www.tjmes.com 铜球阀 截止阀 蝶阀-Conductivity Testing of Unsaturated Soils

ConductivityTestingofUnsaturatedSoilsAPresentationtotheCaseWesternReserveUniversityMay6,2004PurposeofPresentationPresentfundamentalconceptsnecessaryforunderstandingmechanicsofunsaturatedflow.Discussconductivitytestingofunsaturatedsoils.http://www.tjhlqz.com/起重机立体停车设备电动葫芦http://www.hygy1688.com/衬塑复合管涂塑复合管钢塑复合管消防涂覆钢SomeFundamentalConceptsMechanicsofUnsaturatedSoilsUnsaturatedsoilsaredistinguishedfromsaturatedsoilsbynegativeporewaterpressures,soilsuction,thatdevelop.Thenegativeporepressuresaffectsoilpropertiesandbehavior.MatricSuctionDefinedComponentofthesoilmoisturesuctionassociatedwiththecapillaryhead.Matricsuction=(ua-uw)ua=soilairpressureuw=soilwatersuctionpressure.ImportanceofMatricSuctionSoilmatricsuctionisaprimarystressstatevariableusedtocharacterizeunsaturatedsoilbehavior.Relationshipsrequiredtomodelflowinunsaturatedsoilsaregivenasfunctionsofporewaterpressureormatricsuction.MassBalanceEquationforWaterPhaseDerivedassuminghomogeneous,isotropicnon-deformingmediumandincompressible,homogeneousfluid.Volumetricwatercontentdependsonporewaterpressure,q(y).Darcy’sLawAflowlawrelatingtheflowratetothedrivingpotentialisneeded.Flowdependsonacoefficient,hydraulicconductivity(),andthetotalheadgradient().HydraulicConductivityHydraulicconductivityisthecoefficientobtainedfromafloworconductivitytest.Hydraulicconductivitydependsonmediumandfluidproperties.Hydraulicconductivitydependsonfluidpressure,K(y).FlowEquationThetworequiredfunctionsareK(y)andq(y)whereyisthepressurehead.Thefunctionscanbegivenintermsofporewaterpressure,pressureheadormatricsuction.Soil-WaterRetentionFunctionAfterMualem(1976)ConductivityFunctionAfterMualem(1976)RelativeConductivityAfterBrooksandCorey(1964)ModelingWiththeFunctionsBothfunctionsexhibithysteresisduringdryingandwettingprocesses.Mathematicalexpressionsareusedtoapproximatetheexperimentalcurves,usingtheboundarydryingorwettingcurve.vanGenuchten(1980)EquationsThecurvefittingparameters,nandm,andotherparametersareobtainedfromthecurves.LaboratoryTestingVariationofMatricSuctionintheLaboratoryTovarymatricsuction,boththesoilairandsoilwaterpressuresareincreased(axistranslationtechnique).Matricsuctioniscomputedasthedifferencebetweenthetwopressures,alwayspositive.HighAirEntryCeramicMaterialAceramicmaterialisusedtopreventflowofairfromthesoil.Oncethematerialissaturated,thecapillarypressureinthematerialpreventsairfromflowingthroughthematerialandoutofthesoil.DirectMeasurementofSoilMoistureSuctionTensiometers.Directlymeasureporewaterpressuresbutarelimitedto90centibarspressure.ThermocouplePsychrometers.Measurerelativehumidityofthesoiltocomputethetotalsuction,tohighsuctionvalues.IndirectMeasurementofSoilMoistureThephysicalpropertiesofsoilmineralsdonotvarysignificantly,buttheydiffersignificantlyfromthepropertiesofpurewater.Consequently,soilmoisturecontentormatricsuctionarecorrelatedtophysicalpropertiesofsoil.IndirectMeasurementSensorsThetypesofsensorsinclude:thermalconductivitysensorstimedomainreflectometyorfrequencydomainsensors(dielectricproperties)electricalresistivitysensorsMeasurementAccuracySensorcalibrationsarenonlinear.Atlowmoisturecontents,largechangesinmatricsuctionsoccurwithonlysmallchangesinwatercontent,sotheaccuracyofthesensorsisreduced.ModifiedTriaxialCellTriaxialcellsweremodifiedbyaddingtwoportsandaloadcellinlinewiththeloadingpiston.WaterVolumeChangeIndicatorFourburettesandagangofzerovolumechangevalvesareusedtomeasureflow.DiffusedAirVolumeIndicatorAburetteisusedtocollectandmeasureairvolume.Anexittubemaintainsconstantpressure.SteadyStateConductivityTestMatricsuctionisvariedandsteadystateflowisinducedtomeasureconductivity.Soilairandwaterpressuresandoutflowratesaremeasured.Testsareverydifficultandtimeconsumingforfinegrainedsoils.InstantaneousProfileTestWaterorairisinjectedintothesoilatsteadyratesandwatercontentorporewaterpressuresaremeasuredatseverallocationsatvarioustimes.Watercontentandhydraulicconductivitycalculationsdependonthetestprocedureandtypeofmeasurements.Single-StepandMulti-StepOutflowTestsThesoilairpressureisvariedandthewateroutfloworinflowratesaremeasured.Theuseofsensorsisoptional.Hydraulicfunctionsarecomputedusingananalyticalornumericalsolution.Geo-centrifugeTestingCentrifugesareusedforevaluatingpetroleumyieldsfromrockcores,formeasuringhydraulicpropertiesofsoilsandcontaminanttransportinsoil.Largeandsmall-scalegeo-centrifugesareused.Includesensorsanddifferentmethodsofanalysistocomputehydraulicproperties.LaboratoryTestsattheUniversityofToledoMulti-steptestsareconductedusingthemodifiedtriaxialapparatus.Hydraulicconductivityiscomputedfromanalyticalsolutionthatusessoildiffusivityandthataccountsforthesystemimpedance.AnalyticalSolutionforDiffusivityThegoverningequationfor1-DflowisHydraulicconductivityiscomputedfromAnalysisProcedureNormalizedoutflowisplottedversusanon-dimensionaltimefactor.Parametersarevariedintheequationfortheoreticaloutflowuntilthereisgoodagreementbetweentheoreticalandexperimentalcurves.Hydraulicconductivityiscomputedfromthediffusivityusedinthecalculation.ComparisonofMeasureandTheoreticalOutflowSoil-WaterRetentionCurveHydraulicConductivityFunction2.00E-101.20E-092.20E-093.20E-094.20E-095.20E-096.20E-097.20E-090100200300400500MatricSuction(kPa)Conductivity(cm/sec)InverseModelingNumericalsolutionsthatusefinitedifferenceorfiniteelementproceduresareusedtobackcalculatethehydraulicfunctionsusinginversemodelingtechniques.Parametersrequiredforthecurvefittingequationsareobtainedusingoptimizationtechniques.VadoseZoneModelsFutureWorkLaboratoryProceduresProceduresformulti-stepoutflowteststhatdonotrequireinstrumentedsamples.Measurementofsystemimpedance.Measurementofsaturated/unsaturatedhydraulicconductivity.DataAnalysisComparisonofhydraulicfunctionsdeterminedfromanalyticalsolutionwithknownsystemimpedancetonumericalmodelingofmulti-stepoutflowtestsusinginversemodeling.Useofnumericalmodelingtoinvestigatehysteresiseffects.BeyondtheLaboratoryModelingflowinthevadosezoneusingprogramsthatcoupleheatandmoistureflowandcontaminanttransport.Investigationofthemovementofbothliquidandvaportransportinthevadosezone.