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TunnellingandUndergroundSpaceTechnology18(2003)161–1690886-7798/03/$-seefrontmatter2003ElsevierScienceLtd.Allrightsreserved.PII:S0886-7798Ž03.00024-5TunnelmaintenanceinJapanToshihiroAsakura,YoshiyukiKojima*ab,KyotoUniversity,Kyoto,JapanaRailwayTechnicalResearchInstitute,Kokubun,Tokyo,JapanbAbstractRecentmaintenancetechnologyandtypicaldeformationcasesofJapaneserailwaytunnelsarepresentedinthispaper.Inspectionoftunnelliningisdividedintoprimaryinspectionandsecondaryinspection.Newtechnologyofnon-destructiveinspectionwhichisintheprocessofpracticableinspectiontomakethisautomaticisintroduced.Repairandreinforcemethodsofdeformationtunnelsaredividedinto:(a)countermeasuresagainstearthpressure;(b)countermeasuresfordeterioratelining;(c)countermeasuresagainstleakageofwaterandfrostdamage;and(d)countermeasuresagainstspalling.Moreover,threecasesconcerningrecenttypicaldeformationofJapaneserailwaytunnelsareshown;oneofthemistheTukayamatunnelconcerningcountermeasuresagainstplasticearthpressureandtheothersaretheFukuokatunnelandtheRebunhamatunnelconcerninganaccidentcausedbyspallingoftunnellining.2003ElsevierScienceLtd.Allrightsreserved.Keywords:Tunnelmaintenance;Tunnelinspection;Tunnelrepair;Reinforcement;Non-destructiveinspection1.IntroductionTunnelsdifferfromon-groundstructures,andthedesignconditions(topography,geology,undergroundwater,etc.)varycasebycase.Thus,itisnoteasytorationallydesignandconstructtunnelsinalltypesoflocations,anditisnotunusualfordeformationtooccuraftertunnelcompletionandduringusage.Forthesereasons,itisimportanttoconductmaintenanceworks,suchasregularinspections,properjudgmentsastothesoundnessofthetunnels,andtheapplicationofcoun-termeasures,inordertomaintainthefunctionofthetunnels.Thecausesofdeformationcanbeclassifiedintothreegroups,namely:(1)earthpressureduetogeologicalfactors;(2)thedeteriorationoftheliningmaterials;and(3)waterleakageandfrostdamage(Asakuraetal.,1991).In1999,incidentsofthespallingofconcreteliningsoccurredintheFukuokaTunnelandintheKita-KyushuTunnelalongtheSanyoShinkansen(BulletTrain)lineandintheRebunhamaTunnelalongtheMuroranMainline.Spalling,broughtaboutbyvariousconstructionworks,hasrecentlybecomeaproblem.*Correspondingauthor.Tel.:q81-42-573-7266;fax:q81-42-573-7248.E-mailaddress:ykojima@rtri.or.jp(Y.Kojima).Inthispaper,investigationandassessmenttechniquesfortunnelliningarereviewed,countermeasuresagainstdeformationsarepresented,andsometypicalexamplesareintroduced.2.Methodsofinspectionanddiagnosis2.1.InspectionanddiagnosisoftunnelsTheinspectionandthediagnosisoftunnelsareconductedinordertograspwhetherornotdeformationhasaninfluenceonstructuralsafetyanddurabilityandthentotakepropercountermeasurestosecurethefunctionofthetunnelsbasedontheevaluationresults.Thus,theinspectionofatunnelandtheresultantdiagnosisarethemostbasicpartsofthemaintenanceandthemanagementofatunnel.‘Inspection’meansanexaminationofthesoundnessofatunnelbasedonacomparisonoftheinvestigation,observationandmeasurementresultsaccordingtothejudgmentstandards.However,a‘diagnosis’meansanevaluationoftheinvestigation,observationandmeas-urementresultsonthebasisofpastexperienceandknowledgeandacomprehensiveproposaloftheevalu-ationofthestructuralfunctionsandcountermeasurestakingintoaccounttheinspectionresults.162T.Asakura,Y.Kojima/TunnellingandUndergroundSpaceTechnology18(2003)161–169Fig.1.Flowchartoftunnelmaintenance.Fig.2.Hammertestingonthelining.Fig.3.Crackmeasurementsintunnelliningusingline-sensorcameras(JRCentral).Inspectionsaredividedintotwostages,asshowninFig.1.1.Theprimaryinspectionisdonetodiscoverwhetherornotdeformationexists,andtojudge,whendefor-mationisdetected,whetherornotasecondaryinspec-tionandyortemporarycountermeasuresoractionsarenecessarybymakinganestimateofthemagnitudeofthedeformation.2.Thesecondaryinspectionisconductedintheformofadetailedinvestigationofthemeasurementsoftheconditionsandthemagnitudeofthedeformationdetectedintheprimaryinspectionandtojudgethenecessityandtheurgencyofapplyingcountermea-sures.Inaddition,whenapplyingcountermeasures,referencematerialsforthedesignandtheexecutionmustbeobtained.2.2.PrimaryinspectionThefrequencyandtheitemsusedfortheprimaryinspectionvarydependingonthepurposeofthetunnel.Inthecaseofrailwaytunnels,periodicinspectionsareconductedasgeneralinspectionsatanintervalofnotmorethanonceineverytwoyears,anddetailedinspec-tionsareconductedevery10oreven20yearsdependingontheimportanceofthelineconcerned.Ifdeformationprogresses,thesecondaryinspectioniscarriedoutinamoredetailedmanner.Theseinspectionworksaremainlydonebyobservingtheliningsurfacewithvisualinspectionandbyhammerknockingonunusuallocations(Fig.2).Recently,how-ever,inspectionshavecomeintogeneralusewithimagesobtainedbylaserbeams,slitcameras,line-sensorcam-eras,CCDcameras,etc.Aninspectiontechniquehasalsobeenintroducedbywhichsurfaceseparationisdetectedbynon-destructivetestsusinginfraredrays(Figs.3–6).Forhammertesting,whichisfundamentaltoinspec-tions,researchisbeingundertakenonthediagnosisofconcreteusinganacousticanalysisofthestrikingsounds.2.3.Secondaryinspe