铁路基础设施(英文简介)

IntroductionTrackisthebaseuponwhichtherailwayruns.Togiveatrainagoodride,thetrackalignmentmustbesettowithinamillimeterofthedesign.Trackdesignandconstructionispartofacomplexandmulti-disciplinaryengineeringscienceinvolvingearthworks,steelwork,timberandsuspensionsystems-theinfrastructureoftherailway.Manydifferentsystemsexistthroughouttheworldandtherearemanyvariationsintheirperformanceandmaintenance.Thispagelooksatthebasicsofinfrastructureandtrackdesignandconstructionwithdrawings,photosandexamplesfromaroundtheworld.SomeinformationwascontributedbyDanMcNaughton,SimonLoweandMikeBrotzman.ContentsBackground-BasicConstruction-TheSub-Structure-Ballast-Track-Sleepers(Ties)-Rails-RailWelding-Gauge-ModernTrackForms-BallastedvsNon-BallastedTrack-Structures-Gauging-MonumentsandDatumPlates-Curves-Cant-Turnouts-Crossings-TypesofTurnouts-ExamplesofTurnouts.BackgroundThetrackisafundamentalpartoftherailwayinfrastructureandrepresentstheprimarydistinctionbetweenthisformoflandtransportationandallothersinthatitprovidesafixedguidancesystem.Thetrackisthesteeringbaseforthetrainandhasevolvedfromanancientdesignofvehicleguidancewithoriginsdating,somehistorianshavesuggested,fromtheSumeriancultureof2000BC.Themodernrailwayversionisbasedonthesteelwheelrunningonasteelrail.Otherformsofguidedvehicletechnologyexist;rubber-tyredtrains,magneticlevitationandguidedbusways,forexample,butthesearenotdealtwithhere.ThereisagooddescriptionoftheFrench-basedrubbertyredtraintechnologyavailableatTheRubberTyredMetro.BasicConstruction(thisfuckingpic！)Trackisthemostobviouspartofarailwayroutebutthereisasub-structuresupportingthetrackwhichisequallyasimportantinensuringasafeandcomfortablerideforthetrainanditspassengersorfreight.Theinfrastructurediagramhereshowstheprincipalpartsofanelectrified,double-trackline.Thetotalwidthacrossthetwo-trackalignmentwillbeabout15m(50ft)foramodernformation.The"cess"showneachsideofthealignmentistheareaavailableforawalkwayorrefugeforstaffworkingonthetrack.TheSub-StructureThispartoftheroadconsistsofthreemainelements;theformation,thesub-ballastandtheballast.Theformationisthegrounduponwhichthetrackwillbelaid.Itcanbethenaturalgroundlevelor"grade"oritcanbeanembankmentorcutting.Itisimportantthattheformationismadeoftherightmaterialsandisproperlycompactedtocarrytheloadsofpassingtrains.Theformationunderthetrackhasa"camber"ratherlikethatseenonaroadway.Thisistoensureeaseofwaterrun-offtothedrainsprovidedoneachsideoftheline.Thetrackitselfissupportedon"ballast",madeupofstones-usuallygraniteor,intheUS,basalt-belowwhichisalayerofsand,whichseparatesitfromtheformation.Forneworrenewedformations,thesandisnormallylaidoversomesortofgeotechnicalscreenormeshtoseparateitfromthefoundationmaterialbelow.Inthepast,asphaltorplasticsheetinghasbeenusedtopreventwaterseepage.Catenarymasts(ifthelineiselectrifiedontheoverheadsystem)arelocatedoutsidethedrainsand,beyondthem,thereisawalkwayarea.Thismayjustbeaclearedpathforstafftowalksafely,avoidingpassingtrainsor,onmodernisedroutes,aproperlyconstructedpath.Nexttothispathwillbeacabletrough.Thesewereoriginallyconcretebutarenowadaysoftenmadeofplastic.Cablescrossingthetrackareprotectedbyaplastictube,usuallybrightorangeintheUK.Propercableprotectionisessentialtopreventdamagebyanimals,trackmaintenancetools,weatherandfire.Usually,theedgeoftherailwaypropertyisoutsidethepathwayorcableruns.Ifthelineisbuiltthroughanarearequiringanembankmentorcutting,theslopeswillbecarefullydesignedtoensurethattheangleofslopewillnottakeanexcessivewidthoflandandallowproperdrainagebutwithoutriskinganearthslip.Theslopeangledependsonthetypeofsoilavailable,theexposure,theclimateandthevegetationinthearea.Drainageditchesareoftenaddedalongtheedgesofcuttingsandembankments.IntheUK,fencesarealwaysprovidedalongtheboundarylineoftherailwaytoprotectthepublicfromwanderingontothetrack.Evenso,thereareafewaccidentseveryyearwhentrespassersarekilledorinjuredbytrainsorelectricconductorrails.Manycountriesaroundtheworlddon'tfencetheirrailways,assumingpeoplewilltreatthemlikeroadsandlookbothwaysbeforecrossing.Theydon't.BallastBallastisprovidedtogivesupport,loadtransferanddrainagetothetrackandtherebykeepwaterawayfromtherailsandsleepers.Ballastmustsupporttheweightofthetrackandtheconsiderablecyclicloadingofpassingtrains.Individualloadsonrailscanbeashighas50tonnes(55USorshorttons)andaround80short

tonsonaheavyhaulfreightline.Ballastismadeupofstonesofgraniteorasimilarmaterialandshouldberoughinshapetoimprovethelockingofstones.Inthiswaytheywillbetterresistmovement.Ballaststoneswithsmoothedgesdonotworksowell.Ballastwillbelaidtoadepthof9to12inches(upto300mmonahighspeedtrack).Ballastweighsabout1,600to1,800kg/cu/m.SeealsoBallastedvsNon-BallastedTrackbelow.TrackTheusualtrackformconsistsofthetwosteelrails,securedonsleepers(orcrossties,shortenedtoties,intheUS)soastokeeptherailsatthecorrectdistanceapart(thegauge)andcapableofsupportingtheweightoftrains.Therearevarioustypesofsleepersandmethodsofsecuringtherailstothem.Sleepersarenormallyspacedat650mm(25ins)to760mm(30ins)intervals,dependingontheparticularrailway'sstandardrequirements.Sleepers(Ties)4Traditionally,sleepers(knownastiesintheUS)arewooden.Theycanbesoftwoodorhardwood.MostintheUKaresoftwood,althoughLondonUndergroundusesahardwoodcalledJarrahwood.Sleepersarenormallyimpregnatedwithpreservative(注入防腐剂)and,undergoodconditions,willlastupto25years.Theyareeasytocutanddrillandusedtobecheapandplentiful.Nowadays,theyarebecomingmoreexpensiveandothertypesofmaterialshaveappeared,notablyconcreteandsteel.4 '■Concreteisthemostpopularofthenewtypes(left).Concretesleepersaremuchheavierthanwoodenones,sotheyresistmovementbetter.Theyworkwellundermostconditionsbuttherearesomerailwayswhichhavefoundthattheydonotperformwellundertheloadsofheavyhaulfreighttrains.Theyofferlessflexibilityandareallegedtocrackmoreeasilyunderheavyloadswithstiffballast.Theyalsohavethedisadvantagethattheycannotbecuttosizeforturnoutsandspecialtrackwork.Aconcretesleepercanweighsupto320kg(700lbs)comparedwithawoodensleeperwhichweighsabout100kgor225lbs.Thespacingofconcretesleepersisabout25%greaterthanwoodensleepers.Typicalconcretesleepersareshowninthephotobelow:

■—FlF--tai—fWiJ!WaWHiBrAnothertypeofconcretesleeperisshowninthisdrawing.Thisisthetwin-blocksleeper.■—FlF--tai—fWiJ!WaWHiBrThedesignconsistsoftwoconcreteblocksjoinedbyasteelbar.Itis30%lighterthanaregularconcretesleeper,allowingittobemovedmanually.ItispopularinFrance(whereitiscalledStedef)andforsomelightertrackformslikethoseusedfortramwaysystems.HereisanexampleinSheffield.Itshowstwinblockandwoodensleepersinthesametrack.Thesleepersshownintheabovephotoaresupplementedwithwoodensleepersatthecrossover,becauseitiseasiertocutthetimbertothecorrectsize.Sleepersatcrossoversandturnoutsvaryinsizeaccordingtotheirpositioninthelayout.Steelsleepersarealsonowusedonmorelightlyusedroads,buttheyareregardedassuitableonlywherespeedsare100mi/h(160km/h)orless.IntheUSmosttiesaremadeofoaksoakedincreosote,costonaveragebetween$22-$29each.Iitusedtobeupto$35-$40pertieinthelate80's.Theycanlastupto20years.MostClass1RR'swillreplacethemafter5-10yearsandthensellthemasused.Concretetiesare$42dollars.TheyarepopularinthewesternUSandonpassengerlinesintheeast.Recently,compositetieshavecomeonthemarket.Theyaremadeofsomethinglikeoldtiresandrecycledplastic.Theycanbeusedandspikedlikeregualarties,costabout50%lessandsaveontrees.RailThestandardformofrailusedaroundtheworldisthe"flatbottom"rail.Ithasawidebaseor"foot"andnarrowertopor"head".TheUKintroducedatypeofrailwhichwasnotusedelsewhere-apartfromafewUKdesignedrailways.Thiswasknownas"Bullhead"railandisshownincomparisonwiththestandardtypeinthediagramleft.Bullheadrailwasoriginallydesignedwithreuseinmind.Itwasintendedthatitwouldbeturnedoverwhenthetophadwornbutthisprovedimpossiblebecause

theundersidealsoworewhereithadbeensecuredtothesleeper.Bullheadrailhastobemountedinaspecial"chair"madeofcastironandsecuredbya"key"wedgedbetweentherailwebandthechair.Thechairsaresecuredtothesleepersby"coachscrews".Thearrangementcanbeseeninthefirstphotobelow:BullheadRailsFlatbottomrailBullheadRailsFlatbottomrailThesecondphotoaboveshowsaflatbottomrailclippedtoabaseplateundertherail.Flatbottomrailscanalsobe"spiked"directlytothesleepers.Awideheadednailisdrivenintothesleeperoneachsideoftherailsothatthefootoftherailisheldbytheheadsofthespikes.LongstretchesoftrackwerelaidinrecordtimesacrosstheUSinthepioneeringdaysofrailroaddevelopmentusingthismethodofsecuringrailsto"ties".Nowadays,heavierloadsandfastertrainsrequiremoresophisticatedsystems.Normally,therailrestsonacaststeelplatewhichisscrewedorboltedtothesleeper.Therailisattachedtotheplatebyasystemofclipsorclamps,dependingonthedesign.TheolderUKstandarddesignwasanelasticspikewithasprung,curvedtopwhichsecurestherail.Thereareanumberofvariationsseenaroundtheworld.Oneofthemostpopularisthe"Pandrol"clipseenabove.Aresilientpadwillbeprovidedbetweentherailandthebaseplateandaroundthesecuringclip,whererequiredtoprovideinsulationforthetrackcircuits,ifinstalled.TheinfrastructureowningcompanyintheUK(currentlyknownasNetworkRail),hasadoptedUIC60rail(whichweighs60kg/mor125lb/yd)asitsstandardforhighspeedlines.ThepresentstandardisequivalenttotheUIC54rail,whichweighsabout113lbs/ydor54kg/m.Didyouknow,thereare2,400sleepers(ties)inamileoftrack?IntheUS,railweightvarriesfrom80-90lb/yd(pounds/yard)insmallyardsto100-110lb/ydonlightdutytrackandbetween130and141lbsonheavydutytrack.Railof141lbsisthenewmainlinestandard.ThePennsylvaniaRRusedaspecial155lb/ydrail,whichwastheheaviesteverrolledformainlineoperations.Someofitisstillinplacewith8-boltjointsinsteadofthemoreusual6-boltjoints.Itisoveraninchtallerthancomparable141poundrail.Highestpricesteelrailcosts$700aton(2000lbs).A133poundrailcosts$46.55peryard(0.92m.).Oldertrackisjointed.IntheUK,about35%oftrackisstilljointed,althoughthisiscontinuouslyfallingasnewrailisinstalled.RailswerenormallylaidinstandardlengthsboltedtogetherbywhatarecalledfishplatesintheUKorsplicesintheUS.Thejointsallowedsufficientspaceforexpansionastheywereprovidedat60footintervalsintheUKand39footintheUS,allowingthemtobecarriedinastandard40ftflatwagon.ThejointswerealwaysstaggeredintheUSwhereastheUKplacedthemsidebyside.TheresultoftheUSstaggeredjointscanbeseeninthecuriousrollingmotionoffreightcarsrunningonpoorlymaintainedtrack.Thereasonforthestaggeringisthat,intheUSitwasdeterminedthatafterjointedrailhasbeeninplaceforatimeitstartstodropandcreatesadepression.Whenawheelfallsintothedepressionandbeginstoclimboutagainitexertsaforce.Ifthetwojointswereinparallelthisforcewouldbemuchlargerandthejointsmightsnap.ThisisnotconsideredaproblemintheUKandEurope,probablybecauseofthelighteraxleloads.Nowadays,railisweldedintolonglengths,whichcanbeuptoseveralhundredmetreslong.Expansionisminimisedbyinstallingandsecuringtherailsintension.Providedthetensionisadjustedtothecorrectlevel,equivalenttoasuitablerailtemperaturelevel,expansionjointsarenotnormallyneeded.Specialjointstoallowrailadjustmentareprovidedatsuitablelocationsasshowninthephotobelow:Adjustmentswitchesarealsoprovidedtoprotectturnoutsandatlocationswhereachangeintheraildesignorsizeoccurs.Railtendstocreepinthemaindirectionoftravelso"railanchors"("anti-creepers"intheUS)areinstalledatintervalsalongthetrack.Theyarefittedundertherailagainstabaseplatetoactasastopagainstmovement.RailWeldingModerntrackworkuseslongweldedraillengthstoprovideabetterride,reducewear,reducedamagetotrainsandeliminatethenoiseassociatedwithrailjoints.Railweldingisacomplexart(orscience)dependingonhowyoufeelaboutit.Therearetwomaintypesofweldingusedforrails:ThermitweldingandFlashButtwelding.GaugeThestandardtrackgauge-thedistaneebetweenthetworails-is4ft.8%inor1435mm.butmanyothergauges,widerandnarrowerthanthis,areinusearoundtheworld.Gaugeisoftenintentionallywidenedslightlyoncurvedtrack.ThereissomeadditionalinformationonTrackGaugesatthePacificSouthwestRailroadMuseumsite.ModernTrackFormsTherearenowarangeofmoderntrackformsusingaconcretebase.Theyaregenerallyusedinspeciallocationssuchastunnelsorbridgeswherearigidbaseisrequiredtoensuretrackstabilityinrelationtothesurroundingstructures.Thistypeoftrack,usuallycalled"slabtrack"or"non-ballasted"track,oftenappearsasshowninthediagrambelow:«jj_Theearthmatisasteelmeshscreenprovidedonelectrifiedrailwaystotrytokeepstrayreturncurrentsfromconnectingtoutilitiespipesandnearbysteelstructures.Earthingmustbestrictlycontrolledotherwiseseriousandexpensiveproblemswilloccur,mademoreseriousandexpensivebecausetheyinvolveotherpeople'sproperty.Someslabtracksystemshavethesleepersrestingonrubberorsimilarpadssothattheybecome"floatingslabtrack".Floatingtrackisusedasawayofreducingvibration.HongKongMassTransitRailwayisfondofit,sinceitslinesrunthroughverydenselypopulatedareas.BallastedvsNon-BallastedTrackThebasicargumentfordifferenttrackdesignswillbebasedonthebottomline-cost;costofinstallationandcostofmaintenance.Therearehowever,otherissuessuchasenvironment-noise,dustandvibration-orengineeringissuessuchasspace,location,climateandthetypeofserviceintendedforthetrack.Thereareawidevarietyoftrackformsandsystemsincorporatingsomeformofconcretebaseorsupportwhichdoesn'tneedballast.Almostalloftheserequirelessdepthofconstructionthanballastedtrack.However,theaccuracyofinstallationmustbehigherthanthatneededforballastedtrack.Slabtrackwillnotbeadjustedafterinstallationbutballastcanbepackedtoaligntrackasrequired.Theabilityofballasttoallowtrackrealignmentisoneofitsmostseriousweaknesses.Thelateralmovementcausedbypassingtrainsoncurvedtrackisoneofthemajorcausesofmaintenancecostsaddedtowhichisthecrushingcausedbyaxleweightanddamageduetoweatherandwater.Ballastdamageleadstotracks"pumping"asatrainpassesand,eventually,railorsleeperdamagewilloccur,tosaynothingofthereducedcomfortinsidethetrainandtheadditionalwearonrollingstock.Apartfromregularrepackingor"tamping",ballastwillhavetobecleanedorreplacedeveryfewyears.Anotheraspecttotheballastedtrackdesign,isthedustwhichiscausedduringinstallationandasitwearsorgetscrushed.Itdoeshowever,offerausefulsounddeadeningquality.Fixedtrackformationsusingslabtrackoraconcretebaseofsomesortdonotsufferfromsuchproblems.However,theinstallationofslabtrackisreportedtocostabout20%morethanballastedtrack.Tobalancethiscost,themaintenancecostshavebeenquotedasreducedby3to5timesthatofballastedtrackonahighspeedlineinJapan.Iflowlevelsofuseareforeseen,oriflowcapitalcostisamoreimportantrequirement,ballastedtrackwouldbethechoice.Foraheavilyusedrailway,particularlyoneinastructurallyrestrictedarealikeatunnelorviaduct,non-ballastedtrackmustbethebestoptionongroundsoflowmaintenancecostandreducedspacerequirements.However,caremustbetakenduringdesignandinstallationtoensurethebestoutofthesystem.StructuresToensurethatthepathrequiredforthepassageoftrainsiskeptclearalongtherouteofarailway,a"structuregauge"isimposed.Thishastheeffectofformingalimitofbuildinginsidewhichnostructuresmayintrude.Thelimitincludesnotonlythingslikewalls,bridgesandcolumnsbutalsopipes,cables,bracketsandsignalposts.The"structuregauge"willvarywiththecurvatureofthelineandthemaximumspeedsallowedalongthesectioninquestion.Althoughthecivilengineerispreventedfromallowinghisstructuretointrudeintothetrainpath,therollingstockengineeralsohaslimitsimposedonthespacehistrainmayoccupy.Thisspaceisreferredtoasthe"kinematicenvelope".Thisareadesignatesthelimitsthetraincanmovelaterallyandverticallyalongtheroute.Asforthestructuregauge,thekinematicenvelopewillbeaffectedbyspeedandfeaturesoftraindesignsuchasthebogiesuspensionandspecialsystemsitmayhaveliketilting.GaugingThelineofroutehastobecheckedfromtimetotimetoensurethatthestructuresarenotinterferingwiththegauge.Alineisalwaysgaugedwhenanewtypeofrollingstockistobeintroduced.Itisimportanttoseethatthesmallvariationsintrackposition,platformedge,cableductlocationandsignalequipmenthasn'tbeenallowedtocreepinwardsduringmaintenanceandrenewalprogrammes.Gaugingusedtobedonebyhandlocally(andstillisfromtimetotimeinspecialcircumstances)butnowadays,itismostlydonewithaspecialtrain.Thetrainusedconsistofaspecialcarwithawoodenframebuiltalmosttothegaugelimits.Theedgesoftheframewerefittedwithleadfingerssothat,iftheyhitanythingasthetrainmovedalong,theywouldbendtoindicatethelocationanddepthofintrusion.Moderngaugingtrainsarefittedwithopticalorlaserequipment.Theopticalsystemuseslightstospreadbeamsoflightoutfromthetrainasitrunsalongtheline.Suitablymountedcamerasrecordthebreaksinthelightbeamstoprovidethegauginginformation.Thetraincanrunatupto50mi/h(80km/h)but,ofcourse,therunshavetobedoneatnight.Laserbeamsarealsousedbut,astheyrotateroundthetrainandforma"spiral"oflight,themethodsuffersfromgapswhichcanallowintrusionstobemissed.MonumentsandDatumPlatesAlongthelineofroutevariouslocationsaremarkedbyafixedpostinthetrackoraplateonanearbystructuretoindicatethecorrectlevelorpositionofthetrack.Thesearecalledmonumentsordatumplates.Measurementsaretakenfromthesetoconfirmthecorrectpositionofthetrack.CurvesCurvesinthetrackarealmostascienceontheirown.Carefulcalculationsarerequiredtoensurethatcurvesaredesignedandmaintainedproperlyandthattrainspeedsareallowedtoreachareasonablelevelwithoutcausingtoomuchlateralstressonthetrackorinducingaderailment.Therearebothverticalcurvesandhorizontalcurves.Thereisalsoasectionoftrackoneithersideofacurveknownasthetransition,wherethetrackischangingfromstraighttoacurveorfromacurveofoneradiustooneofanotherradius.CantCantisthenameusedtodescribethecrosslevelangleoftrackonacurve,whichisusedtocompensateforlateralforcesgeneratedbythetrainasitpassesthroughthecurve.Ineffect,thesleepersarelaidatananglesothattheouterrailonthecurveisatahigherlevelthantheinnerrail.IntheUS,itisknownassuperelevation.Ofcourse,therewillusuallybetrainsofdifferenttypes,permittedspeedsatdifferentlevels,whichtravelthesamecurve.Also,therewillbeoccasionswhentrainsstoponthecurve.Thismeansthatthedegreeofcanthastobefixedatacompromisefiguretoallowthesafetyofstoppedtrainsandthebestspeedsforallthetrainsusingthecurve.Inpractice,fastertrainsareallowedtotravelroundthecurveataspeedgreaterthantheequilibriumlevelofferedbythecantsetting.Passengerswillthereforefeelalateralaccelerationsimilartowhattheywouldfeeliftherewasnocantandthetrainwastravellingatalowerspeedroundthecurve.Thedifferencebetweentheequilibriumcantrequiredbythehigherspeedandtheactualcantisknownasthecantdeficiency.Cantismeasuredeitherindegreesorinlineardimensions.Onstandardgaugetrack(1435mmor4ft.8%ins.)150mmor6ins.ofcantisequalto6degrees.ThisisthenormalmaximumintheUK.Themaximumamountofcantdeficiencyallowedis110mm(4%ins.).Turnouts"turnout"todescribethejunctionsin"turnout"todescribethejunctionsintrackworkwherelinesdivergeorconvergesoastoavoid"points"(UK)or"switches"(US),bothofwhichtermscanbeconfusing.Intherailway"trade",turnoutsarereferredtoas"switchandcrossingwork".Aturnoutconsistsofanumberofpartsasfollows:Themovingpartoftheturnoutistheswitch"blade"or"point",oneforeachroute.Thetwobladesarefixedtoeachotherbyatiebartoensurethatwhenoneisagainstitsstockrail,theotherisfullyclearandwillprovideroomforthewheelflangetopassthroughcleanly.Eithersideofthecrossingarea,wingandcheckrailsareprovidedtoassisttheguidanceofthewheelsetsthroughthecrossing.Crossingscanbecastorfabricated.Railsaresteelwithalargeironcontentbutalittlemanganeseisaddedtocrossingsandsomeheavilyusedrailstoincreaseresistancetowear.Belowisaphotoofanexampleofacastmanganesecrossing.Acrossingisalsosometimesreferredtoasa"frog".Ty