土木工程 建筑 外文翻译 外文文献 地铁地表沉降

外文原文SurfacesettlementpredictionsforIstanbulMetrotunnelsexcavatedbyEPB-TBMS.G.Ercelebi•H.Copur•I.OcakAbstractInthisstudy,short-termsurfacesettlementsarepredictedfortwintunnels,whicharetobeexcavatedinthechainageof0?850to0?900mbetweentheEsenlerandKirazlıstationsoftheIstanbulMetroline,whichis4kminlength.Thetotallengthoftheexcavationlineis21.2kmbetweenEsenlerandBasaksehir.Tunnelsareexcavatedbyemployingtwoearthpressurebalance(EPB)tunnelboringmachines(TBMs)thathavetwintubesof6.5mdiameterandwith14mdistancefromcentertocenter.TheTBMintherighttubefollowsabout100mbehindtheothertube.Segmentalliningof1.4mlengthiscurrentlyemployedasthefinalsupport.SettlementpredictionsareperformedwithfiniteelementmethodbyusingPlaxisfiniteelementprogram.Excavation,groundsupportandfacesupportstepsinFEManalysesaresimulatedasappliedinthefield.Predictionsareperformedforatypicalgeologicalzone,whichisconsideredascriticalintermsofsurfacesettlement.Geologyinthestudyareaiscomposedoffill,verystiffclay,densesand,verydensesandandhardclay,respectively,startingfromthesurface.Inadditiontofiniteelementmodeling,thesurfacesettlementsarealsopredictedbyusingsemi-theoretical(semi-empirical)andanalyticalmethods.TheresultsindicatethattheFEmodelpredictswelltheshort-termsurfacesettlementsforagivenvolumelossvalue.Theresultsofsemi-theoreticalandanalyticalmethodsarefoundtobeingoodagreementwiththeFEmodel.Theresultsofpredictionsarecomparedandverifiedbyfieldmeasurements.Itissuggestedthatgroutingoftheexcavationvoidshouldbeperformedasfastaspossibleafterexcavationofasectionasaprecautionagainstsurfacesettlementsduringexcavation.FacepressureoftheTBMsshouldbecloselymonitoredandadjustedfordifferentzones.KeywordsSurfacesettlementprediction_Finiteelementmethod_Analyticalmethod_Semi-theoreticalmethod_EPB-TBMtunneling_IstanbulMetroIntroductionIncreasingdemandoninfrastructuresincreasesattentiontoshallowsoftgroundtunnelingmethodsinurbanizedareas.Manysurfaceandsub-surfacestructuresmakeundergroundconstructionworksverydelicateduetotheinfluenceofgrounddeformation,whichshouldbedefinitelylimited/controlledtoacceptablelevels.Independentoftheexcavationmethod,theshort-andlong-termsurfaceandsub-surfacegrounddeformationsshouldbepredictedandremedialprecautionsagainstanydamagetoexistingstructuresplannedpriortoconstruction.Tunnelingcostsubstantiallyincreasesduetodamagestostructuresresultingfromsurfacesettlements,whichareabovetolerablelimits(Bilginetal.2009).Basicparametersaffectingthegrounddeformationsaregroundconditions,technical/environmentalparametersandtunnelingorconstructionmethods(O’ReillyandNew1982;Arioglu1992;KarakusandFowell2003;TanandRanjit2003;Minguezetal.2005;Ellis2005;SuwansawatandEinstein2006).Athoroughstudyofthegroundbysiteinvestigationsshouldbeperformedtofindoutthephysicalandmechanicalpropertiesofthegroundandexistenceofundergroundwater,aswellasdeformationcharacteristics,especiallythestiffness.Technicalparametersincludetunneldepthandgeometry,tunneldiameter–line–grade,singleordoubletracklinesandneighboringstructures.Theconstructionmethod,whichshouldleadtoasafeandeconomicproject,isselectedbasedonsitecharacteristicsandtechnicalprojectconstraintsandshouldbeplannedsothatthegroundmovementsarelimitedtoanacceptablelevel.Excavationmethod,facesupportpressure,advance(excavation)rate,stiffnessofsupportsystem,excavationsequenceandgroundtreatment/improvementhavedramaticeffectsonthegrounddeformationsoccurringduetotunnelingoperations.Theprimaryreasonforgroundmovementsabovethetunnel,alsoknownassurfacesettlements,isconvergenceofthegroundintothetunnelafterexcavation,whichchangestheinsitustressstateofthegroundandresultsinstressrelief.Convergenceofthegroundisalsoknownasgroundlossorvolumeloss.Thevolumeofthesettlementonthesurfaceisusuallyassumedtobeequaltotheground(volume)lossinsidethetunnel(O’ReillyandNew1982).Groundlosscanbeclassifiedasradiallossaroundthetunnelperipheryandaxial(face)lossattheexcavationface(Attewelletal.1986;Schmidt1974).Theexactratioofradialandaxialvolumelossesisnotfullydemonstratedorgeneralizedinanystudy.However,itispossibletodiminishorminimizethefacelossinfull-facemechanizedexcavationsbyapplyingafacepressureasaslurryofbentonite–watermixtureorfoam-processedmuck.Thegroundlossisusuallymoreingranularsoilsthanincohesivesoilsforsimilarconstructionconditions.Thewidthofthesettlementtroughonbothsidesofthetunnelaxisiswiderinthecaseofcohesivesoils,whichmeanslowermaximumsettlementforthesameamountofgroundloss.Timedependencyofgroundbehaviorandexistenceofundergroundwaterdistinguishshort-andlong-termsettlements(Attewelletal.1986).Short-termsettlementsoccurduringorafterafewdays(mostlyafewweeks)ofexcavation,assumingthatundrainedsoilconditionsaredominant.Long-termsettlementsaremostlyduetocreep,stressredistributionandconsolidationofsoilafterdrainageoftheundergroundwaterandeliminationofporewaterpressureinsidethesoil,anditmaytakeafewmonthstoafewyearstoreachastabilizedlevel.Indrysoilconditions,thelong-termsettlementsmaybeconsideredasverylimited.Therearemainlythreesettlementpredictionapproachesformechanizedtunnelexcavations:(1)numericalanalysissuchasfiniteelementmethod,(2)analyticalmethodand(3)semi-theoretical(semi-empirical)method.Amongthem,thenumericalapproachesarethemostreliableones.However,theresultsofallmethodsshouldbeusedcarefullybyanexperiencedfieldengineerindesigningthestageofanexcavationproject.Inthisstudy,allthreepredictionmethodsareemployedforacriticalzonetopredicttheshort-termmaximumsurfacesettlementsabovethetwintunnelsofthechainagebetween0?850and0?900mbetweenEsenlerandKirazlıstationsofIstanbulMetroline,whichis4kminlength.Plaxisfiniteelementmodelingprogramisusedfornumericalmodeling;themethodsuggestedbyLoganathanandPoulos(1998)isusedfortheanalyticalsolution.Afewdifferentsemi-theoreticalmodelsarealsousedforpredictions.Theresultsarecomparedandvalidatedbyfieldmeasurements.Descriptionoftheproject,siteandconstructionmethodThefirstconstructionphaseofIstanbulMetrolinewasstartedin1992andopenedtopublicin2000.Thislineisbeingextendedgradually,aswellasnewlinesarebeingconstructedinotherlocations.OneofthesemetrolinesisthetwinlinebetweenEsenlerandBasaksehir,whichis21.2km.TheexcavationofthissectionhasbeenstartedinMay2006.Currently,around1,400mofexcavationhasalreadybeencompleted.Theregionishighlypopulatedincludingseveralstorybuildings,industrialzonesandheavytraffic.AlignmentandstationsofthemetrolinebetweenEsenlerandBasaksehirispresentedinFig.1.Totallyfourearthpressurebalance(EPB)tunnelboringmachines(TBM)areusedforexcavationofthetunnels.ThemetrolinesinthestudyareaareexcavatedbyaHerrenknechtEPB-TBMintherighttubeandaLovatEPB-TBMinthelefttube.Righttubeexcavationfollowsaround100mbehindthelefttube.SomeofthetechnicalfeaturesofthemachinesaresummarizedinTable1.Excavatedmaterialisremovedbyauger(screwconveyor)throughthemachinetoabeltconveyorandthanloadedtorailcarsfortransportingtotheportal.Sincetheexcavatedgroundbearswaterandincludesstabilityproblems,theexcavationchamberispressurizedby300kPaandconditionedbyapplyingwater,foam,bentoniteandpolymersthroughtheinjectionports.Chamberpressureiscontinuouslymonitoredbypressuresensorsinsidethechamberandauger.Installationofasegmentringwith1.4-mlength(innerdiameterof5.7mandouterdiameterof6.3m)and30-cmthicknessisrealizedbyawing-typevacuumerector.Theringisconfiguredasfivesegmentsplusakeysegment.Afterinstallationofthering,theexcavationrestartsandthevoidbetweenthesegmentouterperimeterandexcavatedtunnelperimeterisgroutedby300kPaofpressurethroughthegroutcannelsinthetrailingshield.Thismethodofconstructionhasbeenproventominimizethesurfacesettlements.Thestudyareaincludesthetwintunnelsofthechainagebetween0+850and0+900m,betweenEsenlerandKirazlıstations.GungorenFormationoftheMiosenageisfoundinthestudyarea.Laboratoryandinsitutestsareappliedtodefinethegeotechnicalfeaturesoftheformationsthatthetunnelspassthrough.Thename,thicknessandsomeofthegeotechnicalpropertiesofthelayersaresummarizedinTable2(Ayson2005).Filllayerof2.5-mthickconsistsofsand,clay,gravelandsomepiecesofmasonry.Theverystiffclaylayerof4misgrayishgreenincolor,consistingofgravelandsand.Thedensesandlayerof5misbrownattheupperlevelsandgreenishyellowatthelowerlevels,consistingofclay,siltandmica.Densesandof3misgreenishyellowandconsistsofmica.Thebaselayerofthetunnelishardclay,whichisdarkgreen,consistingofshell.Theundergroundwatertablestartsat4.5mbelowthesurface.Thetunnelaxisis14.5mbelowthesurface,closetothecontactbetweenverydensesandandhardclay.Thisdepthisquiteuniforminthechainagebetween0+850and0+900m.SurfacesettlementpredictionwithfiniteelementmodelingPlaxisfiniteelementcodeforsoilandrockanalysisisusedtopredictthesurfacesettlement.First,therighttubeisconstructed,andthenthelefttube100mbehindtherighttubeisexcavated.Thisisbasedontheassumptionthatgrounddeformationscausedbytheexcavationoftherighttubearestabilizedbeforetheexcavationofthelefttube.ThefiniteelementmeshisshowninFig.2using15stresspointtriangularelements.TheFEMmodelconsistsof1,838elementsand15,121nodes.InFEmodeling,theMohr–Coulombfailurecriterionisapplied.StagedconstructionisusedintheFEmodel.Excavationofthesoilandtheconstructionofthetunnelliningarecarriedoutindifferentphases.Inthefirstphase,thesoilinfrontofTBMisexcavated,andasupportpressureof300kPaisappliedatthetunnelfacetopreventfailureattheface.Inthefirstphase,TBMismodeledasshellelements.Inthesecondphase,thetunnelliningisconstructedusingprefabricatedconcreteringsegments,whichareboltedtogetherwithinthetunnelboringmachine.Duringtheerectionofthelining,TBMremainsstationary.Oncealiningringhasbeenbolted,excavationisresumeduntilsufficientsoilexcavationiscarriedoutforthenextlining.Thetunnelliningismodeledusingvolumeelements.Inthesecondphase,theliningisactivatedandTBMshellelementsaredeactivated.Whenapplyingfiniteelementmodels,volumelossvaluesareusuallyassumedpriortoexcavation.Inthisstudy,theFEMmodelisrunwiththeassumptionof0.5,0.75,1and1.5%volumelosscausedbytheconvergenceofthegroundintothetunnelafterexcavation.Figures3and4showtotalandverticaldeformationsafterbothtubesareconstructed.TheverticalgroundsettlementprofileaftertherighttubeconstructionisgiveninFig.5,whichisintheshapeofaGaussiancurve,andthatafterconstructionofbothtubesisgiveninFig.6.Figure7showsthetotaldeformationvectors.ThemaximumgrounddeformationsunderdifferentvolumelossassumptionsaresummarizedinTable3.Surfacesettlementpredictionwithsemi-theoreticalandanalyticalmethodsSemi-theoreticalpredictionsforshort-termmaximumsettlementareperformedusingtheGaussiancurveapproach,whichisaclassicalandconventionalmethod.Thesettlementparametersusedinsemi-theoreticalestimationsandnotationsarepresentedinFig.8.Thetheoreticalsettlement(Gaussian)curveispresentedasinEq.1(O’ReillyandNew1982):(1)where,Sisthetheoreticalsettlement(Gausserrorfunction,normalprobabilitycurve),Smaxisthemaximumshort-term(initial,undrained)settlementatthetunnelcenterline(m),xisthetransversehorizontaldistancefromthetunnelcenterline(m),andiisthepointofinflexion(m).Todeterminetheshapeofasettlementcurve,itisnecessarytopredictiandSmaxvalues.Thereareseveralsuggestedmethodsforpredictionofthepointofinflexion(i).EstimationofivalueinthisstudyisbasedonaveragesofsomeempiricalapproachesgiveninEqs.2–6:where,Z0isthetunnelaxisdepth(m),14.5minthisstudy,andRistheradiusoftunnel,3.25minthisstudy.Equation3wassuggestedbyGlossop(O’ReillyandNew1982)formostlycohesivegrounds;Eq.4wassuggestedbyO’ReillyandNew(1982)forexcavationofcohesivegroundsbyshieldedmachines;Eq.5wassuggestedbySchmidt(1969)forexcavationofclaysbyshieldedmachines;Eq.6wassuggestedbyArioglu(1992)forexcavationofalltypesofsoilsbyshieldedmachines.Asaresult,theaverageivalueisestimatedtobe6.6minthisstudy.Thereareseveralsuggestedempiricalmethodsforthepredictionofthemaximumsurfacesettlement(Smax).SchmidtsuggestedamodelfortheestimationofSmaxvalueforasingletunnelin1969asgiveninEq.7(throughArioglu1992):where,Kisthevolumeloss(%).Arioglu(1992),basedonfielddata,foundagoodrelationshipbetweenKandN(stabilityratio)forface-pressurizedTBMcasesasinEq.8:wherecnisthenaturalunitweightofthesoil(kN/m3),theweightedaveragesforallthelayers,whichis19kN/m3inthisstudy;rSisthetotalsurchargepressure(kPa),assumedtobe20kPainthisstudy;rTisTBMfacepressure(kPa),whichis300kPainthisstudy;andCUistheundrainedcohesionofthesoil(kPa),theweightedaveragesforallthelayers,whichis50kPainthisstudyassumingthatCUisequaltoSU(undrainedshearstrengthofthesoil).Allaveragesareestimateduptoverydensesand,excludinghardclay,sincethetunnelaxispassesaroundthecontactbetweenverydensesandandhardclay.Themodelyields17.1mmofinitialmaximumsurfacesettlement.HerzogsuggestedamodelfortheestimationofSmaxvaluein1985asgiveninEq.9forasingletunnelandEq.10fortwintunnels(throughArioglu1992):where,Eistheelasticitymodulusofformation(kPa),theweightedaveragesforallthelayers,whichis30,000kPainthisstudy,andaisthedistancebetweenthetunnelaxes,whichis14minthisstudy.Themodelyields49.9and58.7mmofinitialmaximumsurfacesettlementsfortherightandthelefttubetunnel,whichis100mmbehindtherighttube,respectively.Thereareseveralanalyticalmodelsforthepredictionofshort-termmaximumsurfacesettlementsforshieldedtunnelingoperations(Leeetal.1992;LoganathanandPoulos1998;Chietal.2001;ChouandBobet2002;Park2004).ThemethodsuggestedbyLoganathanandPoulos(1998)isusedinthisstudy.Inthismethod,atheoreticalgapparameter(g)isdefinedbasedonphysicalgapinthevoid,facelossesandworkmanshipvalue,andthenthegapparameterisincorporatedtoaclosedformsolutiontopredictelastoplasticgrounddeformations.Theundrainedgapparameter(g)isestimatedbyEq.12:whereGpisthephysicalgaprepresentingthegeometricclearancebetweentheouterskinoftheshieldandtheliner,isthethicknessofthetailshield,distheclearancerequiredforerectionoftheliner,U*3Distheequivalent3Delastoplasticdeformationatthetunnelface,andwisavaluethattakesintoaccountthequalityofworkmanship.Maximumshort-termsurfacesettlementispredictedbytheoreticalEq.13(LoganathanandPoulos1998):where,tisundrainedPoisson’sratio,assumedtobeofmaximum0.5;gisthegapparameter(m),whichisestimatedtobe0.0128minthisstudy;andxistransversedistancefromthetunnelcenterline(m)anditisassumedtobe0mforthemaximumsurfacesettlement.Themodelyields23.0mmofundrainedmaximumsurfacesettlement.Otherparametersofsettlementsuchasmaximumslope,maximumcurvatureandsoonarenotmentionedinthisstudy.VerificationofpredictionsbyfieldmeasurementsanddiscussionTheresultsofmeasurementsperformedonthesurfacemonitoringpoints,byIstanbulMetropolitanMunicipality,arepresentedinTable4fortheleftandrighttubes.Asseen,theaveragemaximumsurfacesettlementsarearound9.6mmfortherighttubeand14.4mmforthelefttube,whichexcavates100mbehindtherighttube.Themaximumsurfacesettlementsmeasuredaround15.2mmfortherighttubeand26.3mmforthelefttube.HighersettlementsareexpectedinthelefttubesincethepreviousTBMexcavationactivitiesontherighttubeoverlapsthepreviousdeformation.TheeffectofthelefttubeexcavationondeformationsoftherighttubeispresentedinFig.9.Asseen,afterLovatTBMintherighttubeexcavatesnearbythesurfacemonitoringpoint25,maximumsurfacesettlementreachesataround9mm;however,whileHerrenknechtTBMinthelefttubepassesthesamepoint,maximumsurfacesettlementreachesataround29mm(Fig.10).Iftheconstructionmethodappliedtothesiteisconsidered,long-term(consolidation)settlementsareexpectedtobelow,sincethetailvoidisgroutedimmediatelyafterexcavation.TheresultsofpredictionsmentionedaboveandobservedmaximumsurfacesettlementsaresummarizedinTable5.ThemethodssuggestedbyLoganathanandPoulos(1998)andSchmidt(1969)connectedwithArioglu’ssuggestion(1992)canpredictthemaximumshort-termsurfacesettlementsonlyforasingletunnel.PlaxisfiniteelementandHerzog(1985)modelscanpredictdeformationsfortwintubes.Herzog’smodel(1985)yieldshighermaximumsurfacesettlementsthantheobservedones.ThereasonforthatisthatthedatabaseofthemodelincludesbothshieldedtunnelsandNATM(NewAustrianTunnelingMethod)tunnels,ofwhichsurfacesettlementsareusuallyhighercomparedtoshieldedtunnels.Schmidt(1969),alongwithArioglu’ssuggestion(1992),yieldspredictionsclosetoobserved.Plaxisfiniteelementmodelinggivesthemostrealisticresults,providedthereiscorrectassumptionofvolumelossparameter,whichisusuallydifficulttopredict.Themodelprovidessimulationofexcavation,lining,groutingandfacepressureinarealisticmannertopredictsurfaceandsub-surfacesettlements.Thevolumelossparameterisusuallyassumedtobe\1%forexcavationwithfacepressure-balancedtunnelboringmachines.Therealizedvolumelossinthesiteisaround1%forthisstudy.Currently,thereisdifficultyyetinmodelingthedeformationbehavioroftwintunnels.OneofthemostimpressivestudiesonthisissuewasperformedbyChapmanetal.(2004).However,Chapman’ssemi-theoreticalmethodstillrequiresenlargementofthedatabasetoimprovethesuggestedmodelinhispaper.ConclusionsInthisstudy,threesurfacesettlementpredictionmethodsformechanizedtwintunnelexcavationsbetweenEsenlerandKirazlıstationsofIstanbulMetroLineareapplied.Tunnelsof6.5-mdiameterswith14-mdistancebetweentheircentersareexcavatedbyEPMtunnelboringmachines.Thegeologicstructureoftheareacanbeclassifiedassoftground.SettlementpredictionsareperformedbyusingFEmodeling,andsemi-theoretical(semi-empirical)andanalyticalmethods.Themeasuredresultsaftertunnelingarecomparedtopredictedresults.TheseindicatethattheFEmodelpredictswelltheshorttimesurfacesettlementsforagivenvolumelossvalue.Theresultsofsomesemi-theoreticalandanalyticalmethodsarefoundtobeingoodagreementwiththeFEmodel,whereassomemethodsoverestimatethemeasuredsettlements.TheFEmodelpredictedthemaximumsurfacesettlementas15.89mm(1%volumeloss)fortherighttube,whilethemeasuredmaximumsettlementwas15.20mm.Forthelefttube(openedaftertheright),FEpredictionwas24.34mm,whilemeasuredmaximumsettlementwas26.30mm.中文翻译基于盾构法的Istanbul地铁施工引起的地面沉降预测摘要在这项研究中，研究的是双线隧道的短期地面沉降，选取线路里程总长为4km的Istanbul地铁从Esenler站到Kirazl站方向850到900m区间为研究对象。Esenler到Basaksehir站掘进线路总长为21.2km。使用两台刀盘直径为6.5m土压平衡盾构机进行双线掘进，两隧道中心距14m。左隧道先于有隧道100m掘进。使用宽1.4m的管片作为支护。使用Plaxis软件进行沉降的有限元。该软件能模拟地下隧道的掘进、支护和掌子面支护等。针对典型的地质特征进行预测，这些特征是决定地面沉降量的关键因素。研究区域的地质构造从地面向下分别为素填土、硬粘土、密实砂、高密砂和硬质粘土。本文不仅使用有限元分析地面沉降，也使用半理论（半经验）和解析模型进行预测。结果表明该FE模型对给定流失值的短期地面沉降预测效果较好。半理论和解析模型得到结果与FE模型得到的结果一致。将预测结果和实际测量值进行对比分析，得到在掘进过程中，灌浆应在管片支护安装到位后尽快进行。刀盘压力应严密监控并及时调整适应不同地质。Keywords：地面沉降预测；有限元模型；解析方法；半理论方法；土压平衡盾构机；Istanbul地铁介绍随着对基础设施需要的增长，人们对在市区中通过浅埋暗挖修建隧道产生了浓厚兴趣。一些地表和次地表岩土结构的变形使地下工程十分脆弱，这些变形应根据可接受级别得到限制和控制。不论什么掘进方式，短期和长期的地表和次地表层变形都应得到预测，在开挖前要对现有的可能受到破坏的结构采取加固措施。隧道建设成本大量增加主要由于其引起的地面沉降超过了允许值(Bilginetal.2009)。反应地层沉降的基本参数有地质条件、技术/环境参数和隧道掘进或构造方法(O’ReillyandNew1982;Arioglu1992;KarakusandFowell2003;TanandRanjit2003;Minguezetal.2005;Ellis2005;SuwansawatandEinstein2006)。应该以勘探方式进行详细地质调查，弄清地层的物理和机械性质、地下水分布、地层的变形特征，特别是岩层的刚度。技术参数包括：隧道深度、几何形状、隧道直径、单线还是双线隧道和邻近建筑物情况。施工方法应该是安全经济的，其选择应考虑地质条件、技术条件，同时也要考虑将地层移动控制在可接受的范围内。掘进方式、刀盘面压力、推进速度、支护系统刚性、掘进后处理和土体处理/改善在掘进过程中对岩土结构的沉降有很大影响。隧道上方土体移动（地面沉降）的主要原因是在挖掘后土体收敛靠近隧道，由于掘进改变了原来土体的压力平衡状态，导致压力重新分布。土体流失和土体体积流失都认为是土体收敛。地表沉降体积一般假设等于隧道内挖走的土体量(O’ReillyandNew1982)。土体流失可分为围绕隧道外围径向流失和在掘进面的中心轴面流失(Attewelletal.1986;Schmidt1974)。现在实际的径向和轴向体积流失率还不能被完全解释和泛化。但是，能做到的是通过调整刀盘面压力，消除和减少在全断面机械掘进中的掘进面土体损失，如在压力仓加入膨润土与水的混合泥浆或发泡处理的填充物，使其达到平衡等。在相同的施工条件下，颗粒土的土体损失一般大于粘性土。隧道两侧的沉降槽宽度在粘性土案例中较宽，这对于相同量的土体流失，粘性土的沉降最大值较小。基于时变的土体行为和地下水的存在可辨别短期和长期沉降(Attewelletal.1986)。假设土体为不排水，短期沉降发生在挖掘后的几天（最多几周）内。长期沉降主要原因是蠕变，在地下水排出和土内孔隙水压消失后，土体才压力重分布和固结，这个过程也许要经历几个月或几年时间才能达到稳定。在干土条件下，认为长期沉降很有限。对于机械隧道掘进主要有三种沉降预测方法：（1）数值分析，如有限元方法；（2）解析方法和（3）半理论（半经验）方法。其中，数值分析是最可靠的。但是对于一个有经验的岩土工程师来说，在掘进项目阶段，所有方法分析的结果要认真对待。在这项研究中，这三个方法都将被使用来预测研究区域的短期最大地表沉降，这个研究区域在4km长的Istanbul地铁从Esenler站到Kirazl站方向850到900m区间的双线掘进隧道的正上方地面。Plaxis有限元建模程序用于数字建模；这个方法由Loganathan和Poulos(1998)提出用作解析解。一些不同的半理论模型也用作预测。结果与实际测量值进行比较，并得到验证。项目、站点和施工方式概况Istanbul地铁的一期工程开始于1992年，2000建成向公众开放。该线路一直被延长，同时修建了其他多条新线，其中之一就是总长21.2km的Esenler到Basaksehir站的双线隧道。该线掘进施工始于2006年5月。现在大约完成了1400m隧道挖掘。隧道施工区域上方人口稠密，古建筑多，有工业区而且交通量大。该先的线路和车站如图1所示。图一隧道掘进使用四台土压平衡盾构机。研究区域的隧道右线使用Herrenknecht土压平衡盾构机，左线使用Lovat土压平衡盾构机。左隧道掘进面在右隧道后100m。相关机械技术参数如表1所示。表1土压平衡盾构机的参数HerrenkenchtLovat掘进直径6.500m6.564m盾壳外径6.45m6.52m前部盾体7.68m9.30m盾构机长度80m65m总重量578t534t刀盘转速0-2.50-6.0组驱动功率963KW1.622KW钻土类型混合地层混合地层钻头功率630KW900KW最大扭矩435tm445tm最大推力32.000KN54．000KN开挖掉的土体使用钻孔机（螺旋传送机）穿过机器运送到传送带，然后将土体装入出土车运送到竖井。考虑到开挖后土体承受的水压和稳定性问，压力舱轴向压力