沥青路面结构设计的低成本农村道路.docx

沥青路面结构设计的低成本农村道路.docx

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沥青路面结构设计的低成本农村道路

沥青路面结构设计的低成本

structuralDesignofAsphaltPavementforLowCost

农村道路

RuralRoads

structuralDesignofAsphaltPavementforLowCostRuralRoads

Indevelopingcountries，ruralroadconstructionismostlycumberedbyshortageoffunds.Engineersconcernsmostinruralareasishowtobuildroadswhichnotonlycostlessbutalsomeetthetrafficdemands.EspeciallyinvastruralareasofChina,thereareagreatvarietyoftransportationpatterns,andthetrafficcompositionisverycomplex.Comparedwithothercountries，thetrafficcompositioninChinaruralareashaveitsownfeatures.Therefore，thereisnoexperienceabouttheruralroadsconstructionforreference.Inrecentyears，thecentralgovernmentofChinahasincreasedthestrengthforruralroadconstruction.Atthesametime，alotofresearchesaboutruralroadconstructionhavebeendonebyresearchersinChina,andsomeconclusionsaboutchinaruralroadshavebeenmade.Intheauthors'opinion，theselectionofthepavementstructurematerialisthekeymeasuretoreducetheconstructioncostofruralroadsaftertheroutehasbeendetermined.Comparedwithconcretepavement，asphaltpavementrelativelycostslessandisthefirstchoiceforruralroadsinChina.Andthen，accordingtotheresearchachievementsaboutruralroadsconstruction，theauthorshavedonesomepreliminaryresearchesonthestructuredesignforlow-costasphaltpavementsforruralroads.

1TrafficCompositionofRuralRoad

Ruralroadsincludecountyroads，townroadsandvillageroads.

Thetrafficonruralroadsisusuallymixed.Onacountyroad,trafficvolumeisbetween300to1500veh/dinaverage，andinacountywithadevelopedeconomy，itreaches1000to2000veh/d.Thetrafficvolumebetweencountyandtownis100to300veh/d，andthetrafficvolumebetweentownsisusuallylessthan100to300veh/d.Inamixedtrafficflow，trucksaccountfor40%to70%ofthetrafficvolume,whicharemainlylighttruckscarryinglessthan2.5tons（includingagriculturalvehiclessuchaselectro-tricycles，walkingtractorsetc.）andmedium-sizetrucksof2.5to5tons.Mostoftheselightormediumtrucksareoverloaded.Theproportionofheavytruckislessthan9%.Onsomeroadstocounties，theproportionofoverloadedtrucksis5%to32%，whileonsomecountyroadsconnectingtonationalorprovincialtrunkhighways，theproportionofoverloadedvehiclesusuallyamountsto20%to32%.

Thetrafficvolumeonruralroadsisnotheavy.However，consideringthepracticalsituationinChina,aswellastheexitenceofoverloadedvehicles，100kN，orBZZ-100wasadoptedasstandardaxleloadintheresearch.

Thepavementdeflectionortheflexural-tensilestressatthebottomofasphaltsurfaceistakenasthedesignparameter.Theaxleloadwascalculatedin

accordancewiththefollowingformula:

和

-theaxleweightofani-levelaxleinkNandtheactionfrequency;

-theaxleweightofstandardaxlein100kNandtheactionfrequency;

Ifthedistancebetweenaxlesislessthan3m，axleloadsarecalculatedas

adouble-axleormulti-axleloads，and

Iftheflexural-tensilestressatthebottomofsemi-rigidbaseistakenasthedesignparameter,theaxleloadiscalculatedinaccordancewiththefollowingformula:

Ifthedistancebetweenaxlesislessthan3m，

2TrafficVolumeonRuralRoads

Minibusesareadoptedasthestandardvehicleforthedesignofruralroads.Table1showsitsexternaldimensions.

Table1Externaldimensionsofthepassengercarm

LengthWidthHeightFrontoverhangDistancebetweenaxlesRearoverhang

6.01.82.00.83.81.4

ThetypicalvehicletypesonruralroadsarelistedinTable2.Andotherssuchasnon-power-drivenvehicles，animal-drawnvehicles，andbicyclescanbetakenintoaccountinthecalculationoftrafficvolumeonruralroads，inviewoftheirroadsideinterference.

Inaccordancewiththetrafficcompositionandvolumes，ruralroadsaredividedintofivegrades.ThetrafficvolumeofeachgradeisshowninTable3.

TrafficvolumespecifiedinTable3wasobtainedbytakingtheminibusasthestandardvehicletype,andconvertingdifferenttypesvehiclesaccordingtothevehicleconversioncoefficientsgiveninTable2.InTable3，

Nereferstothecumulativeequivalentaxleloadactionfrequency;

Nsreferstotheequivalentaxleloadactionfrequencyinthedesignedtrafficlaneinthebeginningoperationperiodofruralroads;

yreferstotheaverageannualgrowthrateoftrafficvolume;

ηreferstolanecoefficient,and1.0forasinglelaneand0.6一0.7foraduallane.

3StrengthofRoadbed

Themodulusofresilienceofroadbedvariesgreatly.Forconvenience，thestrengthofroadbedcanbedividedintofourclassesaccordingtoitsmoisturecontentandmodulusofresilience，asshowninTable4.

TheparametersinTable5aredeterminedbycombiningdesignprincipleswithpracticalexperience.ByapplyingelasticmultilayertheorytothepavementstructurespecifiedinTable5，theinfluenceofNeonthepavementthicknessofruralroadswasanalyzed，andtheresultshowthatforgivenh，h2，E0，theroadbasethicknessforneighboringtrafficclasseschangesinarangeof4-5cm.ThisresultindicatesthattheclassificationoftrafficvolumeonruralroadsshowninTable3isreasonableandfeasibleintermsofthedesignandconstructionofasphaltpavementstructures.

Byusingtheelasticmultilayertheory，theasphaltpavementstructureofordinaryruralroadinTable5isanalyzed.WhenNe，thecumulativeequivalentaxleloadactionfrequency，thethicknessofroadsurface（h=3cm），andthethicknessofsubbase（h2=20cm）remainthesame,theinfluenceofneighboringroadbedstrengthclassificationsonthethicknessofroadbaseis3cm一5cm.Thisconclusionindicatesthatthestrengthclassificationofroadbedisreasonableandapplicabletothedesignandconstructionofasphaltpavementstructure.

4DeterminationofThicknessesofAsphaltPavementStructure

Sensitivityanalysisofthedesignparametersofroadbedandpavementstructuresistofindouttherelationshipbetweenstructuralstrengthofasphaltpavementstructureandthedesignparametersofeachlayer,anddeterminethemostsensitivelayerinthepavementstructure.Theasphaltpavementstructureofruralroadsisgenerallycomposedofaroadsurface,aroadbase，andasubbase，asshowninTable6.Thepavementstructurewasanalyzedaccordingtoelasticmultiplayertheoryunderthedoublecircularuniformload，withanassumptionthatthereiscontinuouscontactbetweentheadjacentlayersoftheasphaltpavementstructure.ThebasicparametersusedinthecalculationandanalysisofasphaltpavementstructurearelistedinTable7.Byanalyzingtheeffectsofthechangeofalltheparametersofpavementstructureonthedistortionoftheroadsurface，roadbase，androadbed,thefollowingconclusionshavebeendrawn.

（1）Increasingthethicknessoftheroadsurfaceeffectivelydecreasestheroadsurfacedeflection，butraisesthecost.Thecomparativelyeconomicalandeffectivemethodistoincreasethethicknessofthesubbase,whichissuperiortoincreasingthethicknessofroadbase，whileincreasingthethicknessoftheroadsurfaceisthelastchoice.

（2）Asthethicknessofpavementstructureincreases，thechangeofroadsurfacedeflectionwilltrendtobegentle.Whenthethicknessofroadsurfacereachesacertainvalue，thevarianceintheroadsurfacedeflectionwillnotbeobvious，andthenitisineffectivetoenhancethebearingcapacityofasphaltpavementstructurebyincreasingthethicknessofroadsurface.Itisrecommendedthatthethicknessesoftheroadbaseandthesubbaseshouldbeequaltoorlarger

than18and20cm,respectively，indesignofasphaltpavementstructuresofruralroads.Fig.1showstheeffectsofthechangesinthethicknessofeachlayeronroadsurfacedeflection.

（3）Roadsurfacedeflectionisverysensitivetothechangeofmodulusoftheroadbed.Theincreaseinthemodulusofroadbaseorsubbaseisalsoeffectivetodecreasethedeflectionoftheroadsurface.Ontheotherhand，thedeflectionoftheroadsurfacedecreasesgraduallywhenthemodulusofthesurfaceincreases，beingtheleasteffectivefactor.Whenthemodulusoftheroadsurfaceincreasestoacertainvalue，decreaseinroadsurfacedeflectionisnotapparent.Fig.2showstheeffectofthemodulusofeachlayeronroadsurfacedeflection.Fromtheabovediscussion，weconcludethatthemostsensitivelayerforroadsurfacedeflectionissubbase，andthenextisroadbase.Todecreasetheroadsurfacedeflectionoflow-costruralroads，thestrengthandstabilityoftheroadbedshouldbeenhanced,andthematerialswithacertainthicknessandrelativelyhighdensityshouldbeusedtopavethesubbase.

Thetrafficvolumeortheaccumulativeequivalentaxleloadactiontimes（frequency）withinthedesignedlifeofroadisusedtodeterminethetypeandthicknessoftheasphaltpavementroadsurface,andtheresultsarelistedinTable8，whereveh/dmeansthenumberoftheequivalentthepassengercarsperday.

ForalowtrafficvolumeruralroadwithNe500000，gradedbrokenstones（orgravel）canbeusedasaflexiblebase.Theflexiblebasehasgoodstrengthandeffectivelypreventsreflectioncracksoftheasphaltpavementroadsurface,providedthegradedbrokenstones（orgravel）meetstherequirementsforhighdensity（degreeofcompaction,100%.Toensurethesufficientstrengthandstabilityoftheflexiblebase，itsthicknessisnotlessthan15cm，thethicknessoftheaggregatesubbaseisnotlessthan20cm，

Asemi-rigidbaseusuallyhasagoodbearingcapacityFortheruralroadswithNe）500000，orthosewithlowtrafficvolumesbutrelatively,theminimumthicknessofsemirigidbase