隧道与城市轨道交通工程土木外文翻译原文和译文Word格式文档下载.docx
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Abstract
Basedontheanalysesoffundamentalmeteorologicalandhydrogeologicalconditionsatthesiteofatunnelinthecoldregions,acombinedconvection-conductionmodelforairflowinthetunnelandtemperaturefieldinthesurroundinghasbeenconstructed.Usingthemodel,theairtemperaturedistributionintheXiluoqiNo.2Tunnelhasbeensimulatednumerically.Thesimulatedresultsareinagreementwiththedataobserved.Then,basedontheinsituconditionsofsirtemperature,atmosphericpressure,windforce,hydrogeologyandengineeringgeology,theair-temperaturerelationshipbetweenthetemperatureonthesurfaceofthetunnelwallandtheairtemperatureattheentryandexitofthetunnelhasbeenobtained,andthefreeze-thawconditionsattheDabanshanTunnelwhichisnowunderconstructionispredicted.
Keywords:
tunnelincoldregions,convectiveheatexchangeandconduction,freeze-thaw.
AnumberofhighwayandrailwaytunnelshavebeenconstructedinthepermafrostregionsandtheirneighboringareasinChina.Sincethehydrologicalandthermalconditionschangedafteratunnelwasexcavated,thesurroundingwallrockmaterialsoftenfroze,thefrostheavingcauseddamagetothelinerlayersandseepingwaterfrozeintoicediamonds,whichseriouslyinterferedwiththecommunicationandtransportation.SimilarproblemsofthefreezingdamageinthetunnelsalsoappearedinothercountrieslikeRussia,NorwayandJapan.Henceitisurgenttopredictthefreeze-thawconditionsinthesurroundingrockmaterialsandprovideabasisforthedesign,constructionandmaintenanceofnewtunnelsincoldregions.
Manytunnels,constructedincoldregionsortheirneighbouringareas,passthroughthepartbeneaththepermafrostbase.Afteratunnelisexcavated,theoriginalthermodynamicalconditionsinthesurroundingsareandthawdestroyedandreplacedmainlybytheairconnectionswithouttheheatradiation,theconditionsdeterminedprincipallybythetemperatureandvelocityofairflowinthetunnel,thecoefficientsofconvectiveheattransferonthetunnelwall,andthegeothermalheat.Inordertoanalyzeandpredictthefreezeandthawconditionsofthesurroundingwallrockofatunnel,presumingtheaxialvariationsofairflowtemperatureandthecoefficientsofconvectiveheattransfer,LunardinidiscussedthefreezeandthawconditionsbytheapproximateformulaeobtainedbySham-sundarinstudyoffreezingoutsideacirculartubewithaxialvariationsofcoolanttemperature.Wesimulatedthetemperatureconditionsonthesurfaceofatunnelwallvaryingsimilarlytotheperiodicchangesoftheoutsideairtemperature.Infact,thetemperaturesoftheairandthesurroundingwallrockmaterialaffecteachothersowecannotfindthetemperaturevariationsoftheairflowinadvance;
furthermore,itisdifficulttoquantifythecoefficientofconvectiveheatexchangeatthesurfaceofthetunnelwall.Thereforeitisnotpracticabletodefinethetemperatureonthesurfaceofthetunnelwallaccordingtotheoutsideairtemperature.Inthispaper,wecombinetheairflowconvectiveheatex-changeandheatconductioninthesurroundingrockmaterialintoonemodel,andsimulatethefreeze-thawconditionsofthesurroundingrockmaterialbasedontheinsituconditionsofairtemperature,atmosphericpressure,windforceattheentryandexitofthetunnel,andtheconditionsofhydrogeologyandengineeringgeology.
Mathematicalmodel
Inordertoconstructanappropriatemodel,weneedtheinsitufundamentalconditionsasaba-sis.HereweusetheconditionsatthesceneoftheDabanshanTunnel.TheDabanshanTunnelislo-totedonthehighwayfromXiningtoZhangye,southoftheDatongRiver,atanelevationof3754.78-3801.23m,withalengthof1530mandanalignmentfromsouthwesttonortheast.Thetunnelrunsfromthesouthwesttothenortheast.
Sincethemonthly-averageairtemperatureisbeneath0`Cforeightmonthsatthetunnelsiteeachyearandtheconstructionwouldlastforseveralyears,thesurroundingrockmaterialswouldbecomecoolerduringtheconstruction.Weconcludethat,afterexcavation,thepatternofairflowwoulddependmainlyonthedominantwindspeedattheentryandexit,andtheeffectsofthetemperaturedifferencebetweentheinsideandoutsideofthetunnelwouldbeverysmall.Sincethedominantwinddirectionisnortheastatthetunnelsiteinwinter,theairflowinthetunnelwouldgofromtheexittotheentry.Eventhoughthedominantwindtrendissoutheastlyinsummer,consideringthepressuredifference,thetemperaturedifferenceandthetopographyoftheentryandexit,theairflowinthetunnelwouldalsobefromtheexittoentry.Additionally,sincethewindspeedatthetunnelsiteislow,wecouldconsiderthattheairflowwouldbeprincipallylaminar.
Basedonthereasonsmentioned,wesimplifythetunneltoaroundtubeandconsiderthattheairflowandtemperaturearesymmetricalabouttheaxisofthetunnel,Ignoringtheinfluenceoftheairtemperatureonthespeedofairflow,weobtainthefollowingequation:
wheret,x,rarethetime,axialandradialcoordinates;
U,Vareaxialandradialwindspeeds;
Tistemperature;
pistheeffectivepressurethatis,airpressuredividedbyairdensity;
visthekinematicviscosityofair;
aisthethermalconductivityofair;
Listhelengthofthetunnel;
Ristheequivalentradiusofthetunnelsection;
Disthelengthoftimeafterthetunnelconstruction;
,
t,tarefrozenandthawedpartsinthesurroundingrockmaterialsrespectively;
and,arethermalconductivitiesandvolumetricthermalcapacitiesinfrozenandthawedpartsrespectively;
Xx,r,tisphasechangefront;
Lhisheatlatentoffreezingwater;
andToiscriticalfreezingtemperatureofrockhereweassumeTo-0.1℃.
usedforsolvingthemodel
Equation1showsflow.Wefirstsolvethoseconcerningtemperatureatthatthetemperatureofthesurroundingrockdoesnotaffectthespeedofairequationsconcerningthespeedofairflow,andthensolvethoseequationseverytimeelapse.
2.1Procedureusedforsolvingthecontinuityandmomentumequations
Sincethefirstthreeequationsin1arenotindependentwederivethesecondequationbyx
andthethirdequationbyr.Afterpreliminarycalculationweobtainthefollowingellipticequationconcerningtheeffectivepressurep:
Thenwesolveequationsin1usingthefollowingprocedures:
iAssumethevaluesforU0,V0;
iisubstitutingU0,V0intoeq.2,andsolving2,weobtainp0;
iiisolvingthefirstandsecondequationsof1,weobtainU0,V1;
ivsolvingthefirstandthirdequationsof1,weobtainU2,V2;
vcalculatingthemomentum-averageofU1,v1andU2,v2,weobtainthenewU0,V0;
thenreturntoii;
viiteratingasaboveuntilthedisparityofthosesolutionsintwoconsecutiveiterationsissufficientlysmallorissatisfied,wethentakethosevaluesofp0,U0andV0astheinitialvaluesforthenextelapseandsolvethoseequationsconcerningthetemperature..
2.2Entiremethodusedforsolvingtheenergyequations
Asmentionedpreviously,thetemperaturefieldofthesurroundingrockandtheairflowaffecteachother.Thusthesurfaceofthetunnelwallisboththeboundaryofthetemperaturefieldinthesurroundingrockandtheboundaryofthetemperaturefieldinairflow.Therefore,itisdifficulttoseparatelyidentifythetemperatureonthetunnelwallsurface,andwecannotindependentlysolvethoseequationsconcerningthetemperatureofairflowandthoseequationsconcerningthetemperatureofthesurroundingrock.Inordertocopewiththisproblem,wesimultaneouslysolvethetwogroupsofequationsbasedonthefactthatatthetunnelwallsurfacebothtemperaturesareequal.Weshouldbearinmindthephasechangewhilesolvingthoseequationsconcerningthetemperatureofthesurroundingrock,andtheconvectionwhilesolvingthoseequationsconcerningthetemperatureoftheairflow,andweonlyneedtosmooththoserelativeparametersatthetunnelwallsurface.Thesolvingmethodsfortheequationswiththephasechangearethesameasinreference[3].
2.3Determinationofthermalparametersandinitialandboundaryconditions.
Determinationofthethermalparameters.Usingp1013.25-0.1088H,wecalculateairpressurepatelevationHandcalculatetheairdensityusingformulaP/GTwhereTistheyearly-averageabsoluteairtemperature,andGisthehumidityconstantofair.Lettingbethethermalcapacitywithfixedpressure,thethermalconductivity,
andthedynamicviscosityofairflow,wecalculatethethermalconductivityandkinematicviscosityusingtheformulasand.Thethermalparametersofthesurroundingrockaredeterminedfromthetunnelsite.
2.3.2Determinationoftheinitialandboundaryconditions.Choosetheobservedmonthlyaveragewindspeedattheentryandexitasboundaryconditionsofwindspeed,andchoosetherelativeeffectivepressurep0attheexitthatis,theentryofthedominantwindtrendandonthesectionofentrythatis,theexitofthedominantwindtrend,wherekisthecoefficientofresistancealongthetunnelwall,d2R,andvistheaxialaveragespeed.WeapproximateTvaryingbythesinelawaccordingtothedataobservedatthesceneandprovideasuitableboundaryvaluebasedonthepositionofthepermafrostbaseandthegeothermalgradientofthethawrockmaterialsbeneaththepermafrostbase.
Asimulatedexample
Usingthemodelandthesolvingmethodmentionedabove,wesimulatethevaryinglawoftheairtemperatureinthetunnelalongwiththetemperatureattheentrya