土木工程毕业论文外文翻译盾构外文原文+中文翻译.docx
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土木工程毕业论文外文翻译盾构外文原文+中文翻译.docx
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土木工程毕业论文外文翻译盾构外文原文+中文翻译
毕业设计(论文)外文文献翻译
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土木工程与建筑系
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盾构
SHIELDS
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SHIELDS
【Abstract】Atunnelshieldisastructuralsystem,usedduringthefaceexcavationprocess.Thepapermainlydiscussestheformandthestructureoftheshield.Propulsionfortheshieldisprovidedbyaseriesofhydraulicjacksinstalledinthetailoftheshieldandtheshieldiswidespreadusedintheundergroundenvironmentwherecannotbeinlongtimestable.Themainenemyoftheshieldisgroundpressure.Non-uniformgroundpressurecausedbythesteeringmayactontheskintendstoforcetheshieldofflineandgrade.Andworkingdecksinsidetheshieldenabletheminerstoexcavatetheface,drillandloadholes.
【Keywords】shieldhydraulicjacksgroundpressuresteeringworkingdecks
Atunnelshieldisastructuralsystem,normallyconstructedofsteel,usedduringthefaceexcavationprocess.Theshieldhasanoutsideconfigurationwhichmatchesthetunnel.Theshieldprovidesprotectionforthemenandequipmentandalsofurnishedinitialgroundsupportuntilstructuralsupportscanbeinstalledwithinthetailsectionoftheshield.Theshieldalsoprovidesareactionbaseforthebreast-boardsystemusedtocontrolfacemovement.Theshieldmayhaveeitheranopenorclosedbottom.Inaclosed-bottomshield,theshieldstructureandskinprovide360-degreegroundcontactandtheweightoftheshieldrestsupontheinvertsectionoftheshieldskin.Theopenshieldhasnobottomsectionandrequiressomeadditionalprovisionisapairofsidedriftsdriveninadvanceofshieldexcavation.Railsorskidtracksareinstalledwithinthesesidedriftstoprovidebearingsupportfortheshield.
Shieldlengthgenerallyvariesfrom1/2to3/4ofthetunneldiameter.Thefrontoftheshieldisgenerallyhoodedtosothatthetopoftheshieldprotrudesforwardfurtherthantheinvertportionwhichprovidesadditionalprotectionforthemenworkingatthefaceandalsoeasepressureonthebreast-boards.Thesteelskinoftheshieldmayvaryfrom1.3to10cminthickness,dependingontheexpectedgroundpressures.Thetypeofsteelusedintheshieldisthesubjectofmanyargumentswithinthetunnelingfraternity.SomeprefermildsteelintheA36categorybecauseofitsductilityandcaseofweldingintheundergroundenvironmentwhereprecisionworkisdifficult.Otherspreferahigh-strengthsteelsuchasT-1becauseofitshigherstrength/weightratio.Shieldweightmayrangefrom5to500tons.MostoftheheaviestshieldsarefoundintheformerSovierUnionbecauseoftheirpreferenceforcast-ironinbothstructuralandskinelements.
Propulsionfortheshieldisprovidedbyaseriesofhydraulicjacksinstalledinthetailoftheshieldthatthrustagainstthelaststeelsetthathasbeeninstalled.Thetotalrequiredthrustwillvarywithskinareaandgroundpressure.Severalshieldshavebeenconstructedwithtotalthrustcapabilitiesinexcessof10000tons.Hydraulicsystemsareusuallyself-contained,air-motorpowered,andmountedontheshield.Workingpressuresinthehydraulicsystemmayrangefrom20-70Mpa.Toresistthethrustoftheshieldjacks,ahorizontalstructuremember(collarbrace)mustbeinstalledoppositeeachjacklocationandbetweentheflangesofthesteelset.Inaddition,somestructuralprovisionmustbemadefortransferringthisthrustloadintothetunnelwalls.Withoutthisprovisionthethrustwillextendthroughthecollarbracestothetunnelportal.
AnEnglishman,MarcBrunel,iscreditedwithinventingtheshield.BrunelsupposedlygothisideabystudyingtheactionoftheTeredonavalis,ahighlydestructivewoodworm,whenhewasworkingattheChathamdockyard.In1818BrunelobtainedanEnglishpatentforhisrectangularshieldwhichwassubsequentlyusestoconstructthefirsttunnelundertheRiverThamesinLondon.In1869thefirstcircularshieldwasdevisedbyBarlowandGreatHeadinLondonandisreferredtoastheGreatHead-typeshield.Laterthatsameyear,BeachinNewYorkCityproducedsimilarshield.Thefirstuseofthecircularshieldcameduring1869whenBarlowandGreatHeademployedtheirdeviceintheconstructionofthe2.1indiameterTowerSubwayundertheRiverThames.Despitethenameofthetunnel,itwasusedonlyforpedestriantraffic.Beachalsoputhiscircularshieldtoworkin1869toconstructademonstrationprojectforaproposedNewYorkCitysubwaysystem.Theprojectconsistedofa2.4mdiametertunnel,90mlong,usedtoexperimentwithasubwaycarpropelledbyairpressure.
Herearesometunnelswhichwerebuiltbyshieldprinciple.
Soft-groundtunnelingSometunnelsaredrivenwhollyormostlythroughsoftmaterial.Inverysoftground,littleornoblastingisnecessarybecausethematerialiseasilyexcavated.
Atfirst,forepolingwastheonlymethodforbuildingtunnelsthroughverysoftground.Forepolesareheavyplanksabout1.5mlongandsharpenedtoapoint.Theywereinsertedoverthetophorizontalbarofthebracingatthefaceofthetunnel.Theforepolesweredrivenintothegroundofthefacewithanoutwardinclination.Afteralltheroofpolesweredrivenforabouthalfoftheirlength,atimberwaslaidacrosstheirexposedendstocounteranystrainontheouterends.Theforepolesthusprovidedanextensionofthetunnelsupport,andthefacewasextendedunderthem.Whentheendsoftheforepoleswerereached,newtimberingsupportwasadded,andtheforepolesweredrivenintothegroundforthenextadvanceofthetunneling.
Theuseofcompressedairsimplifiedworkinginsoftground.Anairlockwasbuilt,thoughwhichmenandequipmentpassed,andsufficientairpressurewasmaintainedatthetunnelfacetoholdthegroundfirmduringexcavationuntiltimberingorothersupportwaserected.
Anotherdevelopmentwastheuseofhydraulicallypoweredshieldsbehindwhichcast-ironorsteelplateswereplacedonthecircumferenceofthetunnels.Theseplatesprovidedsufficientsupportforthetunnelwhiletheworkproceeded,aswellasfullworkingspaceformeninthetunnel.
UnderwatertunnelingThemostdifficulttunnelingisthatundertakenatconsiderabledepthsbelowariverorotherbodyofwater.Insuchcases,waterseepsthroughporousmaterialorcrevices,subjectingtheworkinprogresstothepressureofthewaterabovethetunnelingpath.Whenthetunnelisdriventhroughstiffclay,theflowofwatermaybesmallenoughtoberemovedbypumping.Inmoreporousground,compressedairmustbeusedtoexcludewater.Theamountofairpressurethatisneededincreasesasthedepthofthetunnelincreasesbelowthesurface.
Acircularshieldhasprovedtobemostefficientinresistingthepressureofsoftground,somostshield-driventunnelsarecircular.Theshieldonceconsistedofsteelplatesandanglesupports,withaheavilybraceddiaphragmacrossitsface.Thediaphragmhadanumberofopeningswithdoorssothatworkerscouldexcavatematerialinfrontoftheshield.Inafurtherdevelopment,theshieldwasshovedforwardintothesiltymaterialofariverbed,therebysqueezingdisplacedmaterialthroughthedoorsandintothetunnel,fromwhichthemuckwasremoved.Thecylindricalshelloftheshieldmayextendseveralfeetinfrontofthediaphragmtoprovideacuttingedge.Arearsection,calledthetail,extendsforseveralfeetbehindthebodyoftheshieldtoprotectworkers.Inlargeshields,anerectorarmisusedintherearsideoftheshieldtoplacethemetalsupportsegmentsalongthecircumferenceofthetunnel.
Thepressureagainsttheforwardmotionofashieldmayexceed48.8Mpa.Hydraulicjacksareusedtoovercomethispressureandadvancetheshield,producingapressureofabout245Mpaontheoutsidesurfaceoftheshield.
Shieldscanbesteeredbyvaryingthethrustofthejacksfromleftsidetorightsideorfromtoptobottom,thusvaryingthetunneldirectionleftorrightorupordown.Thejacksshoveagainstthetunnelliningforeachforwardshove.Thecycleofoperationisforwardshove,line,muck,andthenanotherforwardshove.Theshieldusedabout1955onthethirdtubeoftheLincolnTunnelinNewYorkCitywas5.5mlongand9.6mindiameter.Itwasmovedabout81.2cmpershove,permittingthefabricationofa81.2cmsupportringbehindit.
Cast-ironsegmentscommonlyareusedinworkingbehindsuchashield.Theyareerectedandboltedtogetherinashorttimetoprovidestrengthandwatertightness.InthethirdtubeoftheLincolnTunneleachsegmentis2mlong,81.2cmwide,and35.5cmthick,andweighsabout1.5tons.Thesesectionsformaringof14segmentsthatarelinkedtogetherbybolts.Theboltsweretightenedbyhandandthenbymachine.Immediatelyaftertheywereinplace,thesectionsweresealedatthejointstoensurepermanentwatertightness.
Shieldsaremostcommonlyusedingroundconditionwhereadequatestand-uptimedoesnotexist.Theadvantageoftheshieldinthistypeofground,inadditiontotheprotectionaffordedmenandequipment,isthetimeavailabletoinstallsteelribs,linerplates,orprecastconcretesegmentsunderthetailsegmentoftheshieldbeforegroundpressureandmovementbecomeadversefactors.
Oneoftheprincipleproblemsassociatedwithshielduseissteering.Non-uniformgroundpressureactingontheskintendstoforcetheshieldofflineandgrade.Thisproblemisparticularlyacutewithclosedbottomshieldthatdonotrideonrailsorskidtracks.Steeringisaccomplishedbyvaryingthehydraulicpressureinindividualthrustjacks.Iftheshiedistryingtodive,additionalpressureontheinvertjackswillresistthistendency.Itisnotunusualtofindshieldwanderingsev
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