土木工程 建筑 外文翻译 外文文献 英文文献 软土地基上分期施工的路堤.docx
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土木工程 建筑 外文翻译 外文文献 英文文献 软土地基上分期施工的路堤.docx
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土木工程建筑外文翻译外文文献英文文献软土地基上分期施工的路堤
Settlementpredictionofembankmentswithstage
LIUSong-yu(InstituteofGeotechnicalEngineering,SoutheastUniversity,Nanjing210096,China)JINGFei(InstituteofGeotechnicalEngineering,SoutheastUniversity,Nanjing210096,China)
Abstract:
Themagnitudeandrateofthesettlementarethekeyelementssubjectedtodesignanalysisofembankmentsonsoftground.Theobservational
InstituteofGeotechnicalEngineering,SoutheastUniversity,Nanjing210096,China
methodsbasedonfieldmeasurementhaveindicatedthepromisingresultsandbecomeeffectivemethodstopredictthefinalsettlement,whiletheuncertaintiesofparametersandtheorieslimitsignificantlytheaccuracyofsettlementestimation.ThispaperpresentsanobservationalmethodtopredictthesettlementperformanceofembankmentswithstageconstructiononsoftgroundbasedonAsaokamethod.Thecasestudiesshowtheaccordanceofthepredictingresultswiththefieldmeasureddata.ItisalsogivenfromthecasestudythatthevalueofEu/Curatiorangesfrom50to100forJiangsuMarineclayanditsactualcoefficientofconsolidationisalmostoneorderofmagnitudelargerthanthelaboratorydata.
Keywords:
settlement,embankment,observationalmethod,stageconstruction
1.Introduction
Settlementandstabilityaretwoprimaryconsiderationssystematicallyrelatedtothedesignofanembankmentonsoftground.Thetoolsavailableforthestabilityevaluationseemtobesatisfactory.Thekeyelementoflongtermbehavioroftheembankmentroutinelysubjectedtodesignanalysisisthesettlement.Inotherwords,thesettlementanalysisisthemostappropriateapproachtotheembankmentanalysis.
Thesettlementsofembankmentsonsoftclaysresultfromtheconsolidationandthelateralflowundertheembankments.Manyresearcheshavebeenmadeonperformanceofembankmentsonsoftground.
Althoughmanyexperienceshaveshownthepracticalvalueofthetheoryforestimatingsettlementsandsettlementsrates,theyalsoillustratedsomeoftheproblemsinvolvedinmakingaccuratepredictionofthesettlement.Duncan(1993)andOlson(1998)analyzedtheuncertaintiescausingtheshortcomingsinthecurrentstateoftheartforsettlementpredictionrespectively.Theseuncertaintiessometimesmakeitdifficultyorimpossibletoestimatethemagnitudeandrateofsettlementforembankments.Althoughthenumericalanalysismaybepossibletoimprovetheaccuracy,thesoilmodelsmayinvolvemanyparametersthatcannotbedeterminedeconomically.However,theevolutionofnumericalmethodswithcomputermayresultinsimplermodelsandcompletecodesthatareincreasinglybecomingavailable.
Itisdesirablethereforetodevelopobservationalmethodsbaseduponwhichthesettlementcanbeestimatedoncesufficientdatahasbeenrecorded.Manyresearchersdevelopedthesettlementpredictionmethodsonfieldmeasurementobservation,whichhaveindicatedpromisingresultsandbecomeanacceptedmethodtoestimatefinalsettlementsandratesofsettlements.
Stageconstructionisatypicalprocedureforembankmentsonthesoftground.Withacertainperiodofconsolidationateverystageconstruction,thesafetyfactoroftheembankmentcanbegenerallyraisedandthepostconstructionsettlementmaybereduced.Thesettlement-timecurveduringstageconstructionmaybemorecomplicatedthanitiswithinstantaneousloading.Theperiodforprimaryconsolidationatadefinitefinalloadwithstageconstructionmaybeincreasedsignificantly,inspiteofthefactthatthepostconstructionsettlementcanbereduced.Inordertospeeduptherateofsettlementandminimizethepostconstructionsecondarysettlementofsoftclays,surchargeisoftenusedinpractice,whichcanbetakenasatypeofstageconstructionwithtemporaryloadingandunloadingstages.
Problemsrelatedtothesettlementanalysisofstageconstructionforembankmentsonsoftclaysareofthefollowingtypes:
(1)Predictionofthedeformationbehaviorofstageconstructionfromtheresultsofboringsandtests.
(2)Predictionofthefinalsettlementatpermanentloadfromthebehaviorofthefirststageconstruction.
(3)Predictionofthepostconstructionsettlementatthepermanentloadandcorrespondingtimeofsurchargeremovedfromthebehaviorofthesurcharge.
Thefirstoftheseproblemsisheavilydependentonthetheory,whichisnecessaryindesign.Theothertwopredictionsrequireempiricalratherthantheoreticalmethodsbecausetheyarebasedonobservationaldata.Inanycase,thefactthatthesecondandthirdpredictionsarederivedfromfieldobservationsmakesthemmorereliablethanthetheoreticalpredictions.
Leroueiletalrevealedtheeffectivestresspathandanalyzedtherelationshipbetweenverticalsettlementandlateraldisplacementduringstageconstruction.StamatopoulosandKotziasdevelopedamethodtodeterminethefinalsettlementatpermanentloadfromthebehaviorofsurcharge,butitisbasedontheelastictheoryanddifficulttocalculatetherateofthesettlement.Thehyperbolicmethodisbasedonthetotalload-settlementrelationshiptopredictthefinalsettlement,whichisnotsensitivetothenatureoftheinitialloadingcondition.
ThispaperpresentedamethodforthepredictionofthefinalsettlementatpermanentloadfromthebehaviorofthefirststageconstructionbasedontheAsaokamethod.
2.Stageobservationalmethod
Asaokaproposedan‘observationalprocedure’toestimatethefinalsettlementandin2situcoefficientofconsolidationfromthefieldobservationaldata.Thismethodisbecomingincreasingpopularbecauseofitssimplicityandeffectivity.
ThemethodisbasedonthefactthatonedimensionalconsolidationsettlementsS0,S1,S2,…,Sjattimes0,
t,2
t,…,j
tcanbeexpressedasafirstorderapproximationby
whichrepresentsastraightlineinaSjvsSj-1plot,where
istheinterceptand
istheslopeoftheline.Whentheultimatesettlementhasbeenreached:
Sj=Sj-1=Sf,therefore,theultimatesettlementSfcanbegivenby
and
ln
=-
(bothtopandbottomdrainage)
ln
=-
(topdrainage)
Theconstant
hasbeensuggestedbyMagnanandDeroytoberelatedtothecoefficientofconsolidationCvasfollows:
forhorizontalradialdrainageonly
forverticaldrainageonly
whereDe,Harethedrainagepathlengthrespectively.
AsaokamethodalsostatedthatthestraightlineinSj-Sj-1spacewouldmovedupinthecaseofmulti-stagedloading,moreover,theshiftedlinesbecomealmostparalleltotheinitialwhenthesettlementisrelativelysmallcomparedtothethicknessofclaylayer.However,itisnotdiscussedandprovidedhowtodeterminetheshiftdistancefromthelineoffirststagetothelineofthenextstage.
Intheexpression
(1),whenj=0thatis:
t=0andS(t=0)=S0,wheretcanbetakenas0fromanytimeafterloadingworks.Iftissetas0attheexacttimeoncetheloadisexerted,then,Sj-1becomes0。
ThismeansthatAsaokamethodcanbeextendedtoobtaintheconstructionsettlement,whichequalstotheintercept
ofthelinerlineinthespaceSj-Sj-1,wheret=0issetjustafterloading.Moreover,thisimmediatesettlementcontributestheshiftdistanceoftheparallellinesduringstageconstruction.
Infact,fromthederivationoftheAsaokamethod,thesettlementofsoillayerscanbeexpressedas
and
whereTandFaretwounknownfunctionoftime.
Withtheverticaldrainageboundaryconditionsandatthegroundsurface,
=T=
(t,z=0).Ift=0,
=
(t=0,z=0)=
=initialelasticstrain.Therefore,S(t=0)=S0givestheimmediatesettlementSe,whichcanalsobeestimatedfromtheelasticmethodbytheequation:
ItisclearlyshownthattheAsaokamethodhasbeenextendedtopredictthesettlementofembankmentswithstageconstruction.Inotherwords,thebehaviorofnextstageconstructioncanbepredictedwiththe
fromthelaststageconstruction.Themorethepreviousstageswithsettlementmeasurement,thehighertheaccuracyofnextstageprediction.Thestageobservationalmethodincludesfollowingsteps:
(1)Sketchobservedtimesettlementcurve.
(2)Chooseatimeinterval
t,whichusuallyrangesfrom10to100days,readthesettlementsSjfromthecurveattimestj(=
tj,j=1,2,3,…).
(3)PlotthesettlementsSj,Sj-1inacoordinatesystemwithaxisSj,Sj-1originatedfrom0.
(4)Fittheplottedpointsbyastraightline,ofwhichcorrespondingslopeisreadas
.TheinterceptattheSjaxisgives
whilethepointofintersectionwiththe45oline,givesthefinalconsolidationsettlementofthefirststage.
(5)Fromthe
ofthefirststageconstructiontodeterminetheundrainedmodulusEubyinverseanalysis(10).
(6)DeterminethenextstageconstructionsettlementwiththeaboveknownEu(10),thusresultingintheshiftdistanceofline.
(7)AssumetheCVremainsconstantduringstageconstructionandsettlementissmallcomparedwiththethicknessofsoftsoils,thismakesthelineofnextstageconstructionparalleltothefirststagewiththeslope
.
(8)Predictingthefinalsettlementofnextstageconstructionfromtheintersectionoftheshiftedlinewiththe45oline.
(9)EstimatetheChandCVfromthevalueof
withtheequation(5)or(6).
3.Casestudy
3.1 Siteandprojectdescription
SectionAofLianxuhighwayisa31kmlonghighstandardexpresswayconnectingtheportcityLianyugangtothenationalhighwaysystemofChina.ItwasbegantoconstructionfromDec.1999.Thereare104bridgesorculvertsorpasswaysinthis31kmlongsectiondesignedtoconnectembankments.Thebottomwidthoftheembankmentis40m,whiletheheightofe
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