Designation:D6758−18StandardTestMethodforMeasuringStiffnessandApparentModulusofSoilandSoil-AggregateIn-PlacebyElectro-MechanicalMethod1ThisstandardisissuedunderthefixeddesignationD6758;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thistestmethodcoversthemeasurementbyelectro-mechanicalmeansofthein-placestiffnessofsoilorsoil-aggregatemixturessoastodetermineaYoung’smodulusbasedoncertainassumptions.Theapparatusandprocedureprovideafairlyrapidmeansoftestingsoastominimizeinterferenceanddelayofconstruction.Thetestprocedureisintendedforevaluatingthestiffnessormodulusofmaterialsusedinearthworksandroadworks.Rapidin-placestiffnesstestingsupportsU.S.federalandstateeffortstospecifythein-placeperformanceofconstructionmaterialsbasedonmodu-lus.Resultsobtainedfromthismethodareapplicabletotheevaluationofgranularcohesionlessmaterials.Theyarealsoapplicabletotheevaluationofsiltyandclayeymaterialswithmorethan20%finesthatarenotsubjecttoachangeinmoisturecontent.Ifthesiltyandclayeymaterialexperiencesachangeinmoisturecontent,thenmoisturecontentshallbetakenintoaccountiftheresultsofthismethodaretobeapplicable.Thestiffnessmeasuredwiththismethodisinflu-encedbyboundaryconditions,specificallythesupportofferedbyunderlyinglayersaswellasthethicknessandmodulusofthelayerbeingtested.Sincethismethodapproximatesthelayer(s)beingevaluatedasahalf-space,thenthemodulusmeasuredisalsoapproximate.1.2Thestiffness,inforceperunitdisplacement,isdeter-minedbyimpartingasmallmeasuredforcetothesurfaceoftheground,measuringtheresultingsurfacevelocityandcalculatingthestiffness.Thisisdoneoverafrequencyrangeandtheresultsareaveraged.1.3ThevaluesstatedinSIunitsaretoberegardedasthestandard.Theinch-poundunitsequivalentsmaybeapproxi-mate.1.4Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associ...
