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HomeMy WebLinkAboutNantucket Short Plat-Pavement Design _LUA16-000217, MODemsawtCommunity&EconomicDevelopmentDepartmentC.E.”Chip”Vincent,AdministratorApril4,2016MichaelCrowsonMundyioHoldings,LLC2800156thAvenueSE,Suite120Bellevue,WA98007Subject:AlternateProceduralRequest—AlternativeStreetPavementSectionNantucketAvenueShortPlat(U15-001403andLUA6-000217)DearMr.Crowson,WehavereviewedyourrequesttoconstructanalternativepavementdesignfortheprivateroadwaywithintheNantucketSubdivisionfromtherequitedfourinches(4”)ofasphaltoversixinches(6”)ofcrushedrocktotherequestedtwoinches(2”)HMAoverfourinches(4”)crushedrockbaseovertwelveinches(12”)minimumofpitrungravelbase.PerRMC4-9-250.E.2,theCityofRentonhasreviewedthealternativerequestandthegeotechnicalreportanalysisenclosed.Baseduponthegeotechnicalanalysisprovided,thealternativepavementdesignprovidesanincreaseinstructuralstrengthoftheroadwayfromtheCoderequiredpavementsection.Inaddition,itdoesnotalterthesuitability,effectiveness,durability,safety,maintainability,orenvironmentalprotectionoftheprivatestreet.Therefore,thealternativepavementsectionisapproved.Notethatthisapprovedalternativepavementsectionisonlyapplicabletotheprivatestreetwithinthisproject.Thedecisiontoapprovethealternativedesignwillbecomefinalifnotappealedinwritingtogetherwiththerequiredfeeto:HearingExaminer,CityofRenton,1055SouthGradyWay,Renton,WA98057onorbefore5:00pmonApril18,2016.AdditionalinformationregardingtheappealprocessmaybeobtainedfromtheCityClerk’soffice,RentonCityHall—Floor,425-430-6510.Ifyouhaveanyfurtherquestionsregardingutilityordrainagerequirementsforthisproject,pleasecontactJanlIlianat425-430-7261orjillian@rentonwa.gov.%ely,BrianneBannwarth,PDevelopmentEngineeringManagerEnclosures:NantucketShortPlat,PrivateDrivePavementSectionpreparedbyTerraAssociates,Inc.onMarch16,2016cc:JenniferHenning,CEDPlanningDirectorJanlIlian,CEDPlanReviewerPatrickDeCaro,CEDSiteInspectorRentonCityHall•1055SouthGradyWayRenton,Washington98057•rentonwa.gov DESIGNTERRAASSOCIATES,Inc.NIE1’VItRJND{_T1TConsultantsinGeotechnicalEngineering,GeologyandEnvironmentalEarthSciencesTo:MichaelCrowsonDate:March16,2016MundyJoHoldings,LLCProjectNumber:T-7303-2from:TedSchepper,P.E.ProjectName:NantucketShortPlatSubject:PrivateDrivePavementSectionRenton,WashingtonRef:TerraGeotechnicalReport,11-4-15Michael:Inthereferencedreportwehadprovidedarecommendedpavementsectionconsistingof2inchesofY2inchhotmixasphalt(HMA)over4inchesofcrushedrockbase(CRB)fortheprivateaccessdriveontheeastsideoftheproject.Thissectionwastobeconstructedoverapreparedstablesubgradeconsistingofonsitenativemineralsoils.LaboratorytestingtodeterminethesupportingstrengthofthesubgradeasmeasuredbytheCaliforniaBearingRatio(CBR)indicatescompactednon-yieldingsubgradeconsistingofthenativesiltysandsoilswouldexhibitaCBRequivalentto26.ThisCBRwouldcorrelatetoasubgrademodulus(Mr)of25,000psi.BackcalculationtodeterminethedesigntrafficthatcouldbesupportedbythesectiondeterminedthatthesectionwouldbestructurallyadequateforanI8-kipequivalentsingleaxleload(ESAL)of100,000.ThisESALrepresentsan80,000poundtractortrailerrigtraversingthepavementstructureapproximately4timesaday,365daysayearovera30yeardesignlife.Thesectionismorethanadequatetosupporttrafficloadingincludingemergencyresponsevehiclessuchasfiretrucksthatcouldbeexpectedfortheshortplat.Asweunderstandpreparationoftheroadsubgradewillbecompletedshortly.Asyouareawarethecurrentoveroptimummoisturecontentofthenativesoilswillnotallowforcompactingthesoilstoastablenon-yieldingcondition.Toprepareastablegrade,werecommendthattheunstablewetsoilsberemovedtofirmandstablesubgradeandgraderestoredusingapitrungravelbase.Basedonconditionsobservedinthefieldthegravelbasethicknesswouldbeaminimumof12-inches.Ifconditionswarrantageotextileseparation/reinforcementfabricsuchasMirafi500Xshouldbeplacedonthenativesoilgradefollowedbyplacementofthegravelbase.Whenincludingthispitrunasagravelsub-baseinthepavementsectionthestructuralcapacityofthesectionasmeasuredbythesectionstructuralnumber(SN)willbegreaterthantheCityofRentonrequiredsectionconsistingof4-inchesofHMAover6-inchesofCRB.LaboratorytestresultsandpavementdesignsectioncalculationssupportingtheaboveareattachedforCityofRentonPublicWorksreview.Pleasecallifyouhaveanyquestionsorrequireadditionalinformation.Attachments:CBRLaboratoryTestResultsPavementDesignSectionCalculations12220113thAveNE,Suite130,Kirkland,Washington98034PhoneNo.(425)821-7777Fax:8214334 CaliforniaBearingRatioSoilTestsSummaryNantucketShortPIatRenton,WashingtonSampleNumber:1SampleLocation:PrivateDriveSubgradeSoilType:SiltySandUSCSClassification:SMGrainSizeDistribution:GravelFraction:7.7%SandFraction:51.6%FinesFraction:40.7%LaboratoryMoistureDensity:Seeattachedproctorcurve.MethodofTest:ASTMDl557MaximumDryDensityfpcf)117.6OptimumMoistureContent(%)13.2CaliforniaBearingRatio(CBR):RemoldedUnitWeight(pcf):115.7RemoldedMoistureContent(%):13.2SurchargeWeight(lbs.):10PercentSwell(48hrs.soak)0.15CBR.1”penetration21CBR.2”penetration26 TERRAASSOCIATES,INC.LaboratoryMoistureDensityCurveProjectName:NantucketShortPlatProjectNumber:7303-2SampleID.:CSampleLocation:RoadSubgradeSoilType:Brownsiltysand(SM)MethodofTest:ASTMD1557MaximumDryDensity(pcf):117.6OptimumMoistureContent(¾):13.2SieveAnalysisUSStandardSieve___ _ _ _ __ _ _ _ __ _PercentPassing98.395.992.340.73/4,,3/8”#4#200ZeroAirVoidsGs=2.65UU,CCC124.0122.0120.0118.0116.0114.0112.0110.0108.0rr..t-t8.010.012.014.016.018.020.022.0MoistureContent(%) AASHTO--PavementAnalysisProgram(2)NantucketShortPlat—PrivateAccessRoadHMASectionFlexibleAnalysis*StructuralNumber1.39*DesignE18’s100,000*Reliability90.00percent*OverallDeviation0.45*ResilientModulus25,000.0psi*InitialServiceability4.50*TerminalServiceablity2.00LayerLayerDrainageLayerNumberCoefficientCoefficientThicknessa(i)*Cd*t==a(1)======Cd===t===HMA0.441.002.00.88CR30.141.004.00.56TotalSN=1.44>1.39DesignLife=30years80,000poundGVWSemi-TractorTrailerTruckFactor=2.39NumberoftrucksrepresentingDesignESALof100,000=l00,000/(30x365x2.39)3.82trucksperdayStructuralNumber(SN)ofsectionwith12inchesofgravelsub-base.SN=(2x.44)+(4x.14)+(12x.1)=2.64SNofCityofRentonSectionSJEL)>ISN=(4x.44)+(6x.14)=2.60