GT18R1A1_Design Sizing Construction of Segments Lining

The design, sizing and construction of precast

concrete segments installed at the rear of a

tunnel boring machine (TBM)

GT18R1A1

www.aftes.asso.fr

ASSOCIATION FRANÇAISE DES TUNNELSET DE L’ESPACE SOUTERRAIN

Organization member of the AFTES

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AFTES RECOMMENDATIONS FOR

THE DESIGN, SIZING AND CONSTRUCTIONTHE DESIGN, SIZING AND CONSTRUCTIONOF PRECAST CONCRETE SEGMENTSOF PRECAST CONCRETE SEGMENTS

INSTINSTALLED AALLED AT THE REAR OF A T THE REAR OF A TUNNEL BORING MACHINE (TBM)TUNNEL BORING MACHINE (TBM)

CONTENTS

Text presented byM. Pascal GUEDON, SIMECSOL

Working Group leader,with the collaboration of :

Messrs. AUTUORI Philippe, BOUYGUES - BACHTANIK Bruno, MINISTERE DE L'EQUIPEMENT,BARTHES Henri,A.F.T.E.S. - BERNARD Simon - BONNA - BILLANGEON Rémi, SPIE BATIGNOLLES

BOCHON Alain, SNCF - CHANTRON Laurent, CETu - CHARDIN Daniel, SOGEA - DARDARD Bruno, SNCFHUEBER Jean, SETEC - LABONNE Hubert, INDUSTRIELLE DU BETON - LEOGANE Jean Paul, RATP

PETIT François, CAMPENON BERNARD SGE - SAMAMA Laurent, SCETAUROUTE - TAQUET Bernard, EDF - CNEHVAN DUC Tri, CAMPENON BERNARD SGE

A.F.T.E.S. reading panel :Messrs. GUILLAUME Jean, RAZEL - LAUNAY Jean, DUMEZ - GTM - LECA Eric, SCETAUROUTE

MAUROY Fabien, SYSTRA - NIQUET Jean-Jacques, SOCIETE DU CANAL DE PROVENCESCHWENZFEIER André, CETu

A.F.T.E.S. will be pleased to receive any suggestions concerning these recommendations

Version 1 - 1997 - approved by the Technical Committee on 13/11/1997 Translated in 1999

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1 - GENERAL 2101.1 - Purpose of recommendations 2101.2 - Scope of application of recommendations 210

2 - HISTORICAL REMINDER 211

3 - TUNNEL LINING DESIGN3.1 - Introduction 2113.2 - Basic data required to design a tunnel lining 2113.3 - Lining functions 211

3.3.1 - Functions associated with operating constraints 2113.3.2 - Functions associated with construction

constraints 2123.4 - Description of the concept 212

3.4.1 - General 2123.4.2 - General aspects of tunnel lining design 2123.4.3 - Tapering of rings 2123.4.4 - Length of rings 2133.4.5 - Composition of a lining ring 2133.4.6 - Segment geometry 2133.4.7 - Nature of lining materials 213

3.5 - Lining installed within the area enclosing the TBM 2143.5.1 - Ring design principle 2143.5.2 - Composition of rings 2143.5.3 - Contact surfaces 216

3.5.4 - Waterproofing gaskets 2193.5.5 - Segment assembly systems 2203.5.6 - Connector inserts, pockets 2223.5.7 - Gaskets for distributing loads at segment

contact joints 2223.5.8 - Back grouting behind ring extrados 222

3.6 - Lining installed outside the area occupied by the TBM 2233.6.1 - Ring design principle 2233.6.2 - Advantages and drawbacks 223

3.7 - Specific aspects of water conveyance pressure tunnels 2243.7.1 - Hydrogeological reminders 2243.7.2 - Tunnel lining structural behaviour 2243.7.3 - Roughness of segment-lined tunnels 224

3.8 - Construction tolerances 2243.8.1 - Specification 2243.8.2 - Identification of main criteria contributing to

tolerance specification 2243.8.3 - Accuracy 225

3.9 - Durability 2253.9.1 - Segment concrete 2253.9.2 - Steel reinforcing bars 2253.9.3 - Waterproofing gaskets 2263.9.4 - Connector inserts 226

TUNNELS ET OUVRAGES SOUTERRAINS – HORS-SERIE N° 1 – 2005

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The design, sizing and construction of precast concrete segments installed at the rear of a tunnel boring machine (TBM)


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I - GENERAL

1.1 - Purpose of recommenda-tions

The aim of the present recommendations isto provide guidelines for the design, sizingand construction of precast concrete seg-ments linings installed at the rear of a TBM.

In par ticular, they are intended to updateand complement past recommendationspresented by A.F.T.E.S. Working Group 7(Tunnel Suppor t and Lining) entit led"récommandations sur les revÍtements pré-fabriqués des tunnels circulaires creusés autunnelier" (recommendations for prefabri-cated linings of TBM-driven circular tunnels)(Tunnels et Ouvrages Souterrains (T.O.S.)Special Issue 05-88).

They are also based on other past recom-mendations published by A.F.T.E.S.

1.2 - Scope of applicationof recommendations

The present recommendations deal exclusi-vely with the case of precast concrete seg-ments linings.

Thus, tunnel lining designs based on usingother materials, such as cast iron or steel, orhaving recourse to a mix of these materialsdo not fall within the scope of these recom-mendations and call for a specific recom-mendation drafting project.

On the other hand, the expression "installedat the rear of a TBM" does not limit thescope of application of this text to onlylinings installed within the TBM shield tail; italso includes linings installed outside thearea occupied by the shield tail, such aslinings formed from expanded segments.

Thus, following a brief historical reminderdescr ibing the emergence of precast

concrete tunnel linings, these recommenda-tions recall in a section covering design:

• the functions which linings must fulfil,

• the different elements forming tunnellinings and their roles,

stressing, in par ticular, the important pointsto be complied with to ensure satisfactorybehaviour of the structure during construc-tion and throughout its life.

The document subsequently reports on thesizing aspect of linings in relation to which itis impor tant to recal l immediately theessential osmosis, in the general sense(design, analysis, construction) of the word,which must prevail between TBM and liningdesigners. This process will result in theavoidance of many sources of malfunctionliable to lead, in some cases, to cer taindesign inconsistencies at times detrimentalto the long-term performance of the struc-ture.

3.10 - Economic considerations 2264 - TUNNEL LINING DESIGN 226

4.1 - Main parameters influencing sizing 2264.1.1 - Implementation conditions 2264.1.2 - Parameters for analysing ring stresses 227

4.2 - Design assumptions 2274.2.1 - Regulations and references 2274.2.2 - Material properties 2294.2.3 - Nature of actions and loadings 2294.2.4 - Combined actions 2304.2.5 - Sizing criteria 231

4.3 - Determination of stresses in the tunnel lining 2324.3.1 - Introduction 2324.3.2 - Hyperstatic reaction method 2324.3.3 - Composite solid method 2324.3.4 - Adaptation of analysis methods to a segments

lining and to TBM-based excavation 2334.3.5 - Parameters which can be integrated in the

different methods of analysis 2334.4 - Proof of concrete and reinforcement 235

4.4.1 - Choice of segment wall thickness 2354.4.2 - Circumferential reinforcement (hoops) 2354.4.3 - Longitudinal reinforcing bars (arranged parallel

to the tunnel axis) 235

5 - DESIGN OF ASSEMBLY SYSTEMS 2365.1 - Design assumptions for bolts and anchor bolts 236

5.1.1 - Regulations 2365.1.2 - Nature of actions and loadings 2365.1.3 - Combined actions - Design stresses 236

5.2 - Proof of assembly and pick-up components using materials other than steel 2365.2.1 - Introduction 2365.2.2 - Actions to be considered 2365.2.3 - Combined actions - Stresses 2375.2.4 - Behaviour of materials and assemblies - Tests 2375.2.5 - Conclusions 237

6 - TRANSITION AND ANCILLARY WORKS 2376.1 - Design of ancillary works 2376.2 - Construction of transition and ancillary works 237

7 - INSTRUMENTATION 2387.1 - Aims 2387.2 - Monitoring methods 238

REFERENCES 239ANNEX : 239TUNNEL LINING CONSTRUCTION - PRECASTING AND INSTALLATION 239

FOREWORD

The present text is aimed first and foremost at the different active par ties (Owners, Owner's Representatives and Engineers, ConsultingEngineers, Contractors) working in the field of TBM-based mechanized tunnel driving.

The prime aim of the present document is not only to avoid cer tain past mistakes in the design, sizing and construction of precast concretesegmental linings installed at the rear of a TBM, but also to contribute to extending know-how in these areas based on the experience gainedover the last decades by the various par ties practising of this technique.

It is hoped that this text will stimulate the wish of all those concerned to make progress in relation to the technical aspect of this type of liningand technology involved.

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Thus, the following aspects will be addres-sed in this section of the recommendations:

• the main parameters influencing sizing;

• design assumptions (regulations andrecommendations, types of mater ials ,actions and combined actions, sizing crite-ria);

• methods available to the design engineerfor analysing soil-structure interactingstresses and where the refinement of thecalculations should be adapted to:

- the design levels implemented (prelimi-nary studies, design studies, constructionstudies),

- the nature of the problems encountered(sensitivity of the site to ground deforma-tions, closeness of other structures, etc.);

• cation of the different structural elementsforming the lining.

Moreover, the recommendations drawattention to the essential control of cer tainunusual design aspects, such as transitionbetween the lining and different types ofunderground structures (stations, terminals,addits, shafts, pipes, etc.), often causing pro-blems which are awkward to deal with.

Finally, consideration is given to the par ticu-lar aspects of monitoring and instrumenta-tion of this type of structure.

An annex specific to tunnel lining construc-tion provides a review of the recommenda-tions advocated to ensure total conformitybetween the structure engineered at designstage and the implemented finished productfrom segment casting stage to segmenterection within the tunnel.

This summary of the content of the recom-mendations reveals the full range of theareas affecting the design and constructionof precast concrete segments linings instal-led at the rear of a TBM. It also highlights thespecial care which must be applied to everystage of the project when working towardscompletion of a quality finished structurewhilst complying with production- andautomation/robotization-related demandsimposed by a concept of this type.

2 - HISTORICAL REMINDERUp to 1930, TBM-dr iven tunnels weremainly l ined using cast iron segments.Thereafter, precast concrete segments tun-nel linings star ted to appear, mainly in GreatBritain, for small diameter tunnels (1.5 to 3m) driven in London clay for use as sewers.

Since that period, several hundred kilo-metres of generally small diameter tunnelsdriven in the London area have been linedwith concrete segments of various shapesand types; they are often ribbed, in otherwords their shape stems from that of castiron segments. It should be noted that, mostof the time, these underground structureswere built in very low permeability groundin which the excavated periphery offeredshort-term stability (London clay).

In time, Br itish manufacturers offered awhole range of standard off-the-shelf tunnellining segments covering a wide range ofdiameters (1.5 to 6 m internal diameters).One of the significant features of these seg-ments was their small size and reducedweight (100 to 400 kg per segment), whichresulted in a large number of ring elementsfor the largest diameter tunnels (12 seg-ments per ring for a diameter of the orderof 6 m).

Since 1965, major development in the useof concrete segments l inings in Europe(Germany, Belgium, Austr ia, France) andJapan is notewor thy, in parallel with thedevelopment of TBMs for excavating largediameter tunnels (approximately 5 to 10 m)in soft and water-bear ing ground.Specifically, mechanized erectors, larger sizesegments with ver y low precasting tole-rances and elastomeric gaskets capable ofguaranteeing lining water tightness even inheavily water-bearing ground, have appea-red.

3 - TUNNEL LINING DESIGN

3.1 - Introduction

It is essential to state that there is no uniquedesign for a segmental lining.

Very often, its design is based on the expe-r ience and skil l acquired by ConsultingEngineers and Contractors on past projects.Consequently, the purpose of this section isto review the main factors entering into thedesign of this type of lining and to drawattention to cer tain vital engineer ingaspects, of which a perfect command isrequired. It cannot recommend a single typeof lining design to reader because too manyinterdependent factors come into play.

On the contrary, over-precise recommen-dations, which do not integrate all the para-meters, could prejudice construction of aquality structure.

3.2 - Basic data required todesign a tunnel lining

Prior to designing any tunnel lining, it isessential that Owners, Owner'sRepresentatives and Engineers specify theaims and constraints which the planned tun-nel structure must satisfy:

• its function(s): rail or road transpor t,water or air conveyance, power or dataconveyance, storage, etc.;

• its operating life;

• the operating constraints:- geometr ical cr iter ia (clearance, route ,construction tolerances, etc.),- type and location of all permanent facili-ties (benches, inver t slab, wall recesses,branches, hangers, connector inser ts, wallpockets, support systems for intermediatefloors and ventilation ducts, etc.),- roughness cr iter ia for the permanentworks compatible with projected water orair flows (precast lining possibly combinedwith and internal cast-in-place lining),- water tightness criteria (acceptable see-page flows both from outside to inside andconversely for water conveyance tunnels),- fire resistance criteria,- possible requirements in relation to steelreinforcement equipotential;• environmental constraints:- geology, hydrogeology,- aggressivity of surrounding ground,- site urbanization (limitation of groundsettlements, etc.),- presence of nearby underground struc-tures (existing or future, if known),- seismicity;

• structural sizing criteria resulting espe-cial ly from the above-mentionedconstraints:

- regulations, standards and recommenda-tions to be applied,

- actions and combined actions to be consi-dered.

3.3 - Lining functions

3.3.1 - Functions associated withoperating constraints

During tunnel operation, the segmentallining may be required to fulfil the followingfunctions, which depend entirely on thepre-established aims of the Owner, theOwner's Representative and the Engineer :

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• To act as permanent tunnel lining/supportcompatible with the various environmentalconstraints;

• To act as an envelope intended to ensurepermanent compliance with tunnel opera-ting clearance(s);

• To ensure imperviousness with respect to:

- water inflows from the enclosing ground,

- possible fluids flowing freely or underpressure within the structure.

It should be recalled that structural imper-viousness depends on the ability of thelining elements to oppose the passage of afluid (water, etc .), both from outside toinside and conversely, within the leakageflow limits specified for its operation;

• To ensure air or water conveyance depen-ding on whether the structure is likely tohave to ensure the flow of air (piston relief)or water respectively;

• To provide support for permanent servicemobile and fixed equipment.

3.3.2 - Functions associated withconstruction constraints

During the construction phase of the tun-nel, the segmental lining may be required tofulfil some of the following functions resul-ting from both construction and environ-mental requirements:

• To provide to the tunnel:

- either immediate suppor t, mainly whendrawing in the TBM shield tail in soft ground,

- or deferred support, when the lining is ins-talled outside the TBM shield tail; the per-iphery of the excavation is stable in theshor t-term within an enclosing soil-rockmass of sufficiently low permeability toallow work to be carried out in satisfactoryconditions, without having recour se toimmediate continuous support;

• To provide protection against waterinflows, when tunnel driving is undertakenin water-bearing ground;

• To provide longitudinal support allowingthe TBM to:

- penetrate the ground,

- if necessary, exer t confinement pressure atthe excavation face to ensure its stabilityand that the hydrostatic pressure applied tothe TBM cutterhead is taken up;

• To support the back-up equipment andconstruction plant required for carrying outthe work;

• To ensure evacuation of drainage water.

3.4 - Description of theconcept

3.4.1 - General

An impor tant cr iter ion for tunnel liningdesign lies in the requirement or not tointerface driving and lining installation func-tions for the purpose of ensuring throu-ghout the tunnelling period:

• total continuity of tunnel support;

• total control of water inflows.

Continuity is thus initially provided by theTBM shell itself (the shield tail with its rearseal) and thereafter by the lining, incorpora-ting its water tight gaskets, installed insidethe shield tail.

It goes without saying that these designoptions depend entirely on the geologicaland hydrogeological conditions of the sur-rounding hydrogeological environmentthrough which the tunnel passes.

3.4.2 - General aspects of tunnellining design

A precast concrete lining for a TBM-driventunnel generally comprises a sequence ofrings placed side-by-side.These rings are divi-ded into sectors and each of these elemen-tary units is called a segment (see figure 1).

The transverse faces of the rings (see figure2) can be formed by:

• either parallel plane surfaces, as in thecase of so-called straight rings;

• or out-of-parallel plane surfaces, as in thecase of so-called tapered rings.

Depending on the arrangement retained,the latter ring geometry allows the lining tobest adapt itself to curvature in the hori-zontal and ver tical alignments of the tunnelor to correct accidental deviations causedby the TBM.

3.4.3 - Tapering of rings

Ring taper "p" is defined as the differencebetween the maximum and the minimumlengths of the ring and must be dimensio-ned to ensure that design curves are com-plied with and to allow TBM deviations tobe taken up. It can attain several centi-metres (see figure 2).

Figure 1 : Lining comprising precast segment rings

Figure 2 : Sequence of rings

Segment

Ring

Straight ring Plan view

Universal tapered ring

Left or right taperedtrapezoidal ring

Plan view

Straight Curved

Straight Curved

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Development of techniques (control ofsupply to the workface) tends to favour theuse of the universal tapered ring.

3.4.4 - Length of rings

The ring length may depend on:

• operation-linked criteria:

- tunnel diameter

- alignment design (horizontal and ver ticalradii of curvature),

- limitation of the length of gasket sealingmaterial and thus of the risk of a defect intunnel water tightness;

• construction-based criteria:

- optimization of dr iving (mucking) andlining installation cycles,

- size of rings (impact on design of TBMthrust mechanisms: stroke of thrust cylin-ders, etc.),

- weight of ring segments (impact on yard-and tunnel-based segment handling equip-ment).

Ring length is generally between 0.60 m and2.00 m.

3.4.5 - Composition of a lining ring

The number of segments comprising a ringvaries widely from one tunnel project toanother and is subject to the followingconstraints:

• operating constraints:

- l imitation of the number of segmentcontact joints, therefore of the risk of adefect in tunnel water tightness,

- limitation of head losses due to seepage ofinternal fluids;

• construction constraints:

- weight of segments (impact on formworkstripping operations, handling, yard storage,ring erection using erector arm),

- size of ring elements (transport from pre-cast yard, supply to the workface),

- impacts on concreting conditions (curva-ture),

- segment behaviour under TBM thrust(limitation of risk that cracks will appearunder temporary stresses resulting frombearing defects between rings),

- positioning of TBM thrust mechanisms.

- ring-to-ring assembly constraints (layoutof ring assembly devices).

3.4.6 - Segment geometry

The geometry of a segment is essentiallylinked to the type of ring assembly systemretained.

The following shapes can be distinguished:

• "Solid" segments:

These are the most frequently used today;almost their full wall thickness contributesto the strength of the ring.They incorporatesmall size pockets allowing assembly of thedifferent par ts of the ring (by anchor bolts,cur ved bolts, plugs, etc . ; see § 3.5.5 -Segment assembly systems);

•"Hollow" or "ribbed" segments:

Although often used in the past, today theiruse is almost exclusively confined to struc-tures such as shafts. They require an largerexcavation diameter than solid segments forthe same sectional area and iner tia.The sizeof the hollows allows implementation of anassembly system based on straight bolts,which requires greater rearward clearanceduring erection than other assembly sys-tems.

3.4.7 - Nature of lining materials

The main constituent materials of a tunnellining are:

• concrete, containing:

- cement,

- aggregates,

- admixtures

• reinforcing steel.

3.4.7.1 - Cement

Preference should be given to using addi-tive-free rapid-hardening cements, whosedurability is unaffected or little affected bysteam curing.

For this type of application, use of standardCPA-CEM I-type cement is therefore pre-ferred to the following cement types:

- CPJ - CEM II

- CLC - CEM V

- CLK - CEM III

- CHF - CEM III.

However, the latter types can be consideredfor tunnel l inings in aggressive ground

Figure 3 : Typical cross-section of a ring

Figure 4 : "Solid" segments(Lille Underground - lines 1 bis - section B)

Figure 5 : "Hollow" and "ribbed" segments (CaracasUnderground - Lines 1 and 2)

➝Segment

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conditions based on special mix design andproduction if necessary.

Use of CPA - PMES-type cement may berecommended for cer tain applications.

3.4.7.2 - Aggregates

In general, the nature of fine and coarseaggregates used depends on the availablequarries in the area where the tunnel is tobe built.

Aggregate sizes must suit perfectly the geo-metrical accuracy of the segments, form-work recesses, reinforcement arrangementsand possible connector inser ts.

The proper ties of these materials will bespecified on the basis of physical and chemi-cal analyses and examinations. In par ticular,aggregates will be sought which are frost-resistant, unreactive, sound, free of fines,non-absorbent, non-brittle and hard. Sandsshould preferably contain (mineral) filler.

Continuous aggregate grading should bespecified to ensure good workability whenplacing the fresh concrete in the moulds.

3.4.7.3 - Admixtures

In cases in which aggregates lack fines, use ofadditional fly-ash or fillers (e.g. limestone-based materials) are recommended. Theorigin of such products should of course bechecked.

The use of standardized water-reducingsuperplasticizers is recommended to obtainincreased workability to achieve higherstrength.

N.B. In France, studies are being conductedon the fire resistance of silica fumes withinthe framework of the BHP 2000 nationalproject.

3.4.7.4 - Reinforcement

Grades of steel used for segment reinfor-cing cages must comply with applicablestandards.

The most commonly used steels are wel-dable hot-rolled or cold-worked Fe E 500and Fe E 235 grades.

Should hot-rolled steel, generally featuring alarge quantity of mill scale, be used, caremust be taken to remove this scale beforewelding (during straightening of coiled steelor by shot blasting steel bars).

3.4.7.5 - Reinforcing fibres

Use of metal fibres, exclusively or in addi-tion to conventional reinforcement, hasbeen experimented in cer tain works. InFrance, studies are in progress for the pur-pose drawing up relevant design rules,within the framework of the national metalfibre reinforced concrete project (BEFIM).

3.5 - Lining installed withinthe area enclosing the TBM

The various operating and environmentalconstraints referred to above very oftenimpose erection of the lining rings undercover of the TBM in the rear par t of itsshield tail.

Different points entering into the design ofthis type of lining are enlarged upon in thefollowing sections.

3.5.1 - Ring design principle

As already referred to above in Section 3.4,this lining design can require the adoptionof:

• either straight rings to be used for thestraight sections and tapered rings (or tape-red wedges) to be used specially for curvedsections of the tunnel route and/or for cor-recting TBM deviations.

• or universal tapered rings to be used on asystematic basis, including for straight sec-tions of the tunnel route; the tapers of onering compensate for those of another ring,thereby cancelling out the overall taperingeffect.

It should be noted that this second type ofdesign, besides being the most frequentlyused, implies fabricating specific moulds foreach segment (the amount of taper beingdifferent from one segment to the another).

3.5.2 - Composition of rings

In general, division of a lining ring into seg-ments depends on the ring erection tech-nology retained.

3.5.2.1 - Rectangular and trapezoidalsegments

This design does not generally allow theexcavation cycle to be restar ted until thering has been completely erected.

The gap available between the extrados ofthe ring being erected and the intrados ofthe shield tail is usually small and ring clo-sure is very often ensured by a longitudinalkey, which requires additional forward spaceto allow inser tion of this final segment.

To par tially satisfy this constraint, use of akey segment of "trapezoidal shape" in plan(see figure 7) is very often resorted to.

Consequently, the geometr y of the seg-ments adjacent to this ring par t will have tobe special to suit that of the key: these adja-cent elements are called counter segments.

Figure 6 gives an idea of the increase in segmental lining wall thickness with respect to the tunnel internal diameter.

final lining - open face TBM temporary lining - open face TBMfinal lining - compressed air TBM temporary lining - compressed air TBMfinal lining - slurry pressure TBM temporary lining - slurry pressure TBMfinal lining - earth pressure TBM temporary lining - earth pressure TBM

Lining internal diameter (m)

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Thus, in this type of design, a lining ringgenerally comprises:

• rectangular vir tually identical (apar t frompossible taper) standard segments, whosenumber can vary from one project to ano-ther (see figure 8);

• two counter segments;

• one key segment.

Assembly of these ring elements is oftenunder taken by means of bolts or anchorbolts (see § 3.5.5 - Segment assembly sys-tems).

In general, contact faces between segmentsare offset longitudinally both to preventdefects in water tightness at the corners andto maintain a cer tain pressure on the seg-ments previously placed to prevent themfrom loosening completely when the TBMthrust cylinders are retracted (see figure 9).

In some cases, these contact faces can bealigned (see figure 10); this configurationcan be adopted in par ticular :

• at future openings (entrances to cross-tunnels, etc.) to be provided in the lining;

• in areas in which alignment correctionsare made essential (special care must thenbe taken in relation to measures to beadopted to guarantee water tightness atsegment corners);

• if defects in water tightness at segmentcorners are not a concern (systematic align-ment of contact faces).

Figure 7 : Longitudinally inserted key segment

Figure 8 : Rectangular and trapezoidal segments - perspective view

Figure 9 : Rectangular and trapezoidal segments - longitudinal offsetting of contact faces between segments

Key

SECTION AA

Directionof advance

Key

DIRECTION OF TBM ADVANCE

Standard segment Counter segment

Key segment

Segments are numbered in accordance with their order of placement

Figure 10 : Rectangular and trapezoidal segments - longitudinal alignment of contact faces between segments


Standard segment Counter segment

Key segment


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Two different ring designs can be conside-red with this type of rectangular or trape-zoidal segment:

• Universal segment

As its name suggests, this design requiresonly one set of rings.

The key segment can then be erected in anyangular position.

• "Left" and "right" rings

This type of design necessitates resor ting totwo sets of rings, to which the followingconstraints apply:

- ring taper,

- key and counter segments with specificgeometry,

- key positions limited to the upper semi-circumference of the ring.

If necessary, "left" and "right" rings can betransformed into universal rings (correctionof tunnel alignment deviations, etc.).

Contractors' final choice of one or theother type of rings is very often based onpractices tested at length on different pro-jects.

3.5.2.2 - Parallelogrammic and trape-zoidal segments

This ring design is associated with the use ofplugs incorporated in the lining wall at thecontact face between successive r ings(transverse contact face) (see § 3.5.5 -Segment assembly systems).

When erected, segments are fitted withthese projecting plugs, which are lined up in

front of the existing pockets in the pre-viously erected ring in order that they canthen be driven in hard.

The segment being erected is pushed longi-tudinally on the projecting section withoutany real oppor tunity for crosswise move-ment. For this reason and for the purpose ofmaintaining gradual transverse compressionof the radial gasket section (between seg-ments) whilst sliding the segment longitudi-nally, standard segment geometry is desi-gned in the shape of a parallelogram.

Thus, this type of lining ring usually com-prises (see figure 13):

• parallelogrammic standard segments ,whose number varies from one project toanother ;

•one reversed key segment;

•one key segment.

Configuration 1, shown in figure 14, requiressegments to be erected in the same orderof placement from one r ing to another.Under the pressure exerted by the longitu-dinally oriented waterproofing gaskets (bet-ween segments of the same ring), the ringscan be gradually subjected to disruptiverotation in the absence of transverse bolts.In time, this rotation can lead to a discre-pancy of several centimetres between theposition of the rings and that of the TBMthrust cylinder ram pads.

To overcome this gradual rotation, a solu-tion based on alternate segment erectionwith respect to the first ring par t placed isrecommended (see figure 15).

3.5.2.3 - Trapezoidal segments

This ring design may allow tunnel excava-tion and lining erection operations to be

carried out simultaneously (stroke of thrustcylinders adapted to two ring lengths).

In general, a ring is broken down into aneven number of trapezoidal segments. Halfthe segments are "counter" type, i.e. wideron the side of the previously placed ring.The other half are "key" type, i.e. narroweron the side of the previously placed ring(see figure 16).

Once in place, the counter segments pro-vide support for the thrust cylinders, the-reby allowing the TBM to advance again.During this time, ring erection can continuewith the key segments, as long as the shieldtail seal is not crossed. Subsequently, rearsupport for the thrust cylinders is transfer-red to the key segments without haltingTBM penetration.

This continuous penetration methodrequires the following problems to be over-come:

• placement of "key" segments between the"counter" segments;

• total thrust can be mobilized using onlysome of the thrust cylinders or continuouspenetration is limited to cer tain favourableground conditions requiring reduced thrust;

• more difficult guidance.

3.5.3 - Contact surfaces

3.5.3.1 - Circumferential or trans-verse contact joints

Contact joints between adjacent rings canbe required to bear :

• compressive (possibly eccentric) loadsresulting from the longitudinal thrust of theTBM;

Figure 11 : Sequence of universal rings

Figure 12 : Sequence of "left" and "right" rings - key sys-tematically positioned above the horizontal diameter

Figure 13 : Parallelogrammic and trapezoidal segments - Perspective view

Key segment atbottom of ring

Key segment attop of ring

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• 217 •

• shear forces due to differential deforma-tions between adjacent r ings associatedwith:

- offsetting of contact faces between rings(see figure 9), shear being transmitted bypermanent ring assembly systems (bolts,anchor bolts, plugs, tenons, etc.),

- non-uniform load distributions resultingfrom the ground or from neighbour ingstructures.

Obviously, assembly systems offer differentcapacities for opposing potential displace-ment of the ring par ts with respect to eachother (out-of-flushness).

The final geometry of these contact jointsand their possible additional equipmentmust be selected in relation to the purposeof the tunnel (wastewater collector, waterconveyance, rail or road tunnel, etc.) andmust be compatible with the out-of-flush-ness tolerance.

•forces resulting from segments overhan-ging (accidentally or otherwise) during ringassembly.

These contact joints usually fall under oneof the following types:

a) plane contact joints

This contact principle is shown diagramma-tically in figure 17.

Depending on the relative intensity of theforces described above, radial slippage canoccur leading to out-of-flushness of onesegment with respect to an adjacent one.Addition of mechanical systems (see §3.5.5.) can help to limit the extent of thisphenomenon.

Out-of-f lushness can be acceptable orunacceptable depending on the purpose ofthe tunnel (temporary or permanent, air orwater conveyance function to be fulfilled).When it is unacceptable, it may be possibleto turn to combined geometr y contactjoints of a form allowing transfer of shearforces.

b) combined geometry contactjoints

This type of contact joint, shownin figure 18, is less common than

Figure 14 : Parallelogrammic and trapezoidal segments - Configuration 1

Figure 15 : Parallelogrammic and trapezoidal segments - Configuration 2

Figure 16 : Trapezoidal segments







Reverse key type segment Key type segment

Key type segment Reverse key type segment

Key type segment Reverse key type segment

Figure 17 : Plane contact joint Figure 18 : Example of combined geometry contact joint

excavation

back grouting

waterproofing gasket

plane contact joint

extrados

intrados

excavation

back grouting


extrados

intrados

boss

boss

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• 218 •

the one above because it is difficult toreconcile erection tolerances with the loadtransfer efficiency which could be assumedfrom such a system.

Moreover, there is a danger that very highlocal stresses will develop in the load trans-fer zones (boss, tenon and mor tise, etc.)and reinforcement of these zones, by meansof reinforcing bars, is often delicate simplybecause of the contact joint geometry. Inthis type of design, it is thus essential tostudy careful ly the geometr y of suchcontact joints.

Finally, normal loads are necessarily concen-trated on reduced surfaces which must becapable of sustaining such loads.

3.5.3.2 - Radial or longitudinal contactjoints

The effects of both the surrounding groundconditions and back grouting cause thesecontact joints between segments of thesame ring to be subjected to:• compressive loads;• bending forces:

It should be noted that bending forces arereduced in the immediate vicinity of theradial contact joint. The iner tia of this zoneis effectively lowered with respect to that ofthe standard section;

• transverse shear forces.

The final geometry of these contact jointsmust therefore be guided by the followingaims:• to allow correct centring of stresses;• to limit the danger of segment out-of-flu-shness, which both generates disruptiveloads and can be detrimental to the pur-pose of the tunnel (e .g. air or waterconveyance).

These contact joints are usually one of thefollowing types:

a) Plane contact joints

This type of contact joint, shown in figure19, is the most commonly used because, ingeneral, it is sufficient for transferring theforces applied to the rings.

A mechanical assembly system is generallyincorporated; it contributes to maintainingerection accuracy by preventing, in par ticu-lar, gradual drift in both segment alignmentand intersegment contact.

b) Cylindrical contact joints

When ring stresses are too high to considerplane contact surfaces, joints are often desi-gned with cylindrical surfaces.

Through plasticizing the concrete , thecontact surface widens gradually in relationto the load and centres it.

These contact joints can be of differenttypes:

• concave-convex cylindrical contact joints(see figure 20):

The radius of curvature of the concave sur-face may be greater than that of the convexsurface in cases when rotation of ring par tsin contact is expected or, conversely, theseradii of cur vature can be essentially thesame (the system is then intended to pro-vide shear strength only);

• convex-convex cylindrical contact sur-faces (see figure 21).

c) Other contact joints (see figure 22).

Incorporation of a guide rod can be adop-ted in some cases.

3.5.3.3 - Flanks

Given the intensity of compressive stressesoften applied to the contact surfaces, whe-ther they be transverse or longitudinal,experience gained from past projects leadsto the recommendation that very specialcare should be taken in designing segmentflanks in order to limit breakage at theiredges to a minimum.

It should be borne in mind that these frac-tures, which are often observed in the seg-ment intrados and repaired by simply resto-ring, can also affect the extrados of liningring par ts and can lead to local damagewhich is difficult to repair and is prejudicial

Figure 19 : Example of plane contact joint Figure 20 : Example of concave-convex cylindrical contact joint

Figure 21 : Example of convex-convex cylindrical contact joint Figure 22 : Example of contact joint incorporating a guide rod

excavation

back grouting


excavation

back grouting


plane contact joint

concave faceconvex face

extrados

intrados

extrados

intrados

excavation

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convex face

extrados

intrados

convex face

excavation

back grouting

extrados

intrados


guide rod

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• 219 •

to the durabil ity of the works (wateringress, corrosion of reinforcement, etc.).

Whilst it is advantageous to provide relativelarge flanks in the contact zones in order toovercome the above problems, it should beensured that the stresses acting on thecontact surfaces remain acceptable, inclu-ding under unfavourable construction confi-gurations (eccentricity of load from thrustcylinders especially in curved alignments,erection tolerances, etc.).

Detailed geometrical design of these flanksshould be undertaken in parallel with thatof the reinforcement in order to guaranteethe highest possible strength at these par ti-cularly highly stressed segment sections.

Similarly, in cases in which lining waterproo-fing is to be provided by means of compres-sible gasket sections, it should be ensuredthat the groove receiving the gasket is posi-tioned sufficiently far away from the extra-dos to avoid the segment edges breaking offwhen the system is compressed under load.

Moreover, whilst it has been the practice toprovide a chamfer around the extradosedges of both transverse and longitudinalcontact joints, this may give rise to cer taindrawbacks such as:

- risk of defective imperviousness of theTBM tail seal with respect to the back grou-ting product, water in the surroundingground or slurry from the forward chamber(in cases involving hydraulic confinement);

- risk of accident to personnel in charge ofsegment mould-based operations (sharpprojecting edges for forming chamfers).

To avoid these risks, it is preferable to pro-vide either sharp edges or, if this chamfer isretained, to incorporate a foam rubber (orsimilar) seal over its ful l length; thisconstruction-based provision will therebysolve the first problem but not the second.

3.5.4 - Waterproofing gaskets

It should be recalled that, when an water-proofing function is sought from a segmen-tal lining, this can be fulfilled by:

• the segments themselves, for which it isimportant to limit in par ticular :

- the mass porosity,

- cracking associated with temporar y orpermanent stresses,

- defects involving formation of the groovereceiving the waterproofing gasket;

• waterproofing gasket positioned betweenthe segments.

Properties of the latter are described in the"recommandations pour les profilés d'étan-chéité entre voussoirs" (recommendationsfor intersegment waterproofing gasket)presented by A.F.T.E.S. Working Group 9(see T.O.S. Issue 116, March-April 1993).

The remainder of this description applies toso-called "conventional" waterproofing gas-kets retained for the design of standard tun-nel projects involving low to medium over-burden.

N.B . These imper vious systems are nottransposable to other tunnel projects invol-ving very high overburden (e.g. major Alpinecrossings). Research work (InternationalEureka Contun) is in fact being conductedconcerning the design of TBMs and tunnell inings suited to the special constraintsimposed by such projects. On account ofthe very high pressures liable to be exertedon these linings (loads induced by bothground and water), thoughts are very natu-rally tending towards seeking a reduction intheir rigidity by incorporating a degree ofdeformability in par ticular at their water-proofing gaskets.

3.5.4.1 - Compressible gasket sections

a) Properties

It should be recalled that these are elasto-meric gaskets, which have been designedand manufactured for fitting to precastconcrete lining segments (see figure 24).Water tigntness is ensured by compressingthem during erection and maintaining thiscompression throughout the life of thestructure.

During construction, the compressive loadis applied by the TBM thrust cylinders orsegment erector and is temporarily maintai-ned by the ring building system.

Water tigntness of gasket sections is guaran-teed for a permanent hydrostatic pressurelaid down in the project specifications.

b) Construction configurations

In general, the gasket is fitted into a grooveformed in the segment faces; it is positionedseveral centimetres from the segmentextrados and fitted around the full perime-ter of the segment.

Gasket section dimensions must be compa-tible with erection tolerances and take intoaccount ring out-of-roundness.

In the specific case of water conveyancepressure tunnels, combined behaviour ofthe ground / lining must be analysed beforepossibly modifying the posit ion of theimper vious gasket within the lining wall(conventional well tested approach).

3.5.4.2 - Water-expansive gasket

a) Properties

It is recalled that these are elastomericwaterproofing gasket with water-expansiveproperties, i.e. they swell in the presence ofwater.These cycles can alternate during thelife of the works.

If necessary, initial water tigntness can beachieved by compression. The presence ofwater then triggers swelling of the water-expansive material, which allows the appliedhydrostatic pressure to be resisted.

Water tightness of gasket is guaranteed for apermanent hydrostatic pressure laid downin the project specifications.

Figure 23 : Spalling and cracking of concrete cover

Figure 24 : Examples of compressible waterproofing gaskets Figure 25 : Examples of water-expansive waterproofing gasket

Water-expansive parts

Neutral parts

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• 220 •

In some cases, these gasket can be reinfor-ced by "neutral" (non water-expansive)par ts (see figure 25).


The gasket is positioned on the segmentsides several centimetres from its extrados.

There are two types of construction confi-guration (see figure 26).

In the double thickness system, gasket arefitted around the full perimeter of each seg-ment.

In the single thickness system, gasket are fit-ted around half the segment perimeter witha return of several centimetres at diagonallyopposing corners.

As in the case of compressible sections,waterproofing gasket dimensions must becompatible with erection tolerances andtake into account ring out-of-roundness.

3.5.4.3 - Combined gaskets

a) Principle

These are products which combine bothtypes of gaskets described above.

The compressible gasket represents thebasic component and the water-expansivegasket is usually fitted into the groove for-med in the former (see figure 27).

This composite product allows the water-proofing system offered by either the com-pressible or the water-expansive gasket tobe complemented.


As in the case of the compressible gasket,

the combined section is fitted around thefull perimeter of each segment and positio-ned several centimetres from its extrados.

3.5.5 - Segment assembly systems

3.5.5.1 - Purpose of assembly systems

Assembly mechanisms implemented at cir-cumferential (transverse) and radial (longi-tudinal) contact joints are aimed at:

• maintaining sufficient erection accuracy bypreventing gradual cumulative out-of-flush-ness between segments and gaps at contactjoints;

• keeping waterproofing gasket compressedin the short-term, during construction, andeven in the long-term, during tunnel opera-tion, especially in the vicinity of stations;

• ensuring segment stability at ring buildingstage, even when there no load is exer tedby the TBM thrust cylinders. However, mea-sures might be adopted to ensure this stabi-lity without necessarily resor ting to the useof assembly systems (e.g. a thrust cylinderanti-retract system);

• ensuring segments are kept in their rela-tive positions (guidance role) in the specificcase of water conveyance tunnels, for whichlinings are required to "breathe" during tun-nel filling and emptying cycles.

In general, longitudinal assembly systems areregular ly spaced along each transver secontact joint (between consecutive rings).

Their number varies from one project toanother depending on:

• the forces to be balanced;

• the desired possibilities for relative rota-tion of a ring with respect to the last oneinstalled (considering the constraints impo-sed by the design, such as offsetting of longi-tudinal contact joints, small deviations in ali-gnment, etc.).

When they exist, assembly systems bet-ween segments in the same ring generallycomprise between one and three units.

In standard rings, longitudinal and trans-verse assembly systems are usually onlyessential during construction (except whenwanting to take advantage of the contribu-tion to r igidity of adjacent r ings whoseradial contact joints are then combined).

As a general rule therefore, these assemblysystems can be removed when the TBM ismore than 200 metres away and all additio-nal grouting operations have been comple-ted.

In the vicinity of stations, longitudinal assem-bly systems are usually necessar y duringtunnel operation to keep the waterproofinggaskets compressed. They are thereforekept in place over a minimum tunnel lengthof two or three diameters.

The durability of all permanent assemblysystems must be the same as that of thestructure itself.

3.5.5.2 - Bolted assemblies

Bolts or threaded rods are fixed from poc-kets provided on the intrados side of thelining.

These bolts are generally of two types:

• straight bolts fixed from hollows formedin the intrados of segments:

- bear ing directly on the concrete (seefigures 28 and 29),

- bearing on steel plates inser ted in the seg-ments (see figure 30);

• curved bolts allowing the volume of thehollows to be significantly reduced (seefigure 31).

3.5.5.3 - Inclined socket bolted assem-blies

This assembly system allows a reduction inthe number of pockets in the intrados of

Figure 26 : Layout principle for waterproofing gaskets

Figure 27 : Example of combined waterproofing gaskets

Removal of strip formingthe groove

State of compressible sectionwhilst "stripping" the groove

Final state with "dovetailed"water-expansive section

"Dovetailed" water-expansive section

Double thickness gasket system Single thickness gasket system

Direction of advance

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• 221 •

the segments.This design also allows tighte-ning up operations to be carried out undercover of a fully erected ring and no longerunder segments only held in place by theerector arm and the TBM thrust cylinders;this system thereby ensures increased safetyof personnel (see figure 32).

3.5.5.4 - Assemblies using plugs, studsor other derivatives

Compared with the assemblies describedabove, such systems (see figures 33 and 34)can offer a number of advantages such as:

• no pockets in the intrados of segments,thereby providing the lining with improvedair or water conveyance properties;

• reinforcement of r ing par ts is ofteneasier ;

• simplified ring erection operations;

• good centring of rings with respect toeach other (reduced out-of-flushness);

• high shear strength (with some types ofplug);

• greater safety of personnel (no humanintervention inside the ring).

Apar t from the fact that most of thesedevices cannot be removed, they can fur-thermore inhibit cer tain degrees of free-dom, which may result in excessive liningstresses.

When designing and sizing these assem-blies, it is therefore essential to evaluate asclosely as possible all the loads to whichsuch connections are likely to be subjected(e.g. dissymmetry of thrust cylinder loads,overhanging of segments, differential ring

Figure 28 : Example of removable assembly using straight bolts Figure 29 : Example of permanent assembly (straight bolts previously inserted into oneof the segments before placing the adjacent segment)

Figure 30 : Example of steel plate assembly using short bolts

Figure 31 : Example of assembly using curved bolts

Figure 32 : Example of assembly using inclined socket bolts

Extrados ExtradosWasher

Intrados

Pocket

Washer WasherPocket

NutBolt

PocketNut Washer

IntradosThreaded

rodNut

PocketExtrados

Steel plate

Intrados

BoltNut

Washer

Connector insert

Extrados

Intrados NutWasher Pocket

Curved bolt

Bolt head

Ring erectedSegment being placed

Extrados

Intrados

Pocket

WasherSegment beingplaced

Socketbolt

Ring erected

Anchor bolt head

SocketFigure 33 : Examples of assembly using plugs

Plug

ExcavationBack grouting

Plug

Extrados

Intrados

Segment being placedPockets

Ring erected

Plug

ExcavationBack grouting

Extrados

Intrados

Segment being placed

PocketsRing erected

Figure 34 : Examples of assembly using pins

Back grouting

ExtradosExcavation

Intrados

Ring erectedSegment

being placed

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• 222 •

out-of-roundness, waterproofing gasketcrushing and distor tion loads, local stressescapable of reducing the assembly capacityof the system, tendency for key ejection,etc.) in order to prevent the appearance ofdisturbances concentrated at these connec-tions, which could adverse affect the durabi-lity of the structure.

3.5.6 - Connector inserts, pockets

Pockets, as well as most connector inser tsfitted to lining segments, represent sourcesof reduced strength of the reinforcedconcrete r ing elements. Their potentialimpact on segment structural behaviour(including during construction stages prece-ding ring erection) as well as on the pur-pose of the tunnel must, therefore, be clo-sely examined.

3.5.6.1 - Connector inserts

In general, connector inser ts can fulfil twosets of functions:

• temporary functions :

- handling, erection (socket for segmentpick-up bolts, etc.),

- adjustment,

- assembly (sockets for bolts, etc.),

- mating (pre-grouted sockets, etc.)

- grouting;

• permanent functions:

- traceability (identification of characteristiczones, etc.),

- fixing (pre-grouted sockets for supportingservice equipment or floors, etc.),

- mating, connection,

- instrumentation (vibrating wire extenso-meters, total pressure measuring cells, etc.),

- inspection.

It should be stressed that their positioningwithin the segments sometimes calls foralterations in segment reinforcement detai-ling in order to:

• comply with concrete coverage require-ments;

• avoid zones occupied by the connectorinser ts;

• reinforce the concrete immediately incontact with these connector inser ts (localstresses, pulling out, etc.).

3.5.6.2 - Pockets

In general, pockets can fulfil two sets offunctions:

• temporary functions:

- handling, erection (e.g. for picking up unitsusing "grippers" or "pins"),

- assembly (holes and boxes for inser ting orfixing assembly mechanisms, etc.),

- grouting (holes through the segment wall),

- precutting (e.g. to facilitate later formationof openings at in-line structures).

• permanent functions

- traceability (recess for identification ofcharacteristic zones),

- building in of specific equipment,

- instrumentation (concrete control blocks,etc.).

These pockets can sometimes lead to struc-tural weakening of the segments concernedand very often complicated detailing of ringpar t reinforcement (local discontinuity ofreinforcing bars, etc.). It is thus important tolimit their number and size to a minimum.Moreover, in the case of designs involvinghigh air- and water conveyance-basedconstraints, their presence on the segmentintrados requires the adoption of oftencostly special measures (sealing of "boxes",internal second lining, etc.).

3.5.7 - Stuffings for distributingloads at segment contact joints

Incorporation of stuffings may be called forto distribute TBM thrust loads over ringinterfaces (circumferential or transversecontact joints), whilst "smoothing out" asmuch as possible inaccuracies resulting fromboth segment precasting tolerances (oftenvery low) and erection tolerances duringring building, or to "channel" these loadstowards specially reinforced sections of thesegments.

These millimetre thick stuffings must pro-vide sufficient surface area to fulfil theirfunction and, on the contrary, must not be asource of "load concentration" through

dimensional underestimation (see figure 35)or an unsuitable layout.

Materials used can be very different depen-ding on design philosophies retained. Theycan be of low stiffness and even behave like"flowing" (e.g. bitumen-based) materials or,on the other hand, they can be relativelystiff (e.g. hard Isorel™).

3.5.8 - Back grouting behind ringextrados

3.5.8.1 - Purpose of back grouting

The purpose of these grouting operations isto fill the annular gap between the liningextrados and the TBM-excavated groundprofile.

The grouting material therefore fulfils seve-ral functions:

• in the short term:

- it ensures efficient blocking of the liningagainst the enclosing ground to reduce thedanger of r ing displacement especial lyduring TBM thrusting and passage of theback-up equipment, when support is essen-tial,

- it minimizes surrounding ground deforma-tions likely to cause disorders both aboveand below ground (especial ly in urbanand/or sensitive environments),

- in the case of pressurized face TBMs, itprovides good control of confinement pres-sure (especially when using compressed air)by ensuring imperviousness at the back ofthe machine;

• in the long term:

- it ensures the most uniform bond bet-ween the lining and the ground and there-fore offers effective distribution of confine-ment loads at this interface; an essentialcondition for guaranteeing the durability ofthe structure, especially when it is a pres-sure tunnel at operating stage,

- in cer tain very special cases, it fulfils a"drainage" function (granular matrix).

Figure 35 : Example of distribution of stuffings for spreading TBM thrust loads over a segment flank

Stuffings for distributing loads in contact with segments

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3.5.8.2 - Nature of infilling material

Except for materials with a granular matrix,the composition of an infilling material willdetermine:

• its rheology:

the infilling material must, on the one hand,be sufficiently fluid to facilitate its placementand to fill completely the annular gap and,on the other hand, be sufficiently firm toavoid leakage through the shield tail sealsand segment waterproofing gaskets, as wellas to avoid seepage flows along the shieldtail towards the front of the TBM.

Moreover, its setting time must suit theconstruction conditions;

•its short- and long-term structural proper-ties:

the infilling material must suit the groundand construction conditions (convergenceof ground, rate of penetration, etc .); itsmodulus of deformation and compressivestrength must be sufficient to prevent liningout-of-roundness.

There are currently two main types of grou-ting material:

•active material:

cement-based grout to which fly-ash, sand,filler, bentonite, lime and admixtures such aswater-reducing plasticizer, retarder or acce-lerator may be added;

• iner t material:

cement-free material comprising a mixtureof bentonite, polymers, filler and sand withthe possible addition of a plasticizer. Thematerial will be termed "semi-iner t" if limeor fly-ash is added.

In the case of sufficiently stable enclosingground, infilling can be carried out in twostages:

• primary infilling with a fine gravel "matrix"to ensure blocking of the lining in step withTBM penetration;

• secondary grouting to improve bond bet-ween the lining and the ground, which isoften deferred and independent from TBMpenetration.

3.5.8.3 - Back grouting implementa-tion

As detailed in Section 3.5.8.1, back groutingis carried out in step with TBM advance forreasons of efficiency.

Two implementation processes are com-monly used:

• grouting through the lining by means ofholes incorporated in the segment struc-ture (grouting operation general ly notcontrolled by the TBM);

• continuous grouting at the rear end of theshield tail through integrated grout pipesarranged longitudinally within the tail (grou-ting operation controlled by TBM).

In general, the latter process provides grea-ter control of ground deformations.

Grouting pressures to be implemented aredetermined in relation to the type of infillingmaterial, geological and hydrogeologicalconditions (ground loads and stiffnesses,hydrostatic pressure), lining strength andconstruction aims sought (formation ofground-based suppor t, control of grounddeformations, etc.).

Dur ing construction, it is impor tant tomonitor continuously the grouting pres-sures as well as the volume of material backgrouted.

3.5.8.4 - Additional grouting

Should the primary back grouting proveinsufficient for the purpose of the structure,resor ting to additional grouting through thelining may be contemplated.

3.5.8.5 - Grouting quality control

In general, grouting quality control is prefe-rable to damaging the lining by taking coresamples. However, the latter do allow thequality of annular gap infilling to be ascer tai-ned, although they should obviously be limi-ted to a minimum.

3.6 - Lining installed outsi-de the area occupied bythe TBM

It may be advantageous to erect segmentsoutside the area enclosing the TBM whenground stability permits and water inflowsare naturally low.

3.6.1 - Ring design principle

In this case, the ring is built outside theshield tail after placing the inver t segment;ring stability is only ensured after longitudi-nal driving in of the key segment which, dueto its trapezoidal shape, expands the ringthereby pushing the segments against thesurrounding ground.

The length of the key in the longitudinaldirection of the tunnel is less than thelength of the ring enabling it to be driven into a maximum between the two counter

segments; the longitudinal travel of this keycan vary slightly depending on the groundand the erected configuration of the firstsegments.

2 to 3 cm thick pads feature on the extra-dos of the segments allowing both a goodbond with the surrounding ground and thepossibility of light back grouting.

Other ring closure systems have also beenimplemented on some projects: double key,spring line jacking system.

3.6.2 - Advantages and draw-backs

The advantages of this expended ring solu-tion are:

• straightforwardness of implementation;

• the simplicity of the structure (no water-proofing gaskets);

• speed of progress in good ground, whenvery regular excavation can be maintained;

• segment erection is very regular and fol-lows the excavated profile because segmentcontact surfaces are cylindrical;

• saving due to no intersegment bolting.

However, there are also quite a number ofdrawbacks to this solution:

• ring building and the TBM guiding systemare not interrelated (no rear cylinders);

• ring geometry does not allow them to bedeviated one way or the other ; shims haveto be slipped between rings to follow cor-rectly the excavation;

• "Wingdings" contact faces between ringsare no impervious and it is impossible toundertake pressure back grouting to fill inproperly the gap left around the extradospads;

Figure 36 : Example of expanded ring

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• nothing at all can be done to ensure anydegree of water tightness if water inflowsare incompatible with tunnel operation; inthis case, a waterproofing membrane and acast in-situ lining should be implemented ifpossible;

• segment erection becomes highly proble-matical when the ground becomes unstableduring excavation or under the action ofthe grippers (overbreak and block falls);

• a void at the crown must be mortar-filledbecause the key segment is shorter than thering length in the longitudinal direction.

This solution can be advantageous as longas, using the same TBM, it allows segmenterection inside the shield tail when difficultground is to be penetrated or water inflowsoccur.

3.7 - Specific aspects ofwater conveyance pressuretunnels

3.7.1 - Hydrogeological reminders

Knowledge of groundwater pressureswithin the soil-rock mass is important whena tunnel is to be pressurized. This involves,not only very conventional installation andreading at regular intervals of piezometers,but also monitoring the regime of surroun-ding springs. The reader is referred to thetext entitled "recommandations pour le choixdes paramètres et essais géotechniques utilesà la conception, au dimensionnement et àl'exécution des ouvrages creusés en souter-rain" (recommendations for the design, thesizing and the construction of undergroundexcavated structures) presented byA.F.T.E.S. Working Group 7 in T.O.S. Issue123, June 1994.

Once the pre-excavation hydrogeologicalconditions have been established, theinfluence of tunnel excavation on behaviourof the groundwater table(s) must be deter-mined. Tunnel-driving in fact often causes acollapse of piezometer levels and thereforealter s significantly the hydrogeologicalconditions in the vicinity of the works.

3.7.2 - Tunnel lining structuralbehaviour

3.7.2.1 - Geotechnical aspects

Behaviour of a segment r ing thereforedepends on the state of equilibrium of thefollowing forces, the first two tending toclose intersegment contact joints and thethird tending to open them:

• confinement pressure;

• external hydrostatic pressure;

• internal fluid pressure (including hydraulictransient pressures, in some cases).

It should be noted that the geotechnicalparameters (E, c, CARSPECIAUX 102 \f"Symbol" ) of the surrounding ground play apreponderant role in the relevant states ofequilibrium and, as a result, they must beknown for each geological formation cros-sed.

In general, cases of adverse loading withrespect to opening of intersegment contactjoints are obtained for moderate overbur-den associated with low geotechnical para-meters.

Analysis of overall structural behaviourmust also take into account the presence ofback grouting which blocks the lining ringswithin the surrounding ground.

3.7.2.2 - Functional aspects

When the zones which will tend to openthe lining r ings have been localized, thehydromechanical behaviour of the tunnellining structure will then depend on:

• the presence of bolting and its sizing;

• the degree of contact joint opening withrespect to compression of the incorporatedwaterproofing gaskets.

In general, take-up of tensile loads by boltscan only be justified in the shor t-term,except if suitable anti-corrosive material orprotection is provided.

Consequently, elimination of bolting in atunnel subject to a tendency for its liningcontact joints to open would appear desi-rable. Structural waterproofing is only thenensured if the lining gaskets open only par-tially with respect to their compressivestrain. A factor of safety of 2 is desirable toallow possible self-adjustment of the seg-ment rings during loading / unloading (tun-nel pressurizing / depressurizing) cycles.

If such conditions cannot be ensured andtotal water tightness is required, an additio-nal waterproofing system is then necessary(cast-in-place concrete ring, membrane orany other suitable process).

3.7.3 - Roughness of segment-lined tunnels

Relatively few loss of head measurementshave been taken on segment-lined waste-water collectors due to the complex natureof the means to be implemented.

However, tests carried out have allowed thefollowing main results to be brought tolight:

• application of the Colebrook formula ispossible with a segments lining;

• loss of head can therefore be calculatedfrom an equivalent roughness Ks;

• equivalent roughness can be related tothe absolute value (s) for the average out-of-flushness between segment rings;

• for 0.60 m long rings and for tunnels withdiameters less than 3.60 m, the followingformula has been established:

Ks (mm) = 0.3 + 60 X (lsl)2/1

where s (positive or negative "step") and l(length of unit) are expressed in mm.

N.B.: it is advisable to use this formula withcare because it has been established from alimited number of cases and for 0.60 m longconcrete segments of var ious types(smooth or incorporating pockets);

• Unlike the behaviour of cast-in-place tun-nel linings, smoothing by deposits of themany out-of-flush locations will tend toreduce the equivalent roughness of a seg-ment-lined tunnel. However, estimating notonly this reduction but also that of boresectional area associated with the presenceof these deposits (reduction in conveyance)remains a delicate task for the engineer.

3.8 - Construction tole-rances

3.8.1 - Specification

Construction tolerances for segments for-ming the permanent lining of an under-ground structure must be specified on thebasis of general service criteria and must belaid down in the project specifications.

Moreover, they can vary depending on thelining design retained (expanded segments,bolted segments, etc.).

Very often, these tunnel operation-relatedtolerances are complemented by othertolerances, in this case associated with liningimplementation to ensure correct structu-ral behaviour, as well as the required qualityof finish and imperviousness.

3.8.2 - Identification of main crite-ria contributing to tolerance speci-fication

3.8.2.1 - Criteria related to tunnelfunction

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Function-related criteria essentially com-prise:

• tunnel internal sectional area

The accuracy sought must satisfy the gene-ral profile of the tunnel bore over its wholeroute;

• operating clearances

For this and for the last point, these criteriainfluence specification of tolerances concer-ning the tunnel construction axis with res-pect to the design theoretical axis;

• water and air conveyance flows

It is important that project specifications laydown geometrical criteria (surface rough-ness, out-of-flushness, etc.) allowing accep-table structural head losses;

• layout of equipment fixings or pockets.

3.8.2.2 - Tolerances associated withsegment implementation

These tolerances can be broken down interms of the following two constructionstages:

• casting:

- mould geometry,

- bending and fixing of reinforcing steel;

• installation:

- ring building,

- lining deformation under the action ofback grouting and surrounding ground.

3.8.3 - Accuracy

All criteria defined above must be conside-red in order to specify tolerances in theconstruction axis with respect to the struc-tural design axis.

The required means should then be imple-mented to ensure compliance with tole-rances for the segments forming the rele-vant ring. Successive combinations of thesetolerances mean that dimensions must bekept within small variations at mould strip-ping. Geometrical proper ties foreseen atconstruction study stage should be repro-duced to obtain contact faces between seg-ments or rings which are capable of trans-ferr ing loads between r ing par ts andensuring proper water tightness.

It is therefore essential to identify clearlythe segments sections requiring par ticularlevels of geometrical accuracy and to quan-tify them.

The main criteria to be examined are:

• general dimensions of the assembled ring;

• ring length (taking into account its pos-sible taper);

• flatness of intersegment contact surfaceswithin the same ring and between rings;

• roughness;

• layout and geometry of pockets provided(waterproofing gasket grooves, recesses forplugs or pins, etc.);

• layout of connector inser ts (pick-up soc-kets, bolts, connectors, etc.);

• clearances allowed for assembly devices;

• dimensions of reinforcing cages andlayout of the different reinforcing bars toensure:

- suitable corrosion protection,

- proper operation of par ts with respect tocontact pressures,

- efficient edge reinforcement.

It is very difficult to recommend the exacttolerance values to be complied with on afinished product because they depend onnumerous parameters such as the overalldimensions of the structure to be built, themethod of erecting segments and theirshape.

To achieve the levels of accuracy sought, it isclear that concrete shrinkage and tempera-ture are parameters which must be consi-dered, especially during segment inspectionat the precast plant.

3.9 - Durability

3.9.1 - Segment concrete

Segment concrete durability depends onthe purpose of the tunnel and may be asso-ciated with the following criteria:

• compactness of concrete mixes;

• concrete mix proportions:

- fine aggregate,

- coarse aggregate,

- cement,

- admixtures,

- water,

all require physical chemical analysis of theirconstituent materials;

• active alkaline balance;

• permeability;

• environment-related internal and exter-nal forms of attack:

- temperature,

- hydrocarbons,

- aggressive chemical agents contained inthe ground, in the groundwater and in theliquid conveyed,

- micro-organisms,

- sulphate,

- condensation,

- frost,

- salts,

- fire, etc.

The use of admixtures inf luencing thestrength of concrete mixes must be chec-ked to ensure satisfactory performance inrelation to the various forms of attack men-tioned above.

Selection criteria referred above must takeinto account the requirements of both thecontract specifications and current stan-dards.

Specific impervious treatment (mineraliza-tion, impregnation, etc.) can be applied tothe extrados of segments to provide pro-tection against par ticular forms of attack.

3.9.2 - Steel reinforcing bars

Durability of steel bars used for segmentreinforcement cages is related to the per-meabil ity of the encasing concrete anddepth of concrete cover, as well as to theinternal and external aggressive environ-ments mentioned above.

The choice of cement types and theircontents influence passivation of steel rein-forcing bars.

Chemical composition and surface condi-tion of these steel bars must ensure goodweldability for reinforcing cage fabrication.

Depth of concrete cover to reinforcementmust be specified with respect to conditionsof structural exposure laid down in the pro-ject specifications. It may vary depending onapplication zone for the stresses encounte-red and the level of protection sought inrelation to the relevant forms of attack(intrados fire resistance , inter segmentcontact, TBM thrust cylinder bearing sur-face, etc.).

In general, these depths of concrete covercan vary from approximately 20 mm (iron-banded reinforced zones) to approximately30 mm (standard intrados and extradoszones).

In some cases, steel protection systems canbe applied:

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• painting;

• metallization (galvanization, cataphoresis,metal-coating);

• epoxy-coating;

• cathodic protection (electrical links).

3.9.3 - Waterproofing gaskets

In material terms, durability in gasket water-tightness is associated with the same crite-ria as those listed above for short- or long-term concrete attack.

Once these criteria have been checked, therate of long-term relaxation of the water-proofing system should be ensured.

Gluing of gaskets is only carr ied out toensure that they remain in their groovesduring segment handling, storage and erec-tion. Adhesive used must be compatiblewith the type of gasket.

3.9.4 - Connector inserts

Connector inser ts must be durable andneutral with respect to their environment.In all cases, they must comply with safetystandards in force.

They must be positioned in accordancewith values of concrete cover to reinforce-ment.

They must cause neither structural weak-nesses nor preferential water seepage orelectrical flux paths.

3.10 - Economic considera-tions

Right from the star t of the project, tunnellining design must integrate constructionmethods and take into account factorsinvolving its adaptation to the tunnelconstruction location (influence on mate-rials, labour, management and supervision,etc.) with both engineering optimizationand cost-saving in mind.

From the beginning, it is important to deter-mine the type of ring best suited to the pro-ject (universal or "left"/"r ight" r ings), themost appropriate ring length, the taper andthe number of types of ring required for theproject.

In general, the universal ring is the mosteconomical from the segment fabricationpoint of view (less moulds required, smallerprecast plant area, less types of segmentreinforcing cage).

Analysis of the tightest curves on a projectalignment compared with the straight sec-

tions must allow standardization in favour ofone or two possible ring lengths. Creationof several ring lengths on a project effecti-vely multiplies the number of mould andreinforcing cage types, leading to morecomplicated and therefore more expensiveprecasting, control and handling.

These considerations are also linked to thetype of TBM used (existing machine possiblymodified for the project, new TBM designedand built for the project).

Reuse of TBMs and segment mouldsundoubtedly provides substantial savings onsimilar projects, even if servicing, adaptationand overhaul is always required.

Thus, on projects such as:

• mass transit railway tunnels, especially forthe Val system;

• rail and high-speed rail tunnels;

• road tunnels;

• wastewater collectors, etc.,

it would appear desirable to retain geome-trical and equipment standards on a projectbasis at national level.This would allow pro-duction capacities to be increased and coststo be reduced. These standards could bebased on the "récommandations sur la stan-dardisation des profils des tunnels circu-laires" (Recommendations for the standar-dization of circular tunnel profi les)presented by A.F.T.E.S. Working Group 11(see T.O.S. Issue 88, July-August 1988): thispr inciple is already in hand in severalEuropean Community countr ies and inthose under Anglo-saxon influence.

4 - TUNNEL LINING DESIGN

4.1 - Main parametersinfluencing sizing

4.1.1 - Implementation conditions

4.1.1.1. - From segment precasting toworkface supply

Between casting in the precast plant andsupply to the tunnel workface in view oferection at the TBM, segments are subjectedto a series of operations which can induceappreciable stresses in some.

Whilst it is difficult to describe all theseoperations, which depend on a processvarying from one project to another, a largenumber of operations never theless recuron a systematic basis. For example, this isthe case for the segment turning stages

after mould stripping (both when castinghorizontally - cf. conditions annexed to thepresent recommendations - and ver tically),for the handling stages from precast plant topreliminary storage then storage areas (e.g.using a lifting beam fitted with grippers, suc-tion pads or slings, etc.), for the storagestages involving segment stacking and inser-tion of timber blocks between units, for thestages of removal from storage and unloa-ding on site, or for the stage involving seg-ment supply to the workface (by trailer orrailcar).

The impact of each of these stages must besubjected to a reinforced concrete designcheck in terms of internal stresses inducedin the segments. These design calculationsmust consider not only the possible dyna-mic effects of handling (e.g. placing a seg-ment on a stack during lifting or storagestages) and implementation tolerances (e.g.accuracy of intersegment block positioningat the storage area), but also the true age ofthe concrete (and thus its characteristicstrength) when carrying out the relevantoperation.

In most cases, the process only involvesdesign checking because the sectional areasof reinforcement and concrete proper tiesfor the segments are most often designedfor tunnel service or TBM-excavation stages(thrust cylinder applied loads). However,cer tain cases can become dimensionally cri-tical and lead to either improving shor t-term concrete proper ties or increasingreinforcement sectional areas, or to moresuitable redesigning of cer tain processstages.

4.1.1.2 - Ring building (erection andbolting)

Assembly of segments behind the TBM iscarried out using an erector. During erec-tion, segments are subjected to a number ofloads such as:

• the load applied by the segment pick-upand lifting system (dead weight of the seg-ments modified by a dynamic coefficient);

• loads applied to compress waterproofinggaskets;

• possible bumping impact loads;

• loads associated with accidental impactsduring approach;

• loads applied by the assembly systemsretained (bolts, anchor bolts or plugs).

Although impact loads are very difficult toestimate and thus to integrate in the liningdesign, the segments must never theless bedesigned to withstand other types of load.

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Special care must be given to checking sec-tions near connector inser ts (unsupportedthrusts, local stresses, r isks of bursting),which often result in special constructionrequirements or local additional reinforce-ment.

4.1.2 - Parameters for analysingring stresses

Reference may usefully be made to thesummary table provided under § 4.3.5.

4.1.2.1 - Parameters associated withthe surrounding ground

The main parameters concerning the sur-rounding ground, which can come into playin terms of analysing the behaviour of a pre-cast concrete segmental tunnel lining, arerecalled hereunder on the basis of theA.F.T.E.S. recommendations entit led "lechoix des paramètres et essais géotech-niques utiles ‡ la conception, au dimension-nement et ‡ l'exécution des ouvrages creu-sés en souterrain" (the choice ofgeotechnical parameters and tests of use inthe design and construction of under-ground excavated structures).

a) Parameter s associated with naturalconstraints

The geological history of the soil-rock massmust be known; it may have been influencedby tectonics, consolidation or erosion.

The basic parameters are:

• intensity of principal stresses (in par ticu-lar, evaluation of the term

Ko = (σ’ Ho ) ;σ’ Vo

• direction of stresses (effects of slope anddipping of ground layers, etc.).

b) Physical parameters

It is essential to have good knowledge ofparameters such as:

• the swelling potential;

• the aggressivity of the surrounding envi-ronment;

• the interfaces between ground layers,anomalies such as discontinuities, non-uni-formities (voids, blocks, faults, etc.).

c) Engineering parameters

Two types of engineering parameter areusually characteristic of the soil-rock mass:

• strength parameters:

- soil shear strength properties (Cu, φ', C')

- direct compressive strength and tensile

strength, rock mass characteristic parame-ters;

• deformation capacity parameters:

- Young's modulus E(x, t),

- Poisson's ratio ν.

In surrounding rock, a reduced value ofYoung's modulus, compared with labora-tory-measured values, should be consideredto take into account the potential deforma-tion capacity of discontinuities influencingthe rock matrix.

Good command of this parameter is ofprime importance for the design of struc-tures such as water conveyance internalpressure tunnels (danger of intersegmentcontact joints opening);

• seismicity

Evaluation of the surrounding ground dyna-mic characteristics may be necessary in highseismic risk areas.

d) Hydrogeological parameters

Knowledge of groundwater pressureswithin the soil-rock mass is essential inever y underground structure project. Inpar ticular, it is necessary to determine theinfluence of tunnel driving on the behaviourof the groundwater table(s) (drainage, bar-rier effect, danger of a collapse in ground-water pressures, etc.).

e) Ground characteristic curves

Ground behaviour can be represented byshor t- and long-term convergence curvesbased on the geological, hydrogeologicaland geotechnical parameter s identifiedabove.

4.1.2.2 - Parameters associated withTBM characteristics

The table below reveals the main functionsof each TBM structural parameter and itspotential impact on stress analysis.

4.1.2.3 - Lining structural properties

The tunnel lining is discontinuous and itsstructural proper ties depend on those ofthe segments and contact joints betweenlining par ts.

a) Segment structural properties:

• sectional area, iner tia

The inclusion of more or less large pocketsneeds to be taken into consideration in theevaluation of these parameters;

• modulus of deformation

This depends essential ly on concretestrength and parameters such as creep, rela-

tive humidity and shrinkage;

• Poisson's ratio.

b) Intersegment contact joint structuralproperties:

• sectional area, iner tia

These properties allow the capacity for loadtransfer between contact joint sectionalareas to be deduced;

• ring composition

The discontinuous nature of a r ing (anassembly of elementary segments) leads toa reduction in its stiffness in bending, whilstits stiffness in compression is, in general,only slightly affected by the presence ofintersegment contact joints.

On the other hand, installation of adjacentrings incorporating combined radial contactjoints, associated with rigid assembly sys-tems between rings, such as plugs, enablesthis effect of reduced ring stiffness in ben-ding to be limited.

4.1.2.4 - Soil - structure interaction

The main parameters influencing behaviourof the tunnel l ining in contact with theground are:

• lining/back grouting material and ground/back grouting material contact conditions.

These can vary between total slippage andtotal adherence; however, they tendtowards total adherence with the use ofmortars grouted under good conditions.

Under cer tain ground and groundwaterpressure configurations, the idea of separa-tion can complement these conditions (lackof contact between lining and surroundingground).

• environment

- nearness of existing or planned structuresunderground or at the surface (buildings,util ities, existing tunnels or shafts, deepfoundations, etc.),

- super imposed loads (traffic , buildingsfoundations, etc.).

4.2 - Design assumptions

4.2.1 - Regulations and references

4.2.1.1 - Foreword

It should be recalled that limit states analysisallows checking of both the structure's fac-tor of safety with respect to failure and itssatisfactory behaviour with respect to servi-ceability.

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The main characteristics of the two limitstates are recalled in the following table.

4.2.1.2 - Applicable regulations andrecommendations

The following regulations or recommenda-tions apply to limit state analyses of reinfor-ced concrete lining segments:

• "Fascicule n° 62 Titre I section 1 - Réglestechniques de conception et de calcul desouvrages et constructions en béton armésuivant la méthode des états limites (RéglesBAEL 91)" (Engineering rules for limit statedesign and analysis of structural andconstructional reinforced concrete based)(French reinforced concrete code of prac-tice).

• Eurocode 2, published and annotated byAFNOR (French Standards Institute) inDecember 1992;

• "Instruction technique sur les DirectivesCommunes relatives au calcul des construc-tions" (Engineer ing guide to CommonDirectives cover ing structural design)(French Govt. Circular n° 79-25 of 13thMarch 1979);

• CEB-FIP International Recommendations,1990;

• NCF (French national railway company)"Livret 2.01" covering railway loadings andreinforced concrete design rules;

• CPC Fascicule n° 61 Titre II covering roadimposed loadings (French code of practice);

• AFTES Recommendations currently inforce;

and, in some cases:

• "CCTG Fascicule n° 62 Titre V - Règlestechniques de conception et de calcul desfondations des ouvrages de génie civil"(Engineering rules for design and analysis ofcivil engineering structures) (French code ofpractice);

• "Récommandations provisoires relatives àla modification des règles de pr ise encompte de la fissuration et à l'emploi desbétons à hautes performances" (Provisionalrecommendations for the amendment ofrules for considering cracking and for theuse of high-strength concrete), edited andcirculated by SETRA (French national high-way engineering agency) in June 1997;

• "DTU n° 14.1 - Travaux de cuvelage"(French unified code of practice - Lining andtanking work), October 1987.

The project specification must detail theregulator y documents applicable to thecontract, as well as their priority of applica-tion.

Failure of a section due to crushing of concrete

Excessive deformation of steel

Instability of shape (buckling, bulging)

Loss of static equilibrium at ring erection

Excessive opening of cracks (infiltration, corrosion)

Excessive compression of concrete causing micro-cracking

Excessive ring deformations

Ultimate limit state Serviceability limit state

a) Confinement pressure- increase in ground deconfine-ment at lining installation,→ decrease in ground loads onlining.

- to ensure excavation face sta-bility,- to limit ground deformations.

- augmentation du déconfinementdu terrain à la pose du revêtement

→ diminution des charges de ter-rain sur le revêtement

- to reduce pressure on TBMshield tail and lining, especiallywhen advancing in a curve,

b) Overcut

- increase in ground deconfine-ment at lining installation→ decrease in ground loads onlining.

- to allow a degree of groundconvergence over the length ofTBM shield tail to reduce fric-tion (especially in expansiveground)

c) Shield tail conicality

- when ground is not in conti-nuous contact with the TBMshield tail extrados, ground loadson the lining are increasinglyreduced as the shield tail length isincreased,- conversely, ground convergenceis limited to the annular gap bet-ween excavation and shield tailextrados.

- to reserve space for fittingdifferent mechanical equipmentfrom head to thrust mecha-nisms.

d) TBM length

- depends on thrust loads imple-mented and thrust cylinder rampad/segment contact conditions(eccentricities due to installationtolerances, curved alignment,buoyancy, localized loads) andring/ring contact conditions (geo-metrical defect in segments,eccentricities due to installationtolerances, localized loads).

- to ensure longitudinal advan-ce,- to ensure a reaction to theconfinement pressure,- to guarantee temporary stabi-lity of lining segments,- to ensure compression ofimpervious gaskets betweenrings prior to installing assem-bly system,- to ensure key segment can bedriven in.

e) TBM thrust

- local pumping thrust, groutingpressure, strength properties ofback grouting material (modulus,Rc, etc.),- reduction in ground deconfine-ment,→ increase in ground loads onlining.

- to ensure blocking betweenlining and ground,- to limit ground deformations.

f) Back grouting

Parameters Main functions Impact on stress analysis

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4.2.2 - Material properties

4.2.2.1 - Lining concrete

Reinforced concrete properties to be intro-duced in design analyses are those specifiedby the BAEL and Eurocode rules in force,i.e.:

• the characteristic compressive strengthFcj;

• the characteristic tensile strength Ftj;

• longitudinal instantaneous and long-termmoduli of deformation;

• stress-strain diagrams;

• Poisson's ration, which is usually taken as0.20.

4.2.2.2 - Steel for passive reinforce-ment

Steel properties to be introduced in designanalyses are those specified by the BAELand Eurocode rules in force, i.e.:

• the guaranteed elastic limit Fe;

• the modulus of longitudinal elasticity,which is taken as 200,000 MPa;

• stress-strain diagrams.

4.2.3 - Nature of actions and loa-dings

4.2.3.1 - Permanent actions (G)

Permanent actions include the followingloads:

a) Dead weight of the structure and weightof fixed equipment,

b) Surrounding ground loads.

The convergence-confinement methodevaluates ground actions on the lining. Thismethod has already been described in seve-ral publications. Recommendations on theuse of this method, presented by A.F.T.E.S.Working Group 7 in T.O.S. Issue 59 ofSeptember-October 1983, will be updatedin the near future.

Moreover, in the case of shallow soils andstructures, various authors have proposedsemi-empir ical formulae , der ived fromtheory or experience, for calculating thever tical load exerted by the ground on thelining in terms of the density, cohesion andangle of internal friction of the soils, theexcavation radius and the depth of overbur-den above the crown (notably the TERZA-GHI, PROTODIAKONOV and LAUFFERmethods).

These methods and their conditions ofapplication are described in detail in "textedes réflexions sur les méthodes usuelles decalcul du revÍtement des souterrains"(recorded thoughts on the usual designmethods for tunnel linings) presented byA.F.T.E.S.Working Group 7 in T.O.S. Issue 14,March-April 1976.

Actions thus determined are then used toanalyse l ining stresses by the differentmethods reviewed in Section 4.3 below.

c) Loads induced by neighbouring struc-tures

These loads are determined from drawingsof neighbouring structures (foundation dra-wings, etc.) passed on by the Owner.

d) Hydrostatic and hydraulic pressures

With regard to the external hydrostaticpressure exer ted by the hydrogeologicalenvironment, this will be determined on thebasis of maximum and minimum waterlevels.

In this connection, the potential impact ofbuoyancy on the lining and its assemblymechanisms, especially during constructionat ring break-away from the TBM, should berecalled.

In the special case of water conveyance tun-nels, the contract must detail values repre-senting internal fluid loads to be consideredand how they should be taken into account.

e) Annular gap back grouting pressures

If back grouting pressures exer ted on thelining extrados are higher than the groundpressure, they should be considered whensizing the segments.

4.2.3.2 - Variable actions (Q)

Variable actions includethe following loads:

a) Operating loads insidethe tunnel

When these are wheel-induced roll ing loadsapplied directly to thetunnel inver t slab, theirinfluence is usually verymodest and they can the-refore be neglected inthe design of the liningcross-section.

On the other hand, whenthese loads are appliedto a road pavement orrail trackbed suppor tedby a slab bearing or builtinto the tunnel l ining,

they must be considered when sizing thesegments.

For example , in the case of waterconveyance tunnels, the contract shouldspecify, if necessary, the value representingthe variation in internal hydraulic pressureto be considered and the manner in whichit is to be taken into account.

b) Loads applied to the ground surface

Most frequently, these are pedestrian orvehicle loads.

c) Loads applied during construction

• Loads induced from precasting to ringbuilding

The sizing of each tunnel segment should bechecked in relation to the differentconstruction stages: segment handling, pos-sible turning, storage, transpor t, loadingonto cars, unloading, pick-up by erector andinstallation.

• Loads induced by TBM penetration

TBM thrust cylinder loads represent longi-tudinal forces applied to the lining segmentsthrough the load distribution pads.

Each thrust load distribution pad is actedupon by one or more cylinders, whoseresultant thrust is eccentrically exer ted.Thiseccentricity, which is measured with respectto the centre of gravity of the ram pad bea-ring surface, comprises a known structuralcomponent and an additional random com-ponent. It should be recalled that when theTBM follows a curved alignment (horizontalor ver tical), the structural eccentricity ofthe resultant thrust from the cylinder(s)with respect to the ram pad bearing surfaceis often increased and must consequentlybe integrated in the analysis.

EXAMPLE OF ECCENTRIC PLANE TRANSVERSE CONTACT JOINT

extrados

intrados

half lining wallthickness

peripheral groove extrados side

width of transverse contact joint

Centre of gravity of thrust cylinder

ram pad bearing surface

resultant load exerted by athrust cylinder group

peripheral groove intrados side

eccentricityof thrust

half lining wallthickness

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The load exerted by each group of thrustcylinders and its eccentricity are two para-meters for which rated working and excep-tional values must be specified.

In a basic combination, the values of thesetwo parameters to be considered are therated working values.

In an accidental combination, only one ofthese parameters reaches its exceptionalvalue, the other parameter maintains itsrated value. It is acknowledged that bothparameters cannot reach their exceptionalvalue at the same time.

Whilst it is rare for the rated thrust to bereached simultaneously by all cylinders, it isfrequently so for each group of cylinders.

Those data are used to prove the strengthof the concrete and reinforcement, in par ti-cular under the localized loads exerted byeach group of thrust cylinders.

Fur thermore, segment sizing must also bechecked under the loads exer ted by thepassage of the TBM back-up equipment.

• Loads induced by the grouting materialwhen filling the annular gap between thelining and the surrounding ground

These transient-type loads result from alocal ized increase in grouting pressure("local pumping thrust") directly behind thesegment grouting holes.

In cer tain special cases, where total controlof this phenomenon is essential, the impactof these actions on the lining should bechecked. Data is then required on the grou-ting system incorporated in the TBM (num-ber of grouting points, grouting process,etc.) and on the procedure for implemen-ting these grouting operations retained bythe contractor.

d) Climatic temperature-induced actions(t°)

• Uniform temperature variations

In general, uniform temperature variationsdo not require consideration.

Note:

In the case of cer tain structures (very deeptunnels, energy conveyance tunnels, etc.),uniform temperature variations must beconsidered; the contract shall detail valuesrepresentative of the corresponding actionsand how they should be taken into account.

• Temperature gradients (∆θ)

In general, temperature gradients do notrequire consideration.

Note:

In the case of cer tain structures, for whichtemperature gradient-based effects must beconsidered, the contract shall detail valuesrepresentative of the corresponding actionsand how they should be taken into account.

4.2.3.3 - Accidental actions (FA)

In the case of cer tain structures, for whichaccidental actions (e.g. ear thquakes, explo-sions, vehicle impacts or "waterhammer" inwater conveyance tunnels) must be consi-dered, the contract shall detail values repre-sentative of the corresponding actions andhow they should be taken into account.

4.2.4 - Combined actions

4.2.4.1 - Design stresses with respectto strength ultimate limit states

a) Foreword

In the case of models which introduce anon-elastic law in terms of ground beha-viour (occurrence of zones in a plasticstate), soil-structure analysis should be car-ried out, without uplifting the actions invol-ved, and the ultimate limit state weightingcoefficients detai led below should beapplied to the resulting forces.

b) Basic combined action put forward byBAEL 91 and Eurocode 2

1,35Gmax + Gmin + γQ1 Q1 + Σγ Qi ΨOi Qi

Gmax : total unfavourable permanentactions (e.g. lining dead weight, ground pres-sure);

Gmin : total favourable permanent actions; insome cases, water pressure can be favou-rable and should then be weighted by 1 ; inother cases, it should be weighted by 1.35;

QI : basic variable action; in the presentcase, such actions would be road, rail orwater conveyance operating loads or loadsapplied during construction;

γQ1 is equal to 1.5 in general, except for rail-way loads (1.45).

ΣγQiΨOiQi are the accompanying variableactions.

The basic combined action can therefore beexpressed as:

1,35Gground + 1,35(ou l)Gwater + 1,50Q1

The largest contr ibutor y factors in thisexpression are obviously the actions on thelining due to water and ground.

Because the action due to the ground isonly weighted by 1.35 (e.g. for permanent

dead weight loads), it is very important toensure the validity of both the ground engi-neering properties taken into account andthe stress analysis method. The non-unifor-mity, anisotropy, jointing and fissuration ofthe soil-rock materials and the difficulty inforecasting their long-term behaviour mustalso be considered.

The 1979 Common Directives are ver yclear on this subject: Section 4.1.3 statesthat "the maximum and minimum characte-ristic values of actions corresponding toear th pressures shall be evaluated takinginto account the uncer tainties resultingfrom their method of calculation".

However, when detailed analysis is notrequired or when a calculation processdoes not allow the effects of the groundand water to be separated, the followingcombined actions shall be retained:

1,35xS{Gground + Gwater + (1,50/1,35)xQ1}

obtained by multiplying the infrequent com-bined action by 1.35:

S{Gground + Gwater + (1,50/1,35)xQ1}

For checking the lining under construction,the basic combined action is expressed as:

1.35Glining dead weight + 1.35QI

QI :TBM thrust cylinder load, back groutingpressure or weight of back-up train.

c) Basic combined action der ived from1979 Common Directives

A combined action more directly derivedfrom § 7.2.1 of the 1979 CommonDirectives and featur ing in BAEL 91Fascicule n° 62 - Titre V "Règles techniquesde conception et de calcul des fondations"(engineering rules for the design and analy-sis of foundations) can also be put forward.

Characteristic values of actions are increa-sed by two coefficients γF3 et γF1 :

γF3S{ γ F1GmaxGmax+ γ F1Gmini Gmini

+ γ F1Q1Q1 + ΣγF1Q1ΨOiQi }- the coefficient γF3 must enable one totake into account the uncer tainty of thestress calculations and the simplificationsresulting from the models and diagrams; itsvalue usually lies between 1.125 and 1.15;

- the coefficient γF1 must allow one to takeinto account the risk of exceeding the cha-racteristic value of the action; it can take avalue very close to 1 for the action due towater if, for example, it represents a hydro-

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• 231 •

static pressure corresponding to an accura-tely known water level and can never beexceeded; but, for the action due to theground, it can attain values near to 1.2, andeven higher if the ground investigation islimited and risky.

The result ing combined action can beexpressed as:

1,35*Gground + 1,15Gwater + 1,50Q1

* this coefficient can be higher if the actiondue to the ground is difficult to estimate.

This type of combined action must be laiddown in the project specification.

d) Accidental combined action put forwardby BAEL 91 and Eurocode 2

Gmax + Gmin +FA +Ψ11Q1 + ΣΨ2iQi

FA : nominal value of accidental action;

Qi : variable accompanying actions.

The maximum capacity of the TBM thrustcylinders is to be considered as an acciden-tal action.

In the case of an ear thquake or explosion:

Gground + water + Ear thquake (or explosion)

+ 0.6QI

Notes :

Another type of stress, comparable to anaccidental stress, can be provided in theproject specifications.

This is the total overburden load and isusual ly considered for shal low tunnels(overburden of 1 to 2 diameters) or deepertunnels likely to be subjected to long-termeffects which are difficult to predict inground surveys (creep, swelling, etc.).

This action is therefore considered with acoefficient of 1:

Goverburden weight + 0.6QI

In this combined action, accompanyingactions are usually neglected and the actiondue to the ground is often assumed to beuniformly distributed over the lining.

This combined action has no geotechnicalsignificance but it has the merit of testingthe factor of safety associated with thelining bearing capacity with respect to theweight of overburden.

It does not apply to very deep tunnels inground with a high modulus of deformation(e.g.Alpine tunnels).

Finally, in the case of impervious jointlessprecast concrete lining installation, projectspecifications can suggest considering an

accident-related situation corresponding toloss of lining permeability; the check willthen be carried out using the following acci-dental combined action:

Gwithout water ground + Gtotal water pressure

+ 0.6QI

4.2.4.2 - Design stresses with respectto serviceability limit state

Gmax + Gmin +Q1 +ΣΨoiQi

When the tunnel is in operation, this combi-ned action is expressed as:

Gground + Gwater + QI

orGground + Gwater

4.2.5 - Sizing criteria

4.2.5.1 - Strength ultimate limit state

Design stresses derived from basic or acci-dent-related combined actions must notexceed the ultimate limit capacities for rein-forced concrete sections specified by §A.4.3 of the BAEL 91 rules or Eurocode 2and resulting from the following limitingstrains established for the relevant mate-rials:

• 10 x 10-3 for the elongation of reinforcingbars;

• 3.5 x 10-3 for the shortening of par tiallycompressed sections comprising concretewith a strength fcj of less than 60 MPa; forhigh-strength concrete (fcj ≥ 60 MPa), thelimit for shortening is given by the relation:(4.5 - 0.025fcj) x 10-3 ;

• 2 x 10-3 for the shortening of concrete ina fully compressed section.

Material design stresses are obtained byapplying the following coefficients to theircharacteristic strengths:

γs = 1.15 for steel under basic combinedaction;

γs = 1 for steel under accidental combinedaction;

γb = 1.5 for concrete under basic combinedaction;

γb = 1.15 for concrete under accidentalcombined action.

Because segments are concreted in a pre-cast plant, coefficient γb can be reduced(only in strength ultimate limit state analy-sis) to 1.3 under basic combined action aslong as quality inspections comply with anISO system; these special provisions mustbe laid down in the project specifications.

4.2.5.2 - Shape stability ultimate limitstate

This involves proving the strength of thesegment ring with respect to the ultimatestates without neglecting so-called secondorder effects such as buckling, bulging, etc.This proof is only to be considered for verythin linings installed in ground with very lowmoduli of deformation.

4.2.5.3 - Static equilibrium limit state

In some cases, non-buoyancy checkingshould be anticipated.

Nominal permanent downward ver ticalloads associated with permanent actionsmust be at least 1.05 x the water-inducedupward loads resulting from exceptionalwater level conditions. Possible time-depen-dent variations in structural overburden(e.g. sinking of a riverbed, etc.) must also betaken into account.

4.2.5.4 - Serviceability limit stateswith respect to structural durability

a) Crack opening limit state

Because concrete is highly alkaline (pH ≈12),reinforcing steel is normally protected bypassivation (formation of Fe(OH)2 at thesurface of the reinforcing bar).

However, care must be taken to ensure that:

• cracks are not excessively open;

• concrete cover is sufficient in relation tothe environment;

• the concrete mix is satisfactory.

The rules specify conditions governingconcrete cover and cracking.

In accordance with the new recommenda-tions amending Section A.5.3. of BAEL 91,reinforcement tensile stresses are limited asfollows:

• for detrimental cracking (lining in the pre-sence of moderately aggressive water):

η : cracking coefficient equal to 1.6 for high-tensile deformed bars (φ > 6 mm), 1.3 forhigh-tensile deformed (high bond) bars (φ ≤6 mm) and 1 for plain (hot-rolled) reinfor-cing bars;

• for highly detrimental cracking (lining inhighly aggressive environment):

In addition to the above limiting tensilestresses, Section A.4.5. of BAEL 91 specifiesthe maximum diameters and spacings forreinforcing bars.

σs=sup[240MPa,110√ηftj]

σs=sup[200MPa,90√ηftj]

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b) Concrete compression limit state

In accordance with Section A.4.5.2. of BAEL91, the concrete compressive stress at theserviceability ultimate limit state is limitedto 0.6 fcj.

4.2.5.5 - Fire resistance

Project specification requirements in rela-tion to fire resistance must state the level offire stability for the lining and this must bejustified by the organization and emergencyfacilities in the event of fire in the tunnel(s).

4.3 - Determination ofstresses in the tunnel lining

4.3.1 - Introduction

Given the circular shape of the tunnel lining,several methods of analysis are possible fordetermining the stresses due to interactionof the soil and the structure.

The two main methods are:

• the hyperstatic reaction method

• the composite solid method.

4.3.2 - Hyperstatic reactionmethod

The hyperstatic reaction method studiesthe behaviour of the lining alone by likeningthe action of the ground to external loads. Ittherefore favours the role of the lining. As aresult, it should preferably be applied to arigid lining located at shallow depth and inenclosing ground comprising weak soils orvery closely fractured rocks.

The drawback of this method is that it doesnot take into account:

• the behaviour of the ground after failureand with respect to time;

• the deformation the surrounding groundhas already reached when the lining is instal-led;

• the different excavation stages.

However, a number of specific assumptionsmade for modelling the structure and theexternal loads enable the principles of thecomposite solid method to be approached(e.g. maintaining of "springs" in tension)when conditions of application are satisfied.

Stresses and strains are calculated using anumerical resolution method usually basedon a 2-dimensional model made up of wire-frame elements with straight or cur vedmembers.

Moreover, this method of analysis remainsequally applicable in the following situations:

• tunnel located at shallow depth;

• non-uniform surrounding ground (severaldifferent formations);

• dissymmetrical external loads (dissym-metrical existing structures, load transfersdue to excavation of nearby structures,etc.);

• dissymmetrical lining (dissymmetrical dis-tribution of radial joints).

The main simplifying assumptions associa-ted with this type of model are as follows:

• ground behaves elastically;

• "spr ings" modell ing the surroundingground are mutually independent.

Because this method is quick, it is used forthe selection of critical sections and forimpact studies of cer tain parameters, espe-cially when the analytical resolution methodcannot be applied. It is used at preliminarydesign, design or construction study stage.

Naturally, this method does not allow pos-sible surface settlements to be tackled.

4.3.3 - Composite solid method

This method enables the behaviour of theground-structure system to be studied.

It considers the surrounding soil-rock massas a continuous medium (basic assumptionoften made).

4.3.3.1 - Analytical solutions

Based on soil and rock mechanics theoriesfor continuous media, analytical solutionsallow the lining forces (normal forces, shearforces, bending moments) and elastic line tobe determined.

Standard assumptions are as follows:

• lining geometry is circular and uniform(joints not directly considered);

• loads are uniform isotropic or anisotropic(Ko ≠ 1); they can be derived using theconvergence-confinement method or takeinto account the total stress exer ted(Erdmann formula);

• the assumed single layer of groundbehaves elastically;

• contact between the l ining and theground can either be considered as in totaladherence or as in total slippage.

Convergence-confinement method

The convergence-confinement methodallows, on the one hand, the loading and, onthe other hand, the ring radial displacement

to be determined.The normal force can bedirectly derived from this.

In this case, initial stresses are considereduniform and isotropic, but the surroundingground can be considered as obeying a lawof elastic-plastic behaviour.

Characteristic of soil-structure interactionand contributing to the application of thismethod, the impor tant parameter is thedeconfinement ratio CARSPECIAUX 108\f "Symbol" . Among its current methods ofdetermination, we find those of:• Panet;• Corbetta;• Bernaud;• Minh-Guo.

The last two methods allow the stiffness ofthe support to be considered.

Because of the simplifying assumptionsreferred to above, analytical solutions arenot valid in the following situations:

• tunnel located at shallow depth;

• non-uniform surrounding ground (severaldifferent formations);

• dissymmetrical external loads (dissym-metrical existing structures, load transfersdue to excavation of nearby structures,etc.);

• dissymmetrical lining (dissymmetrical dis-tribution of radial joints).

However, because these methods are veryquick, they are often applied for the selec-tion of critical sections and for impact stu-dies of cer tain parameters.

4.3.3.2 - Numerical resolution

Based on the use of finite element, or some-times finite difference, numerical models,this method allows 2- and 3-dimensionalproblems to be tackled. It favours neitherthe role of the lining nor that of the sur-rounding ground. As a result, it applies to alining of any stiffness located at any depth inuniform or non-uniform surroundingground comprising several different forma-tions and in the presence of symmetrical ordissymmetrical existing structures.

This method of analysis has the advantageof taking into account:

• the deformability of the ground and, inpar ticular, its behaviour after failure andwith respect to time;

• the redistribution of loads resulting fromlining deformation;

• the 3-dimensional nature of the excava-tion associated with the presence of a cut-

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• 233 •

ting face, through the concept of a deconfi-nement ratio CARSPECIAUX 108 \f"Symbol" introduced either in the 2-dimen-sional model or directly in a 3-dimensionalmodel;

• the excavation stages.

In standard cases analysis is limited to 2-dimensional modell ing in which theinfluence of the cutting face is consideredby applying the convergence-confinementmethod referred to in the above section.

This numerical resolution method of analy-sis is also valid for non-uniform and aniso-tropic initial stresses, i.e. even when a dis-symmetr ical feature is present in thestructure (dissymmetrical distr ibution ofradial intersegment contact joints), in thesurrounding ground (several different for-mations, etc .) or in the external loads(nearby existing structures, etc.).

Several types of ground behaviour can bemodelled: elastic, fully elastic-plastic, elastic-brittle with softening (uncommon), aniso-tropic with respect to deformation and/orstrength, etc..

The simplifying assumptions remain as fol-lows:

• initial deformation after lining installationis neglected;

• every segment is not usually consideredindividually;

• segment blocking tolerances are nottaken into account;

• the lining is installed behind the cuttingface and becomes effective at a cer tain dis-tance from it;

• concrete shrinkage is neglected.

In general, this more elaborate method isrestricted to the final design of a few criticalsections. Apar t from empirical settlement

estimation methods, which are easy toimplement but for which the area of appli-cation is limited to situations consideredthrough the feedback of experience onwhich they depend (cf. Recommandationsrelatives aux tassements liés au creusementdes ouvrages en souterrain -Recommendations concerning settlementsassociated with the excavation of under-ground structures - T.O.S. Issue 132,November-December 1995), numer icalresolution is the only method of analysisvalid for approaching surface settlements.

4.3.4 - Adaptation of analysismethods to a segments lining andto TBM-based excavation

The specific nature of designing a tunnellining to be installed behind a TBM arises, onthe one hand, from the tunnelling methodand, on the other hand, from the nature ofthe structure.

When it allows confinement of the excava-tion face, the tunnelling method can bereflected in the analyses by:

• either using a deconfinement cur ve ,based on a (σ0 - ps) stress condition, combi-ned with the application of a pressure psrepresenting the confinement pressureapplied at the workface;

• or adopting an extension in space of thedeconfinement curve behind the excavationface; thus, the deconfinement ratio takeninto account at a cer tain distance from theworkface (i.e. at the last ring installed) ismuch lower than the value used in theconventional method (or when tunnellingusing a TBM in open face conditions).

Moreover, confinement can result in addi-tional excess porewater pressures in thesurrounding ground.

Impacts of specific structural characteristicson design assumptions are as follows:

• installation of lining at a cer tain distancefrom the excavation face: lining sustains loa-ding from par t of the ground deconfine-ment, from the back grouting pressure andfrom delayed effects;

• the lining is not monolithic: reduced iner-tia at the contact joints is reflected in redu-ced lining flexural stiffness. This phenome-non can be taken into account either bymodelling contact joints directly or by desi-gning an equivalent ring with a smaller iner-tia (Muir-Wood formula); however, it shouldbe noted that this behavioural assumption isno longer borne out in the case of adjacentrings incorporating combined radial contactjoints in association with rigid assembly sys-tems between rings (e.g. plugs or tenon-and-mortises) nor in the presence of verysoft ground.

4.3.5 - Parameters which can beintegrated in the different methodsof analysis

Based on the design stage and the contextof the project, the following table shows thepossible status of taking into account para-meter s for the different consideredapproaches to analysis.

These modes of parametric considerationare identified by the following coding:

0 not necessary

1 desirable

2 necessary

I indirect consideration

D direct consideration

N not considered

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- Definition of loading and/or actions

* Initial constraints- levels of ground layers 1 2 2 2 I I D

- groundwater level° minimum groundwater level 0 1 2 2 I I D° maximum groundwater level 2 2 2 2 I I D- dry unit weight 2 2 2 2 I I D- Ko 2 2 2 2 D D D - Ko obeys Jaky's law for sands and

normally consolidated clays;- Ko depends on tectonics, consolidation and erosion for rocks and overconsolidated soils.

- superimposed load:° uniform superimposed load 1 2 2 2 D I D° linear superimposed load

(Bc truck, load-bearing wall), 0 1 2 2 D N Dsurface superimposed load

- direction of principal stresses 1 2 2 2 D D D - slope effect- dip effect (ground layers)

- continuous medium assumption:° continuous medium 2 2 2 2 D I D° fissured medium 0 1 2 2 D N D

* Loading:- segment installation distance 2 2 2 2 I I I in 2-d. Shield tail effect only to be considered in

D in 3-D. very soft ground and in an urban/sensitive context- confinement pressure - max. value for stress calculations;

- min. value for settlement calculations.

° considered as artificial support 2 2 2 2 I I I° considered by means of equivalents 0 0 0 1 D D D

stress condition- back grouting pressure 0 1 2 2 D I D- overcutting, shield tail conicality 0 0 0 2 I I I Effect only to be considered in very soft ground

and in an urban/sensitive context- ground deconfinement law:° convergence-confinement method 2 2 2 2 I I I in 2-d.

D in 3-d.° method of similarities (Corbetta’s law) 0 0 0 1 I I I in 2-d.

D in 3-d.- ground convergence curve:° unsupported (elastic-plastic behaviour) 2 2 2 2 I I I in 2-d.

D in 3-d.° supported (Bernaud’s law) 0 0 0 1 I I I en bi-dim

D in 3-d.- delayed effects (behaviour law):° E(x,t) 1 2 2 2 I I Iin 2-d.

D in 3-d.° long-term shear parameters 1 2 2 2 I N D° effective stress analysis (excluding 2 2 2 2 D D D

porewater pressures)° physical chemical swelling 1 2 2 2 I I I- change of groundwater pressure° drainage 1 2 2 2 D D D

Parameters

Project stage / context Methods of analysis

CommentsPreliminary

Studies

Design Construc-tion

studies

Urban/

Sensitive

Hyper-static

reactionmethod.

Compositesolid

method.Analyticalsolutions

Compositesolid

method.Numericalresolution

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4.4 - Proof of concrete andreinforcement

4.4.1 - Choice of segment wallthickness

Segment wall thickness must satisfy severalcriteria:

• the segment strength capacity with res-pect to combined circumferential bendingmust be sufficient when the percentage oflongitudinal reinforcing bars contributing tothis strength is less than 1 % and is generallyclose to the minimum percentage; if seg-ment wall thickness is constant throughoutthe tunnel alignment, an economic studyshall be conducted to examine whether itwould be preferable to vary the concretestrength (new mix design, alteration ofmixing plant parameter s, feasibi l ity ofincreasing strength) or, on the other hand,the percentage of steel in order to satisfythe calculated stress variations along thetunnel;

• the minimum segment wall thicknessmust satisfy the conditions imposed by the

contact joints between units: bearing sur-face area, installation of waterproofing gas-ket, chamfers, etc.;

• the minimum segment wall thicknessmust be compatible with the bearing sur-face area of TBM longitudinal thrust cylin-ders.

4.4.2 - Circumferential reinforce-ment (hoops)

The sectional area of circumferential rein-forcing bars arranged behind the internaland external segment faces shall be derivedfrom:

• analysis of combined bending (normalload - bending moment interaction dia-gram) in relation to anticipated loadings inultimate limit state and serviceability limitstate combinations. If bending moments arelow compared with the normal force, thesectional area can be justified in "simplecompression" (BAEL 91, Section B.8);

• analysis of simple bending during handlingand storage of segments. It should also benoted that the loading case involving thrustof the TBM main cylinders on the lining seg-

ments can be dimensionally critical (burs-ting forces due to spreading of this thrust);

• minimum percentage of reinforcing steelconsiderations:

- for units in compression (BAEL 91, SectionA.8.1,21),

- for units in bending: especially under theaction of TBM main cylinder thrust (BAEL91, Section A.4.2.).

Hoop diameter s and arrangement(concrete cover and spacing) must be deri-ved in accordance with Section A.8.1,22 forunits in compression, Section A.7.1. forconcrete cover protection of reinforcingbars and Section A.4.5,3 for cracking. Itshould be noted that the use of high-strength concrete mixes of very high com-pactness allows the concrete covers pres-cribed by Section A.7.1. to be reduced.

4.4.3 - Longitudinal reinforcingbars (arranged parallel to the tun-nel axis)

Outside segment end zones subjected tolocalized loads requiring iron-banding rein-forcement, these longitudinal bars must

° restoration of hydrostatic pressure 2 2 2 2 D D D Application of pressure:- to ground and to lining;- to lining only;

II - Structure disign- overall structural design (possible 1 2 2 2 I I I Ring inertia is reduced by applying the Muir-Woodconsideration of contact joints, etc.) formula, except in the case of combined contact

joints in very soft ground or rigid assembly systemsbetween rings

- section and inertia of segments 2 2 2 2 D D D- properties of each contact joint 0 0 0 1 D N D- moduli:° short-term modulus >< long-term 1 2 2 2 N N Dlmodulus

° use of average modulus 1 1 1 1 D D D- back grouting material (model) 0 0 1 1 N N D

III - Soil-structure contact conditions- adhérence 2 2 2 2 I D D- slipping 1 1 1 2 I D D- friction (Coulomb’s law) 0 1 1 2 I N D- separation 0 1 2 2 I N D

IV - Environnment- nearness of other underground 1 2 2 2 I I Dstructures

- existence of transition structures 1 1 2 2 I N I in 2-d.D in 3-d.

Paramètres Phase / Contexte Méthodes de calcul Commentaires

EtudesPrélim

Projet Exécut Urbain/

Sensib

Méthodedes

réactionshyperst.

Méthodedu solidecompositeSolutions

analytiques

Méthodedu solide

compositeRésolutionnumérique

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• 236 •

satisfy both the requirement of BAEL 91Section A.5 concerning shear force if this islarge in relation to the accompanying nor-mal force (τu>0,07fcj /γb) and SectionA.8.1.3. concerning transverse reinforcinglinks for units in compression.

It is perfectly acceptable not to incorporatetransverse reinforcing links around circum-ferential bars with a diameter less than 20mm, which are not in corners and not takeninto account in the relevant strength calcu-lations (i.e. only derived from minimum per-centages of reinforcing steel).

In some rather exceptional cases, such asfire resistance checking, stirrups must alsobe checked in relation to their potentialrole in preventing unsuppor ted thrust ofcur ved bar s under tension (BAEL 91,Section A.7.4,2).

Finally, correctly designed longitudinal rein-forcing bars contribute to balancing theshear force resulting from the TBM cylindersthrust loads.

At unit ends, the loads transferred from onesegment to another through each localizedreduced bearing zone are spread throughthe total thickness of the segment. Surfaceand bursting reinforcement must be provi-ded in these bearing zones. These can bedesigned in accordance with the recom-mendations provided in BAEL 91,Annex E.8(not taking into account the minimum sec-tional area of bursting reinforcement underTBM thrust cylinder temporary loading).Reinforcement can comprise small diameterbars bent into coils or welded bars (§ 5.25of Eurocode 2).

5 - DESIGN OF ASSEMBLYSYSTEMS

5.1 - Design assumptionsfor bolts and socket bolts

5.1.1 - Regulations

The following regulations or standards applyto the design of steel bolts or anchor bolts:

• Design rules for structural steelwork orCM 66 design rules for steel buildings;

• Additional Clause 80, which takes intoaccount the concepts of plasticity and limitstates;

• CPC Fascicule n° 61 Titre V "Conceptionet calcul de ponts et constructions métal-liques en acier" (Design and analysis ofbr idges and structural steelwork) for

bridges and civil engineering structures;

• French standards NF P 22-430 and NF P22-431 for non-prestressed (plain) boltedassemblies;

• French standards NF P 22-460 and NF P22-469 for control-tightened bolted assem-blies;

• Eurocode 3 "Design of steel structures"adopted by the European StandardizationCommittee in 1992.

5.1.2 - Nature of actions and loa-dings

5.1.2.1 - Permanent actions (G)

These actions are associated with keepingthe waterproofing gaskets compressed andare to be considered especially near sta-tions.

They will be determined from crushingforce - deformation curves provided by thewaterproofing gasket supplier.

5.1.2.2 - Variable actions (Q)

These are represented by loads appliedduring construction. In par ticular, thoseassociated with:

- crushing of waterproofing gaskets,

- segments overhanging from the previouslyinstalled ring during erection, when a thrustring is used for TBM penetration (rare),

- action resulting from the erector arm(possible).

5.1.2.3 - Accidental actions (FA)

Possible accidental actions will be detailedin the project specifications.

It should be recalled that a commonly retai-ned accidental loading case is that associa-ted with overhanging of a segment espe-cially following a hydraulic failure in the TBMthrust cylinders.

This loading case must also be combinedwith possible action resulting from thewaterproofing gaskets.

5.1.3 - Combined actions - Designstresses

a) Basic combined action put forward bythe CM 66 rules

4/3 Gmax + Gmin + 3/2 Q

b) Basic combined action put forward byEurocode 3

1.35 Gmax + Gmin + 1.5 Q

c) Accidental combined action put forwardby the CM 66 rules and Eurocode 3

Gmax + Gmin + FA

5.2 - Proof of assemblyand pick-up componentsusing materials other thansteel

5.2.1 - Introduction

Amongst the assembly systems most oftenused can be mentioned sockets for boltsand pick-up bolts or plugs positioned bet-ween consecutive rings.

Although the design and analysis of steelassembly systems is based on regulatorydocuments and standards, the use of diffe-rent materials is not necessarily included inan engineering regulation framework cove-r ing the behaviour of the componentsconcerned.

The forces likely to be imposed by suchcomponents must therefore be surveyed,then factors of safety to be applied to theinherent strength of these elements as wellas their behaviour under service conditionsmust be evaluated on the basis of suitablemechanical tests.

It should be recalled that, because of theactions applied, these different segment-inser ted components transmit often highlocal stresses to the concrete. Additionalreinforcement may be required to balancethese stresses and ensure concrete integrity.

5.2.2 - Actions to be considered

The same type of actions as for steel assem-bly systems (cf. § 5.1) are found in relationto bolt sockets and plugs.

Attention should be drawn to the followingspecific characteristics associated with theuse of plugs in relation to the actionsalready referred to:

• high local pressures around interlock poc-kets when installing segments;

• structural continuity of the lining betweenconsecutive rings ensuring greater longitu-dinal rigidity (limited relative mutual displa-cement of components);

• systematic permanent presence.

Structural continuity may be the cause ofstresses which are difficult to quantify:

• Thus, when an iner t or semi-iner t grout isused for back grouting behind the segmentsat the rear end of the shield tail, overriding

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buoyancy with respect to the lining weightcan induce significant loads in assembly sys-tems;

• It should also be noted that in smallradius cur ves, thrust cylinder action caninduce large forces resulting from the trans-verse component of thrust.

Most of these actions occur in the shor t-term. One should also mention long-termactions which can be associated with, forexample, local defects or losses of contactbetween lining and surrounding ground dueto par ticular geological conditions (dissol-ving of gypsum, presence of karsts, etc.) orresulting from the construction of laterstructures.

5.2.3 - Combined actions - Stresses

The different combined actions must bequantified on the basis of project data.

If no regulation applies, a factor of safety ofone is applied to each action. Stressesapplied to assemblies are then evaluated byconsidering models and simple behaviour.

5.2.4 - Behaviour of materials andassemblies - Tests

In practice, actual material and assemblybehaviour can only be fully understoodthrough static and dynamic testing (shear,tension, etc.). These types of test can go asfar as testing the capacity of the wholeassembly chain including the surroundingconcrete (with its design strength), as wellas the reinforcement measures adoptedaround the connector inser ts.

In general, test stresses differ from actualstresses; consideration of factors of safetywhich are adequate with respect to testresults and conditions par ticular to the pro-ject therefore appears necessary.

5.2.5 - Conclusions

Tests on anchor and pick-up sockets, forexample, fall within the scope of conventio-nal testing. On the other hand, because theplug system is relatively recent, experimentsshould be pursued to define more accura-tely the sizing problems and advantageshould be taken of experience feedbackfrom different projects in order to extendknowledge in relation to the operation ofthis intersegment connection system.

However manufacturers must supply a fullengineering file covering whatever systemsare adopted.

This file will focus specifically on:

• a description of tests carried out;

• the statistically aspect of the results;

• technical data-sheets for the productsused.

6 - TRANSITION ANDANCILLARY WORKSDesign of underground works is not limitedto designing just the running tunnel; civilworks for an underground project usuallycomprise:

• tunnels, which are continuous structuresallowing circulation of trains, vehicles, fluidsor transmission of energy;

• transition works:

- with the surface: specific examples are sta-tions, ventilation shafts, emergency shafts,inspection shafts and galleries, etc.,

- between tunnels: specific examples arebranches providing communication, pistonrelief, ventilation, rolling stock depot andturning galleries, etc.;

• ancillary works: specific examples are

- ventilated refuges or collection areas,

- safety recesses,

- fire recesses,

- plantrooms,

- vehicle turning galleries,

- sand traps,

which are essential for the operation of thestructure.

The present section is simply aimed at dra-wing attention to a number of design andconstruction aspects of these transition andancillary works, which commonly representunusual points in terms of precast concretesegmental l ining design. Moreover, theyrepresent a major burden on the project interms of cost and time.

6.1 - Design of ancillaryworks

Design of ancillary works is closely depen-dent on their functions.

In par ticular, functions resulting in extensivegeometry can involve:

• transfer and safety of the public;

• venti lation (with respect to its twinaspects of health-related ventilation and firesafety);

• refuges for vehicles;

• wastewater drainage;

• collection and discharge of groundwater ;

• maintenance of the structures.

Internal sizing and spacing of in-line works isoften codified under reference documents.Thus, in France, the following documentsapply:

• the Dossier Pilote des Tunnels (guidelinesfor tunnels) published by CETu and thelatest circulars in force covering road andmotorway tunnels (and, by extension, allroads);

• Owner-published (SNCF, RATP, etc.) rulesfor rail tunnels;

• the Instruction technique relative auxréseaux d'assainissement des aggloméra-tions (Engineering directive covering waste-water systems for urban areas) (Circular n°77.284 INT of 22 June 1977).

6.2 - Construction of transi-tion and ancillary works

Communication between transition ansancillary works and the running tunnel inva-riable requires the construction of varioussize openings in the running tunnel lining.

For example, construction of a transverseopening from inside the running tunnelusually involves the following operations:

• special spacing of the lining rings;

• temporary support of rings to be cut intoby propping or bolting;

• possible treatment of ground around thefuture opening;

• in one or several stages, cutting out andremoval of segments in front of the openingunder construction;

• in one or several stages, excavation andconcreting of the final reinforced concretelining of the strengthening structure aroundthe opening;

• removal of temporary support.

Construction of in-line works must be fore-seen as early as possible; consequently, theirgeometr ical proper ties and method ofconstruction must be fully defined by theEngineer and Owner's Representative rightfrom design stage.

Their construction stage must have a mini-mum impact on progress of TBM-excavatedconstruction of the main works.

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7 - INSTRUMENTATION

7.1 - Aims

Precast concrete segments lining instru-mentation and monitoring schemes mustsatisfy several aims:

• to check that lining actual behaviour com-plies with forecasts resulting from plannedtheoretical sizing and, in turn, to verify thelevel of safety of the structure in terms offorces and deformations;

• to gain greater knowledge of:

- the intensity and distribution of externalactions impacting on the lining during thedifferent stages construction progress (TBMthrust, annular gap back grouting, short- andlong-term pressures exer ted by the sur-rounding ground),

- the intensity and distribution of segmentinternal loads, especially:

• resulting from TBM thrust (presence orabsence of defects in bearing between diffe-rent elements, evaluation of TBM lengthinfluencing the lining),

• resulting from successive actions involvingback grouting and the surrounding groundunder par tial cutter section confinementand showing, for example, possible loadredistribution due to alternation of radialcontact joints over a succession of rings.

In any case, Owners and contractors shouldbe made aware that these instrumentationschemes do not originate from the researchfield but must be regarded as a driving fac-tor in terms of fur ther ing the technicalnature of this type of lining and allowingboth acquisition of quantifiable referencedata, concerning the quality of the comple-ted tunnel, and advantage to be gained fromanalysing information fed back in order torefine the actual behaviour of this form ofdiscontinuous lining.

7.2 - Monitoring methods

To achieve the above aims, the principaleffects to be measured are as follows:

• stresses and pressures:

- measurement of pressures exerted by theback grouting material and ground on thelining extrados,

- measurement of pressures exer ted at seg-ment contact joints.

These measurements are often disruptedby the effect of sensor interaction (totalpressure cells) with the medium in which ithas been installed. Results should always besubjected to careful analysis;

• segment deformations:

These are often measured using vibratingwire tensometers embedded in the seg-ments and arranged:

- in a longitudinal direction, with a view toanalysing stresses induced by TBM maincylinder thrust,

- in a radial direction, with a view to analy-sing stresses induced by back grouting, thesurrounding ground and possible disruptiveeffects associated with TBM thrust.

A concrete control block fitted with sensorsis often provided as a reference, although itsbehaviour is somewhat different of that ofthe lining segments.

• convergences:

- Invar wire or optical convergence measu-rement, with a view to evaluating short- andlong-term deformations withstood by liningrings.

Temperature probes and relative humiditysensors must also be implemented at ins-trumented sections in order to comple-ment effectively the data collected.

Whilst tunnel lining monitoring has, untilnow, been carried out conventionally by atechnician, this method is now being chal-lenged by automatic data acquisition, whichoffers many advantages such as:

• rapid and vir tually simultaneous measure-ments; data acquisition from a large numberof sensors therefore provides an "instanta-neous picture" compared with TBM pene-tration rates;

• scheduled frequency of measurement sui-ted to both the nature or var iability ofactions concerned and data sought duringdifferent construction stages;

• data acquisition facilitated, in par ticular,when instrumented r ings are within thearea enclosing the TBM back-up equipment.

Conversely, several drawbacks inherent inthe use of automatic data acquisition shouldbe mentioned:

• danger of a systematic loss of data due todefective installation or malfunction of acomponent after fixing (closely supervisedinstallation then periodic checking to becarried out by body in charge of measure-ment);

• compatibility of recording box spatialrequirements with respect to clearances tobe provided temporarily for shor t-term(erector arm, segments being erected, tem-porary equipment, back-up equipment, etc.)and long-term (rolling stock, permanentequipment, etc.);

• possible problem of energy supply andindependence; depending on the quantity ofdata to be collected, various options can beenvisaged: large-capacity batteries, sophisti-cated power plant controlled by energy-saving electronics).

In par ticular, all monitoring schedules mustspecify who is responsible for interpretingresults, the timescale and the data transmis-sion chain. The validity of the monitoringsystem must be questioned if this oftenneglected interpretation stage does notexist.

In general, reference should be made toA.F.T.E.S. "Auscultation" (Monitor ing)Working Group n° 19 recommendations ontunnel monitoring measurements.

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ANNEX :

TUNNEL LINING CONSTRUC-TION - PRECASTING AND INS-TALLATION

1 - GENERALThe aim of the present section is to des-cribe the main tunnel lining constructionstages in such a way that actions applied tothe segments dur ing construction arerecorded.

In general, these operations are covered byconstruction procedures describing generaland specific requirements for productionorganization and which are consolidatedunder a single more general document: theproject Quality Assurance Plan (Q.A.P.).

2 - DESCRIPTION OF SEG-MENT PRECASTING

2.1 - Mould preparation

2.1.1 - Cleaning

Careful brush-cleaning of the peripheralends and flanks (especially their bearingfaces) and mould bottom is under takenwith the mould in an open position. The

impervious seals of the mould are then cor-rectly positioned.

Concrete contact surfaces are spray-lubri-cated with a release agent.

2.1.2 - Reassembly of mould ele-ments

The mould will be reclosed in accordancewith the specified flank and end closingorder.

2.1.3 - Self-inspection

After closing the mould, the operator willensure proper closure of the mould by kee-ping a watch on alignment of flank and endreference marks and by undertaking otherchecks detailed in the Q.A.P..

The operator will then examine visuallyeach mould; these operations will be ente-red on the compliance inspection recordspecified in the Q.A.P..

2.2 - Placement of reinfor-cing cages

With respect to the logical sequence ofprecasting operations, it is assumed thatreinforcing cage production has followed itsown fabrication Q.A.P., incorporating alljoint contracting and subcontracting fabri-cation Q.A.Ps. as well as all the supply itemsentering into the composition of a cage.

2.2.1 - Cage preparation

Each reinforcing cage will be fitted with spa-cers designed to ensure its accurate positio-ning in the mould and, thus, compliance withspecified concrete cover to the reinforcingbars.

2.2.2 - Self-inspection and placingof the reinforcing cage

Before placing the cage in the mould, theoperator will ensure, in accordance with thereinforcing cage production Q.A.P., that thiscage:

• is not deformed in any way;

• corresponds perfectly with the mould forwhich it is intended;

• is fitted with all the designed spacers, bothin number and in position.

After placement of the reinforcing cage inthe mould, the operator will ensure that thecage is correctly centred with respect to themould and will then fill in the complianceinspection record.

2.3 - Mounting of connectorinserts and accessories

Whatever the systems selected, they will bepositioned generally after installing the rein-forcing cage in the mould.They usually com-prise:

REFERENCESREFERENCES ••••••••••••••••

TERZAGHI K. - Rock defects and loads on tunnel support - Rock Tunnelling with Steel Supports, Commercial Shearing Co - Youngstown,Ohio, pp. 15-99, 1946.

PROTODIAKONOV M.M. - Klassifikacija Gornych Porod - Tunnels et Ouvrages Souterrains I, pp. 31-34, 1974.

LAUFFER H. - Gebirgsklassifizierung f¸r den Stollenbau - Geologie Bauwesen, 74, pp. 46-51, 1958.

DUDDECK H., ERDMANN J. - On structural Design Models for Tunnels in Soft Soil - Underground Space,Vol 9, pp. 246-259, 1985.

CORBETTA F., BERNAUD D., NGUYEN-MINH D. - Contribution à la méthode convergence-confinement par le principe de lasimilitude. Revue Française de Géotechnique n° 54, pp. 5-12, 1991.

BERNAUD D., ROUSSET G. - La nouvelle méthode implicite pour l'étude du dimensionnement des tunnels - Revue Française deGéotechnique n° 60, 3e trim., pp. 5-26, 1992.

PANET M. - Le calcul des tunnels par la méthode convergence-confinement - Presses de l'Ecole Nationale des Ponts et Chaussées, 1995.

NGUYEN-MINH D., GUO C. - Sur un principe d'interaction massif-soutènement des tunnels en avancement stationnaire - Eurok'93,Lisbon, Portugal, 1993.

NGUYEN-MINH D., GUO C. - Tunnels creusés en milieu viscoplastique - Géotechnique et Environnement, Colloque Franco -Polonais,Nancy, 1993.

MUIR WOOD A.M. - The circular tunnel in elastic ground - Geotechnique 25, n° 1, 1975.

HOEK E., KAISER P.K., BAWDEN W.F. - Support of Underground Excavations in Hard Rock - A.A. Balkema, Rotterdam, Brookfield,1995.

…/…

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• 240 •

• a pick-up device;

• sockets and pins for implementing socketbolts or any other connection system;

• a system for possible grouting behind seg-ments, etc..

As in other fabrication operations, self-ins-pection will be carried out by the operator,who will check the correct positioning of allthese connector inser ts and accessoriesbefore fil l ing the compliance inspectionrecord.

2.4 - Concreting

The concrete Q.A.P. or CONCRETE FILEspecifies the type of concrete, its proper-ties, constituent materials and, in par ticular :

• the concrete mix;

• the physical chemical analysis of consti-tuent mater ials : fine aggregate , coar seaggregate, cement, water ;

• the active alkali balance;

• admixture engineering data sheet(s);

• test results for trial mixes produced fordesign and suitability purposes;

• the Q.A.P. for the approved testing labora-tory.

2.4.1 - Concrete production andpreliminary checks

At the star t of each concreting shift, theoperator will check proper operation of:

• the concrete plant PLC-controlled systemfor weighing and accurately recording theweights of constituent materials;

• the water, admixture, plasticizer, accelera-tor, etc., regulation system;

• the mixing time control system.

2.4.2 - Concrete placement

Continuous uniform placement in themould of the segment concrete volume willbe ensured.

2.4.3 - Finishing of extrados ornon-shuttered surfaces

On completion of concreting, the free sur-face of the concrete will be floated as accu-rately as possible.

After waiting for the init ial set of theconcrete (approximately 20 - 40 minutes),final trowelling of the top of the segmentwill be carried out to eliminate bug holesand unevenness.

2.4.4 - Heat treatment, preheatingof concrete

Depending on the type of concrete thermalmaturing selected, several methods can beenvisaged:

• hot water mixing of concrete (maximumwater temperature 80 °C);

• heating of mould underside;

• steam curing under controlled tempera-ture and relative humidity.

2.5 - Mould stripping -Handling - Pre-storage

Unbolting and removal of connector inser tand accessory supports;

Release of lock-bolts for opening flanks andends of mould;

Positioning of lifting beam fitted with suc-tion pads, or other gripper- or sling-basedhandling system.

After mould stripping, segments will be setdown and stacked on supports located inprepared sections of the pre-storage(curing) area inside the precasting shop oroutside under suitable protection. Timberblocks will be placed between segmentstaking care that they are aligned with thesupports. Curing time will be approximately8 hours and in general imposed by thesequencing of mould str ipping, stor ing,gluing, turning, packing and then loading-outoperations.

Self-inspection

The operator will then carry out the neces-sary inspections and fill in the relevant com-pliance inspection report.

2.6 - Inspections

Moulds for the same lining ring must befabricated and inspected from every anglein relation to the ring. Similarly, in the caseof several ring moulds, the type of mouldmust be identical irrespective of the ring itforms.

The following inspections are usually car-ried out:

• Prior to star ting mass production of seg-ments

- inspection of mould fabrication,

- inspection of ring geometry and assemblyusing reinforced concrete segments frominitial precast shop casting,

- inspection of moulds on delivery to pre-cast plant,

- inspection of first reinforcing cages fabri-cated in accordance with mass productionprocedures.

• During production

Segment precasting involves mass produc-tion, therefore procedures specifying detailsof inspections to be carried out at regularintervals throughout the production periodshould be established to ensure that tole-rances for moulds, segments and reinforcingcages, as well as concerning reinforcing cageassembly quality, always remain less than theinitially established values.

- inspection of moulds approximately every50 casting operations,

- same frequency inspection of correspon-ding segments at line output and correctionof mould adjustment if deviations areobserved.

These inspections are essentially based on:• overall dimensions of the assembled ring;• lengths of segments generating ring taper ;• segment wall thickness;• flatness of ring/ring contact surfaces;• roughness;• geometry of designed pockets and theirlayout (impervious gasket grooves, etc.);• positioning of connector inser ts (pick-upsocket, connection system, etc.);• geometry of reinforcing bars, quality ofreinforcing cages and their position in themoulds.

2.7 - Repairs

A repair report, which will be attached tothe relevant compliance inspection report,will be drawn up for every repair.

The Q.A.P. will specify repair proceduresand materials to be used for the differentcases encountered:• honeycombing;• bubbles in waterproofing gasket grooves;• spalling at edges, etc.Self-inspection after repair• inspection of waterproofing gasket groovesurface condition;• inspection of extrados surface condition;• inspection of bearing surfaces.

2.8 - Installation of water-proofing gasket

In the case of a glued waterproofing gasketsection, gluing will be carried out using anadhesive payer recommended by the sup-

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plier of the gasket and installed in accor-dance with his instructions and procedures.

2.9 - Packing and marking

In general, segments of the same ring will bepacked together on timber blocks.

Timber blocks between segments must beperfectly aligned.

Each segment will be marked according toinstructions given on the contract drawings(intrados bearing face), to enable it to beidentified and cross-referenced with therelevant inspection record (traceability).

2.10 - Internal preshipmentinspection

The segment loading supervisor will indi-cate the transported ring number, as well asthe precasting date of its component seg-ments, on the preshipment inspectionreport.

He will check that connector inser ts andaccessories are clean and protected, thatthere is no concrete spalling, that water-proofing gaskets and possibly pads are pro-perly glued.

He will also check segment packing, align-ment of timber blocks and the size of thepack.

A copy of the inspection report will be sentto site along with the delivery note.

3 - STORAGE AT PRECASTPLANT YARDSpecial care is required in relation to sto-rage and possible thermal protection condi-tions to prevent segment concrete micro-cracking at the precast plant storage yard.

Handling will be undertaken using a liftingbeam fitted with either suction pads orslings, which allows a pack of several seg-ments to be picked up.

Segments will be positioned at the precastplant storage yard to avoid a segment tur-ning operation between yard storage andpick-up by the segment erector, whose suc-tion pads or handling mechanisms pick upthe segment from the intrados side.

When the erector is supplied in the uppersection of the TBM, segments are storedintrados lowermost.

When the erector is supplied in the lowersection of the TBM, segments are storedintrados uppermost and, in this case, a seg-ment turning machine enables this opera-tion to be carried out at the precast plant.

In its storage position, the segment rests ontwo timber blocks of the same length as thesegment itself and positioned directly in linewith the longitudinal assembly systems.

Segments are stored by stacking each set ofsegments comprising a ring.

Segments must be stored after precastingand can only be installed if their strengthexceeds or is equal to that required by theproject specifications.

4 - SEGMENT COLLECTION,TRANSPORT AND ACCEP-TANCE ON SITEIn principle, the precast plant loading super-visor is responsible for collecting segmentsfrom the plant storage yard and the haulagecontractor is responsible for transport.

Segments are picked up at the precast plantstorage yard by lifting beam fitted with suc-tion pads, grippers or slings and they arethen loaded onto lorries or another meansof transport.

On-site segment inspection for acceptancepurposes will be conducted on the lorry orother means of transpor t. Prior to unloa-ding, the site representative will sign andmake any written remarks on the deliverynote.

Detailed observations will be included onthe pre-unloading inspection report and a

copy will be returned to the segment manu-facturer.

5 - SEGMENT SUPPLY TOTHE WORKFACEAfter segment acceptance, unloading andstorage in an area near the tunnel access(shaft, adit, etc.), supply to the workfaceusually depends on the area available and itrepresents a minimum stock.

Storage can be organized by:

• segment;

• by segment pair ;

• by rings palletized on steel frames.

Storage design is therefore based on theselected transport methods within the tun-nel and to the TBM, where the segments areunloaded, then placed on a belt or rollerfeed conveyor which delivers them to thefront where they are picked up by the seg-ment erector.

6 - LINING RING BUILDINGSection 3.5.5 "Segment assembly systems"of the present recommendations specifiesand describes:

• the different assembly systems;

• the aims sought under construction andservice conditions.

The following table complements this infor-mation by considering an example of buil-ding a lining ring comprising rectangular-(standard) and trapezoidal-shaped (key andcounter) segments. It details:

• the successive segment erection stages;

• recommendations associated with theoperating environment for each erectionstage;

A few remarks of a general nature comple-ment the table.A

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1) Supply of first segment to erector. Supply possible from:- upper level;- lower level.

2) First segment pick-up. Pick-up possible using suction pads, grippers, bolts.

3) Retraction of thrust cylinders corresponding to placement of first segment.

4) Positioning of first segment by Detailed analysis of loads in each pick-up system Light ray guidance systems can facilitaterotating erector. position and of indirect loads on segments. approach and final positioning of segment.

5) Radial approach of first segment.

6) Final approach with rotational, longitudinal and Control of approach speeds by selection oftransverse balance adjustment. proportioning hydraulic controls.

7) Holding of first segment on ring. Pads of other thrust cylinders remain under pressure TBM main cylinder thrust on the other segmentsin contact with other segments to safely ensure: must prevent any forward displacement ofsegments holding and assembly, the machine.- compression of waterproofing gaskets and At this time, the segment is simultaneously held by prevention of their decompression, the erector and the thrust from the main cylinders.- stability of the machine under the confinement pressure.

8) Fixing of first segment see § 3.5.5 "Segment assembly systems" By ring/ring (longitudinal), segment/segment (transverse) connection.

9) Installation and fixing of standard segments. Same recommendation as for the first segment. ame remark as for the first segment.Provide alternate installation of segments in each ring to minimize tube roll effects.

10) Installation of counter segments. Use of template to calibrate gap between Same remark as for first segment.counter segments.

11) Key segment installation. Use of template prevents: It should be noted that on completion of erection,- tearing of waterproofing gaskets, the ring is stabilized by the prestress between theconcrete chipping. erection jacks and the previously installed ring.- greasing of waterproofing gaskets. The only contact between the shield tail and

the segmental lining is the shield tail seal.

SCHEDULE OF OPERATIONS RECOMMENDATIONS REMARKS

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GT18R1A1_Design Sizing Construction of Segments Lining

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