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50 Tunnel 5/2001

BetonauskleidungenConcrete linings

1 PreliminaryRemarks

These recommendationsrelate to the compilation ofdemands applicable to per-manent concrete linings fortunnels with regard to theircharacteristics for use, theircomposition, the execution ofconstruction and quality as-surance. Regulations that arealready available in Germanysuch as Guideline 853 [1], theZTV-Tunnel [2, 3] and the cor-responding Austrian guide-lines [28] as well as findingsobtained in conjunction withconcrete linings are sum-marised and presented in re-lation to one another. In thisway, recommendations forproducing qualitatively high-grade tunnel linings will beprovided, which assure ser-viceability over a life span ofaround 100 years with lowmaintenance costs. Static cal-culations are not included.

2 Function andDesign of theTunnel Lining

The final tunnel lining hasto sustain a large number ofinfluences. The main ones are:

Stemming from the ground:■ ground pressures of allkinds (dead load, relaxationpressures, creeping pres-sures, swelling pressures, etc.)■ landslips, earth subsidence

■ earthquakes■ water pressures ■ chemical actions resultingfrom aggressive water or ag-gressive subsoil components.

Resulting from construc-tion activities:■ construction activities suchas dead weight in fresh state,intermediate construction ac-tivities with part lining of thecross-section■ removal of the hydrationheat, shrinking■ annular gap grouting, roofgrouting■ transport activities forready-made parts (segments,ready-made pipes)■ jacking forces, back-uploads.

Through utilisation:■ influences of temperatureon the air or from sewage orthe likes

■ chemical attacks from gas-es, sewage, thawing salt andthe likes■ traffic influences■ transportation of rubble orstones in the case of waterpressure tunnels■ fire in the case of transporttunnels.

The permanent tunnel lin-ing has to be dimensionedboth in static and construc-tional terms to cope withthese influences.

The lining’s sealing effectcan be attained either by en-suring that impermeable con-crete is used or by attaching amembrane to the outside ofthe shell. Watertight concretestructures generally requiregreater expenditure on theconcrete production often in-volving reworking (crackgrouting). However, they pos-sess the advantage that faultsare normally easier to localiseand seal. External membranesensure that the concrete shellis protected against water andin turn, possible chemical in-fluences but they are hard toredevelop.

The requirements posedon the sealing systems aredealt with in detail in the Ril853 [1] for railway tunnels andin [2] and [3] for road tunnels.

The design and productionof the final concrete liningcome about through the inter-play of tunnel cross-section,geological and hydrologicalconditions, driving length andlength of tunnel.

The following forms of exe-cuting permanent tunnel lin-ings will now be examined:■ shell concrete■ shotcrete■ reinforced concrete seg-ments■ reinforce concrete pipes.

3 Tunnel Liningmade of ShellConcrete3.1 General

Tunnel linings made of shellconcrete are usually pro-duced using a formwork car.At the point when the perma-nent tunnel lining is installed,the drive has already beencompleted or the concretingwork takes place far behindthe actual face: The tempo-rary support has been in-stalled and ground deforma-tions have long since ceased.The inside contour of the finallining can be chosen as re-quired. It can be adapted tothe subsequent use and thestatic requirements. Normally,the inner shell is created in 8to 12 m blocks, which are sep-arated from one another byexpansion joints. Usually, theindividual blocks are split upinto two or even more con-creting sections in the event

Owing to the length of this article, theGerman text was published in Tunnel3/2001. In this issue follows the Englishversion.

Concrete Linings forTunnel built byundergroundConstructionRecommendations by DAUB, December 2000

The ”Concrete inner Shells“ working group of the GermanCommittee for Underground Construction compiled therecommendations. The group consisted of:Dr.-Ing. A. Städing (chairman)Prof. H.-J. Bösch (former chairman of group)Dr.-Ing. Breitenbücher, Dr. G. Brem, Dipl.-Ing. H. Bretz,Dipl.-Ing. G. Denzer, Dipl.-Ing. Dietz,Prof. H. Duddeck, Dipl.-Ing. Grüter,Dipl.-Ing. K. Kreuzberger, Dr.-Ing. K. Kuhnhenn,Prof. B. Maidl, Dipl.-Ing. M. Muncke,Dipl.-Ing. H. Petruschke, Dipl.-Ing. D. Stephan

GERMAN COMMITTEE FORUNDERGROUND CONSTRUCTION INC.

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of very large cross-sections.Should the marginal condi-tions be suitable, it is also pos-sible to produce a block in asingle working phase.As far asthe bond between the outerand inner shells is concerned,there are 3 solutions:■ inner shell without anybond with the outer shell (two-shell construction method)■ inner shell bonded with theouter shell (monocoque con-struction method)■ inner shell in undesiredbond with the outer shell.

In the case of the innershell without bond, the outershell and the permanent tun-nel lining are installed sepa-rately. This is accomplishedthrough inserting separatinglayers (such as e.g. plasticmembranes, non-woven fab-

rics or air cushion mem-branes). In this connection,the thickness of the separat-ing layer has to be geared tothe roughness of the outer

shell and the outer shell mustbe sufficiently even over alarge area. Through separa-tion, the transference of shearforces is avoided.

When the solution „innershell bonded with the outershell“ is applied, a statically ef-fective bond between the in-ner and outer shells has to bearrived at. In this case, thesame quality demands areplaced on the outer shell as onthe inner one. The transfer-ence of shear forces in theworking joints between the 2shells is secured solely by theconcrete matrix bond. Mea-sures to secure a bond suchas interlinking reinforcementor the likes generally lead towater movements and impairthe tunnel’s tightness. Whenthe inner shell is being pro-duced, the increased inducedstrain compared with 2-shelldesigns with separating mem-brane and the resultant devel-opment of cracks must be tak-

Table 3.1: Quality Assurance through accompanying Monitoring

Planning Determining the concrete technology, execution ofconstruction and quality assurance taking demands on the structure into account

Suitability tests Testing according to DIN 1045 (BII) and Point 3.6.2, todiscover whether and with which starting materialsand methods the desired planning parameters canbe fulfilled (otherwise, the planning has to bemodified accordingly)

Material producer Initial checks on the materials according to pertinentstandards and Point 3.6.3

Concrete producer Initial and output checks on the materials accordingto Pertinent standards and Point 3.6.4

Construction site Initial checks on the fresh concrete according toDIN 1048 and Point 3.6.5. Monitoring of execution-according to EN 206 and Point 3.6.5. Comparisonbetween desired and actual values for the executed-performance according to Point 3.6.5

Client Controls on the part of the client

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en into account. Careful cur-ing is of decisive importancein this case.This solution is notrecommendable for tunnellinings that have to sustainpressure water and consider-able seepage water.

As long as no special mea-sures are undertaken to sepa-rate the outer and inner shellsand the outer shell is not in-stalled as a permanent bear-ing structure, it must be as-sumed that the worst possiblescenario exists in each case,i.e. the inner shell is complete-ly prevented from shrinking, isaffected by ground pressureetc. albeit in the form of a sin-gle shell.

3.2 Demands on theServiceability3.2.1 Strengths

The concrete strength ofthe inner shell is determinedaccording to static require-ments and amounts to at leastB 25. To avoid cracks, it is es-sential that the requiredstrength should not be unnec-essarily exceeded, as thestrains resulting from settingtemperatures generally in-crease as the strength growsand the working capacity di-minishes i.e. the concrete be-comes more brittle. The con-crete strength needed for theouter shells must be deter-mined by static calculation.When the tunnel has a circularshape with diameters of up to15 m, the roof concretestrength has to be at least3 MN/m2.

3.2.2 Water impermeableConcrete

Water impermeable con-crete must comply with therequirements contained inDIN 1045, Section 6.5.7.2. Ad-ditionally, a water penetrationdepth of less than 30 mm iscalled for in the case of railand road tunnels, [1] and [2].

As far as the permissible crackwidth is concerned, referenceis made to the Ril 853 [1[ andthe ZTV-Tunnel, Part I [2], ac-cording to which the crackwidth Wk,cal < 0.15 mm [2]must be adhered to.

3.2.3 Special PropertiesTunnel inner shells must

possess high resistance tofrost in the portal zone (gener-ally over the first 100 to 500 m)and also a high resistance tothawing salt in the case ofroad tunnels. Cement with ahigh sulphate resistance mustbe employed against chemi-cal attack resulting from wa-ters containing sulphates(> 600 mg SO4/l) or subsoil con-taining sulphates (> 3,000 mgSO4/kg). In the event of sulphatecontents of up to 1,500 mg/l inthe groundwater, fly ash in ac-cordance with the DafStbGuideline [19] can alternative-ly be used. Please refer to DIN1045, Section 6.5.7 for require-ments on concrete with spe-cial properties.

3.3 Production3.3.1 Formwork

The production of inner shellsshould be standardised as faras possible for economic andquality assurance reasons.Me-chanically and hydraulically col-lapsible and mobile formworkcars are available here. Fortransport tunnels of standardsize and comparable struc-tures, it is advisable to divideup the formwork into a floorformwork car and one for thevault and to concrete eachtunnel block in 2 steps. An all-round formwork car is particu-larly useful for smaller tunnelcross-sections, by means ofwhich each tunnel block canbe concreted in a single step.Dividing the formwork into 2units has the advantage thatthe formwork parts can be in-stalled and positioned moreeasily and faster and in eachcase the amount of concreteto be processed is restricted.The working joints betweenthe floor and the vault repre-sent a disadvantage.

An all-round formworkavoids working joints and theassociated disadvantages(danger of leaks, inducedstrains during setting). In addi-tion, time and work are re-duced both for setting up theforms and for concreting com-pared with dividing the form-work into 2 units. Similarly,savings are made with respectto the amount of reinforce-ment required for the workingjoints. These advantages areprimarily to be set against thehigher investments. The form-work construction has to spanat least 2 block lengths andbe supported at the bottomand the top (secured againstuplift) outside of the blockthat is in the process ofbeing concreted. In this con-nection, special measuresmust be undertaken to pro-tect the sealing membranesshould plastic membranes beused for waterproofing pur-poses.

The length of formworkcars is above all governed by

1 Vault formwork car in the Engelberg Base Tunnel

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the handling capacity of thecars, through restricting theamount of concrete to beworked to a reasonableamount and through stipula-tions relating to the maximumpermissible block length.Block lengths of < 10 m arelaid down for rail and road tun-nels with inner shells consist-ing of water impermeableconcrete. The block lengthshould not exceed 12.5 mwhen plastic membranes areused for sealing purposes.

The number and size of theconcreting windows in theformwork car should be prop-erly dimensioned so that it ispossible to insert the concretehose without any trouble, toensure that concreting can beobserved from the next win-dow and that the concretedoes not fall freely from aheight exceeding 1 m.

3.3.2 Block JointsBlock joints that are in-

stalled in tunnel zones, whichare exposed to major temper-ature fluctuations, shouldgenerally be produced in theform of expansion joints withsuitable insertions in order tocreate clear constructionalconditions. Compression jointscan be installed in sectionwhere minor temperaturefluctuations prevail. In thecase of water impermeableconcrete inner shells, theblock joints should be sealedusing expansion joint strips at-tached to the inside.The widthof the expansion joint stripsmust be adapted to the antici-pated water pressure, how-ever, it should not be any lessthan 30 cm. When installingthe joint strips, it must be ob-served that the shell layersseparated by the joint strip be-tween the strip and the shellsurface are at least as thick asthe length of the joint striplimb embedded in the innershell. The shell edges should

be sufficiently reinforced bothradially and in the direction ofthe ring. It is advisable to in-stall outer joint strips at theblock joints in the case of tun-nels sustaining water pres-sure with outer seal and toweld the outer seal with thesejoint strips so that a bulkheadis created at every block jointin the longitudinal direction ofthe tunnel. In the roof zone,special measures should beundertaken to ensure that thespaces between the retainingbolts for the joint strips areproperly filled, please see [1].

3.3.3 Working JointIn the event of pressure

water and the utilisation ofwater impermeable concrete,it is advisable to insert a jointplate which is b > 25 cm wideand t > 1.0 mm thick. At theblock joint, the joint plateshould be welded watertighton to the block joint strip’ssteel bracket. The workingjoint’s surface should be freedof cement slurry as soon aspossible after stripping and becarefully cleaned prior toerecting the formwork for thesecond concreting section.The transference of shearforce in the working joint be-tween the floor and the risingvault should be worked out bycalculation. If it is not possibleto verify that a smooth jointsuffices, then the workingjoint should be produced witha roughened or serrated form.

3.4 Concrete Composition3.4.1 Cement

As far as the compositionof the concrete is concerned,in some cases, contradictoryrequirements relating to highstrength and early strength inparticular (short strippingtimes) on the one hand andlow setting temperatures onthe other have to be opti-mised. Towards this end, Port-land cements 32.5 R as well as


54 Tunnel 5/2001


furnace cements 32.5 to 42.5for the floor have provedthemselves with quantities of280 to 320 kg/m3 in summer or300 to 320 kg/m3 of compact-ed fresh concrete in winter.

3.4.2 Concrete AdmixturesIt is recommended that fly

ash should be added to sup-plement the amount of ce-ment and augment the finegrain content. This improvesworkability, reduces the dan-ger of demixing and bleedingof the concrete, caters for adenser concrete texture anddiminishes the developmentof hydration heat. As a result,the addition of more than60 kg/m3 of fly ash to the freshconcrete is possible althoughthis does not actually con-form to what is laid down inthe ZTV-K.

3.4.3 Concrete AdditivesIn order to improve worka-

bility, it is advisable to add plas-ticisers to the fresh concrete.Retarders should only be addedto ready-mixed concrete incases of exception. When

plasticisers are added, theDafStb Guideline for flow con-crete should be observed [20].

3.4.4 AggregatesThe grading curve for the

concrete aggregate should liebetween grading curves A andB according to DIN 1045. Thismeans that both sufficientcompactness and strengthare possible and that it can beworked easily without an ex-cessive amount of water be-ing needed. The maximumgrain should be chosen in ac-cordance with the reinforce-ment density, but not greaterthan 32 mm. Connecting mix-es directly over a previousconcreting section should beproduced with a smaller max-imum grain. In order to con-fine shrinking as far as possi-ble, the water content shouldlie below 170 l/m3. In the caseof a 32 mm maximum grain, itis advisable to use a fine grainand fine sand content of450 kg/m3 of compacted freshconcrete. In order to reduceinduced strains caused by set-ting heat, aggregates with a

lower temperature elasticityreciprocal value (basalt, lime-stone) should be selectedrather than those possessinga high temperature elasticityreciprocal value (e.g. quartziteaggregates). Crushed aggre-gates (splits) also decreasethe inclination to crack on ac-count of the somewhatgreater concrete tensilestrength. In order to arrive at auniform concrete composi-tion, there should be no morethan a 7.5 percentage byweight discrepancy from thedetermined grain distribution.

3.4.5 Steel FibresSteel fibre concrete can be

an alternative to reinforcedconcrete. The crack-distribut-ing effect of the steel fibres inthe concrete exerts a positiveinfluence on the crack widthdevelopment and in turn, onthe tunnel shell’s serviceabili-ty. Steel fibre concrete alsohas advantages to offer inprocess engineering terms asthere is no need to install thereinforcement [40]. As thesteel fibre content increases,

the effectiveness of steel fibreconcrete is enhanced. How-ever, there are limits imposedon account of the poorerworkability of the fresh con-crete owing to the productionprocess. The steel fibres,which are used, must possessan approval certificate award-ed by the Institute for Con-struction Technology in Berlin.The basis for dimensions inprovided by the DBV Code „Di-mensioning Principles forSteel Fibres in Tunnelling“ [26].The danger posed to plasticsealing membranes by steelfibres should be clarified priorto use.

3.4.6 Mixing WaterThe DBV Code „Mixing Wa-

ter for Concrete“, Jan.1982version [24] should be re-ferred to as far as the mixingwater is concerned. Whenresidual water is used, caremust be taken to ensureabove all that hydration is notnegatively influenced by anyretarders that it might contain.

3.5 Execution ofConstruction3.5.1 Concreting Subsurface

The demands posed on theconcreting subsurface are de-fined in Ril 853 [1] and in theZTV-Tunnel [2] for water im-permeable concrete innershells. The concreting subsur-face must be clean and free ofloose particles of all kinds.

3.52 Shell Thickness,Reinforcement and ConcreteCovering

Inner shells for convention-al tunnels should be at least30 cm thick. A minimum thick-ness of 35 cm is recommend-ed for reinforced inner shellsand water impermeable con-crete inner shells. For trans-port tunnels, the shell thick-ness, the reinforcement andthe concrete covering are laiddown in the Ril 853 [1], in the

2 Vault reinforcement for the inner shell with distance holders in the Nebenweg Tunnel atVaihingen/Enz

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ZTV-Tunnel [2] and in the DBVauthorised report [27].

The inner shell can be exe-cuted without a reinforce-ment providing the strains andrequirements allow it.

3.5.3 Concrete Productionand Installation

The production target is toattain a concrete quality thatis as good and constant aspossible. In order to achievethis, the starting substanceshave to be accuratelyweighed. Deviations from themix should be confined to< 3 % of the amount of theadded quantities or < 5 % inthe case of additives. All com-ponents with the exception ofwater are added according toweight.

The fresh concrete tem-perature at the point of instal-lation should amount to < 18 °C.It should not be allowed to ex-ceed 25 °C.

When the vault is beingconcreted, the permissibleheight differences for the con-crete level, which are ob-tained from the design andanchoring of the formworkcar, must be observed.

Particular care should betaken in the roof zone to en-sure that the concrete is in-stalled void-free. Suitable ma-chines have to be employedto make sure that the air canescape when the concrete isbeing placed, e.g. throughconcreting upwards and visu-al or other suitable checks(control pipe at the highestpoint).

Internal vibrators are usedto compact the floor concrete.A vibrator beam has emergedto be most suited for workingthe floor surface. Formworkvibrators are recommendedfor the vault (one vibrator for 3to 4 m2) with an effectivedepth of 40 to 50 cm.The addi-tional application of inner vi-brators is recommended as

far as possible particularly forthe joint zone in conjunctionwith the formwork vibrators.

When steel fibre concreteis utilised, the general nega-tive influence of the steel fi-bres on the fresh concrete’sworkability has to be consid-ered when selecting the con-creting equipment. It is advis-able here to undertake pro-cess engineering suitabilitytests with the chosen steel fi-bre concrete mix and equip-ment technology prior tocommencing the concretingoperations.

3.5.4 Measures followingShotcreting

The concrete mix and com-mensurate curing normally al-low stripping to be carried outafter 9 h. This is in keepingwith an economic working cy-cle. Stripping should avoidjolts and bumps as far as pos-sible to avoid cracks and split-ting. Prior to stripping, a non-destructive test should be car-ried out in the roof to confirmthat the concrete strength issufficient (e.g. using an impacttesting machine). It is recom-mended that the concretetemperature is measured atregular intervals during thesetting phase in order tocheck the concrete mix andthe strength development.

The purpose of curing is toprotect the concrete from dry-ing out and cooling too quicklyand in turn, to prevent cracks.In this connection, it is advis-able to protect the concretevault against cooling directlyfollowing stripping (< 1 h) us-ing a curing car with heat insu-lation and to gently spray theconcrete surface with waterto prevent it drying out. In thisconnection, an effort shouldbe made to ensure that the airhumidity is at > 90 %. In thismanner, the concrete temper-ature can gradually drop toreach the surrounding tem-

perature within the course of3 or 4 days. When water is be-ing sprayed on to the con-crete, care should be taken toensure that it is not too cold inorder to prevent the concretereceiving a shock while cool-ing. Further requirements onthe curing car are listed in theZTV-Tunnel [2] under 5.1.3.

The roof gap should first begrouted continuously at theearliest after the concrete hasattained its 28-day strengthusing flowable grouting mor-tar possibly containing aswelling agent via injectionnozzles.These nozzles have tobe installed along with the re-inforcement in the roof at ap-prox. 3.0 m gaps. The groutingpressure should be set in sucha way that no damage iscaused either to the innershell or to the ground. Ril 853indicates that a grouting pres-sure of < 2 bar has proved it-self here.

ZTV-Crack [4] and Ril 853 [1]refer to the grouting of cracksin the reinforced inner shells.

3.6 Quality Assurance3.6.1 Overview

A monitoring programmethat accompanies the entireplanning and production cy-cles is recommended to as-sure the quality of the com-pleted inner shell. The follow-ing table shows the continu-ous accompanying checksand the given responsibilitiesduring the course of produc-tion.

The continuity of the moni-toring programme should beassured by advance and finalcontrols at each station andthrough passing on the moni-toring recordings to whoeveris involved next. In this fash-ion, any discrepancies at vari-ance with the suitability testare identified at an early stage,mistakes eradicated and re-sponsibilities clearly regulated.

3.6.2 Suitability TestDIN 1045, 7.4.2 applies for

the suitability test.It is advisable to provide

proof of the compressivestrengths in each case with 3concrete cubes at the aspiredpoint of stripping as well as af-ter 12, after 24 h, after 3, 7, 28days and if need be, at a laterpoint in time after 56 or 90days. In addition, with respectto the suitability test, the prob-able installation temperaturesand transport or waiting timesshould be taken into account.Similarly, the registering ofheat development should alsobe undertaken.

The parameters obtainedduring the suitability testserve as intended values forongoing quality assurancewhile the tunnel inner shell isbeing produced.

3.6.3 Starting MaterialsThe starting materials have

to comply with the valid stan-dards. The relevant record-ings, which have been under-taken within the scope of self-monitoring are to be passedon to the concrete manufac-turers.

For cement, DIN 1164 andthe test method according toDIN EN 196 apply for cement.

DIN EN 450 applies for flyash as an admixture.

Additives must be ap-proved by the German Insti-tute for Construction Technol-ogy.

3.6.4 ConcreteManufacturers

Investigations should becarried out at the concretefactory to determine whetherthe existing dosing and mixingunits are suitable for unprob-lematic production of the re-quired amounts that have tobe delivered. Generally, acomputed controlled mixingplant is called for on accountof the high demands placed

56 Tunnel 5/2001


on tunnel inner shells. Itshould be capable of storingthe concrete mix, of measur-ing the water content of thesand with < 4 mm and be ableto correct the water added ifthe need should arise. Fur-thermore, the mixing unitshould check the weighing ofall concrete components foreach mix and automaticallymeasure the fresh concretetemperature. The data print-out should contain a batch re-port including mixing time,fresh concrete temperature anda error report with weighingdeviations. It should be hand-ed over on the constructionsite when it is supplied togeth-er with the delivery note. Theweighing units must be checkeddaily to see how they are func-tioning. The accuracy of thewater metre and the dosingunits has to be controlled whenthey are set up and subse-quently at monthly intervals.

3.6.5 Construction SitePrior to placing the con-

crete and if need be, the rein-forcement, the concretingsubsurface on the site has tobe examined with respect toits cleanliness and evenness.

In the case of reinforced in-ner shells, it has to be estab-lished whether the deter-mined concrete covering canbe adhered to in construction-al terms. Similarly, the jointstrips must be examined tofind out whether they are inthe proper position and se-curely mounted. Immediatelyafter the first blocks havebeen produced, the concretecovering is inspected to es-tablish whether there are anyflaws in the system. Prior topouring the concrete into theformwork, the fresh concretetemperature for the concretefrom every delivery must bechecked and documented.

Prior to stripping, the con-crete strength in the roof has

to be examined on the freefront side.

The curing car has to beconstantly controlled to makesure it functions properly.

3.6.6 ClientSpecialists on behalf of the

client should constantly su-pervise the execution of theconstruction project so thatfaults can be identified inplenty of time and possiblyavoided.

4 Tunnel Liningmade of Shotcrete4.1. General, Production

Shotcrete is not a specialconcrete but a concrete in ac-cordance with DIN 1045,which is merely produced andplaced in keeping with a spe-cial method. Depending onthe way the concrete is con-veyed to the spraying nozzle, adistinction is drawn betweenthe dry-mix and the wet-mixspraying processes.

In the case of the dry-mixprocess, a dry concrete mixwithout or with only a low wa-ter content (naturally moist) isdelivered to the spraying noz-zle by means of compressedair (thin flow conveyance).Wa-ter and accelerator are addedat the nozzle. Accelerator isnot added when spraying ce-ments are utilised. The readymix is then sprayed on to theconcreting subsurface at highspeed.

In the case of the dry-mixprocess, a ready-mixed con-crete mix is delivered to thespraying nozzle by means ofpressurised air (thin flow con-veyance) or by a concretepump (dense matter con-veyance). At the nozzle, liquidaccelerators are added andthe concrete is sprayed ontothe placing surface by meansof pressurised air [41,42].

DIN 18551 and DIN 18313as extensions of DIN 1045 ap-

ply both for shotcrete produc-tion and its quality control.Furthermore, the Guideline853, Module 0017 [1] governsother demands. On account ofthe fact that shotcrete can beinstalled very flexibly, namelywithout formwork and onpractically all inclined sur-faces, shotcrete is used pri-marily in tunnelling as an im-mediate support and as atemporary support for thefreshly excavated cavity. How-ever, it is also employed as apermanent tunnel lining andfor repair jobs.

The quality of the complet-ed shotcrete shell largely de-pends on the skill of the noz-zleman (gap to spraying sur-face, spraying direction, con-sideration of installed partssuch as reinforcement or an-choring plates). In addition,the shotcrete shell, which isproduced during the drive,possesses numerous joints.These are subjected to strainby the ground during the hard-ening process, resulting incracks being formed. For thisreason, the temporary shot-crete shell is not generally ac-cepted to be the permanenttunnel lining and particularlynot when underground wateris present. Usually, a secondshell is installed, on whichhigher demands can beplaced on account of themore straightforward installa-tion conditions that are en-countered. Shell concrete ismostly employed in such cas-es for cost reasons. However,under certain conditions, theapplication of shotcrete canbe the economically morebeneficial solution, which alsocomplies with the technicalrequirements.

4.2 Demands on theServiceability Properties4.2.1 Strengths

The permanent tunnelshell’s strength is governed by

the static requirements. In thecase of shotcretes, it must beobserved that they generallypossess a greater proportionof fine grain and cement incomparison to shell concrete.Shotcrete with strengths inexcess of 35 N/mm2 is not rec-ommendable on account ofassociated high creeping andshrinking properties.

4.2.2 Water impermeableShotcrete

Shotcrete can be producedin water impermeable quality.On account of the fact that thematerial tends to shrink to agreat extent, the danger ofspraying shadows and prob-lems resulting from the water-tight design of expansionjoints (spraying joint strips),shotcrete shells are generallynot to be recommended aswater pressure resistantstructures.

4.2.3 Special PropertiesThe high frost resistance

called for in the tunnel portalzones can also be attainedwith shotcrete.Through the in-clusion of sprayed air in theconcrete texture (in porousform), shotcrete possesses alarger pore volume than nor-mal concrete and generally asufficiently high density aswell [41]. The addition of airpore entraining agents is notadvisable in the case of shot-crete as the desired porescannot form due to the spray-ing process. Instead, it is pos-sible to add “micro hollowglobules“ to the shotcrete.These are tiny, self-containedhollow plastic spheres, whichare added to the starting mixas “prefabricated air pores“ inorder to improve its frost andfrost-thawing salt resistance.

The high frost and thawingsalt resistance that is calledfor in the case of road tunnelscan also be attained withshotcrete through using cor-

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responding cements (Port-land, iron-Portland, furnace orPortland oil shale cement) andaggregates.

Furthermore, a shotcretewith a high resistance againstaggressive sulphates can beproduced through the use of acorresponding cement.

4.3 Concrete Composition4.3.1 Cement

The cement has to complywith cement standard DIN1164 or be approved by theconstruction authority. In ad-dition, the required service-ability properties (strength,sulphate resistance, etc.) haveto be complied with.

DIN 1045, Table 4 can beemployed for determining theamount of cement. For an ini-tial estimate, this starting val-ue should be reduced by 80 %of the probable amount of re-bound as the proportion ofcement in the rebound onlyamounts to roughly 20 % ofthe cement quantity con-tained in the starting mixture.The position of the placingsurface has a considerable in-fluence on the rebound and inturn, the amount of cement inthe ready concrete. See Ruf-fert for more precise calcula-tions relating to the cementquantity [41].

4.3.2 Concrete AdmixturesIt is advisable to add fly ash

or micro silica to increase theproportion of fine grain. In thisway, the density of the con-crete and its elution behaviourare improved and the reboundreduced. The admixtures haveto be standardised and gener-ally be approved by the con-struction authority or possessa test certificate. The totalamount of admixtures de-signed to increase the finegrain share should not be inexcess of 25 % of the bindingagent.

4.3.3 Concrete AdditivesUnless a sprayed cement is

used, an accelerator has to beadded. As accelerators nega-tively affect the shotcretequality (final strength, moduleof elasticity, creeping andshrinkage, leachability), assmall an amount as possibleshould added. The permissi-ble highest tolerable amountof accelerator equals 5 per-cent by weight with respect tothe amounts of cement in themix. All additives have toposses a valid test certificateand are only allowed to beemployed under the condi-tions laid down in the test re-port. The interaction of ce-ment and accelerators shouldbe examined in suitability testsunder site-related conditions.Retarders and plasticisers arealso added to wet-mix shotcreteto improve its workability.

4.3.4 AggregatesAll aggregates, which con-

form to the aggregate stan-dard DIN 4226, can be utilisedfor shotcrete. Generally, thelargest grain should be re-stricted to 16 mm. The graindistribution should lie be-tween grading curves A and B(DIN 1045, Figs. 1 and 2, Area3). When the grading curve ischosen, it should be taken intoaccount that it reverts up-wards owing to the increased

rebound of the larger grainsduring the spraying process,e.g. from Area 3 to Area 4. Par-ticular attention should be fo-cused on a steady gradingcurve without omitted-sizegrain mix as otherwise theproportion of rebound in-creases [41]. For the dry-mixprocess, the inherent mois-ture of the aggregate mixshould not exceed 4 % so thatperfect processing and con-veyance are assured.

4.3.5 Mixing WaterNormal utility water (drink-

ing water) is normally suitableas mixing water for shotcrete.When residual water is used(which is often the case withthe wet-mix process), caremust be taken to ensure that itcomplies with the require-ments of the Guideline for theProduction of Concrete usingresidual Water, residual Con-crete and residual Mortar [21].When the mixing water is tak-en from rivers or ponds, it isadvisable to carry out an in-vestigation to determine itssuitability for producing con-crete. In this connection, set-ting tests and strength investi-gations can be executed (DIN1164, Sheets 5 and 7). In casesof doubt, a chemical testshould be undertaken.

As far as the amount of wa-ter is concerned, the same

rules apply for the starting mixfor the wet-mix process as forpumped concrete. Generally, awater-cement value of lessthan 0.5 should be aimed at.However, in the case of shot-crete, its workability especiallyits bonding with the placingsurface determines just whatamount of water is suitable sothat narrow w/c parametersmake little sense.

4.3.6 Steel FibresThe details contained in

3.4.6 also essentially apply forsteel fibre shotcrete. Owing tothe process involved, normal-ly shorter steel fibres are usedwhen they are incorporated inshotcrete. The length shouldnot exceed 2/3rds of thesmallest hose diameter in theshotcrete unit.

4.4. ExecutingConstruction4.4.1 Concreting Subsurface

If a gravity-actuated bondbetween the final shotcreteshell and the subsurface is re-quired, the placing surfacemust be free from running wa-ter and sufficiently rough-ened. Furthermore, the sub-surface itself has to possess asufficient surface strength tobe in a position to transfer theforces occurring in the con-creting joint. Generally, it is ad-visable to pre-treat hardenedconcrete surfaces with high-pressure water jets or sandjets. Additionally, the placingsurface should be adequatelywetted in advance so that nowater is extracted from thefresh concrete. If a structuraldivision is needed betweenthe placing surface and the fi-nal shotcrete shell, it is recom-mendable to install a latticematting membrane or a napmembrane adhered to a lat-tice structure (water can runoff in the intermediate layer).

3 Producing a shotcrete shell

58 Tunnel 5/2001


4.4.2 Shell Thickness,Reinforcement, ConcreteCovering

The shotcrete shell thick-ness depends on the static re-quirements. Providing that theshell has no bearing functionto fulfil and e.g. is only re-quired to carry and protect themembrane needed to disposeof seepage water, the requiredshell thickness is determinedby a covering that is adequatefor the reinforcement androof-bolt heads etc. Thick-nesses of 15 cm can sufficefor such purposes.

The reinforcement in theshotcrete shells has to be at-tached prior to spraying insuch a manner that no harm-ful vibrations occur when theshotcrete is being placed. Thedistance between reinforce-ment bars should not be lessthan 10 cm, the bar diametershould be maintained at < 16 mm,The concrete covering for thereinforcement should not beless than the nominal size nomc = 6 cm on account of theroughness of the shotcretesurface. In the case of a two-layer shell reinforcement, theinside reinforcement layer shouldfirst be installed once the requiredshell thickness is attained.

4.4.3 Shotcrete InstallationThe quality of the finished

shotcrete shell depends to alarge degree on the nozzle-man’s experience and skill. Asa consequence, it is essentialthat sufficiently well-trainedpersonnel are available forproducing shotcrete tunnellinings.The shotcrete shell hasto be produced in several lay-ers for technical reasons. Af-ter creating the statically re-quired shell thickness, a finalthin compensating layer withsmaller grain diameter can beplaced if need be in order toarrive at a smoother surfacethat is easier to coat. Whenplacing steel fibre shotcrete,

the generally negative influ-ence on the workability of thestarting mix should be takeninto consideration. This alsoapplies to the choice of equip-ment. It is advisable to under-take suitability tests with theshotcreting unit and the mixthat is being applied well be-fore shotcreting operationsare carried out.

4.4.4 CuringShotcrete needs especially

careful curing owing to its highmortar content. It is recom-mended that the concretesurface is kept wet for at least3 days after the shell is com-pleted to minimise shrinkageand temperature cracks.

4.5 Quality Assurance4.5.1 General

Essentially, the quality as-surance of the permanentshotcrete tunnel shell shouldcomply with that of a shellconcrete tunnel shell. As aconsequence, Section 3.6.1“Quality Assurance, Over-view“ and Table 3.1 are re-ferred to with regard to moni-toring construction progress.

4.5.2 Suitability TestThe suitability of the select-

ed concrete compositionshould be tested under siteconditions, preferably on thesite itself, through producing

test samples with the appro-priate machines. The testsamples should be sufficientlylarge (at least 0.5 x 0.5 m2) andproduced to correspond withthe subsequent type of execu-tion (horizontal or sprayedoverhead). All the shotcreteproperties required for subse-quent execution have to beproved on the basis of thesetest slabs or rather the coresthat are obtained from them.

4.5.3 Starting Materials The starting materials cho-

sen for the shotcrete have tocorrespond with the validstandards or be approved bythe German Institute for Con-struction Technology. The giv-en suppliers bear the respon-sibility for this. The suppliers’delivery notes must also con-tain evidence that the regula-tions are complied with or thatapproval by the constructionauthority has been obtained.

4.5.4 Concrete Producers,Construction Site

The delivery notes must bechecked on the constructionsite and the material visuallyinspected when it is delivered.In addition, it is advisable tocheck the grain compositionof the aggregates by means ofa grading test on the occasionof the first delivery and then atappropriate intervals. When

ready-mixed concrete is sup-plied, it is recommendable totest the moisture content ofthe dry-mix and to carry out aslump test for the wet-mix toavoid difficulties when work-ing with the mix in question.

On account of the numer-ous influences on the finalcomposition of the shotcrete,it is recommended that sam-ple cylinders are tested to as-certain that the required prop-erties are being adhered to atregular intervals and at leastonce per 100 m3.

Furthermore,checks shouldbe undertaken on site to con-trol the shell thickness and toensure that the intended con-crete covering complies withrequirements.

4.5.5 ClientSpecialists on behalf of the

client should constantly su-pervise the execution of theconstruction project so thatfaults can be identified inplenty of time and possiblyavoided.

5 ReinforcedConcrete Segments5.1 General

Both single and two-shelldesigns are possible in thecase of segmental tunnel lin-ings. Generally, two-shell tun-nels are provided with a shellconcrete inner shell as thepermanent lining. This is dealtwith in Chapter 3.

In the case of a single-shellconstruction, the segmentsform the final lining so thatthey have to comply with allthe demands, resulting fromthe construction conditions,the ground, the groundwaterconditions and utilisation.Usually, the segments aremade of reinforced concreteready-made parts. Unrein-forced segments are onlyused in the case of small tun-nel cross-sections and low

4 Block segments with neoprene seal and load distribution plates

Tunnel 5/2001 59


quality requirements. As far asthe future is concerned, theapplication of steel fibre con-crete seems imminent, whichcould result in a reduction inbar steel reinforcement or itbeing renounced altogether.

Steel segments are cus-tomarily used for special sec-tors such as fork-off points forcross-passages.

5.2 Demands on theServiceability Properties

The demands on the ser-viceability properties of seg-mental linings result from theground and water pressures,from utilisation and here to aparticular extent on the con-struction state. The need forhigher concrete strengths isgoverned both by construc-tion (force transference in the

joints) as well as constructionconditions (jacking forces,back-up loads). Generally, re-inforced concrete segmentsare made of strength class B45 concrete, in some cases, B55 or even higher.

The concrete must pos-sess a water impermeabletexture in accordance withDIN 1045, Section 6.5.7.2 anda water penetration depth of< 30 mm according to DIN 1048.

In the tunnel access zone,the concrete for the segmentsmust possess high frost resis-tance and in the case of roadtunnels, high frost and thaw-ing salt resistance, please seeDIN 1045, Sections 6.5.7.3 and6.5.7.4.

In the event of chemical at-tack resulting from waterscontaining sulphates (> 600 mg

SO4/l) or a subsurface con-taining sulphates (> 3,000 mgSO4/l) cement with high sul-phate resistance must be ap-plied, please see DIN 1045,Section 6.5.7).

5.3 The Design ofSegments5.3.1 Ring Geometry

Normally, a segment com-prises 5 to 7 segments. Ver-sions that do not form aclosed ring have failed toprove themselves in practice.

The ring division and thesegment dimensions have tobe optimised in accordancewith the project-related para-meters.

In order to produce curva-tures of the tunnel tube and tocompensate for inevitable de-viations of the driving path

from the intended route, thesegmental rings are createdwith a conical form so that thering face areas are not paral-lel. In practice, both the pro-duction of 2 conical rings thatsupplement each other aswell as the construction of asingle conical ring has proveditself. Through corresponding-ly rotating the ring, it is possi-ble to form any desired curve.If only a single ring is used, thisfacilitates storage and poten-tial mistakes are excluded.

5.3.2 Longitudinal JointsIn the longitudinal joints,

ring normal forces and bend-ing moments are transferredthrough eccentric normalforces and lateral forces.

In practice, even jointshave proved to be the most

60 Tunnel 5/2001


commonly used. They are ca-pable of transferring normalforces 2-dimensionally andare also capable of transfer-ring bending moments inkeeping with their width to alimited degree through possi-ble eccentricity of the normalforces.

The tongue and groove de-sign for the longitudinal jointprovides good guidance forassembly and improves thepossibility of transferring lat-eral forces. On account of thestronger force transferencearea, the bending momentbearing capacity is smallerthan that of the even joint. Asit is not possible to reinforcetongue flanks and grooves,the danger of the concretesplitting exists should the jointtolerance only be slightly ex-ceeded during the construc-tion of the ring.

Other joint designs, as e.g.convex joints at both sides,can scarcely be contemplatedfor permanent segmental lin-

ings on account of their inade-quate sealing possibilities. Thelongitudinal joints of neigh-bouring rings should be set upas a staggered arrangementso that sealing problems(cross joints) are avoided andto enhance the stiffness of thesegmental tube.

5.3.3 Ring JointsNormal and lateral forces

affect ring joints. In construc-tion state, the ring joints resultfrom the jacking forces duringthe drive and in their finalstate they are caused by wa-ter pressure. Lateral forces inthe ring joints result fromvarying deformations affect-ing neighbouring rings.

As far as the ring joints areconcerned, either even jointsurfaces or inter-toothed ver-sions in the form of tongueand groove constructions orcam and pocket systems arecustomary.

Even joints are only capa-ble of transferring lateral

forces via friction and onlyproviding that there is suffi-cient normal force derivedfrom the thrusting jacks. In thisconnection, it must be ob-served that particularly whenelastic ring joint inlets (see be-low) are not included, pre-stressing of the segmentaltube in the longitudinal direc-tion from the jacking forcescan be completely negatedthrough shrinking and creep-ing. Even ring joints are lesssusceptible to splitting al-though under certain circum-stances, they also permit larg-er differential displacementsin the case of neighbouringrings so that the ring joint’stightness is jeopardised. Jointswith effective toothing pre-vent impermissibly excessivedifferential displacements ofneighbouring rings and fur-thermore can increase thebending bearing capacity ofthe segmental tube.The antici-pated coupling forces have tobe ascertained in the static

calculation along with the di-mensioning of the tongue andgroove construction and thecam and pocket system (di-mensions, reinforcement) [46].Tongue and groove or camand pocket systems should beprovided with sufficiently largetolerances and the peripheralzones of the groove and pock-et should be designed in sucha way that they can easily re-gain their position.

The insertion of forcetransference plates, e.g. madeof hard-fibre materials in thering joints has proved itself inorder to avoid damage result-ing from stress peaks and toimprove force transference.The inclusion of adhesiveKaubit strips or similar materi-als is also recommendedwhen using cam and pocketsystems. Practice reveals thatowing to its design, the tongueand groove system consider-ably increases the danger ofconcrete splitting. As a result,it is wise to create even ringjoints providing that thestrains allow this.

5.3.4 Segment Bolting andDowelling

It is advisable to bolt thesegments together via thelongitudinal and ring jointswhen assembling the seg-mental ring and to secure thescheduled geometry. Normal-ly, bolting is not required in thefinal state as the longitudinaljoints are subjected to pres-sure by the earth and waterpressure and pre-stressingfrom the resilience forces ofthe sealing profile at least isavailable. Securing the pre-stressing of the joint strips inthe ring joints by construc-tional means, however, is nec-essary in the tunnel portalzones.

Dowels can also be madeuse of to connect the seg-ments in a longitudinal or ringdirection. To what extent

5 Segmental lining in Duisburg’s Ruhr Tunnel

Tunnel 5/2001 61

dowel connections can trans-fer tensile forces (avoidingbreathing) to a sufficientlysafe degree has to be lookedinto in each individual caseand needs to be substantiatedthrough tests. For assembly,wooden or plastic dowels canbe of help for centering pur-poses during ring construc-tion. Similarly, they can be em-ployed as a support againstcollapsing.

5.3.5 Segmental Sealing StripsThe ring and longitudinal

joints are sealed via syntheticrubber strips, which are at-tached in the form of prefabri-cated frames in the continu-ous groove in the joint areas.The effective water tightnessof the joint strips has to beverified through suitabilitytests, which have to take pos-

sible displacements of thesealing strips against one an-other as well as possible inad-equate compression of thestrips into consideration. Sim-ple sealing frames are cus-tomary and are normally suffi-cient. Double frames make anadditional groove in the jointareas necessary, which re-sults in the pressure transfer-ence areas becoming smallerwith the danger of splitting in-creasing. As a consequence,they can only be contemplatedfor thicker segments > 60 cm.

The segments should alsohave foam plastic strips at-tached to their outer edge. Inthis way, it is possible to pre-vent grouting mortar pene-trating the outer joint area sothat the tightness betweenthe shield tail and the tunneltube is improved.

5.3.6 ReinforcementEven although only a very

small reinforcement cross-sec-tion is needed for static rea-sons, it is nonetheless advis-able to plan a minimum rein-forcement in the segments sothat any unscheduled constraints,which can occur in particularduring ring construction, arecatered for. The minimum rein-forcement cross-section shouldnot be less than 10 % of theconcrete cross-section. Espe-cially, the ring reinforcementat the ring joints should not bedimensioned too scantily. Fur-thermore, it should be ob-served that when dimension-ing the segmental reinforce-ment, it is imperative that thesplitting tensile strains andmarginal tensile strains exert-ed on the segments at theirjoints should be examined.

The reinforcement cagesfor the segments can be pre-produced at the factory withthe cages being welded informwork moulds. Usually,both bar steel as well as spe-cially produced matting areused towards this end. In thisconnection, all curved barsare installed in pre-curvedstate so that the cage can beproduced free of stress. Thefollowing recommendationsapply to the concrete cover-ing:nominal size: nom c = 3.5 cmminimum concretecovering: min c = 3.0 cm.

A smaller concrete cover-ing is also acceptable at thejoint areas in order to improvethe bearing capacity of inter-toothing: roughly c > 2.0 cm.

Coated reinforcement barshave also been utilised for


62 Tunnel 5/2001


7 Pipe butt given pressure water

special requirements. Cur-rently, the application of steelfibres on their own or com-bined with bar steel reinforce-ment is being tried out.

5.4 Segment Production5.4.1 Formwork, dimensionalStability

Generally, segments areproduced in an existing facto-ry for finished parts or fieldfactories that have been setespecially for the project. Nomatter what the case may be,the Requirements posed onFactories for finished Parts,please see DIN 1045, Section5.3, apply as far as the de-mands on their compositionand monitoring are concerned.Generally,massive steel mouldsare employed to ensure thatthe high demands on the di-mensions of the segments areadhered to. These have to beproperly cleaned and then in-spected after each applica-tion. The following values canbe cited as a recommendationfor the dimensional tolerancesthat have to be adhered to:Segment width + 0.6 mmSegment thickness + 3.0 mmSegment archlength + 0.8 mmLongitudinal jointevenness + 0.5 mmRing joint evenness + 0.5 mmTorsional angle inthe longitudinal joint + 0.04°Angle of longitudinaljoint conicity + 0.01°

The dimensional toler-ances can be laid down inkeeping with the require-ments of a particular project.For the DB AG (German Rail-way), Ril 853, Module 19 ap-plies [1]. The concrete surfaceintended for the tongue of thesealing frame must be com-pletely free of shrink holes toprevent any water from circu-lating. Curing must also becarried out at the factory ifnecessary in such cases.

5.4.2 Concrete CompositionAs far as the aggregate ce-

ment, concrete admixtures,concrete additives and mixingwater are concerned, they aresubjected to the same re-quirements as are placed oninner shell concrete, pleasesee Chapter 3.4.

Generally, the requiredwithdrawal strength of thesegment is decisive for theconcrete composition. De-pending on the point of with-drawal from the mould, a ce-ment content of betweenroughly 340 and 380 kg/m3

has developed. If the segmentis withdrawn at a much earlierpoint in time, then the additionof silica suspension improvesthe early strength develop-ment. Roughly 7 to 8 % of solidmatter should be added, relat-ed to the cement content. Thew/c value should on no ac-

count be less than 0.5. In prac-tice, water/cement values ofbetween 0.43 and 0.48 haveproved themselves. The maxi-mum grain of the aggregateshould be selected as large aspossible taking account of thereinforcement density. Thefine grain content should beadapted to the maximumgrain. In the event of a maxi-mum grain of 32 mm, it is ad-visable to have a fine grainand ultra-fine sand content(grain size < 0.25 mm) of 450to 470 kg/m3.

The fresh concrete consis-tency should be arrived at byusing an air entraining agentfrom the KP/KR (standard con-sistency) range. An air entrain-ing agent should be addedto segments with high frostand thawing salt resistance sothat the air content in thefresh concrete corresponds to

the values of Table 5 in DIN1045.

The strength developmentcan be decisively influencedby heat treatment during thehardening of the concrete.

As long as the segment isremoved from the mould afterapprox. 16 to 20 h at the earli-est, a fresh concrete tempera-ture of 20 to 25 °C is adequate.Additional heat treatment isnot required under these cir-cumstances. However, if strip-ping is carried out after only 6to 8 h, then additional mea-sures are needed to attain anadequate stripping strength.In order to accelerate harden-ing, the method of installingthe fresh concrete at a tem-perature of 40 to 45 °C in themould and then to retain it atthis temperature in a heatchamber, please see theGuideline for Heat Treatmentof Concrete from the DafStb[22] has proved itself. In thisconnection, segments havealways to be classified inmoisture category WF.

After stripping, the seg-ment has to be carefully curedto avoid cracks and changesin form occurring on the fin-ished part. A strength ofroughly 15 to 20 N/mm2 isnecessary for removing thesegment from the mould de-pending on the dimensions ofthe finished part.When settingit down on the store lumber,care must be taken to avoid vi-brations and to ensure thatthe timber is aligned properly.In order to make sure that theheat gradually dissipates in acontrolled fashion, it is advis-able to cover the segment orrather the stack of segmentswith a film, which reaches theground at all sides. In this way,it is ensured that the finishedparts do not dry out too rapidly.

5.5 Installing SegmentsSegments should first be

installed once the required

6 Pipe butt without special requirements

Head bolt Steel sleeve Rubber ring

soft wood, free of knots

Head boltSteel sleeve

Wdge slip ring

Steel collar ring

Safety device

Joint closure soft wood, free of knots

Tunnel 5/2001 63


strength has been attained.Immediately prior to installa-tion, the segments should beinspected to establish whetherthey are damaged and to con-firm that the sealing strips arein the proper place. Damagedfinished parts must on no ac-count be installed. The ringhas to be constructed in sucha manner that damage to thesegments is avoided and thescheduled geometry of thesegmental ring is attained pro-tected by the shield cylinder. Itis not always possible to avoidslight concrete splitting owingto constraints during ring con-struction. As a rule, in fact, it isnecessary to undertake re-pairs to the concrete surface.

Grouting of the annular gaphas a major influence on thebearing behaviour of the seg-mental tube. A distinction canbe drawn between 2 groutingmethods:■ continuous grouting of theannular gap through the shieldtail of the shield machine and ■ subsequent grouting throughgrouting nozzles in the segments.

In soft ground, the currentstate-of-the-art calls for theannular gap to be grouted im-mediately behind the shieldcylinder. The annular gap isfilled – with the volume andpressure both being con-trolled so that surface settle-ments are confined to a mini-mum – and the segmentaltube is embedded in the sub-surface by gravity actuation.Grouting has to controlled insuch a manner that no imper-missible deformations of thesegmental rings and damageto the segments occurs.

Grouting through nozzlesin the segments takes place ata relatively late stage so thatsoil cannot always be prevent-ed from falling into the annu-lar gap in soft ground. As aconsequence, grouting is notalways uniform and the pres-sure build-up in the grout can-

not be properly controlled. Inhard rock, subsequent grout-ing through the segment orbackfilling the annular gapwith gravel with follow-upgrouting with mortar is the lat-est state-of-the-art.

Rapid stabilising of thegrouting mortar is imperativefor restricting the deforma-tions and for the bearing be-haviour of the newly con-structed segmental ring. Theannular space grouting mor-tar should thus initially pos-sess good flowing propertiesduring the processing phaseand then be in a position to ac-cept high shear stresses aftergrouting. In addition, it shouldrelease as little filtrate wateras possible to attain volumet-ric constancy. The hardeningof the grouting mortar should,however, not take place tooquickly so that negative ef-fects in operating the shieldmachine are avoided. As a re-sult, the grouting mortar mix isof key importance.

5.6 Quality Assurance5.6. 1 General

Segments are only allowedto be produced in factories forfinished parts, which complywith the requirements of DIN

1045, Section 5.3. The con-crete has to be produced inkeeping with Regulations B IIand monitored according toDIN 1048, Part 2.

5.6.2 Suitability TestsThe suitability of the con-

crete composition and theproduction method for the re-quirements placed on the seg-ments have to be verified un-der factory-related conditionsin the form of suitability tests.In this connection, it is recom-mended that the temperaturecourse should also be contin-uously measured and regis-tered on a sample during hy-dration. In addition, it is advis-able to make sample seg-ments in the appropriatemould with the proposed con-crete using vibration units pri-or to actual production itselfand to carry out tests includ-ing the formation of pores onthe concrete surface.

5.6.3 Monitoring SegmentProduction

DIN 10784, Part 2, appliesfor monitoring segment pro-duction. In addition to thetests it prescribes, verificationof the following aspects is alsorecommended:

The actual early strengthshould be determined by non-destructive means (randomrebound hardness tests with ahammer) prior to the with-drawal of a series of seg-ments.

The temperatures at thecore of the segment and on itssurface should be measuredand recorded on at least oneoccasion – preferably duringthe cold part of the year. In thisconnection, the temperaturegradient must not exceed 20 °C.

5.6.4 Monitoring thedimensional Stability

Regular random tests onthe mould form and the com-pleted segments have provedthemselves as far as ensuringthat the required tolerancesare adhered to is concerned.3-D surveying of the segmentsis recommendable at the startof a series. It is advisable tomake sample rings and to as-semble them prior to the be-ginning of series productionfor test and acceptance pur-poses.

6 ReinforcedConcrete Pipes6.1 General

Reinforced concrete pipesare generally installed in theground by means of the jack-ing method.The size of the fin-ished part pipes is governedby their transportation to theconstruction site, the installa-tion process in the jacking pitand the frictional forces dur-ing jacking itself. Reinforcedconcrete pipes are thus em-ployed for tunnels with small-er cross-sections, above all,for supply and disposal tun-nels. Depending on require-ments they are produced inthe form of:■ slackly reinforced concretepipes according to DIN 4035■ pre-tensioned pre-stressed

8 Welded reinforcement cage

64 Tunnel 5/2001


concrete based on DIN 4035and DIN 4227■ reinforced concrete pipeswith outer or inner steel jacket.

A summarised presenta-tion of pipe jacking is provid-ed among others by Scherle,M. [47]. The following recom-mendations apply for cross-sections with > 1.5 mm innerdiameter.

6.2 Requirements on theServiceability Properties

The specifications con-tained in 3.2 correspondinglyapply. The loads in construc-tion state (jacking forces,curved passage) have to beespecially taken into consid-eration during the dimension-ing stage. Special measures inaccordance with Section 6.3.3are possibly required for pres-sure water lines so that suffi-cient water tightness is at-tained.

6.3 Reinforced ConcretePipe Design6.3.1 Cross-sectional form,Dimensions

Reinforced concrete pipesthat have to be installed bymining means are generallybuilt with a circular cross-sec-tion. The pipe’s inner contourcan be adapted to the require-ments of the subsequent use.The pipes’ construction lengthshould be at least 2.5 m in ac-cordance with the stipulationscontained in DIN 4035. Themaximum dimensions of thepipes above all depend on thetransport conditions (clear-ance profile, weight) and onthe conditions encounteredduring pipe installation andpipe jacking (curved passage,frictional forces).

6.3.2 Pipe ConnectionsThe connections between

the individual pipes have tofulfil a number of tasks:■ further transference of thejacking forces

■ securing play of neighbour-ing elements against one an-other (buckling angle forcurved passage)■ securing tightness■ transference of shear forceslaterally to the pipe axis.

The insertion of soft wood-en rings free of knots be-

tween the pipe front endshas proved itself for the trans-ference of the jacking forces.The wood should be at least20 mm thick to avoid splin-tering of the edges at thepipe ends and a gap of atleast 20 mm in each caseshould be maintained to the

outer and inner formwork sur-face.

A combination of steelsleeve and elastic sealing ringhas proved itself for sealingthe pipe joints. The steelsleeve is concreted in place atthe end of the previous pipeusing head bolts and pro-

Table 1: Production Methods for reinforced Concrete Pipes

Production Vibration method Centrifugal Vibration squeeze method Packer headmethod method method

Range of DNB 4400 and larger DN 3500 DN 3000 DN 2500application

up to nominal Largely used for jacking pipes only in cases predominantly DN 250 to predominantly width Application With construction lengths of exception DN 3000, also for jacking pipes DN 250 to frequency >3.00 m as well as in the case of DN 1200

pipes > DN 3000

Stripping after concrete sets after concrete immediate stripping immediate sets stripping

Position during vertical horizontal vertical verticalConcreting

Type of formwork outer and inner only outer outer and inner outer steel steel formwork steel formwork steel form shell only

Compacting Form centrifugal force Vibration table, Form Centrifuging,method vibrator through the Upper pipe end vibrator, upper rolling and

form rotating (mostly tapered pipe end smoothingend) formed by (mostly by a rotatingsqueezing tool tapered end) packer head

formed bysqueezing tool

Concrete consistency KP (plastic) KP (soft) KS (slightly moist) KS (slightly moist)

Pros – major accuracy of the forms – major accuracy – high production speed – high and dimensions of the outer requiring low form production

– smooth concrete surface formsand expenditure speed – simple concrete technology dimensions requiring

– smooth outer low form concrete expendituresurface

– simplepossibility tovary the pipe lengths andwall thickness

Cons – major form expenditure – major form – low accuracy of forms and as underand low form turnover expenditure dimensions 3a and 3b

– cost-consuming possibility and low form – surface rough and porousturnover – concrete technology must be

– complex adjusted to methodcentrifugal tovary theconstruction length driveand wall thickness

– the innerform anddimensionsrequirereworking

– disposal ofthe surpluswater

Tunnel 5/2001 65


trudes beyond the end of thereinforced concrete pipe. Thesleeve encases the corre-spondingly formed front endof the next pipe (tapered end).The joint between the taperedend and the sleeve is closedso that it is watertight with anelastic sealing ring.The above-mentioned heads bolts shouldbe set < 25 cm apart to ensurethe sleeve is anchored prop-erly and be installed behindthe pipe end’s reinforcement.In addition, a closure that pro-trudes into the concretecross-section, e.g. in the formof a steel sealing elbow is alsorequired to ensure that thesleeve connection is water-tight. The steel sleeve must bedimensioned geometrically tosustain the anticipated buck-ling angle and statically tocope with the effective lateral

forces. For the tapered end ofthe following pipe, which isencased by the sleeve, rein-forcing the outer front edgewith a steel collar ring hasproved itself. The ring shouldalso be anchored in the pipewall by means of head bolts.The collar ring at the sametime forms the front flank ofthe tongue at the taperedhead, in which the sealing rub-ber is adhered. Special sealingprofiles to guarantee watertightness at the pipe butt arenecessary given water pres-sures in excess of 0.5 bar.Their sealing function has tobe determined in keeping withVerification for Segment Seals(see Chapter 5.3.5).

As far as jacking pipes with-out special requirements areconcerned, the pipe butt is de-signed more or less in accord-

ance with Fig. 6. Fig. 7 displaysa pipe butt that also fulfils higherdemands placed on the tight-ness of the pipe connection.

With respect to the require-ments placed on the pipe con-nection and the relevant tests,reference is made to DIN 4060“Sealing Agents for Pipe Con-nections for Sewers andSewage Lines“ and CIN 19453“General Demands on PipeConnections for Sewers andSewage Lines“.

6.3.3 SealingNormally, reinforced con-

crete pipes are made of waterimpermeable concrete and donot require any additionalseals. An additional seal can,however, be needed shouldspecial demands, e.g. highwater inner pressure, have tobe complied with. In such cas-

es, an additional steel jacketcan be installed,which is eithermounted on the inner or outerside of the pipe or within thepipe wall.Tightness at the pipebutts is then carried out bymeans of a ring welding seamor via a special interlockingsocket connection.

6.3.4 ReinforcementThe minimum require-

ments for reinforcing rein-forced concrete pipes are laiddown in DIN 4035. In addition,the Requirements accordingto Ril 853, Module 9 apply tojacking pipes used for railwayfacilities [9].

6.4 Production ofreinforced Concrete Pipes6.4.1 Production Methods

In Europe, reinforced con-crete pipes are essentially

66 Tunnel 5/2001


produced according to 4methods, which can largely bedistinguished according to theamount of formwork used andthe applied sealing method.The methods are describedin Table 6.1. The vibrationmethod has particularly prov-ed itself above all, for largerpipes (roughly > DN 2000) onaccount of good adherence tothe accuracy of the pipe di-mensions and the concretecovering.

6.4.2 Concrete CompositionThe same requirements

are placed on aggregate, ce-ment, concrete admixtures,concrete additives and mixingwater as on the inner shellconcrete, please see Chapter3.4. The required consistencyands the concrete mix dependon the selected productionmethod for the pipes.

In DIN 4035, a minimumconcrete strength of B 45 islaid down for reinforced con-crete pipes. In order to attain adense, early and high strengthconcrete, the water-cementvalue is set at w/c < 0.4. De-pending on the type of ce-ment, the cement strengthclass and the compactionmethod employed, cubecrushing strengths of up to

90 N/mm2 and ring bendingstrengths of between 6 and10 N/mm2 can be attained.

6.5 Pipe Installation6.5.1 Installation byPipe-jacking Method

The production of apipeline or a tubular tunnel bymining means is mainly un-dertaken by the pipe-jackingmethod. This means that ajacking station is set up in astarting pit, with the aid ofwhich the reinforced concretepipes that are set up one be-hind the other are thrust intothe subsurface. At the front ofthe pipeline, the soil is re-moved by means of a conven-tional means of excavation,e.g. the shield driving method,which is in keeping with thesoil and water conditions. Anew pipe is set at the end ofthe column of pipes in thestarting pit following eachjacking stage. Thixotropic lu-bricants such as e.g. bentonitesuspension reduce the fric-tion between the subsurfaceand the pipe wall. The lubri-cant is injected into the annu-lar gap between the subsur-face and the pipe wall bymeans of grouting nozzles inthe concrete pipes. The dis-tance between grouting noz-

zles in the ring and longitudi-nal direction depends on thesubsurface and water condi-tions and on the roughness ofthe pipe wall. In the ring direc-tion, the gap should not nor-mally exceed 3 m, in the longi-tudinal direction, it should beno more than 10 m in non-co-hesive material.

In order to prevent damageto the jacking pipes, the jack-ing forces of the main and in-termediate stations should berestricted to forces that arebased on how the pipes are di-mensioned.

In order to minimise settle-ments on the surface of theterrain and to ensure that thestatically required lateral bed-ding of the pipes is assured, itis recommended that the an-nular gap between the drivensubsurface and the concretepipe is kept as small as possi-ble. Generally, an annular gapof 10 to 15 mm is sufficient.

6.5.2 Installation with PipeTransport Vehicles

In stable ground, it is possi-ble to drive the entire cavityincluding a generous overcutand then to install the rein-forced concrete pipes. In thisconnection, the pipe seg-ments are carried into the tun-

nel on a special transport ve-hicle and then coupled to-gether. When the pipeline isproduced, the annular gap be-tween the ground and the tun-nel tube has to be backfilled.

6.6 Quality Assurance6.6.1 General

The production of rein-forced concrete pipes is onlypermitted in stationary worksand field factories, which fulfilthe requirements relating topipe works contained in DIN4035, Section 7.1. The specifi-cations contained in 3.6.3 and3.6.4 apply for quality assur-ance on the part of the mater-ial producer and the concreteproducer. The suitability of theconcrete composition and theproduction method should beverified under factory-relatedconditions by means of suit-ability tests according to DIN1045.

6.6.2 Monitoring ProductionThe quality demands laid

down in DIN 4035 pertainingto bearing capacity and waterimpermeability must be ful-filled.Towards this end, check-ing the formwork’s dimen-sional stability, the com-paction, the reinforcementand the concrete covering aswell as the proper curing ofthe concrete is essential.

6.6.3 Monitoring PipeInstallation

During the installation ofthe pipes, it is necessary tocheck the positional accuracyof the line, the form of thejoints and the backfill or groutfor the annular gap. In the caseof pipe jacking, the jackingforces also have to be con-trolled so that the longitudinalcompressive strengths to beaccepted by the pipe are notexceeded.

Bibliography: see German original

9 View of a jacking shaft

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