2023年全國碩士研究生考試考研英語一試題真題（含答案詳解+作文范文）_第1頁
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1、TunnelStabilityAnalysisofTunnelExcavationAspillwaytunnelfanembankmentdamistobeconstructedinapoqualitysstone.Theexcavateddiameterofthetunnelisabout13mthecoverovertheroofis8m.Thetunnelistohavea1.3mthickunreinfcedconcreteli

2、ningafterplacementofthisliftinga28tohighptionoftherockfilldamwillheovertheconstructedtunnel.Thequestionstobeaddressedare:(1)Whatsupptisrequiredindertoexcavatethetunnelsafelyundertheveryshallowcover(2)Istheproposedtophead

3、ingbenchexcavationsequenceusingdrillblastmethodsappropriatefthistunnel(3)Howwilltheconcreteliningrespondtotheloadingimposedbytheplacementof28mofrockfilloverthetunnelIndertoanswerthesequestionsaseriesoftwodimensionalfinit

4、eelementanalyseswerecarriedusingtheprogramPHASE`.Thefirstoftheseanalysesexaminedthestabilitysupptrequirementsfthetopheadingexcavation.Thefinalanalysisincludedtheentireexcavationsupptsequencetheplacementoftherockfillovert

5、hetunnel.Therockmassisapoqualitysstonethatbeingclosetosurfaceisheavilyjointed.ThemechanicalpropertiesassumedfthisrockmassareacohesivestrengthC=0.04Mpaafrictionangleof40amodulusofdefmationE=1334MPa.Noinsitustressmeasureme

6、ntsareavailablebutbecauseofthelocationofthetunnelinthevalleysideithasbeenassumedthatthehizontalstressnmaltothetunnelaxishasbeenreducedbystressrelief.Themodelisloadedbygravityaratioofhizontaltoverticalstress0.5isassumed.A

7、simplifiedversionofthemodelwasusedtoanalysethestabilitysupptrequirementsfthetopheading.Thismodeldidexcludetheconcreteliningthebenchexcavations.Thefirstmodelwasusedtoexaminetheconditionsfafullfaceexcavationofthetopheading

8、withoutanysuppt.Thisisalwaysausefulstartingpointinanytunnelsupptdesignstudysinceitgivesthedesigneraclearpictureofthemagnitudeoftheproblemsthathavetobedealtwith.embeddedintheshotcretewheregroundconditionswereparticularlyd

9、ifficult.Inthecaseofthetopheadinginsstoneunderconsiderationheretheshotcretesolutionwasrejectedbecauseinspiteofthefiniteelementanalysisthedesignersdidnothavesufficientconfidenceintheabilityoftheshotcretelayertosupptthelar

10、gespanofblockysstone.Inadditionthecontractonthisdamprojectdidnothaveagreatdealofexperienceinusingshotcreteintunnelsitwasunlikelythatthewkerswouldhavebeenpreparedtooperateunderacoverofshotcreteonly.Anotheralternativethati

11、scommonlyusedinexcavatingtunnelptalsistousesteelsetstostabilisetheinitialptionofthetunnelunderlowcover.Thissolutionwkswellinthecaseofsmalltunnelsbutinthiscasea13mspantunnelwouldrequireveryheavysets.Anadditionaldisadvanta

12、geinthiscaseisthattheinstallationofsetswouldpermittoomuchdefmationintherackmass.Thisisbecausethesteelsetsareapassivesupptsystemtheyonlycarryaloadwhentherockmasshasdefmedontothesets.Sincethistunnelisindefmationofadamexces

13、sivedefmationisclearlynotacceptablebecauseoftheadditionalleakagepathswhichwouldbecreatedthroughtherockmass.Thesolutionfinallyadoptedwas“browed“fromtheminingindustrywhereuntensionedfullygrouteddowelsarefrequentlyusedtopre

14、suppttherockmassaboveundergroundexcavations.Inthiscaseapattern3mx3mpatternof15mlong60toncapacitycableswereinstalledfromthegroundsurfacebefeexcavationofthetopheadingwascommenced.Whenthesecableswereexposedintheexcavationfa

15、ceplateswereattachedtheexcesscablelengthwascutoff.Inadditiona2mx2mpatternof6mlongmechanicallyanchedrockboltswereinstalledradiallyfromtheroofofthetopheading.TheresultsofananalysisofthissupptsystemareillustratedinFigure18.

16、3Figure18.4whichshowtheextentoftheyieldzonethedefmationsintherockmassabovethetopparingFigure18.1Figure18.3showsthattheextentoftheyieldzoneisonlyreducedbyasmallamountbytheenstallationofthesupptsystem.Thisisnotsurprisingsi

17、ncesomedefmationoftherockmassisrequiredindertomobilizethesupptingloadsintheuntensionedcables.Thisdefmationoccursasaresultoffailureoftherockmass.Figure18.4showsthatthedisplacementsintheroofofthetopheadinghavebeenreducedsu

18、bstantiallyasaresultoftheplacementofthesuppt.Howeverasmallproblemremainsthatistheexcessivedisplacementoftherockbetweentherockboltfaceplateswhicharespacedona2mx2mgrid.Unlessthisdisplacementiscontrolleditcanleadtoprogressi

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