采礦08-3設(shè)計城郊英文原文

20122012PAGE115ResultsandTovalidatetheresultsoftheproposednumericalmethod,threetestcaseswerestudied.Inthefirsttestcase,theresultswerecomparedtotheresultsoftheyticalsolutionofa2Dconductioninahomogeneoussquare-shapedslabofbackfillsurroundedbyconstanttemperaturewalls[10].Thesquareshapedslabofbackfillisonemeterbyonemeterinsizeanditsinitialtemperatureisassumedtobe15℃whilethetemperatureofthesurroundingwallsisassumedtobe5℃.TheresultsofthisstudyaredemonstratedinFig.2a.AsFig.2ashows,thenumericalresultsareinagreementwiththeyticalsolutionof?zisik[10].Thesecondtestcaseisbasicallyidenticaltothefirstoneexceptthatithasaconstantheatsourceof100W/m3insidethebackfillslab.Fig.2bshowstheresultofthistestcase.Itisfoundthatthenumericalresultsagreewiththeyticalsolutionof?zisik[10].Inthethirdtestcase,theresultsoftheproposedmethodwerecomparedtotheresultsofKhokholovandKurilko[6].TheresultsofthistestcaseareshowninFig.3.AccordingtoFig.3,KhokholovandKurilko[6]havereportedhighercentertemperaturesthanthepredictionsoftheproposednumericalmethod.Inordertoexaminethevalidityoftheresults,anenergybalanceassessmentwascarriedoutontheresultsof[6].Inthisassessment,thetotalsensibleheatneededtoachievetheassociatedtemperaturefieldwithinthebackfill,givenintheresultsof[6],wascalculated.Itwasfoundthatthetotalsensibleheatneededwillbe1599kJ/kgofcementwhichis4.77timeslargerthanthecementhydrationheatreportedinKhokholovandKurilko[6](335kJ/kgofcement).Consequently,onecansaythatthetemperatureriseinsidethebackfillandtherockmass,andthethawingeffectduetocementationheatgeneration,areoverestimatedin[6].Fig.2.Resultingcentertemperatureof(a)thefirsttestcaseand(b)thesecondtestInordertogainaclearunderstandingofheattransferandphasechangeinthefillingzoneandtherockmass,webeginwithasimplerockmasszonehavingonlyonestopeexcavationinside.TypicalstopegeometriesemployedwillhavedimensionofL=10mandW=10mandtheinitialtemperatureconditionswillbeconsideredtobeTinit1=15℃andTinit2=10℃whichresembletherealconditionsinpermafrost-impactedmines.Inordertoachievethethermalpropertiesofbackfillandrock,aseriesofexperimentswereconducted.TheconsideredvaluesofthermalpropertiesofrockandbackfillaregiveninTable1.Thecementcontentandthemoisturecontentofthefillmaterialareconsideredtobe200kg/tonneofcementand5%,respectively.Also,assumingtheuseofPortlandcement,therateofheatgenerationduetocementhydrationinbackfillwastakenfrom[6].Theseauthorssuggestedaheatgenerationfunctionwhichisdependentonthetemperatureofbackfill,thecementcontentofbackfillandtime.TheresultingheatsourcetermwascalculatedbyinterpolationbetweenthevaluesgiveninTable2bothintermsoftimeandtemperature.Notethatthevaluesofheat(generatedduetocementhydration)giveninTable2,areinkJ/kgcement.Thismeansthatifthebackfillincludesmorecement,moreheatwillbegeneratedinitduringthecuringperiod.Alltheseassumptionswillcreatethesimplegeometrymodelthatcanbeusedtocreateacomprehensiveinterpretationofpermafrostgenerationinsidebackfill.ThenumericalmodelwasbuiltonthebasisofthismodelthroughthefollowingFig.3.ComparisonofthenumericalresultsandtheresultsofTable1ThermalpropertiesofrockandThermalFrozenUnfrozenSpecificheatcapacityThermalconductivityDensity(kg/mTable2ThevaluesofcementhydrationheatgeneratedinPortlandcementTimeofcuringofcementfilling1237–––Fig.4.TemperaturefieldforsinglestopegeometryindifferentAsthefirststep,aninvestigationonthesizeofthephysicalwasconductedandtheeffectofrockmasssizeonthetemperaturefieldwasstudied.Consequently,itwasobservedthat,asthedimensionsofLbandWbareincreased,theireffectontheresultingtemperaturefieldand esnegligible.Eventually,itwasfoundthatarockmasssizeof50mby50misaproperchoice,resultinginarelativedifferenceof10-6incomparisontoa40mby40msize.Inthenextstep,thesuitablegridsizewasexamined.Insimilarfashiontotheprocedurecarriedoutinthepreviousstep,thenumberofnodes,NxandNy,werechangedandtheireffectsonthetemperaturefieldandRthawwerestudied.Finally,NxandNywerebothchosentobe200inordertomeetthecriteriaofarelativedifferenceof10-6incomparisontoa150by150grid.Also,asensitivitystudywascarriedoutfordeterminingthetimestepandδt=225swasselected.Fig.4showstheresultsofthetemperaturefieldforthistypicalcase.AscanbeseeninFig.4,thegenerationofheatinsidebackfillraisesitstemperatureanddiffusesheatfromfillzonestotherockmass.However,after30days,theheatgenerationeffectisdiminishedandthebackfillbodyiscooleddownandeventuallyfrozen.TheradiusofthawingandthetemperatureofthecenterpointofthebackfillzoneareshowninFig.5.NotethatRthawisaparameterthatisusedtoassessthedepthofthethawaffectedzoneofrock.Thus,asitistheumvalueofthedepthofthawaffectedzone,itmayundergosomespontaneouschangesduetotheextensionofthethawingzoneindifferentdirections.AccordingtoFig.5a,duringthefirstday,Rthawisnegativemeaningthatthebackfillinitiallyzes(evenforthecaseinwhichitactsasaheatsource).Thisisduetothefactthat,accordingtotheemployedheatsourcemodel(Table2),thecementhydrationheatisinitiallynotpowerfulenoughbutgraduallystrengthens.However,Rthawincreasesandreachesaumvalueinapproximay65days.Afterwards,Rthawdecreasesandfinally esnegativemeaningthattheentirerockzoneisfrozenagainandthereforesafe.Ontheotherhand,iftherewasnocementhydrationheat,RthawwouldcontinuouslydeclineuntilalloftheMFMwouldbefrozen.Thisshowsthat,inthiscase,thediffusionofheatfromtheMFMtotherockmasscannotthawtherockmass.However,iftheinitialtemperaturedifferencebetweentheMFMandtherockmasswasbigger,itcouldcontributetothawingtherockmass.Fig.5bshowsthetemperatureprofileofthecenterpointofthebackfillmassfortwocases,thesebeing“withheatsource”and“withoutheatsource”.AccordingtoFig.5b,consideringcementhydration,thetemperaturerisesfromitsinitialvaluetoabout29℃atthecenterofthebackfillduring28days.Afterthat,asthecementhydrationreactionends,thetemperaturewilldeclineandreturnstoitsinitialvalueafteralmost123days.EffectofcementFig.6showstheeffectofcementconsumptiononRthaw.Whentheamountofcementconsumedislow(50and75kgofcementpertonneofbackfill)theheatgenerationwillnotbestrongenoughtomakethawinghappenandtheresultingRthawwillbenegative.Astheamountofcementconsumptionisincreased(to150kgofcementpertonneofbackfillormorewhichisthecaseformostapplicationsinminingoperations),moreheatisgeneratedinsidethebackfillmass,andtheresultingRthawwillbepositive,promotingdeeperbackfillthawingandeventuallylongerwillbethetimethattherockmassneedstozeagain.EffectofinitialFig.7presentstheinfluenceofinitialtemperatureofthefill.Whentheinitialtemperatureofthebackfillincreases,thethawedradius eslargerandittakeslongertocooldown.ForT=5℃,thecoldeduetoinitialheatdiffusionisverysteepandduringthefirst20daysRthawisnegative.However,after20days,theeffectofhydrationheatingthawstherockmassslightlythoughthisriseinRthawwilldiminishafter40days.Astheinitialtemperatureofbackfillincreases,thiseisweakenedandeliminatedatT=25℃.TheinfluenceofinitialtemperatureoftherockmassisshowninFig.8.Itisseenthat,whentheinitialtemperatureoftherockmassis-25℃,Rthawisallnegativeandnothawinghappensintherockmass.However,astheinitialtemperatureoftherockmassrises,thawingwilloccur.Fig.5.(a)Rthawand(b)temperatureincenterpointofback?ll,forasinglestopegeometryminewithandwithoutcementhydrationheat. Fig.6.Effectofcementcontent(kgofcement/toneofbackfill)onRthaw

Fig.7.EffectofinitialtemperatureofbackfillonRthawEffectofpropertiesofrockandTheeffectsofthepropertiesofrockandbackfillonthethawingmechanismisstudiedinthispart.Fig.9showshowthethermalpropertiesofrockcanaffectthepermafrost.Thethermalproperties(heatcapacityandthermalconductivity)ofrockandbackfillweremeasuredinaccordancetoASTMD5334usinganeedleprobe.TheseexperimentswerecarriedoutforrockandbackfillmaterialswhichareoftenfoundinCanadianminesandthepropertiesofwhicharegiveninTables1and4.Theresultsareshownfordifferenttypesofrockmaterial(thepropertiesofwhichareshowninTable3).Fig.9showsthatnothawinghappensforthecasesofDolomiteandGraniterockmaterialsasopposedtoShaleandKimberliterockbodies.Thephysicalinterpretationofthisobservationisthat,inamaterialwithlowthermalconductivity,theheatgeneratedbycementationhydrationcannotbediffusedandwillbestoredintheformoflatentheatinrockresultinginthawing.Inotherwords,ifthethermalconductivityoftherockishigherthan3W/mK,thethawingeffectofbackfillwillbenegligible.Table3ThermalpropertiesofdifferentRock5中國礦業(yè)大學(xué)2012屆本科生畢業(yè)設(shè) 第121 Fig.8.EffectofinitialtemperatureofrockonRthaw.

Fig.9.EffectofthermalconductivityoftherockmaterialonRthawSimilarly,theeffectsofthethermalpropertiesofbackfillareshowninFig.10,whichhappentobeoppositetotheeffectsofrockthermalproperties;Asthethermalconductivityofbackfillincreasesthethawingstrengthens.Table4showsthethermalpropertiesofstudiedbackfills.ItisalsoseenthatthawinghappensforallthebackfillFig.11demonstratesanotherimportantparameterwhichisthewatercontentoftherockmass.Asthisfigureshows,forthecaseofrockhaving5%watercontent,theresultingumRthawis1.5timesofthecaseofrockhaving10%watercontent.Thereasonisthat,asthewatercontentofrockincreases,moreheatenergyandlongertimeisrequiredtothawtherock. Fig.10.EffectofthermalpropertiesoffillingmaterialonRthaw.

Fig.11.EffectofrockwatercontentonEffectofmultiplestope20122012PAGE122Inordertoclarifytheeffectofhavingmultipleadjacentstopesinamineonthawingoftherockmass,twocases,showninFig.1(caseshavingthreeandnineadjacentstopes),wereyzed.Ineachcasethesizeoftherockmass(LbandWb)werechosentobe90mby90mforthreeandninestopescasesandthenumberofnodeswereaccordinglyincreasedtoNx=Ny=360.Thedistancebetweenstopeswaschosentobeequaltothestopesize(d=10m)thusresemblingtwoadjacentprimarystopeswhicharebackfilledsimultaneously.TheresultingtemperaturefieldandthawradiusforthesecasesareshowninFig.12.Thisfigurecomparestheresultsofsingle-stope,three-stopeandnine-stopecasesrevealingthatathree-stopegeometryhasalmostthesamethawingradiusasasingle-stopebutanine-stopegeometryreachesalargerum(0.4m)andcoolsdownmoreslowly.Consequently,theresultsofthismendthatnofurtherexcavationshouldbeperformedbetweenthetwoadjacentbackfilledstopesduringthefirst30daysafterthefillingoperationduetothethawingeffect,whichweakenstherockandmaycreatdamage.backfillbackfillbackfillbackfillbackfillbackfillbackfill3SummaryandAfinitevolumemethodwithharmonicmeaninterpolationofthermalpropertiesofmaterialswasdevelopedtostudythephasechangethatoccursduetobackfillinginfrozenhardrockmines.Inordertomodelthelatentheattransferhappeninginthefrozenrock,theheatcapacity,thermalconductivityanddensityconditionswereassumedtobetemperaturedependent.Theresultingnumericaltechniquethatwasdevelopedisabletosimulatetherockandthebackfillzonesasonebodywithnoneedtoimposeboundaryconditionsbetweenthem.Usingthepre