二级公路毕业设计外文文献

'外文资料及翻译EffectsofDesignFeaturesonRigidPavementPerformanceTheperformanceofrigidpavementsisaffectedbyavarietyofdesignfeatures,includingslabthickness,basetype,jointspacing,reinforcement,jointorientation,loadtransfer,dowelbarcoatings,longitudinaljointdesign,jointsealant,tiedconcreteshoulders,andsubdrainage.AstudywasmadebyERESConsultants,Inc.underFHWAcontractontheeffectsofthesefeaturesonrigidpavementperformance.Ninety-fivepavementsectionslocatedinfourmajorclimaticregionswerethoroughlyevaluated.Thefollowingconclusions,whichprovidesomerevealinginsightsintopavementperformance,areabstractedfromthereport(Smithetal.,1990a).SlabThicknessTheeffectofslabthicknessonpavementperformancewassignificant.Itwasfoundthatincreasingslabthicknessreducedtransverseandlongitudinalcrackinginallcases.Thiseffectwasmuchmorepronouncedforthinnerslabsthanforthickerslabs.Itwasnotpossibletocomparetheperformanceofthethinnerslabsandthethickerslabsdirectly,becausethethickslabswereallconstructeddirectlyonthesubgradeandthethinnerslabswereallconstructedonabasecourse.Increasingthethicknessofslabdidnotappeartoreducejointspallingorjointfaulting.Thickslabsplaceddirectlyonthesubgrade,especiallyinwetclimatesandexposedtoheavytraffic,faultedasmuchasthinslabsconstructedonabasecourse.BaseTypeBasetypes,includingbase/slabinterfacefriction,basestiffness,baseerodibility,andbasepermeability,seemedtohaveagreateffectontheperformanceofjointedconcretepavements.Themajorperformanceindicators,whichwereaffectedbyvariationsinbasetype,weretransverseandlongitudinalcracking,jointspalling,andfaulting.Theworstperformingbasetype,consistedofthecement-treatedorsoilcementbases,whichtendedtoexhibitexcessivepumping,faulting,andcracking.Thisismostlikelyduetotheimperviousnatureofthebase,whichtrapsmoistureandyetcanbrea-kdownandcontributetothemovementoffinesbeneaththeslab.Theuseofleanconcretebasesgenerallyproducedpoorperformance.Largecurl-ingandwarpingstresseshavebeenassociatedwithslabsconstructedoverleanconcretebases.Thesestressesresultinconsiderabletransverseandlongitudinalcrackingoftheslab.Thepoorperformanceofthesebasescanalsobeattributedtoabathtubdesign,inwhichmoistureistrappedwithinthepavementcrosssection. Dense-gradedasphalt-treatedbasecoursesrangedinperformancefromverypoortogood.Thefactthatthesetypesofbaseswereoftenconstructedasabathtubdesigncontributedtotheirpoorperformance.Thisimproperdesignoftenresultedinseverecracking,faulting,andpumping.TheconstructionofthickerslabsdirectlyonthesubgradewithnobaseresultedInapavementthatperformedmarginally.Thesepavementswereespeciallysusceptibletofaulting,evenunderlowtrafficlevels.Pavementsconstructedoveraggregatebaseshadvariedperformance,butweregenerallyinthefairtoverygoodcategory.Ingeneral,themoreopen-gradedtheaggregate,thebettertheperformance.Anadvantageofaggregatebasesisthattheycontributetheleasttothehighcurlingandwarpingstressesintheslab.Eventhoughaggregatebasesarenotopen-graded,theyaremorepermeableandhavealowerfrictionfactorthanstabilizedbases.Thebestbasesintermsofpavementperformancewerethepermeablebases.Typicalbasecourseshavepermeabilitiesrangingfrom0tolessthan1ft/day(0.3m/day);goodpermeablebaseshavepermeabilitiesupto1000ft/day(305m/day).Specificareasofconcernwerethehighcornerdeflectionsandthelowloadtransferexhibitedbythepermeablebases.Thesecanaffecttheirlong-termperformance,sotheuseofdowelbarsmightberequired.Anunexpectedbenefitofusingpermeablebaseswasthereductionin"D"crackingonpavementssusceptibletothistypeofdistress.SlabLengthForJPCP,thelengthofslabsinvestigatedrangedfrom7.75to30ft(2.4to9.1m).Itwasfoundthatreducingtheslablengthdecreasedboththemagnitudeofthejointfaultingandtheamountoftransversecracking.Onpavementswithrandomjointspacings,slabswithjointspacingsgreaterthan18ft(5.5m)experiencedmoretransversecrackingthandidtheshorterslabs.ForJRCP,thelengthofslabsinvestigatedrangedfrom21to78ft(6.4to23.9m).Generally,shorterjointspacingsperformedbetter,asmeasuredbythedeterioratedtransversecracks,jointfaulting,andjointspalling.However,severalJRCPwithlongjointspacingsperformedquitewell.Inparticular,thelongjointedpavementsinNewJersey,whichwereconstructedwithexpansionjoints,displayedexcellentperformance.Anexaminationofthestiffnessoffoundationwasmadethroughtheuseoftheradiusofrelativestiffness,f.Generallyspeaking,whentheratioL/E,whereListhelengthofslab,wasgreaterthan5,transversecrackingoccurredmorefrequently.This factorwasfurtherexaminedfordifferentbasetypes.Itwasfoundthatstifferbasecoursesrequiredshorterjointspacingstoreduceoreliminatetransversecracking.ReinforcementTheamountofsteelreinforcementappearedtohaveaneffectincontrollingtheamountofdeterioratedtransversecracking.Pavementsectionswithlessthan0.1%reinforcingsteeloftendisplayedsignificantdeterioratedtransversecracking.Aminimumof0.1%reinforcingsteelisthereforerecommended,withlargeramountsrequiredformoresevereclimateandlongerslabs.JointOrientationConventionalwisdomhasitthatskewedjointspreventtheapplicationoftwowheelloadstothejointatthesametimeandthuscanreduceload-associateddistresses.Theresultsfromthelimitedsamplesizeinthisstudywereambiguous,butallofthenondoweledsectionswithskewedjointshadalowerPSRthansimilardesignswithperpendicularjoints.Theavailabledataprovidenodefiniteconclusionsontheeffectivenessofskewingtransversejointsfornondoweledslabs.Skewedjointsarenotbelievedtoprovideanybenefittodoweledslabs.LoadTransferDowelbarswerefoundtobeeffectiveinreducingtheamountofjointfaultingwhencomparedwithnondoweledsectionsofcomparabledesigns.Thediameterofdowelshadaneffectonperformance,becauselargerdiameterbarsprovidedbetterloadtransferandcontroloffaultingunderheavytrafficthandidsmallerdowels.Itappearedthataminimumdoweldiameterof1.25in.(32mm)wasnecessarytoprovidegoodperformance.NondoweledJPCPslabsgenerallydevelopedsignificantfaulting,regardlessofpavementdesignorclimate.Thiseffectwassomewhatmitigatedbytheuseofpermeablebases.However,thesectionsinthisgrouphadamuchlowernumberofaccumulatedESAL,sonodefiniteconclusionscanbedrawnyet.DowelBarCoatingsCorrosion-resistantcoatingsareneededtoprotectdowelsfromtheadverseeffectsofmoistureanddeicingchemicals.Whilemostofthesectionsinthisstudydidnotcontaincorrosion-resistantdowelbars,thosethatdidgenerallyexhibitedenhancedperformance.Verylittledeterioratedtransversecrackingwasidentifiedonthesesections.Infact,onesectioninNewJerseywithstainlesssteel-claddowelbarswasperformingsatisfactorilyafter36yearsofservice.LongitudinalJointDesignThelongitudinaljointdesignwasfoundtobeacriticaldesignelement.Bothinadequateformingtechniquesandinsufficientdepthsofjointcancontributetothedevelopmentoflongitudinalcracking.Therewasevidenceoftheadvantageofsawingthejointsovertheuseofinserts.Thedepthoflongitudinaljointsisgenerallyrecommendedtobeone-thirdoftheactual,not designed,slabthickness,butmighthavetobegreaterwhenstabilizedbasesareused.JointSealantJointsealingappearedtohaveabeneficialeffectonperformance.Thiswasparticularlytrueinharshclimateswithexcessiveamountsofmoisture.Preformedcompressionsealantswereshowntoperformwellformorethan15yearsunderheavytraffic.Exceptwhere"D"crackingoccurred,pavementsectionscontainingpreformedsealantsgenerallyexhibitedlittlejointspallingandwereingoodoverallconditions.Rubberizedasphaltjointsealantsshowedgoodperformancefor5to7years.TiedConcreteShouldersItisgenerallybelievedthattiedconcreteshoulderscanreduceedgestressesandcornerdeflectionsbyprovidingmorelateralsupportstothemainlinepavement,thusimprovingpavementperformance.Surprisingly,thisstudyshowedthat,althoughtiedconcreteshouldersperformedbetterthanasphaltshoulders,manyofthetiedshoulderswerenotdesignedproperlyandactuallycontributedtopoorperformanceofthemainlinepavement.Thetiebarswerespacedtoofarapart,sometimesataspacingof40in.(1016mm),andwerenotstrategicallylocatednearslabcornerstoprovideadequatesupport.Insomecases,tiedconcreteshoulderswereconstructedoverastabilizeddense-gradedbaseinabathtubdesign,resultinginthepoorperformanceofmainlinepavement.SubdrainageTheprovisionofpositivesubdrainage,eitherintheformoflongitudinaledgedrainsorthecombinationofadrainagelayerandedgedrains,generallyreducedtheamountoffaultingandspallingrelatedto"D"cracking.Withfewexceptions,theload-associateddistresses,especiallyfaultingandtransversecracking,decreasedasthedrainagecharacteristicsimproved.Theoverallpavementperformancecanbeimprovedbyusinganopen-gradedbaseorrestrictingthepercentageoffines.Afilterlayermustbeplacedbelowthepermeablebase,andregularmaintenanceoftheoutletsmustbeprovided. 译文结构特点对刚性路面性能的影响刚性路面的性能受种种结构特点的影响，如板厚、基层类型、接缝间距、钢筋用量、接风方向、荷载传递、传力杆涂层、纵缝设计、接缝填封料、有拉杆混凝土道肩和地下排水等。ERES咨询公司于联邦公路局（FHWA）签订合同，研究这些结构特点对刚性路面的影响。对四个主要气候区内95个路面段作了详细的评定。从研究报告（Smith等，1990a）摘录了以下结论，以便对路面性能有一透彻的理解。一、板厚板厚对路面性能的影响很大。发现在所有的实例中，增加板厚，是纵向和横向开裂减小。这种影响对对薄的路面板，比厚板更为明显。不可能直接将薄板的想能与厚板进行比较，因为板厚都直接铺筑在土基上，而薄板都铺筑在基层上。增加板厚并不能减少接缝剥落及接缝错台。厚板直接铺在土基上，尤其是气候潮湿交通繁重的情况下，产生的错台同铺筑在基层上的薄板同样也很多。二、基层类型基层类型，包括基层与板的界面摩擦力、基层刚度、基层抗冲刷能力和基层透水性，看来对有接缝混凝土路面性能有很大影响。受各种基层类型影响的主要性能指标是横向额纵向开裂、接缝剥落和错台。性能最差的基层类型是水泥稳定或水泥土基层，最容易于楚翔很对唧泥、错台和开裂。这很可能是因为基层不透水，它吸收水分，易于断裂，使得板下的细颗粒发生移动。应用贫混凝土基层，一般工作性能都很差。很大的翘曲应力是与贫混凝土基层上铺筑路面板有关系的。由于这些应力，使得面板产生很多横向和纵向的裂缝。这些基层的性能差，还可能是由于路面横截面按盆状设计，造成水分集中。密级配沥青稳定基层的性能从很差到好都有。性能低劣的原因是这些基层类型经常采用盆状设计，这种错误设计结果将产生严重的开裂、错台和唧泥。厚的面板直接铺筑在不舍基层的土基上，路面勉强合格。这些路面特别容易错台，即使交通量不大也是如此。铺筑在集料基层上的路面具有不同性能，但是一般属于良好到很好等级。通常，集料开集配空隙越多。性能越好。集料基层的优点是由于基层引起的面板翘曲高应力是最小的。即使集料基层不是开集配的，也比稳定基层具有较好的透水性和较低的摩擦系数。在路面性能方面最好的基层是透水基层。常用基层的渗透率在0至0.3m/d(1ft/d)，而好的透水基层渗透率达305m/d(1000ft /d)。需要特别考虑的问题是透水基层板角部位挠度大，且传荷能力低。由于这将影响其长远性能，要应用传力杆是必不可少的。应用透水基层有一种意想不到的好处，它能够是容易产生“D”裂缝的路面，裂缝数量减少。三、板长调查的JPCP路面板长度在2.4--9.1m（7.75--30ft）之间，发现板长减小，接缝错台的大小和横向开裂的数量两者都减少。在接缝间距不规则的路面上，接缝间距大于18ft（5.5m）的板，横向开裂多余较短的板。对于调查的JRCP路面板长度在6.4—23.9m（21--78ft）之间。一般地，从调查损坏的横向裂缝、接缝错台和接缝剥落来看，接缝间距有短的一些的路面性能好些。然而，有些接缝间距长的JRCP，性能也很好。尤其是新泽西州的长接缝路面，筑有膨胀缝，呈现出极好的性能。通过相对刚度半径l调查了地基的刚度。一般来说，当L/l比值（L为板长）大于5，横向开裂较多。这一因素对不同基层类型作了进一步研究。发现基层刚度愈大，所需的接缝间距愈短。这样便能减少或消除横向开裂。四、钢筋用量看来钢筋用量对控制横向开裂损坏时有影响的。钢筋用量小雨0.1%的路面段经常呈现明显的横向开裂损坏。因此建议最小钢筋用量为0.1%，对于气候恶劣以及采用较长的路面板时，需要较多的钢筋用量。五、接缝方向一般看法认为斜接缝避免了两个车轮同时通过接缝，因此可降低与荷载有关的损坏。从有限尺寸板的研究结果却相反，所有不舍传力杆的斜向接缝，他的PSR值小于同样设计的垂直接缝。现有的数据无法对无传力杆板斜向横缝的有效性作出肯定的结论。不能认为斜接缝比有传力杆的板有任何优点。六、荷载传递若与设计相仿的不舍传力杆路段作比较，传力杆对减少接缝错台是有效的。传力杆的直径对路面性能有一定的影响，因为在重型车辆的作用下，直径大的传力杆比直径小的传力杆更能底荷载和控制错台。看来，为了保证路面有良好的性能，传力杆的最小直径应为32mm（1.25mm）。通常，不设传力杆的JPCP板有明显的错台，这与路面设计和气候无关。若采用透水基层，这种影响有所缓和。不过，这种路段的累计当量单轴荷载（ESAL）很低，因此还不能作出肯定的结论。七、传力杆涂层为了防止传力杆受水分和除冰化学物质的有害影响，必需采用防锈涂层。在此项研究的大部分路段，都没有防锈传力杆。事实上，在新泽西州一个用不锈钢包裹过传力杆的路段，使用了36年后，路面性能仍然良好。 八、纵缝设计经研究发现，纵缝设计是最关键的设计部位。接缝施工不恰当或深度不够，均可造成纵向开裂。锯缝法比欧诺个嵌条有明显欧典。纵缝深度，不设计的一般建议取路面厚度的三分之一，若采用稳定基层，还可以更深一些。九、接缝填封料看来接缝填封料对路面性能是有利的。这在水分过量的不利气候地区，更是如此。欧诺个预压成型的填缝料，在重型车辆作用下使用15年以后，仍然能很好地工作。除了有“D”裂缝产生的位置之外，有预压成型填缝料的路面段一般只有很小的接缝剥落，总的情况是良好的。橡胶沥青接缝填封料使用5—7年后性能仍然良好。十、设拉杆的混凝土路肩通常认为设拉杆的混凝土路肩为主车道路面提供了侧向支承，可以减小板边应力和板角挠度，从而改善了路面的性能。可是意想不到，在此项研究中，一方面发现设拉杆的混凝土路肩的性能优于沥青路肩，然而，许多设拉杆的路肩设计不当，实际上使主车道路面的性能变坏。拉杆相隔间距太远，有时达到1016mm（40in），又不能有针对性地放在靠近板角的至，以提供适当的支承。有时候，设拉杆的混凝土路肩铺筑在密级配稳定基层上，按盆状设计，结果是主车道路面性能变坏。十一、地下排水提供良好的地下排水，无论是纵向边沟排水，还是综合应用排水层和边沟排水，一般都可以减小与“D”裂缝有关的错台剥落。除少数情况之外，随着排水状况的改善，与荷载的有关的损坏，尤其是错台和横向开裂都减少了。应用开集配基层，或者限制细颗粒的百分数，都可以改善整个路面的性能。在透水基层西面必须设置过滤层，必须对出水口做定期维护。'