ORIGINALPAPERAmethodforassessingadhesionofclaystotunnelingmachinesI.SassU.BurbaumReceived:21December2007/Accepted:23August2008/Publishedonline:31October2008C211Springer-Verlag2008AbstractTunnelboringmachinespassingthroughcohe-sivesoilssometimesexperiencesignificantclogging,leadingtodelaysandincreasedcosts.Thepaperdescribesatesttoassessthelikelihoodofadhesionproblemsoccurring,simulatingthesituationwhereaclaystickstothecuttingwheelofthemachine.Theresultsoftestsusingkaolinclaysuggestthattheadhesionchangeswiththecompressionforce.Furtherstudiesarebeingundertakentoelucidatethefactorswhichinfluencethis,includingclaymineralogyandroughnessofthefaceofthecuttingwheel.Itishopedthattheworkwillleadtoanindustrialstandardmethodofassessingadhesionwhichcanbeusedinsiteinvestigationandonsite.KeywordsAdhesionC1ClayC1SurfaceeffectsC1BoundarylayereffectsC1TunnelingC1SoilmechanicsResumeLestunnelierstraversantdessolscohesifssontparfoissujetsablocage,conduisantadesretardsetaug-mentationsdecouts.Larticledecrituntestpermettantdevaluerlesrisquesdencrassage,simulantlasituationouuneargilecolleaumolettedecoupedelamachine.Lesresultatsdutesteffectueavecuneargilekaoliniquesugge-rentqueladherencechangeavecleffortdecompression.Denouvellesetudessontentreprisespouridentifierlesfacteursresponsables,incluantlanaturemineralogiquedelargileetlarugositedumolettedecoupe.Onesperequeletravailrealiseconduiraaladefinitiondunessainormalisepermettantdevaluerladherencedunsolargileuxetpouvantetremisenuvrelorsdereconnaissancesdester-rainsetsurchantier.MotsclesAdherenceC1ArgileC1EffetsdesurfaceC1EffetsdecouchelimiteC1TunnelierC1MecaniquedessolsIntroductionInundergroundconstruction,theadherenceofclaystothesteelsurfacesofmachinerymaysignificantlyreducethemachinesefficiencyorindeedresultinatotallossofcapacity.Recently,thisproblemoccurredinsometunnelingprojectsdrivenbyahydro-shieldTBM(Janczecz1997；Thewes1999).Figure1showsthecuttingwheelofatunnelboringmachinenearlycompletelycloggedwithclayeysoil.Whensuchcloggingoccurs,thetunneldrivingprocesshastobestoppedtoallowcleaningofthecuttingwheeland/orextractionchamber,withconsequentialdelaysandimpactonthebudget.Itisthereforeimportantthattheadhesiveprop-ertiesofthesoilsaredetailedinthegeotechnicalsurveyreporttoprovidebothqualitativeandquantitativeinformation.Thesephenomenahavebeeninvestigatedsince1838.Intheearlydays,suchagriculturalworkastillingencounteredproblemswithstickycohesivesoils.Thefirstresearchstudiesfortheconstructionindustrywerereportedinthe1960swhilesystematicresearchontheadhesionofsoilsrelatedtotunnelinghasbeenundertakensincethelate1990s.Despitethis,theinteractionofsoilandthesteelsurfaceisstillnotveryclear.Avarietyofsoiladhesiontestmethodsandtestconditionsweredevelopedandinvesti-gatedbuttodatethereisnocommonlyacceptedtestmethodtoestablishtheadhesivepropertiesofsoils.Futuretunnelprojectsarelikelytobeundertakenmoreandmoreindifficultadhesivesoilconditions,thusitisI.Sass(&)C1U.BurbaumTechnischeUniversitatDarmstadt,Schnittspahnstrae9,64287Darmstadt,Germanye-mail:sassgeo.tu-darmstadt.deU.Burbaume-mail:burbaumgeo.tu-darmstadt.de123BullEngGeolEnviron(2009)68:2734DOI10.1007/s10064-008-0178-6importantthatthereisanagreedindustrialstandardtestmethodwhichprovidesqualitativeandquantitativeinfor-mationabouttheadhesivepropertiesofthesoilwhichcanbeusedbysiteinvestigation,tenderingandconstructioncontractorsaswellasforbudgetplanning.AdhesionofsoilsAdhesionoccursonlyincohesivesoilswithsome1020%minimumclaymineralcontent,dependingonthesoil.Theadhesionofcohesivesoilstosolidsurfacesisfoundtobedependentonawaterfilminsidethesoilsolidinterfaceandcanbeunderstoodasaboundarylayereffect.Theinteractionbetweenthiswaterfilmintheinterface,thewatercontent,theporewaterpressure,thewaterabsorp-tion,theswellingcapacity,tensilestrength,capillaryforcesandotherphysicalpropertiesofthesoilandtheadhesionforcesaswellastheeffectsofthe(steel)surfaceproperties,thewayinwhichtheTBMoperatesandtheboringslurryqualityarenotwellunderstood(Fig.2).Thewes(1999)suggestedaphysicalsoilmodeltoexplaintheadhesiveeffectbetweensoilandasteelsurface.Thepaperproposesatestwhichmayassistinabetterunderstandingofthephysicalprocessesofadhesion.CharacteristicsofasoiladhesiontestmethodAlaboratorysoiladhesiontestmethodappropriateasanindustrialstandardinconstructionindustriesshouldinclude:(a)preciselydefinedparameters；(b)highresolutionmeasurement；(c)highreproducibilityinstandardgeotechnicallaboratories；(d)easyandquicktoperformingeneralsoiltestinglaboratories；(e)simpletestequipment,appropriateforsiteuse(f)simpletestprocedure；(g)theuseofotherestablishedstandardtestingmethods,ifpossible；(h)referencetostandardizedsoilparameters.Thetestmethodhastobeacceptabletothemaintestinginstitutionsasmanyfutureprojectswithadhesionproblemsmaybeexpectedworldwide.Forthisreason,thetestequipmentandprocedureshouldbeassimpleaspossibleandshouldreferto/includeotherwellestablishedstandardtestingmethodsandsoilparameters.PrinciplesofsoiladhesiontestingThreemainprinciplesforthetestingofthebondingforcesbetweentwomaterialsareroutinelyused(Habenicht2006):peeling,shearinganddirecttension.Peelingtestsareofinterestforthelooseningofsoilsinexcavations,trenching,etc.Sheartestswouldleadtoresultswhichinterferewiththeresultsoftheshearstrengthtestwhichistypicallyusedinsoilmechanics.Itwouldthennotbepossibletodistinguishshearstrengthfromadhesionforce.Furthermore,thestressconditionsofsheartestsmakethelocationoftheshearplaneveryundefined.Itislikelythatthemathematicalinterpretationofsoiltestswiththeshearprinciplewouldproducemisleadingresults.Withadirecttensiontestsimilartoaninverseuncon-finedcompressiontestthematerialsareseparatedbyforcesnormaltotheirsurfaces.ForamonoaxiallayoutofthetestFig.1CuttingwheelofaTBMnearlycompletelycloggedwithclay,SydneyAirportRailLink,Photo:CopyrightFa.BouyguesAdhesionsoiltosteelsurfaceSoilSurface/handlingmanner-Grainsizedistribution-Mineralogicalcomposition-Watercontent-Porosity-Cationexchangecapacity-Specificsurface-Waterabsorptioncapacity-Swellingcapacity-Contentofswellableclayminerals-Plasticity-Consistency-Cohesionandtensilestrength-Surfaceroughness-Wettingofsurface-Forcesonsoilparticles-Pressureforcessoil-surface-Contactdurationsoil-surface-SlurrypropertiesFig.2Effectsonadhesion28I.Sass,U.Burbaum123themaximumtensionforceinseparatingsoilfromsteelistheadhesionforceoradhesionstrength.Thestressstateinthiscaseisverywelldefinedandsimplyinterpreted.Tocarrythisprincipleoverintothefieldofsoilmechanics,asolidmaterialhastobepressedonasoilsurfaceandpulledaway.Thistestprincipleisalreadyusedforsoiladhesiontesting(Schachbasian1890；Riek1963；Schlick1989；Fountaine1954；Thewes1999).Thewes(1999)rec-ommendedthisasanindustrialstandardtestingmethod.Onemajorproblemwiththistestprincipleistodistin-guishadhesionstrengthinthematerialsinterfacefromtensilestrengthinthesoil.Iftheruptureisnotattheinterfacebetweenthesteelandthesoilbutinsidethesoilitself,theadhesionstrengthishigherthanthetensilestrengthofthesoilandhencecannotbemeasured.Onlyifthereisnosoilleftonthesolidsurfacecantheadhesionbemeasured.AdhesiontestAdhesiontestequipmentThesuggestedadhesiontestdeviceconsistsofasteelsampleringof9.0cmdiameterandaheightof4.9cm,whichisheldbetweenabaseplateandaheadplate(Figs.3,4).Thesoilsampleisplacedintotheringunderdefinedconditions,e.g.watercontent,compaction,coag-ulatedorsinglegrained,etc.A6.2cmdiameteradhesiontestcylinderisusedasthesurfacetowhichthesoiladheres.Thecrosssectionsurfaceareaofthecylinderis30.2cm2.Thistestarrangementcanbeusedforvariousmaterials,e.g.metal,ceramics,plastics,etc.AdhesiontestprocedureFollowingsomepreliminaryinvestigationstoestablishthebestpracticeforinstallingthecohesivesoilsamplesinthesoilsamplering(Hug2007；Hempel2008),itwasfoundthatthesoilisbestplacedinthreelayers,compactedasinthestandardProctortestusingthe2.5kgrammer.Aftercom-paction,thesurfaceofthesoiliscarefullylevelled/smoothedandthesampleplacedinthecompressionandtensiontestingmachine(Fig.5)withtheadhesiontestcylinder.Thetestprocedureisasfollows.Thesoilsurfaceiswettedwithde-ionizedwater.Itisessentialtousede-ionizedwatertoavoiduncontrolledevaporationandtoproduceanadhesionfilmbetweenthesteelofthecylinderandthesoil.Thewaterisde-ionizedtoavoidundefinedionFig.3Adhesiontestdevice,cross-sections1-1and2-2Fig.4AdhesiontestrigThemeasurementofadhesivepropertiesofcohesivesoils29123exchangeintheclayfractionofthesoilsample,althoughintheorythistestcanbecarriedoutwithotherfluids,e.g.tunnelboringordrillingfluids.Theadhesiontestcylinderisthenpressedverticallyontothewettedsoilsurface,usingacontrolledforcewhichshouldbemaintainedforaspecificperiodoftime.Theadhesiontestcylinderisthenpulledaway,whilecarefullymonitoringtheforceandvelocity.MeasurementsandinterpretationoftestresultsTointerpretthetestresults,themeasurementsrecordedduringthetensionphasesareplottedonaforcetimedia-gram(Fig.6).Thedifferencebetweenthemaximumtensileforceandtheabscissa(ifthedeadweightoftheadhesiontestcylinderisincorporatedinthetestprogram)providestheadhesionforce(orthetensileforceofthesoilsampleifthefailureisobservedinthesoilitself).Tocomparetheresultswiththosereportedbyotherauthors,theforceswereconvertedtostressesbydividingtheforcesbytheareaofsurfaceoftheadhesiontestcylindersurface.Tovalidatethetestmethod,aseriesofadhesiontestswereundertakenonindustrial,homogeneousclays.Ineachcase,onlyonetestparameter(e.g.consistency)wasvariedwiththeothersparameterskeptthesame.SystemtestsThefirsttestserieswerecarriedouttochecktheoperationoftheadhesiontestdev