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1、JournalofRockMechanicsandGeotechnicalEngineering.2012,4(2):115–126ReducingriskinlongdeeptunnelsbyusingTBManddrill-and-blastmethodsinthesameproject–thehybridsolution*NickBartonNB&A,Oslo,Norway,www.nickbarton.comReceived13April2012;receivedinrevisedfor
2、m2June2012;accepted5June2012Abstract:TherearemanyexamplesofTBMtunnelsthroughmountains,orinmountainousterrain,whichhavesufferedtheultimatefateofabandonment,duetoinsufficientpre-investigation.Depth-of-drillinglimitationsareinevitablewhendepthsapproacho
3、revenexceed1or2km.Uncertaintiesaboutthegeology,hydro-geology,rockstressesandrockstrengthsgohand-in-handwithdeeporultra-deeptunnels.Unfortunately,unexpectedconditionstendtohaveamuchbiggerimpactonTBMprojectsthanondrill-and-blastprojects.Therearetwoobvi
4、ousreasons.Firstlythecircularexcavationmaximizesthetangentialstress,makingtherelationtorockstrengthahighersourceofpotentialrisk.Secondly,theTBMmayhavebeenprogressingfastenoughtomakeprobe-drillingseemtobeunnecessary.Ifthestress-to-strengthratiobecomes
5、toohigh,oriffaultedrockwithhighwaterpressureisunexpectedlyencountered,the“unexpectedevents”mayhavearemarkabledelayingeffectonTBM.Asimpleequationexplainsthisphenomenon,viatheadverselocalQ-valuethatlinksdirectlytoutilization.Onemaywitnessdramaticreduct
6、ionsinutilization,meaningultra-steepdeceleration-of-the-TBMgradientsinalog-logplotofadvancerateversustime.SomedelayscanbeavoidedorreducedwithnewTBMdesigns,wherebeliefintheneedforprobe-drillingandsometimesalsopre-injection,havebeenfullyappreciated.Dri
7、ll-and-blasttunneling,inevitablyinvolvingnumerous“probe-holes”priortoeachadvance,shouldbeusedinstead,ifinvestigationshavebeentoolimited.TBMshouldbeusedwherethereislowercoverandwheremoreisknownabouttherockandstructuralconditions.Theadvantagesofthesupe
8、riorspeedofTBMmaythenbefullyrealized.ChoosingTBMbecauseatunnelisverylongincreasesriskduetothelawofdecelerationwithincreasedlength,especiallyifthereislimitedpre-investigationbecauseoftunneldepth.Keywords:tunnelboringmachine(TBM);rockstrength;deeptunne
