英文翻译简版地铁站结构变形

SafetyAnalysisontheStructureofanExistingMetroStationImpacted

bytheConstructionofanAdjacentBuilding

LihengMaa,QinghuaiLiangb,LiuYifancandHeMingrand

BeijingJiaotongUniversity,Beijing,China

amaliheng1984@,bqhliang@,c

liuyifan@

,

dhemingran@

Keywords:metrostation;adjacentconstruction;foundationexcavation;safetyassessment.

Abstract.Structuraldeformationsoftheexistingmetrostationcausedbyadjacentbuildingconstructionshouldbecontrolledstrictlysoastokeepthenormaloperationoftheexistingmetrostationandguaranteethesafetyofthestationstructure.BasedonafoundationpitexcavationandbuildingprojectwhichisadjacenttoanexistingmetrostationinBeijing,a3Dfiniteelementmodeloffoundationpit,metrostationandsurroundingsoilisestablished.Then,thestructuraldeformationsofthemainbodystructure(railarea),thepassagewayandthefirefightingpassagewayindifferentconstructionstagesareobtained.Thecontrolvaluesofthestationstructuredeformationduringbuildingconstructionprocessareproposedaccordingtothecalculationresults.

Introduction

Withthelarge-scaledevelopmentandutilizationofurbanundergroundspaceandtherapidconstructionofurbanrailtransitfacilities,moreandmorehousingprojectsareconstructednearbytheexistingmetrostation.Foundationpitexcavationandnewhousingloadcanaffectthesurroundingsoils,causingstressredistribution,breakingtheinitialequilibriumstateandleadingtodeformationofthestation[1].Inordertoensurethesafetyoftheexistingstation[2],itisnecessarytoassessthestructuralsafety,andchoosethedeformationcontrolvaluesbeforetheconstructionbegins.What’smore,thestructuraldeformationofstationmustbecontrolledstrictlyduringthewholeprocessofconstruction.Manyscholarshadstudiedonthisproblem,andgotsomebeneficialresults[3-6].

Basedonafoundationpitexcavationandbuildingconstructionproject,whichisadjacenttoaexistingmetrostationinBeijing,a3-Dfiniteelementmodelisestablishedinthispaper.Throughmodelingthewholeprocessofconstruction,thedeformationsofmulti-partsofstationstructuralatdifferentconstructionstagesaregotten,andthedeformationcontrolvaluesareproposed,whichisimportanttoensurethesafetyoftheproject.

EngineeringSituation

JIAOMENXIundergroundstationofBeijingmetroline4islocatedatthecrossroadsoftheMAJIAPUXIroadandtheSHILIUZHUANGroad.Thestationrunsnorth-south,andisdouble-layeredandthree-spanned.Thelongitudinalspanofthestation’smainbodyis193.4m,thealtitudeofthestation’sbottomplateis23.5mwhichisabout6mbelowtheground.ThematerialforprimarystationsupportisC20earlystrengthshotcrete;thesecondaryliningmaterialisC35waterproofconcrete,ofwhichtheimpermeabilitygradeisS10;thematerialofcolumnsandjointareaisC50concrete;thebackfillingplainconcreteofstationbottomplateisC15.

Theplanningbuildingisnearbythesoutheastpassageway,three-layerframestructure,oneundergroundlayerandtwoabove-groundlayers.Theplanningfoundationpitis34.5mlong,17.5mwide,and5mdeep.Bothretainingwallsandcantileverpilesforfoundationpitsupportingareneededintheexcavationoperationfortherestrictionofthesurroundingroads,buildingsandarea.Thecantileverpiles,whicharemadeofC25concrete,and0.6mindiameter,8.0minlength,5.0minanchoragelength,1.0minpilespacing,isboredpile.AsshowninFig.1,thereare84cantileverpilesintotal,whicharedistributedaroundthefoundationpit.Theretainingwallsarebrickwallof2.0mhighand240mmthick.Thesectionsizeofconstructionalcolumnsofretainingwallis240mmX240mm,andthecolumnspacingis3.0m.Thewholeconstructionprocesscanbedividedintothreemainsteps:foundationpitexcavationfretainingpileandretainingwallconstructionfnewbuildingconstruction.

Asthehorizontaldistancefromexcavationfoundationpittosoutheastfirefightingpassagewayisonly6.8m,andthefoundationpitlocatesintheprotectedareaoftheurbanrailtrafficaccordingtorelevantregulations,safetyassessmentoftheconstructionprojectisneeded.ThespecificlocationoftheexcavationpitisshowninFig.2.

ScopeofAssessment

The“UrbanRailTransitOperationManagementMethod[7]mentioned“thefollowingareasshouldbesetastheurbanrailtransitprotectedareas:(a)within50mawayfromundergroundstationsandtunnels;(b)within30mawayfromgroundandelevatedstations,aswellasrailwayline;(c)within10mawayfrompassageways,ventilationshaftandotheraccessorystructureofstation."Accordingtotheaboveregulations,theassessmentscopeofthisprojectincludesexcavationpit,thesoutheastpassagewayandfirefightingpassagewayofthemetrostation,andthesouthpartofthestation.Thesizeoftheassessmentareais82mx95.75m,whichisshowninFig.2.Thenorthpartofthestationandtheotheraccessorystructuresarefarawayfromtheexcavationpit,andareseparatedbydeformationjointsbetweenthesestructureswhicharerelativelyindependent,hence,theassessmentmodeldoesnotcontainthesestructures.

ModelandCalculationParameters

HypothesisofModel.Thefollowingassumptionsaredemandedinfiniteelementmodelingcalculation:

Thesurfaceandallthesoilbelowarelayersdistributed,horizontalandhomogeneous.

Thesoilgravityisreckonedinthecalculationofinitialgroundstress;thetectonicstressofsoilisignored.

TheconstitutivemodelofsitesoilisDrucker-Pragermodel.

Soilparametersofthemodelusethemeasuredvaluesofgeologicsurveyreport.

ThematerialstrengthofJIAOMENXIstationreachesthedesigningstrength,andthematerialstrengthdoesn’treduce.

Thematerialofstationstructureiselastic-plasticmaterial.Allthepartsofstationstructureandthesoillayersconformtotheprincipleofdeformationcompatibility.

CalculationParameters.Accordingtothegeologicalsurveyreport,theterrainofconstructionsiteisflat.Groundsurfaceisartificialaccumulationlayerof2.20mto2.80minthickness,themaincomponentsofwhichisclayeysiltandsandysilt.Recentlydepositedlayerisbelowtheartificialaccumulationlayer,whichcontainssandysilt,clayeysilt,finesandandgravel.Undertherecentlydepositedlayerisquaternarysedimentlayerofgravel.ThemeasuredsoilparametersofthegeologicalsurveyreportareshowninTable1.

Groundwaterwasn’tfoundbythedrillingdepthof20.0maccordingtothegeologicalsurveyreport.AccordingtothehydrogeologydataofBeijing,theburieddepthofgroundwaterisabout25mbelowthegroundintherecent3〜5years.Becausetheburieddepthofgroundwaterisdeeperthanthedepthofexcavationpit,sotheinfluenceofgroundwaterisn’tconsidereinthisconstructionproject

FiniteElementModel.ANSYSsoftwareandthree-dimensionalfiniteelementmethodareusedinnumericalsimulationandmodeling.Boundaryconditionsofthestructuremodelstrictlyaccordwiththerequirementsofthetunnelmechanics.Thesurroundingsoilandstructurecaninteractwitheachother.TheSOLID45elementisusedtosimulatethestructureofthemainbody,passageway,firefightingpassageway,surroundingsoil,retainingpileandretainingwall;thegroundsurfaceofthewholemodelisfreeboundary,andtheotherfiveboundariesarenormalconstraint.Thesizeofthewholemodelis82mx95.75mx17m,asshowninFig.3.Fig.4showsthemodelofexcavationpitandthestationstructure,Fig.5showsthemodelofretainingpileandwall.

CalculationResultsandAnalysis

CalculationResultsofInitialSelf-weightStressField.Inordertosimulatetheundisturbedsoilofwhichsettlementhasbeencompletedastheinitialstateofexcavationsimulation,initialself-weightstressfieldneedtobeconstructedinfiniteelementmodelingcalculation.Thecalculationresultsofinitialself-weightstressfieldareshowninfigure6andfigure7.Themaximumsettlementofthewholemodelis7.29mm,whichincludesthefoundationpit,metrostationandsurroundingsoil.Thedistributionofsettlementishorizontal,alongthedirectionofsoillayer.Thesettlementdecreaseswiththedepth.Themaximumsettlementpositionisnearground.

InfluenceofFoundationPitExcavation.Afterthefoundationpitexcavation,thedeformationamplitudesofeachpartofthemodelareshowninTable2,andthedisplacementcontourplotsofthemaximumdeformationdirectionofeachpartarelistedinTable3.

Table2andTable3showthatthemaximumdeformationofthewholemodelisvertical,whichappearsonthesurroundingsoiloffoundationpit,andtheamplitudeis3.9mm.Themaximumdeformationofthemainbodyofstation(railarea)islateral,whichappearsonthejointpositionthatconnectedtofirefightingpassageway,andtheamplitudeis0.04mm.Themaximumdeformationofthepassagewayislateral,whichappearsonthepositionthatclosetothegroundandonthesideoffoundationpit,theamplitudeis0.37mm.Themaximumdeformationofthefirefightingpassagewayisvertical,whichappearsontheperipheralpositionandthepositionthatnearthefoundationpit,theamplitudeis0.23mm.Apparently,theinfluencesofexcavationtothepassagewayandfirefightingpassagewayislargerthantothemainbody,theinfluencetomainbody(railarea)isverysmall.

InfluenceofRetainingPileandRetainingWall.Aftertheretainingpileandretainingwallconstructioncomplete,thedeformationamplitudeandthedisplacementcontourplotsofthemaximumdeformationdirectionofeachmodelpartareshowninTable4andTable5.Itisknownthatthemaximumdeformationofthewholemodelislateral,whichappearsonthesurroundingsoilofretainingwall,andtheamplitudeis3.11mm.Themaximumdeformationofthemainbodyofstation(railarea)islateral,whichappearsontheperipheralpositionandthejointpositionthatconnectedtofirefightingpassageway,theamplitudeis0.04mm.Themaximumdeformationofthepassagewayislateral,whichappearsonthepositionthatclosetothegroundandonthesidenearthefoundationpit,theamplitudeis0.62mm.Themaximumdeformationofthefirefightingpassagewayislateral,whichappearsonperipheralpositionthatnearthefoundationpit,theamplitudeis0.17mm.Whenretainingpileandretainingwallconstructioncomplete,thedeformationofthepassagewayandthefirefightingpassagewayislargerthanthemainbody.Thedeformationofthemainbody(railarea)isverysmall,stillremainsat0.04mm.

TheTable6andTable7showthatthemaximumdeformationofthewholemodelisvertical,whichappearsonthesurroundingsoilofthenewbuilding,andtheamplitudeis4.29mm.

Themaximumdeformationofthemainbody(railarea)isvertical,whichappearsontheperipheralpositionandthepositionthatconnectedtofirefightingpassageway,theamplitudeis0.009mm.Themaximumdeformationofthepassagewayislateral,whichappearsonthepositionthatclosetothegroundandonthesidenearthenewbuilding,theamplitudeis0.87mm.Themaximumdeformationofthefirefightingpassagewayisvertical,whichappearsonperipheralpositionandthepositionthatnearthenewbuilding,theamplitudeis0.14mm.

Apparently,theinfluenceofbuildingloadtothepassagewayandthefirefightingpassagewayislargerthantothemainbody.Thedeformationamplitudeofmainbody(railarea)isverysmallwithonly0.009mm.

SuggestionsonDeformationControlValues

Thedeformationcontrolvaluesofstationisproposedbasedonthecalculationresultsabove,theengineeringexperienceandfieldmonitoringdataofothersimilarprojects,andtheneedofsafetymargin.Thealarmvaluesare80%ofcontrolvalues,andtheprecautionvaluesare70%ofcontrolvalues,whichareshowninTable8.

Conclusions

Duringthewholeprocessofconstruction,themaximumdeformationofstationmainbody(railarea)is0.04mm.Themaximumdeformationappearsonthepositionthatconnectedtofirefightingpassageway,whichhasacertaindistanceawayfromtherail.Atthesametime,thedeformationamplitudeofthestationmainbody(railarea)isverysmallandthesafetymarginisenough,sothethirdpartymonitoringforstationmainbodyisnotnecessary.

Themaximumdeformationofthepassagewayis0.87mm,whichisthemaximumdeformationofthewholestationstructure.Thepassagewayisclosetothefoundationpit,sothethirdpartymonitoringforstationmainbodyissuggestediftheconditionspermit.

Themaximumdeformationofthefirefightingpassagewayis0.23mm,whichisthecloseststructuretothefoundationpit,sothethirdpartymonitoringforstationmainbodyissuggestediftheconditionspermit.

Thedeformationcontrolvaluesofstationareproposedasfollows:0.05mmformainbody;0.9mmforaccesschannel;0.9mmforfirefightingpassageway.Thealarmvaluesare80%ofcontrolvalues,andtheprecautionvaluesare70%ofcontrolvalues.

Whenthedeformationamplitudereachestheprecautionvalues,w