Corporation) and Head Wrightson, although a number of foundries will manufacture small quantities of special linings. The present capacity is between 20,000 and 40,000 tonnes of cast iron with variations depending upon the ratio of grey iron to spheroidal graphite iron.

Steel has been used relatively little for primary tunnel linings in the United Kingdom mainly on account of its high cost. Its main use has been for special lengths of tunnel where the loads from the ground or from the shield have caused high bending moments or tensile stresses in the lining. In these instances steel has been used as

a replacement to a grey iron lining. Fabricated steel segments have been used at openings or at special and transitional sections in tunnels where it would have been uneconomical or inadequate to cast a small number of segments in grey iron.

The main types of steel lining which have been used in the United Kingdom are:

a) Bolted fabricated flanged steel lining of a form generally similar t o the bolted cast iron linings.

b) Expanded fabricated flanged steel linings which are also generally similar to the bolted cast iron

lining but with special jacking recesses at the points of expansion of the linings.

c) Steel liner plates pressed from steel sheet metal. Although these have been used extensively in the

United States they have only been used in the United Kingdom for short sections of tunnel as temporary ground support.

d) Steel circular membranes. These have not been used as a structural primary lining, their main use

being as a secondary lining in water tunnels as discussed in Appendix 2.

The preference for spheroidal graphite iron, providing comparable strength characteristics at lower costs than fabricated steel, will probably confine the use of the bolted form of steel linings to short lengths of tunnel

subject to high or uneven loading except for the possible use of liner plates for small diameter tunnels.

Brief details of the types of cast iron and steel linings used in the United Kingdom are given in the following sections with further details including the characteristics and manufacture in Appendix 3.


4.1 Cast iron tunnel linings

4.1.1 Bolted grey iron tunnel linings: Although grey iron had been used since the end of the eighteenth century for permanent linings for shafts, it was not until 1869 that it was first used as a permanent lining for a

tunnel, the Tower Subway under the Tlianies. Before that date the tunnels constructed,with the exception of some

sewer tunnels were of a non-circular cross-section. It is possible that, following Marc lsambard Brunel's patent for

a shield in 1818, he would have incorporated a bolted grey iron lining in the Thames Tunnel (1815) if a circular

cross-section had been chosen, but it was not until J.H. Greathead designed the first circular shield for the Tower 15 Subway that the linings were used in a tunnel .

A large number of tunnels, mainly in soft ground, have been constructed with bolted grey iron linings during

the last 100 years for all forms of tunnel use, but the majority have been for medium and large diameter tunnels

for railways and roads. Except for special sections in bad ground, outfalls, tunnels under rivers and for large 15 chambers these linings have not been used extensively for small diameter tunnels .

Medium diameter bolted grey iron linings were first used in deep running tunnels for the City and South

a n d o n Railway in 188615 and for the Waterloo and City Railway for station and other associated tunnels in

89416. During the next 45 years these linings were always specified for the deep tunnels in the London Under-

ground. With the increased demands on raw materials for re-armament purposes in 1937 and subsequently due to

the increased cost of bolted grey iron linings and to technical advances, concrete bolted linings (see Section 5.4)

expanded concrete linings (see Section 5.5) and expanded grey iron linings (see Section 4.1.3) have been

introduced. Although these latter linings have been used extensively for running tunnels in good ground conditions,

linings for escalators, machine chambers, concourse and station tunnels have still been in bolted grey iron. Bolted

grey iron linings have continued t o be widely used for all tunnels in underground railways in waterbearing non-

cohesive ground where adequate waterproofing of the tunnels is essential (see Plate 1).

All circular road tunnels under rivers have been constructed using bolted grey iron linings (see Plate 2) since

the first Blackwall road tunnel under the River Tharnes (1892-97)17 until the construction of the Mersey Kingsway

~ u n n e l s l ~ (1967-74) in Bunter Sandstone and the Dartford Duplication Tunnel, at present under construction,

in chalk. These two latter tunnels are lined, in good ground, with steel-faced precast concrete smooth bore grouted

lining (see Section 5.6) while the short sections at the ends of the tunnel in less stable ground are lined in grey iron.

In the early years of the use of grey iron for tunnel linings an original design of lining was produced for each

scheme as each project was owned by a different client1'. Details of some of these linings and the evolution of the

joint details are discussed in Appendix 3. Two types of lining were normally used, a heavy lining for sections in 16 waterbearing strata and a light section for London Clay or similar ground .

The grey iron linings were usually erected behind a shield with the excavation carried out by hand. In the

1890's mechanical excavators were introduced, but due to teething troubles, there was little increase in the rates

of progress. At the turn of the century the Price machine was used on the London Underground Charing Cross to

Hampstead Railway and maximum rates of progress increased from 3 to 4 m per day for hand excavation to 5 m

per day1 6. The 3.1 t o 3.8 m internal diameter linings were erected in 20-30 minutes.

Table 2 4 in Appendix 3 shows how the internal diameters of the deep underground running tunnels in the London Underground have gradually increased from 3.1 nl internal diameter, for the City and South London

Railway in 1886, t o the present LTE Fleet Line tunnels of 3.85 m internal diameter. The London Underground

system consists of shallow lines, which were constructed using cut and cover methods to carry large rolling stock

and the deep lines constructed in tunnels t o carry smaller rolling stock than most underground railways.


Fig. 3 shows a graph of the weights of grey iron tunnel linings per metre, excluding the more recent road

tunnels, plotted against the external diameter of the ring. The Curves (a), (b) and (c) are best fit curves for a large

variety of lining types and diameters. Since the 1330's a single lining has been specified in most types of strata up

to depths of the order of 40 to 50 m, rather thall the two types used previously. The early linings were generally

cast in low quality grey iron there being no system of grading in existence. During the last 4 0 years Grades 10 or

12 iron (see Appendix 3) have been specified, and only occasionally the higher Grades, 1 4 and 17. For larger

schemes with a single diameter such as road tunnels, when large quantities are involved, two types of linings of different widths have often been used for different ground conditions.

A comparison of the standard imperial linings Curve (c), and the new metric linings Curve (d), shows that for external diameters below 8 m the two curves are virtually identical, while above 8 m the metric linings are lighter.

The imperial linings are 0.5 1 m wide up to 4.9 m internal diameter and 0.46 m wide above 4.9 m internal diameter,

while the new metric linings are 0.6 m wide throughout the range.

Grey iron bolted linings are available with machined longitudinal flanges, and with either machined or

unmachined circumferential flanges. Where the circumferential flanges are machined a caulking groove, preferably

of wedged shape, is milled on the front edge of the flange. These linings can normally be erected more accurately

than linings with unmachined circumferential joints although treated timber packings may be required to keep the

tunnel correct to line and level. For both grey iron and spheroidal graphite iron rusting of the two faces in contact

partly seals the joints which are subsequently caulked. The metric linings were designed to have machined

circumferential flanges but due to production schedules this was not generally possible for the first stage of the

LTE Fleet Line. Recent subaqueous tunnels have had linings with all joints machined; caulking is thereby easier and quicker and the volume of lead required considerably reduced. Although the additional cost of machining

exceeds these savings, the stiffness of the adjacent rings is greatly increased and if well built the linings will sustain

higher thrust loads from the shield rams.

With unmachined circumferential flanges a lip is cast at the back of the flange and the caulking carried out

behind the bolts. Timber or other packings are necessary in the joints to spread the thrust forces from the shield,

while yarn or plastic tubing may be used in the joints for hand driven tunnels and shafts. Grummets are fitted on all bolts for both machined and unmachined joints where watertightness is required. Fig. 4 shows typical details of a grey iron bolted lining for the 1890's and the present day.

Tapered rings have been incorporated for many years for vertical and horizontal curves but more recently they have been used for controlling the alignment of the tunnel. These rings are rolled to the required pitch to give

the horizontal and vertical adjustment necessary to keep the tunnel correct for line and level without using timber

or other packings. This method has the additional benefit of improving the watertightness of the tunnel.

One main improvement in cast iron linings in the last 30-40 years has been a reduction in the

number of circumferential bolts (see Table 24 in Appendix 3). The minimum number of bolt holes per segment (apart from the key) for erection purposes is three. Bolt holes were originally cast into the flange as circular holes,

but later elongated holes were introduced to allow for the inaccuracies in machinifig the radial joints with respect

to the locations of the circumferential bolt holes. With modern machining techniques, employing jigs for precision

location, the bolt holes are now normally drilled circular.

Through the years much discussion has taken place on the advantages and disadvantages of staggering or

breaking joints - i.e. rolling one ring compared with the next. The first tunnels constructed with cast iron linings

were built with continuous longitudinal joints but by the early 1900's it was customary to erect linings with

staggered joints. Although in very soft strata this may now be specified it is not a general practice except for large


diameter subaqueous tunnels in very weak ground where stiffness in bending is desirable. The method was intro-

duced originally to help the building of the lining although it was also felt that there would be additional

strength against bending in the longitudinal direction. It is unlikely, however, that this effect would be obtained

without also using high strength friction grip bolts. If large deformations of the lining occur, however, the flanges

may crack at the bolt holes.

Apart from any question concerning the use of special expedients, the rate of progress with bolted cast iron

linings depends on the following factors:

a) rate of excavation and removal of the material

b) speed of erection of the lining

c) speed of grouting

d) width of ring

Through the years the rate of excavation has generally increased considerably, as a result of the increasing

use of mechanical aids in the face and full face tunnelling machines. The speed of erection of the lining, however,

has increased only marginally in small diameter tunnels, although mechanical methods of erection have helped

considerably in the medium and large diameter tunnels. Until the 1950's, it was customary to grout each ring

immediately it was erected as the shield was shoved forward; this standard is still widely specified. In good cohesive

materials or in weak rock under open ground and in particular where there is sufficient cover of good ground above

and below the tunnel, some relaxation has often been allowed. In such circumstances grouting may be carried out

at the end of the shift or during the erection of subsequent rings. In non-cohesive ground, or where mixed faces

are expected, it is not recommended that any relaxation of grouting procedures are given. In these instances,

failure to grout immediately may cause uneven loading on the lining after grouting, leading to overstressing and

possible failure of the lining accompanied by more settlement at the surface, with possible undesirable effects on

the stability of the face.

Except for large diameter subaqueous tunnels, the width of cast iron rings used in the United Kingdom has

generally been between 0.46 m and 0.61 m. For the larger subaqueous tunnels the widthshave varied between 0.46 m and 0.76 m as discussed above. The width of the LTE linings has been restricted as they are required to be used either with or without a shield and the main criterion has been the weight of the segment for hand-driven

tunnels. Other factors favouring lower widths have been the lower grade of cast iron, grouting capacities and risks

of possible additional settlement. Wider rings of spheroidal graphite linings may be used more readily since lighter

sections may be designed with this material.

4.1.2 Bolted spheroidal graphite iron tunnel linings: Spheroidal graphite bolted linings have only been used to date for short lengths of tunnel in the United Kingdom. The annual production of this form of lining,

which has mainly been for export, is shown in Fig. 2. The first experimental length of tunnel with this form of

lining was constructed in June 1968 as a pilot tunnel for an enlargement for a crossover tunnel for the LTE Victoria Line extension to ~ r i x t o n ' ~ > ~ ~ , details of which are given in Appendix 3. The results of this experimental

length have encouraged a more general use of spheroidal graphite iron. In the United Kingdom spheroidal graphite

iron has been used subsequently for a short length of arch construction for large concourses for two stations for

the BR Liverpool Loop (see Plate 3) . for short lengths of the service tunnel, at cross passages and in areas of bad

ground, for the Stage 2 Channel Tunnel* works, and for parts of the Tyneside Rapid Transit Scheme.

* The Channel Tunnel Scheme was abandoned in 1975.


Spheroidal graphite bolted linings have been exported to San Paulo for the metro scheme and for the

Washington Metro. These linings were 1.0 and 1.22 m wide respectively being generally wider than those used in

the United Kingdom. More economical sections can be designed in spheroidal graphite iron with the neutral axis

near the median of the cross section. Spheroidal graphite iron is currently being used on the Continent where its

first extensive use was for the Vienna Underground railway.

In the early 1970's the use of spheroidal graphite bolted linings for small and medium diameter tunnels, below 5 to 6 m, was not economical, when compared with grey iron bolted linings, because of the minimum

casting thickness. With improved techniques in casting, and the introduction of large capital cost equipment,

however, spheroidal graphite iron is likely to be used for smaller diameters. The present normal minimum casting

thickness for the skin is of the order of 12.5 mm compared with 19 mm for grey iron. For larger tunnels the

saving in the weight of the lining more than offsets the large increase in the cost of the cast material over that of

grey iron linings (see Chapter 11). In addition the use of wider segments, with fewer bolts, leads to consequential

savings in the cost of erection.

Bolted spheroidal graphite linings are likely to be specified in the future more frequently for tunnels in the United Kingdom. However, this form of lining is unlikely to be used in preference to bolted or expanded concrete

linings, except in waterbearing unstable strata or for lengths of tunnel subjected t o special conditions of loading or stability.

One application meriting further study is that of fabricating segments from a number of simple pan-shaped

sub-segments. Each sub-segment may be cast at high speed and accuracy, eliminating the need for machining, and

the sub-segments glued together with epoxy resin to form the main segment. An experimental lining of this type was manufactured by Pont et Mousson for the French side of the Channel Tunnel Stage 2 Works.

4.1.3 Expanded grey iron tunnel linings: The expanded articulated grey iron lining was developed between 1949 and the late 1950's. A short experimental length was driven in 1958 which was later followed by a 1.9 km

length of experimental tunnel for the LTE Victoria Line in 1960-6121. The lining, with only minor modifica-

tions, was later used for a total length of 3.0 km of the Victoria ~ i n e ' ~ . The lining is shown in Plate 4 and discussed in detail in Appendix 3.

The lining, which was interchangeable with the conventional bolted grey iron lining of 3.71 m internal

diameter, had six segments per ring. The flanges were approximately half the depth of those for the bolted lining

but slightly thicker, while the width of the ring was increased from 0.5 1 to 0.61 m. The total weight of each ring

was similar.

The small flange depth of 63.5 mm gave a relatively narrow width for locating the shoes of the shield rams.

The reduced moment of resistance of the segments, which were of comparable length to the conventional grey

iron lining, also made the segments more susceptible to damage during handling. When point loads built up on the

lining, on account of voids or soft areas behind the lining, fractures could occur and a number of the segments in

the crown had to be either replaced or strengthened with steel plates after the tunnel was complete. There was a

saving in the weight and therefore the cost of the grey iron per unit length of tunne1,but the main advantage of the

lining was the speed of erection and therefore the increase in the rate of advance of the tunnels.

Station tunnels in London Clay may be constructed with or without a shield and often running tunnels are

taken through the station as pilot tunnels. These pilot tunnels have normally been lined in bolted grey iron or,

more recently,in good cohesive ground, in expanded concrete linings if the future station tunnels are to be

constructed with a shield. When a mechanical shield is used for the running tunnel the rates of progress for the


construction of these pilot tunnels in conventional bolted grey iron are low. During the construction of the LTE

Victoria Line, experiments were carried out with methods of expanding these bolted linings22. A form of expanded

temporary lining using timber packings in the longitudinaljoints between segmentswas developed and used for a

number of station pilot tunnels (see Appendix 3). This form of lining has recently also been used in the LTE Piccadilly Line extension to Heathrow, for approximately 0 .3 km of pilot tunnels for the crossover to the east of

Heathrow Central Station (see Plate 5).

Following the experimental use of the expanded bolted grey iron lining for pilot tunnels, lengths of running

tunnels were constructed using this lining as an alternative to the expanded articulated cast iron or concrete linings.

In these permanent conditions steel wedges and packings or cast iron machined packings and wedges were used.

The total length constructed for both pilot and permanent tunnels for the LTE Victoria Line and Piccadilly Line

extension was 1.4 km.

Future applications of expanded cast iron linings for permanent conditions will probably be in spheroidal

graphite iron which has superior tensile characteristics to grey iron thus avoiding some of the difficulties

encountered to date.

4.1.4 Expanded spheroidal graphite iron tunnel linings: Expanded tunnel linings in spheroidal graphite iron have not been used for lining tunnels to date, although designs were considered for possible use in sections of

the Channel Tunnel. These linings would be cast and expanded in much the same manner as the grey iron expanded

lining, discussed in Section 4.1.3. The saving in the weight of the material, compared with grey iron, and the

reduced erection time would considerably reduce the cost differential between cast iron linings and concrete linings.

4.2 Steel tunnel linings

4.2.1 Bolted steel tunnel linings: The fabricated bolted flanged steel linings are made up of segments of a similar form to the bolted cast iron lining. The lining? have been used in two main conditions:

a) For lengths of tunnel where excessive loads have been expected either from the shield during the

construction or from the ground, causing high bending moments or tensile stresses.

b) For special segments at openings in cast iron tunnels where it would be uneconomical to use cast

iron segments or where lintel beams are required.

In the United Kingdom there has only been one recent example of a long tunnel in bolted steel linings. At

Dungeness 'A' Power Station the original lining for the inlet tunnel was of cast iron but, due to excessive shove forces resulting from the small size of the ports in the diaphragm of the shield, the flanges of the iron cracked.

The lining for the inlet tunnels was redesigned in steel to take these excessive loads, When Dungeness 'B' Power Station was constructed, a few years later, a new steel lining was designed for both the outfall and inlet tunnels.

Details of these linings are given in Appendix 3.

Steel linings have been used in several schemes in the United States and in Europe - in particular at Chicago,

San Francisco and Vienna. A bolted steel lining has also been designed for twin railway tunnels in compressible

silt under the River Ij in Amsterdam where a strong stiff lining would be required (see Appendix 3).

The use of special segments at openings in cast iron lined tunnels is discussed in Section 8.3. (See Plate 6).


4.2.2 Expanded steel tunnel linings: Expanded flanged steel linings were used for short lengths of tunnel on two contracts for the LTE Victoria Line, where heavy or eccentric loads were expected close to the lining. The

2 3 linings were used a t Oxford Circus Station, and at Kings Cross Station .

At Oxford Circus Station the crown of the 6.48 m internal diameter southbound station tunnel was only a

metre or so below the third basement of Peter Robinson's store. Complete details of the foundations were not

available before excavation commenced but loads of the order of 0.4 M N / ~ ' were indicated. An expanded steel lining which was grouted in the crown was designed to prevent possible settlement of the footings and to accommodate the jacking stresses. Details of the lining construction are given in Appendix 3 (see Plate 7).

At King's Cross, the Victoria Line tunnels passed beneath three BR lines and the LTE Circle Line tunnel, and over the LTE Northern Line and Piccadilly Line tunnels. The crown of the northbound station tunnel, 6.32 m

internal diameter, and the concourse tunnel, 5.63 m internal diameter, passed some 1.5 m below the footings of the brick arches of the BR twin track Midland Curve and single track Hotel Curve which were built without inverts. To prevent settlement of the brick arches an expanded steel lining was designed for bo th the northbound station

tunnel and the concourse tunnel, details of which are given in Appendix 3 (see Plate 8). The design of the upper half of the lining was complicated by the fact that the tunnels passed below the brick arches at an oblique angle,

and thus the new tunnels gradually traversed below the concentrated point loads from these arches giving eccentric

loadings.

At both Oxford Circus and King's Cross these tunnels were instrumented and details of the results are given

in Appendix 6. At Oxford Circus the hoop load built up within five months to approximately 90 per cent o f the

overburden pressure based on the loadings from the store and depth of the clay24. This, however, was only

equivalent to about 50 per cent of overburden based on the full depth of clay. No significant deformation of the

lining was recorded and the columns in the store settled less than 1.5 mm. At King's Cross the hoop load after

seven months was approximately 55 per cent of the overburden pressure for the northbound station tunnel and after five months was just over 9 0 per cent for the concourse tunnel. The maximum settlement of the brick arch

tunnels was of the order of 37.5 mm half of which was associated with the construction of the cross passages.

For both the Oxford Circus tunnel and the King's Cross tunnels, jacks of 100 tonne capacity were used for

expanding the linings, the load later being taken by steel wedges or wedges and rockers.

4.2.3 Liner plates: Two forms of thin pressed steel segmental linings, called liner plates,are generally available in the United Kingdom, both of which are manufactured on the continent. The Armco liner plate, designed as a

primary lining for the permanent ground conditions, is galvanised and does not require an internal lining unless a

smooth bore is required2' (see Plate 9). The segments are flanged and bolted in the circumferential direction and lapped and bolted in the radial direction. A second form is also available with more corrugations, which is used for

relining old tunnels. This lining is lapped and bolted in both the circumferential and longitudinal directions (see

Plate 10). This Multiplate lining is manufactured in the UK.

The Commercial Hydraulics lining is flanged and bolted in both the circumferential and radial directions;

this is used as a temporary ground support with a cast in-situ concrete primary lining26 (see Plate 11). In tliese

conditions the plates are not given special protection against corrosion.

These linings have been used in only a few instances in the United Kingdom although their use has increased

during the last few years. While the demand is small it is not economical to manufacture the plates in this country

and thus there are additional importing costs. Recently the linings have been used for a number of contracts which

were specified as pipes laid in timber headings and for which the contractor put forward liner plates as an alternative for the ground support before laying the pipes.

Details of these linings and data on a number of schemes in which the linings have been used are given in

Appendix 3. 17 L

icensed copy from CIS: URS, URS Infrastructure, 04/03/2015, Uncontrolled Copy.

5. PRECAST CONCRETE TUNNEL LININGS

Precast concrete tunnel linings were first introduced in the United Kingdom in 1903 but were not used extensively

until the 1930's and were not available as standard linings until the late 1940's and early 1950's. Four main types

of lining have been used:

a) Bolted precast concrete linings, or dowelled linings of a similar form to the bolted cast iron linings.

These linings were first introduced in the late 1930's and are available as a standard lining and cover

the majority of the present day market in precast concrete linings. These linings are suitable for most

ground conditions.

b) Expanded precast concrete flexible linings were first introduced for small diameter tunnels in London

Clay. These linings, which are of the smooth bore type, are not generally available as standard linings,

but their use in self supporting clays has increased considerably during the last decade.

c) Smooth bore grouted precast concrete linings were the first form of precast concrete lining to be

introduced (1903) but only became available as standard linings in the late 1950's. Use of these

linings is generally confined to tunnels in soft ground or weak rock.

d) Expanded grouted precast concrete linings are the latest form of precast concrete lining and have

recently been used for the first time in weak rock in the Service Tunnel for the Channel Tunnel Stage

2 Works.

Records of the delivery of precast concrete segments and of site cast segments are given in Section 3.2 and

Appendix 2 for the period 1970-76. Records were only available from some of the precasting manufacturers for the previous years, and the incomplete data for the 1960's have therefore not been included. For expanded

linings, however, on account of the relatively small number of schemes, records are available since 1950 when these linings were first used (see Section 5.5).

Precast concrete linings are generally cast in manufacturer's works and transported to the sites by road. For

a relatively small number of schemes, usually of large size and using special linings, the segments have been cast on

or close to the site. This is not usually economical for standard linings, except where the size of the individual

segments is large.

In the following sections, the different types of precast concrete tunnel linings and their manufacture are

discussed, with further data in Appendix 4.

5.1 Moulds

Little information is generally available on the manufacture of the early concrete segments but these were

generally cast in steel or cast iron moulds. During the 1939-45 war various types of moulds were investigated 77 including timber, steel and concrete ~noulds- .

Concrete segments may be cast in all-concrete moulds, concrete moulds with timber sides, all steel moulds,

composite steel/aluminium moulds or , for the smaller segments, fibre glass. A few segments have been cast from aluminium moulds with timber sides, but such moulds have been found to distort excessively.

Concrete moulds for each particular manufacturer's bolted segments are all cast from concrete master

segments in the casting yard; thus all segments should be identica~'~. Additional moulds may be cast whenever


required to suit the programme or to replace wornout moulds. Although steel moulds have occasionally been fabricated at the precasting yard, they are usually obtained from an outside supplier. All moulds should be regularly inspected and concrete moulds refurbished when required: the refurbishing of steel moulds is often expensive. Both forms of moulds are normally used for between 250 and 350 castings. In some instances 600 or 800 uses of the moulds have been obtained where special care has been taken in the design, fabrication and use of the moulds (see Appendix 4).

The segments for the bolted linings and for many of the smooth bore grouted linings are cast in a horizontal position, with their extrados upwards. The smaller solid concrete segments with plane or slightly curved radial joints may be cast in a vertical position on their sides in groups of 2 , 4 or 6 segments thus saving considerable

space in the casting area and the mould storage area. The special segments for larger diameter tunnels are normally

cast in a vertical position, on their sides, in steel moulds and often in special precasting yards at or near the site.

The methods of manufacture of concrete moulds are discussed in Appendix 4 and Plates 12 and 13 show typical concrete andxteel moulds. Table 4 summarises the different moulds and linings.

TABLE 4

Moulds for precast concrete segments

5.2 Steel reinforcement

Type of linings

Bolted grouted

Smooth bore grouted or expanded

Special segments

Steel reinforcement may be provided in precast concrete segments either (i) to increase the section resistance to tensile and bending stresses imposed during the temporary conditions of handling and erecting the lining, and

Types of mould

Concrete with timber sides

All steel

Composite steel and aluminium

Concrete with timber sides

All concrete

All steel


Fibre glass

All steel


shoving the shield, or (ii) to withstand the permanent ground load conditions. Reinforcing bars have also been used to a small extent as aids to building the ring of the lining, as in the case of the McAlpine lining and the Charcon

Casting method

Horizontally

Horizontally

Horizontally

Horizontally

Horizontally or Vertically in 2 , 4

or 6 segments

Horizontally

Horizontally

Horizontally

Vertically, singly or in pairs

Vertically

Average number of castings per mould

250-350

250-350

250-350

250-350

250-350

250-350

250-350 generally, 600 in certain instances

up to 600

100-350 but depends more on programme

Up to 800 have been obtained


Universal lining (see Section 5.6). A number of examples of reinforced precast segments are discussed in Appendix 4.

Reinforcement is costly to use in precast concrete segments as the labour costs of bending and fixing the

relatively short lengths, often to close tolerances, are high in relation to the weight of the steel. In addition the

presence of the reinforcement in the mould will add to the costs of casting the segments. This point is discussed in some detail in Section 11.1.1 where the option of adding reinf~rcement is compared with the alternative of

an additional thickness of concrete. When designing segments for special schemes the principal factors concerning

the use of reinforcement to be considered are as follows:

1) The reinforcement required for handling: consider

a) reductions of aspect ratio of the segment, i.e. the ratio of the length or width of segment to the

thickness,

b) alternative means of reducing vulnerability to damage.

2) The reinforcement required in the vicinity of the longitudinal joint: consider alternative joint design and

the possibility of packing pieces to improve load distribution.

3) The reinforcement required to withstand secondary stresses caused by ground loads: consider changes of .aspect ratio of segment (see l(a) above).

In Appendix 4 the minimum cover to reinforcement is discussed in relation to the corrosion of reinforced

precast concrete. In general the cover to reinforcement for precast segments is 13 to 25 mm except for special

linings which may be in contact with seawater or a similar aggressive environment where the cover should be 25 mm to 40 mm.

5.3 Joints

Four main types of joints are used in precast concrete linings:

a) Plane or helical joint

b) Concave/convex joint

C) Convex/convex joint

d) Tongue and groove joint

These types of joints are shown in Fig. 5 .

5.3.1 Plane or helical joints The longitudinal joint for all standard bolted linings (see Section 5.4), the expanded Wedge Block lining (see Section 5.5) and the smooth bore grouted Universal lining (see Section 5.6)

are all plane joints and similarly the circumferential joint of most other forms of lining. For wedge shaped

segments all longitudinal joints are helical. For plane joints some relief from local overstress between abutting

concrete faces may be achieved by coating the surfaces with bituminous paint or similar compound or, with

greater effe.ct, a bituminous felt or other packing piece inserted in the joint. The edges of solid segments with

plane joints may be chamfered to reduce the risk of local spalling.


5.3.2 Concave/convex and convex/convex joints: The concave/convex joint and the convex/convex joint are articulated longitudinal joints which ensure that the load is transmitted near the centroid of the

section and allow the ring to take up the shape of the excavation. The principle of the design of articulated linings

is that inequality in applied loading from the ground will cause the ring to deform until sufficient passive loading,

by compression and shear between the ground and the lining, is mobilised to achieve equilibrium. To limit bending

moments in the individual segments, and thus the need of reinforcement, it is desirable that the ring should

consist of a number of segments, probably a minimum of 1 0 to 12, to give adequate flexibility of movement at

the joints. For a solid segment of aspect ratio L (circumferential length to radial thickness) the secondary stresses r 2 caused by uneven loading around the ring, may be taken to vary approximately linearly with L .

The design of an articulated joint is a critical feature in the design of the lining as it largely determines the

areas of maximum compressive and tensile stress concentration.

The convex/convex joint is more readily designed as an unreinforced joint than the concave/convex joint

for which reinforcement is generally required near the concave face to prevent bursting. The concave/convex joint

is intended to act as a self-centering joint which helps in the erection of the lining; in practice with expanded

linings this does not always happen, on account of friction in the joint, and eccentric loading can occur. When

former rings are used for the erection of the lining, as for the smooth bore grouted Flexilok and Rapid linings (see

Section 5.6), the joints can be considered to be placed centrally as there is little play in the bolting of the former-

ring. The longitudinal joints of the expanded lining for the LTE Fleet Line (see Section 5.5) were convex/convex

in both the longitudinal and radial directions (see Fig. 5). This form of joint avoided the risk of concentrations of load near the edge of the segment which may be a cause of damage where the ring has not been built square and

true. Further developments are proceeding to refine the geometry of such joints.

5.3.3 Tonge and groove joints: The tongue and groove profile is normally confined to the circumferential joint. For thin segments in shield driven tunnels,distribution of load from thrust rams may present problems on account of the thin concrete section available. The shaped joint provides some security in locating segments during erection.

In Appendix 4 the different types of linings that have recently been used are listed with details of their joints.

5.4 Bolted and dowelled tunnel linings

In 1937, during the construction of the eastward extension of the LTE Central Line, there was the likelihood

of a shortage of cast iron; investigations were started on a precast reinforced concrete lining of similar form t o the

traditional cast iron lining. The history of the lining is discussed in Appendix 4. The internal diameter of the final lining was 3.74 m and a total length of 4.4 km of running tunnel was constructed using the lining.

The main features of the lining were the introduction of concrete stiffeners which helped to take the shield ram

forces, and the reduction of the number of bolts in each circumferential joint from 52 for the corresponding 29 conventional grey iron lining to 3 1 .

Although the lining was introduced originally to overcome the difficulty arising out of the shortage of cast

iron it was hoped that the lining would lead to appreciable reductions in the cost of tunnelling and on that contract

the manufacturing cost of the concrete lining was about 60 per cent of the cost of the grey iron lining. It was

realised that the concrete segments would not stand up to the rough handling given to the grey iron segments and

that additional care would be required by the miners. It was expected, however, that with the slightly reduced

weight of the concrete ring (1.4 tonnes) compared with the cast iron ring (1.6 tonnes) the same progress would be


obtained. In practice, after educating the miners in new techniques, the time required to erect both types of rings

was approximately 20 minutes. Special steel thrust ribs and rubber pads were designed for the shield rams to

enable the thrust t o be transferred through the skin of the linings.

During the 1939-45 war this form of lining was used extensively for tunnels and air raid shelters. Two

interesting uses during this period were:

a) eight air raid shelters each of twin 5.03 ni internal diameter tunnels, 430 m long, in London, adjacent

to existing LTE Stations, two thirds of which were lined with bolted concrete linings. (See Plate 14).

b) a series of tunnels for the War Office on the Dorset coast of 2.44 m, and 5.03 m internal diameter 27 mainly at a minimum depth of 37 In .

The design of all these linings was based on the original design for the LTE Central Line running tunnels. For

the larger diameter tunnels the width of the ring was 0.5 1 m but this was increased to 0.61 m for the smaller

diameters. The depth of the flanges of the larger diameter tunnels was similar to that for the cast iron linings to

provide the same internal diameter for corresponding external diameters and to allow for the interchange of the

two types of lining when used behind a shield.

During the construction of the 5.03 m internal diameter tunnels in London a number of segments fractured;

this was partly caused by distortion of the ring by the faulty erection of the key segments. These segments were

later replaced3' (see Section 5.5): Bituniinous packings were inserted in the radial joints for most of the early

schemes; when such packings were omitted squatting of the tunnel sometimes caused excess local loading of the

flanges with consequential cracking.

Following the 1939-45 war the use of the bolted concrete linings increased considerably, especially in the

diameters below 3 m for the sewer market. The linings for the standard range of diameters now available are of a

design modified from those used in the war years31. The width of the ring has been increased to 0.61 m for the

whole range of diameters while the depth of the flanges has been increased and the flange width decreased. The

number of circumferential bolts has been reduced and the number of reinforcing bars in each of the flanges reduced

from four to two (see Plate 15).

These standard linings have been used in all types of ground conditions and account for the major part of

the small diameter market. This market has increased considerably over the last decade and with the help of

improved production and quality control methods the cost of these linings, in real terms, has reduced (see

Chapter 1 1).

Where it is necessary for a tunnel t o have a smooth bore finish, as for a sewer or water tunnel, an internal or

secondary lining is required when a bolted concrete lining is used for the primary lining. These internal linings

were originally of brick, but with increases in cost and the reduction in the number of skilled tunnel bricklayers,

cast in-situ concrete or precast infill panels are now normally used. A number of tunnels have been lined internally

with sheets of resin mortar or fibre glass reinforced plastic. These internal linings are discussed in Appendix 2 .

Originally the standard linings were used mainly in tunnels of small diameter (up to 4 m) and for shafts for

the larger diameters. The niiijority of these tunnels were at depths of less than 30 In, Inany being shield driven.

Only in the last few years have these standard linings been used more generally for larger diameter tunnels.


In a shield driven tunnel, high ram thrusts may impose excessive loads on the skin of the lining. The lining should therefore be designed for the expected ram thrusts to avoid cracking of the skin. Excessive thrusts are

normally avoidable if adequate supervision is provided at the face. Where ground conditions permit the degree of burial of the cutting edge should be controlled with the minimum trimming of the excavation carried out by the

shield during the shoving. Where steering is a problem a compensating bead should be fitted to the shield. Recently an alternative design with a solid invert called the Smoothvert lining has been introducted by Buchan Concrete

31 . Ltd with locating dowels and sockets for the interlock between the solid segments both longitudinally and circumferentially. The use of solid invert segments reduces the cost of cleaning up the tunnel compared with the conventional bolted lining and reduces t

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