RoadbedConstructionTechnologyBasicknowledgeofRoadbedEngineeringBasicrequirementsofroadbedThestructureoftheroadbedSubgradeGeometricElementsBasicrequirementsofroadbedSubgradeGeometricElementsSubgradewidth:

DeterminedbyroaddesigncapacityandtrafficvolumeSubgradewidth:

Determinedbylongitudinalslopedesign,topography,geologyandhydrologySubgradeSlopeSlope:Determinedbygeological,hydrologicalconditions,packingproperties,etc.Basicrequirementsofroadbed1.SubgradewidthConceptTrafficlane+shoulder+medianbelt+speedchangelane+climbinglane+emergencyparkinglane+wronglane+overtakinglaneBasicrequirementsofroadbed1.SubgradewidthDeterminationofsubgradewidthRoadway:Itisrelatedtovehiclewidth,designtrafficvolume,trafficcompositionandvehiclespeed.Generallytake3.50~3.75m.Shoulder:Protectstheroadsurfaceandtemporaryparking,andactsasalateralsupportfortheroadsurface.Generallytake0.5~2.5m.Middlebelt:Separateround-triptraffic,avoidvehiclesturningaroundmidway,andpreventglareatnight.Withthechangeofterrainandroadgrade,generallytake2~4.5m.Shiftlane:Forvehicleaccelerationanddeceleration.Forexample,tollstations,serviceareas,andtheouterlanesneartherampentrance,generallytake3.5m.Climbinglane:Whenthelongitudinalslopeisgreaterthan4%,itissetontheoutersideoftheoriginallaneontheuphillsection,andisaspeciallaneforslow-speeduphillvehicles.Generallynotlessthan3.5m.Basicrequirementsofroadbed1.SubgradewidthThesubgradestandardcross-sectionsofexpresswaysandfirst-classhighwaysaredividedinto

IntegralandSeparatetwocategories.Integralsection:

Includinglane,middlebelt(centraldividerbeltandleftcurbbelt),roadshoulder(righthardshoulderanddirtshoulder),emergencystopbelt,climbinglane,acceleration(deceleration)laneandotherparts;Splitsection:

Itconsistsoflanes,roadshoulders(righthardshoulderanddirtshoulder),emergencystopbelts,climbinglanes,acceleration(deceleration)lanesandotherparts.Thesecond,thirdandfourthgradehighwayadoptstheformofintegralsubgradesection,andthestandardsubgradecrosssectionincludesthelane,theshoulderandthewronglane.BasicrequirementsofroadbedSubgrademonolithiccrosssectionSubgradeseparatedcrosssectionBasicrequirementsofroadbed2.Subgradeheightconcept:Thefillingheightoftheembankmentortheexcavationdepthofthecutting,thatis,thedifferencebetweenthedesignelevationofthesubgradeandthegroundelevationofthemiddlepile.Thedesignelevationofthenewlybuilthighwaysubgradeexpresswaysandthefirst-classhighwayshalladopttheelevationoftheouteredgeofthecentralseparationzone;thesecond-class,third-class,andfourth-classhighwaysshouldadoptthesubgradeedgeelevation.Basicrequirementsofroadbed2.SubgradeheightSubgradeheightisdividedintocenterheightandsideslopeheightSubgradecenterheight:Thedifferencebetweenthedesignelevationatthecenterlineofthesubgradeandtheoriginalgroundelevation;Subgradeslopeheight:

Thedifferencebetweenthefilltoeorcuttopelevationandthesubgradeedgeelevation.Basicrequirementsofroadbed3.Subgradeslopeslopeconcept:ItisexpressedbytheratiooftheslopeheightHtotheslopewidthb(H/b),andtakeH=1andexpressitby1:m.SlopeSlopeConsiderations:Slopegeology,hydrologicalconditions,fillingproperties,slopeheight,etc.（a）（b）（c）Basicrequirementsofroadbed3.SubgradeslopeslopeSubgradeslopetypeStraight:Thesameslopeisadoptedfromthetoptothefootoftheslope,whichissuitableforlowandmiddleembankments.Polyline:Steepupandgentledown,inlinewiththecharacteristicsofforce,suitableforhighembankments.Steptype:Setupa1-2mslopeprotectionroadatacertainheightofthesideslope;itissuitableforhighembankment.Basicrequirementsofroadbed1)EmbankmentSlopeTheformandsloperateoftheembankmentslopeshallbedeterminedaccordingtothephysicalandmechanicalpropertiesofthefiller,theheightoftheslopeandtheengineeringgeologicalconditions.Thegeologicalconditionsaregood,andwhentheheightoftheslopeisnotmorethan20m,thesloperateoftheslopeshouldnotbesteeperthanthevaluespecifiedinTable1-6.TypeoffillersloperateUpperheight(H≤)Lowerheight(H≤)fine-grainedsoil1：1.51：1.75coarse-grainedsoil1：1.51：1.75macrograinsoil1：1.31：1.5Table1-6SloperateofembankmentBasicrequirementsofroadbed2)CuttingslopeThecuttingslopeformandsloperateshouldbecomprehensivelydeterminedaccordingtotheengineeringgeologicalandhydrogeologicalconditions,slopeheight,drainageprotectionm