1、 TunnellingandUndergroundSpaceTechnology18(2003)115126 DesignandconstructionofmountaintunnelsinJapan KatsushiMiura* ShizuokaConstructionBureau,JapanHighwayPublicCorporation,Shizuoka,Japan Received10September2002；receivedinrevisedform29January2003；accepted4February2003 Abstract Thispaperpresentsthest
2、ateoftechnologiesofthemountaintunnelingmethodinJapan.Inadditiontothereviewofthedesignandconstructiontechnologies,thepaperfocusesonthedevelopmentoftechnologiesfortunnelswithlargecross-sections,urbantunnelsinnon-cementedsoilground,andapplicationsofTBMs,whicharetechnicallyevolvingnowadays. 2003Elsevier
3、ScienceLtd.Allrightsreserved. Keywords:Mountaintunneling；Urbantunnel；TBM 1. Present state of design and constructiontechnologies 1.1. Introduction InJapan,themountaintunnelingmethodhasbecomepopularsincetheendofthe19thcentury.Manytunnels,includingthoseunderdifficultconditionssuchastheSeikanTunnel,hav
4、ebeensuccessfullyconstructedwithadvanced technologies. Approximately20yearsago,theJapanesemountaintunnelingmethodwaschangedwhenitadoptedtheuseofsupportswhichcombineshotcreteandrockbolts,orinsomecases,steelsupports.Sincethen,designandconstructiontechnologieshavemademoreprogress.Attemptshavebeenmadeto
5、createtechnicaldevelop-ment for high-speed construction,usingadvancedmech-anization,andchallengestohandletechnicallydifficulttunnelingconstructionworks,suchastunnelswithlargecross-sections, urban tunnels in non-cementedsoilgrounds,havebeenmet.Theseeffortshavesucceededinadvancingthedesignandconstruct
6、iontechnologiesofmountaintunnels. 1.2. Initialdesignandmodificationofthedesign Ingeneral,astandardcross-section,specifiedbyanadministrator,isadoptedintheinitialdesignstage. *Tel.:q81-54-272-4881；fax: q81-54-272-4891. E-mailaddress:katsushi.miurajhnet.go.jp(K.Miura). Thegroundcanbeclassifiedintosever
7、algeneraltypes,andapreliminarydesignshouldbemadeforeachgroundtype. Theinitialdesignmethodsareasfollows. a. :2(2,6,1)Applicationofstandarddesigns. InJapan,administratorsofrailways,roadways,etc.maintainalistofgroundclassificationsandcorre-spondingstandarddesignsbasedonpastexperiences.Thesestandarddesi
8、gnsareemployedfortheconstruc-tionoftunnelsundernormalconditions. b. Applicationofdesignsundersimilarconditions. c. Applicationofanalyticalmethods. Fortunnelswithspecialcross-sectionsorspecialgroundconditions,numericalanalysesareemployed.Themostgeneraltypeofnumericalanalytsisisthefiniteelementmethod(
9、FEM). 1.3. Observations,measurementsandmodifieddesigns Designsaremodifiedduringtheconstructionstagebymakingjudgmentsandevaluationsfromtheview-pointofwhetherornotthegroundconditionsarethesameasthoseanticipatedduringtheinitialdesignstage.Ifmodificationsarerequired,thefollowingproblemsmustbesolved,name
10、ly:(1)howtochangetheamountofsupportandyortheinstallationtime；(2)whetherornotthestabilityofthecuttingfacecanbemaintainedifconstruction iscontinued； and (3)ifunstable, whatrationalmeasuresshouldbetaken. 0886-7798/03/$-seefrontmatter2003ElsevierScienceLtd.Allrightsreserved.PII: S0886-779803.00038-5 116
11、 K.Miura/TunnellingandUndergroundSpaceTechnology18(2003)115126 1.3.1. Evaluationoftheground Itisveryimportanttoobservethecuttingfaceandtoevaluatethegroundconditions.However,therearemanyfactorswhichhavetobesystematicallytakenintoaccount.Anattemptismadetocomputethepercentagethateachfactorcontributesby
12、analyzingpastrecordsandbyexpressingthegroundconditionsintermsofevaluationpoints. 1.3.2. Probingexploration Inordertospeeduptheconstructiontime,itisparticularlyimportanttoproperlyevaluatethegroundconditions.Tomeetthisgoal,aninvestigationshouldbeconductedtoevaluatethegroundconditionsaheadofthecuttingf
13、ace.Inadditiontopilotboring,anestimationmethodwhichinvolvesdrillingenergyorelasticwavesisadopted. 1.3.3. Useofmeasurements Inordertoevaluatethepresentstateofthegroundconditionswiththemeasurements,thefollowingmain-tenancetargetsareoftensetup. Evaluationofthestabilityoftheground；Sakurai(1982)andSakura
14、ietal.(inpress)proposedamethodforestimatinganallowablevalueofdisplace-mentfromrelationshipbetweenthelimitstrainandtheuniaxialcompressivestrength. Maintaininglimitsforthesoundnessofthesupports. Limitsnottoinfluencethesurroundingstructures. 1.4. Supportdesigns 1.4.1. Shotcrete Astrengthof18MPa(acuring
15、periodof28days),ashighasliningconcrete,isusedasthestandarddesignstrength.Incaseswherethethicknessneedstobeincreased,attemptsaresometimesmadetoeitherapplyreinforcementsusingsteelfiberortoincreasethestan-darddesignstrength,justlikethetunnelsfortheNewTomeiandtheNewMeishinExpresswaysortunnelswiththickov
16、erburdens(Miuraetal.,inpress). Shotcreteissometimesreinforcedbytheinsertionofwirenets.Steelfiberreinforcedconcreteisusedwhencomplicatedstressorlargedeformationdevelops. Anewsupportisunderdevelopmentalongwithnewconstructionmethods,namely,shotmortar,extrudedconcretelining(ECL),prelining,andsoon. 1.4.2
17、. Rockbolts Rockboltsareusedasprimarysupportmaterialsjustlikeshotcrete.Themainanchoragemethodforrockboltsisafull-facedanchorage.Forcasesinwhicharockboltholecannotstandalone,aself-boringtypeofrockboltmay be employed. When rockbolts are anchoredtotheground,thefrictionisincreasing.Theboltsarenotonlyeff
18、ectiveimmediatelyafterinstalla-tion,butalsoworkevenwhenwaterinflowisencountered. 1.4.3. Steelsupports Steelsupportsareconsideredtohavepositiveeffectssuchasearlystabilizationofthecrownface,reinforce-mentofshotcrete,supportingpointsoffore-piling,etc.,andtheyaregenerallyusedinJapanwhengroundconditionsa
19、repoor. 1.5. Designofthelining Atgeneralsitesandundernormalgroundconditions,thepurposeofaliningistoincreasethesafetyofthesupports.Thus,noparticularconsiderrationisgiventothemechanicalfunctions.Itisconventionalpracticetoapplyastandarddesign. Mechanicalconsiderationdoesneedtobegiventothedesignofthelin
20、inginsomecases；forexample,theearthpressureorthewaterpressureactsafterthecompletionofthetunnel.Someengineersrefertopastsimilarcases,andthenconductastructureanalysisorafiniteelementanalysis. 1.6. Auxiliarymethods Inmountaintunneling,theauxiliarymethodscanbeusedinordertostabilizeanunstablecuttingface,t
21、ocontroltheprecedingdisplacementaheadofthecuttingface,toimprovethegroundconditionssoastoobtainthefulleffectofthesupports,andsoon. 1.6.1. Stabilizingthecrown Thecrownisstabilized inorder to prevent itscollapsebefore theshotocretehasbeenappliedandhashardened.Fore-poling,inwhichrockboltsaredrivenintoth
22、egroundaroundtheexcavatedface,iseasytoconductwithoutchangingthearrangementoftheconstructionmachinesusedatconventionalconstructionsites. Piperoofprotection,horizontaljetgrouting(Fig.1),long-spansteelpipefore-piling,prelining(Fig.2),etc.,arelikelytoyieldhighlyeffectiveresults.Sincespecialconstructione
23、quipmentsarerequired,however,thesemethodsareadoptedonlyincaseswhereextremelypoorgroundconditionscontinueoveralongworkingsectionorthesettlementofthesurfacegroundisseverelyrestricted. Amongthelong-spansteelpipefore-pilingmethods,amethodwhichusesaconventionaldrillingjumbohasbeendeveloped.Itisoftenuseda
24、ttheportaloratfracturedzonesduetoitssimplicityinapplication(Fig.3). K.Miura/TunnellingandUndergroundSpaceTechnology18(2003)115126 117 Fig.1.Groundstabilizationmethodbyhigh-pressurejetgroutfore-piling(Koizumietal.,1990). 1.6.2. Stabilizingthecuttingface Thereisamethodwhichforcesthecuttingfacetostanda
25、lonebysubdividingtheface.However, sincesuchpoorgroundconditionsrequirelong-spanrockboltsortheearlyclosureofthecross-section,alarge cuttingfaceisnecessary.Thus,stabilizationbymeansofauxiliarymethodshasbecomepopularinrecentyears. Faceshotcreteandfaceboltscanbeaddedduringaconventionalworkingcycleandare
26、easilyemployed.Injectionmethodsareusedtoimprovethemechanicalpropertiesoftheground；cementorurethaneisbeingappliednowadays.Insomecases,alongboltoracableboltisfirstinsertedaheadofthecuttingface；theboltisthencutdownwhiletheexcavationisbeingcarriedout. 1.6.3. Methodstocounteractwaterinflow Drainagemethod
27、ssuchasdrainageboringanddrain-agetunnelsareappliedascountermeasures.Fornon-cementedsoilgroundsinparticular,undergroundwatermaycausethegroundtoliquefy,leadingtoadifficultconstruction.Forthisreason,well-pointdrainageanddeepwellsareoftenconstructed. In caseswherethereis an exhaustible amount of undergroundwater,likeinunderseatunnels,whereinifdrained,thesurroundinggroundmaysettle,acut-offmethodisapplied.Groutingisthemainmethod,how-ever,anditstechnologyhasbeendevelopedthrough Fig.2.Prelining(new-PLSmethod)(Fujishitaetal.,1998). Fig.3.Longspanfore-piling(GeofrontResearchGroup,1997).
