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RoadDesign

专业：

交通工程

英文原文

TheBasicsofaGoodRoad

Wehaveknownhowtobuildgoodroadsforalongtime.ArchaeologistshavefoundancientEgyptianroadsthatcarriedblockstothepyramidsin4600BCE.Later,theRomansbuiltanextensiveroadsystem,usingthesameprinciplesweusetoday.Someoftheseroadsare

stillinservice.

Ifyoufollowthebasicconceptsofroadbuilding,youwillcreatearoadthatwilllast.Thetencommandmentsofagoodroadare:

（1）Getwaterawayfromtheroad

（2）Buildonafirmfoundation

（3）Usethebestmaterials

（4）Compactalllayersproperly

（5）Designfortrafficloadsandvolumes

（6）Designformaintenance

（7）Paveonlywhenready

（8）Buildfromthebottomup

（9）Protectyourinvestment

（10）Keepgoodrecords

1．Getwaterawayfromtheroad

Wecan’toveremphasizetheimportanceofgooddrainage.Engineersestimatethatatleast90%ofaroad’sproblemscanberelatedtoexcesswaterortopoorwaterdrainage.Toomuchwaterinanylayerofaroad’sstructurecanweakenthatlayer,leadingtofailure.

Inthesurfacelayer,watercancausecracksandpotholes.Inlowerlayersitunderminessupport,causingcracksandpotholes.Acommonsignofwaterinanasphaltroadsurfaceisalligatorcracking—aninterconnectedpatternofcracksformingsmallirregularshapedpiecesthatlooklikealligatorskin.Edgecracking,frostheaves,andspringbreakupofpavementsalsopointtomoistureproblems.

Topreventtheseproblemsrememberthatwater:

•flowsdownhill

•needstoflowsomeplace

•isaproblemifitisnotflowing

Effectivedrainagesystemsdivert,drainanddisposeofwater.Todothistheyuseinterceptorditchesandslopes,roadcrowns,andditchandculvertsystems.

Divert—Interceptorditches,locatedbetweentheroadandhighergroundalongtheroad,keepthewaterfromreachingtheroadway.Theseditchesmustslopesotheycarrywaterawayfromtheroad.

Drain—Creatingacrownintheroadsoitishigheralongthecenterlinethanattheedgesencourageswatertoflowofftheroad.Typicallyapavedcrownshouldbe1⁄4"

higherthantheshoulderforeachfootofwidthfromthecenterlinetotheedge.Forgravelsurfacesthecrown

shouldbe1⁄2"

higherperfootofwidth.Forthisflowpathtowork,theroadsurfacemustberelativelywatertight.Roadshouldersalsomustbeslopedawayfromtheroadtocontinuecarryingtheflowaway.Superelevations（banking）attheoutsideofcurveswillalsohelpdrain

theroadsurface.

Dispose—Aditchandculvertsystemcarrieswaterawayfromtheroadstructure.Ditchesshouldbeatleastonefootlowerthanthebottomofthegravelroadlayerthatdrainstheroadway.Theymustbekeptcleanandmustbeslopedtomovewaterintonaturaldrainage.Ifwaterstaysintheditchesitcanseepbackintotheroadstructureandundermineitsstrength.Ditchesshouldalsobeprotectedfromerosionbyplantinggrass,orinstallingrockandothererosioncontrolmeasures.Erosioncandamageshouldersandditches,clogculverts,undermineroadbeds,andcontaminatenearbystreamsandlakes.Evaluateyourditchandculvertsystemtwiceayeartoensurethatitworks.Inthefall,cleanoutleavesandbranchesthatcanblockflow.Inspring,checkforandremovesiltsfromplowingandanydeadplantmaterialleftfromthefall.

2．Buildonafirmfoundation

Aroadisonlyasgoodasitsfoundation.Ahighwaywearsoutfromthetopdownbutfallsapartfromthebottom.Theroadbasemustcarrytheentirestructureandthetrafficthatusesit.

Tomakeafirmfoundationyoumayneedtostabilizetheroadbedwithchemicalstabilizers,largestonecalledbreakerrun,orgeotextilefabric.Whenyourunintoconditionswhereyoususpectthatthenativesoilisunstable,workwithanengineertoinvestigatethesituationanddesignanappropriatesolution.

3．Usethebestmaterials

Withallroadmaterialsyou“paynoworpaylater.”Inferiormaterialsmayrequireextensivemaintenancethroughouttheroad’slife.Theymayalsoforceyoutoreplacetheroadprematurely.

Crushedaggregateisthebestmaterialforthebasecourse.Thesharpanglesofthecrushedmaterialinterlockwhentheyarecompacted.Thissupportsthepavementandtrafficbytransmittingtheloadfromparticletoparticle.Bycontrast,roundedparticlesactlikeball

bearings,movingunderloads.

Angularparticlesaremorestablethanroundedparticles.

Asphaltandconcretepavementmaterialsmustbeofthehighestquality,designedfortheconditions,obtainedfromestablishedfirms,andtestedtoensureitmeetsspecifications.

4．Compactalllayers

Ingeneral,themoredenselyamaterialiscompacted,thestrongeritis.Compactionalsoshrinksoreliminatesopenspaces（voids）betweenparticles.Thismeansthatlesswatercanenterthestructure.Waterinsoilcanweakenthestructur