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Plate Composite Foundation of High-Speed Railway

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Plate Composite Foundation of High-Speed Railwayof,OF,Plate,plate,High,Speed

    Plate Composite Foundation of High-Speed

    Railway

    Vo1.18No.1JournalofSouthwestJiaotongUniversity(EnglishEdition)Jan.2010 ArticleID:1005-2429(2010)01-0013-06

    SettlementCharacteristicsofCementFlyAshGravel

    Pile-PlateCompositeFoundationofHigh?SpeedRailway

    ZHUMing(朱明),LENGKuang.dai(冷旷代),MAJianlin(马建林)

    .

    SchoolofCivilEngineering,SouthwestJiaotongUniversity,Chengdu610031,China 2.StateKeyLaboratoryofHydroscieneeandEneering,TsinghnaUniversity,Beijing100084,China

    Abstract

    Fieldtestsonsettlementcharacteristicswerecarriedoutonthecementfly

    ashgravel(CFG)pile.platecompositefoundationon

    Be~ing-XuzhousectionofBeijing-Shanghaihigh

    speedrailway.TheseRlementsofthepilesandthesoilbetweenpileswere measuredandanalyzed.Theresultsshowthatthesettlement

    timedependencyexperiencedthreephases:rapiddevelopmentphase,

    stabledevelopmentphaseandstablephase.Therefore,surchargepreloadingwasnecessarytoreducetheseRlementafter

    construction.ThefiniteelementsoftwarePlaxiswasusedtocalculatethedeformationsofthepiletopandthesoilbetweenpilesat

    theembankmentcenter,aswellasthesettlementsofCFGpilereinforcementareaandtheunderlyingstratumundersurcharge

    preloading.Thecalculationresultsandthefieldtestresultswerecomparedandanalyzed.Boththeresultsshowthatthesettlementof

    thecompositefoundationmainlyoccuredinunderlyingstratum.Thesettlementcharacteristi

csofpileplatecompositefoundation

    underhighembankmentarealsoconcluded.

    KeywordsHighspeedrailway;CFGpile

    platecompositefoundation;Settlementcharacteristics;Fieldtest

    Introduction

    Cementflyashgravel(CFG)pileplatecompos

    itefoundationiscomposedofCFGpiles,soilbetween piles,andcushion.Todate,theCFGpileplatecom

    positefoundationunderrigidfoundationshasbeenex

    tensivelystudied,includingbearingcapacity,deform

    ation,stressratioofpiletosoil,lawofloadtransmis

    sion,cushioneffects,dynamiccharacteristicsandre

    liability,etc.D-6];whileonlyalimitednumberofre

    searches[]focusontheCFGpileplatecomposite

    foundationunderflexiblefoundations.Becausethere isnosophisticatedtheoreticalinvestigationorexperi

    enceavailableOllCFGpile-?platecompositefounda-

    tionunderflexiblefoundations,experimentalresearch ReceivedOct.13,2009;revisionacceptedNov.2,2009 $Correspondingauthor.Te1.:+8613980908891;Email

    925237924@qq.corn

    isstillrequiredfortheconstructionofhigh--speedrail?- waysandpassengerdedicatedfines(PDLs)inChina. Inthispaper,fieldtestswerecarriedouttofind thesettlementlawsofCFGpile-platecompositefoun--

    dationunderembankmentloadinthephasesofcon

    struction,preloadingandserving.Andthesimulation wasmadebyPlaxisforcomparingwiththeresultsof fieldtests

    1FieldTest

1.1Background

    ThenorthlineofBeijing-ShanghaiPDL.Beijing

    Xuzhousection.DK190+l24——DK190+356.2.is

    themainlinewithsoftfoundation.Thissectionis1o. catedbetweentwosupermajorbridgesnamedTianjin andQingcangandontheleftsideofLiyaotracklay- ingbase.Thelandscapeisflatandbroadened.The embankmentsis6.8to7.2minheight,with3.5m 14Journa/ofSouthwestJiaotongUnwers~y(EnglishEdition)

    preloadedoverburden.Thegeoconditionofsoillay

    ersfromtoptobottomiSshowninTable1.

    ThetestmileagewasDK190+140-1189.6.The CFGpileplatecompositefoundationWascomposed ofCFGpilesin18rOWSwim27ineachrow.Thedi. ameterofCFGpileWas0.5mandthedistancebe. tweenpilesWas1.8m.Theelevationofthepiletop Was3.95mandthebottomwasl9.4m.Thepile

    topwascoveredwith0.15mthickhardcorebedand 0.5mthickreinforcedconcreteplate,thewidthof theplatewas23.9m.Thehardcorebedandtwolay- ersofgeogridswhichWas4.5mwideand0.6m thick.werefwcedonbothsidesofthereinforcedCOn. creteplate.Thesectionofthesubgradeisshownin Fig.1.

    Table1Geoconditionofsoillayersinfieldtest :1./:l\:Centerof"",,\1"1.50150subgr~bed:1./Ieftack,\:;nll?ac\'

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    1.2Testandresultsanalysis

    Fig.1Sectionofsubgrade(unit:m)

    ThesettlementanddeformationofCFGpiles weremonitoredandmeasuredusingliquidlevelme

    ters,singlesettlementmeters,andsettlementplates.

    Theloadtimedependencycurvesofembankmentin filingandpreloadingphaseareshowninFig.2and Fig.3,respectively.

    1.2.1Resultsmeasuredbyliquidlevelmeters Liquidlevelmeterswerefixedonthesideslope, shoulder,andcenterlineoftheembankment,theleft

    sideofthesubgradecenterbetweentwopiles,the rightsideofthesubgradecenteroffourpiles,piletop

    andsoilbetweenpilesnearthesubgradecenter.The settlementtimecurvesaleshowninFig.4toFig.7. 250

    l50

    100

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    Fig.2LOadtimecurveinfillingphase

    Date

    Fig.4Settlementtimedependencycurvesofpile topandsoilbetweenpilesnearthetoeofslope Date

    Fig.6Settlementtimedependencycurvesof

    soilbetweentwopilesandfourpiles Theresultsshowthat:

    (1)Thesettlementdifferencebetweenthepiles

andthesoilbetweenpilesattheslopetoe,shoulder

    Date

    Fig.3Loadtimecurveinpreloadingphase Fig.5

    topand

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    Settlementtimedependencycurvesofpile soilbetweenpilesneartheshoulder ?

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    Fig.7Settlementtimedependencycurvesofthepiletop

    ontheleftsideofcenterlineandsoilbetweenpiles

    15

    andsubgradecenterisorderedfrombigtosmallas: slopetoe,shoulder,thensubgradecenter.Atthe sametime,thesettlementdifferenceattheslopetoeis 0

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    16JournalofSouthwestJiaotongUniversity(EnglishEdition) muchbiggerthanthoseattheshoulderandthesub

    gradecenter.Thefillingloadismaximalatthesub

    gradecenteranddiminishattheslopetoe,theloadat theslopetoeisnotuniform,andthereisnoconcrete plateonthecushionattheslopetoe,sothesettlement differencereachesitsmaximumneartheslopetoe whileminimumnearthecenterline.

    (2)Thedifferencebetweensettlementsofpile topontheleftsideofsubgradecenterandontheleft shoulderisonly2.2ITIITIontheexpiryof26days afterunloading.Itcanbeconcludedthatbecausethe reinforcedconcreteplatehomogenizesthestressdistri

    butionofthepiles,settlementsofdifferentpilesunder oneplatedonotvaryalot.

    (3)Becauseoftheconstraintofpiles,thesoil betweentwopileshasbiggerbearingcapacitythan thesoilatthecenteroffourpiles,whichmeansthat

    thesoilbetweentwopilesmusthavebiggerstressbut smallersettlementthanthesoilatthecenteroffour piles.

    (4)Thesettlementmainlyoccursduringloading phaseandreboundstittleafterunloading.Thesettle

    mentdifferencebetweenpileandsoilbetweenpiles keepsconstantduringthefillingphaseandpreloading phase.

    (5)AUcurvesshowthatthesettlementtime

    dependencypassesthroughthreephases:rapiddevel- opmentphase,stabledevelopmentphase,andstable phase,asshowninTable2.Theaveragerateofset- tlementinthethirdphasewas0.019mm/d?

    0.088mm/d,whichsatisfiesthedemandforlaying ballastlesstrackofhigh.speedrailwayt.

    Table2Settlementdevelopmentphases

    NOte:$istheratioofthesettlementatdifferentstagestothetotalsettlementatpiletop

    1.2.2Resultsofsinglesettlementmeters Thecompressiondeformationofthesoilbetween pilesinthereinforcedareaisshowninTable3. Table3Compressiondeformationofthesoil betweenpilesinthereinforcedareamm

    Theresultsshowthat.ontheexpiryof26days afterunloading,thesettlementofsoilbetweenpilesin thereinforcedareawas10.23IILrn.thetotalsettle

    meritwas40.84inl/l(seeFig.4),sothesettlement ofreinforcedareawas74.95%ofthetota1. 1.2.3Resultsmeasuredbysettlementplates ThesettlementdeformadonoftheboRomofsub. gradeinthepreloadingphasemeasuredwithsettle-

mentplateisshowninFig.8.

    Itshowsthatthesettlementcurveisconcave. Thesettlementinthemiddleisbiggerthanthatonthe side.

    Thesettlementofsubgradebodymeasuredwith settlementplateisshowninTable4.Itiscanbeseen thatontheexpiryof260daysafterpreloading,the settlementofsubgradebodyis14.77mm,accounting for2.11%oofthefillingheightf1]hefillingheightis 7.0mhere).

    Table4Settlementofsubgradebodyonthe expiryof260daysafterpreloadingmm

    ZHUMingetal?/SettlementCharacteristicsofCementFly-AshGravelPilePlateComposite.

    

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    Note:Originpointofabscissaisthecenterofembankment. Fig.8Settlementpositiontimecui-veofsoil

    2SimulationbyPlaxis

    2.1Model

    Plaxiswasusedtocalculatethesettlementfor comparingwjththeresultsoffieldtest.Theconsoli

    daft0ntimeiSsetas182dinthecalculation.Thefi

    niteelementmodelisshowninFig.9.

    Fig.9Finiteelementmodel

    2.2Resultanalysis

    2.2.1Subgradebody

    Thesettlementofthesubgradebodyisthesettle. mentdifferencebetweenthetopsectionandthebot

    tomsectionofthesubgrade.Theresultsareshownin l7

    Table5.Thefinalsettlementofsubgradebodyis about10.66m.Theconvergenceofconsolidation processonlytakessixmonths,acceleratedbypreload. ing.Thesubgradebodyisstable,whichisinconsis. tencewiththeresultsmeasuredbysettlementplate. Table5Calculationresultsofsettlementofthesubgradebody 2.2.2Reinforcedarea

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