evaluation of the effect of lime-stabilized subgrade on the performance ... · pdf...
Post on 31-Jan-2018
234 Views
Preview:
TRANSCRIPT
Originalscientificpaper
Croat. j. for. eng. 36(2015)2 269
Evaluation of the Effect of Lime-Stabilized
Subgrade on the Performance of an Experimental Road Pavement
József Péterfalvi, Péter Primusz, Gergely Markó, Balázs Kisfaludi, Miklós Kosztka
Abstract
Forest roads should be constructed to provide economic wood transport routes while causing minimal environmental impact. Therefore, the extended use of local materials (soil, stone) is essential. As cohesive soils cannot be drained by gravity and saturated cohesive soils have low bearing capacity, their use as a building material raises problems. This issue can be solved by lime stabilizing the soil. An experimental road was constructed to evaluate the effect of lime stabilized cohesive soil on the pavements built on top of it. Nine pavement versions were built on three different thickness (15, 25 and 35 cm) of lime stabilized soil. A traditional pavement without lime stabilization was also built for comparison. The bearing capacity of the stabilized layers and the finished pavements were calculated. The long term performance of the pavements was tested by measuring the effect of artificial traffic on their bearing capacity. Results showed that the bearing capacity modulus of the lime stabilization was around 500 MPa. 25–35 cm of lime stabilization under the pavements was necessary for good long term performance. 35 cm thickness of the stabilized local soil was enough to withstand the applied traffic without serious damage. Therefore, lime treated cohesive soil can be recommended as a subgrade layer in for-estry conditions.
Keywords: forest opening up, lime-stabilization, road test, bearing capacity
1. IntroductionStabilizedlocalsoilcanusuallybeappliedasthe
subgradecourseofaroadpavement.Cohesivesoilscanbestabilizedbylime.Between1960and1970ap-proximately53kmofforestroadswerebuiltonlimestabilizedsubgradeinSouth-WesternHungary.Theeconomicandtechnologicalconditionsofthefollow-ingperiodwerenotconductivetothespreadingofthelimestabilizationmethod.Asaresultthestabilizationexperimentswereneglected.Nowadays,thetighten-ingeconomicsituation,theincreasingecologicalre-quirementsandtheappearanceofmodernrotarymix-ers and binding material feeders have led to therediscoveryofstabilizingmethods.Forreasonsofen-vironmentalprotection,theuseoflocalsoil,advanta-geousasinputofexternalmaterial(e.g.crushedstone)ontothearea,canbereduced.Limeasanadhesiveispresentinnatureandthequantityofapplicationisnotsignificant.
CurrentpublicroadregulationsinHungarydonot consider stabilized local soil as a bearing layer in thepavementdesignprocess.Stabilizationsarecon-sideredonlyassoil improvementmethods. Itwashypothesized that stabilized local soil canactasastandalonepavementtypeforlowvolumeroads.Toevaluatetherelevanceofthishypothesisanexperi-mentalroadwasbuilt.Thefirstaimoftheexperimen-talroadwastodeterminethebearingcapacityoflimestabilizedlayersthatcanbetakenintoaccountinthedesignprocessofforestroadpavements.Thestudyoftrafficresistanceofpavementsbuiltonlimestabi-lizedlocalsoilwasthesecondaimoftheexperimen-talroad.Byconstructingoneofthetestsectionswithonlylimestabilizedsoil,wehavetheopportunitytoexaminethepossibilitiesofthismethodintheim-provementoftrafficabilityofdirtroads.Finalpurposeoftheexperimentalroadistoprovethattheactualthicknessofcrushedstonelayerinapavement,builtontoalimestabilisedlocalsoilisreducible.Ifthevol-
J. Péterfalvi et al. Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282)
270 Croat. j. for. eng. 36(2015)2
umeofcrushedstonecouldbereduced,notonlyma-terialcostswouldbelower,buttransportationcostscouldbedecreasedaswell.
1.1 Soil treatment with limeLimehasbeenusedforalongtimetoimproveme-
chanicalpropertiesof cohesive soils.Byabsorbingwater,limetransformstolimehydrate,whileproduc-ingheat.Iflimehydrateismixedintothesoil,theCa++ ionsbindtothesurfaceofclayparticlesandtheyre-movewaterandotherionsfromthere.Asaresult,theplasticityindexofthesoildecreasessignificantly,andthesoilbecomesgranular(Szendefy2013).Ifenoughlimeisadded,thepHincreasessomuchthatclaypar-ticlesstarttodisintegrate.Theresultingaluminiumandsiliconionsreactwiththecalciumionsandto-gethertheyformhydrates.Thesehydratesformanet-workthatfurtherincreasesthebearingcapacityofthesoil(NLA2004).Accordingtoexperiences,moistco-hesivesoilscanbedriedbytheadditionof1–3masspercentageoflime.Inadditiontothedryingeffect,theresultofa3–5masspercentagelimetreatmentissig-nificant increase in the bearing capacity, the shearstrengthandtheoptimummoisturecontentofthesoil.Thequantityofthelimeisdeterminedbytheproper-tiesofthesoiltobetreatedandthelimeitself.Thecurrentpracticeofthequantitydeterminationistoconductlaboratorytests(Tárczy2007).Limestabilizedsoilscanbeproducedon-siteorat
amixingplant.Incaseofon-sitemixing,limecanbemixedrightintothesoilorsoilcanbeexcavatedandmixedwithlime.Thefirststepofon-sitemixingistospreaddryquicklimeordryhydratedlimeonthesur-faceof the soil tobe treated in thepredeterminedamount.Applicationofquicklimeismorefavorableduetoitshigherlimecontentandfasterreactions.Theproducedheatisalsohigherand,therefore,thecon-structionperiodmaybeextended.Thedownsideofquicklimeisthatitrequiresmorewateranditismoredifficulttomixwithsoilsthanhydratedlime.Limeapplicationcanbedonebyhandorbyma-
chines.Mechanical spreading ismore efficient.Theamountofappliedlimecanberegulatedbythefeederopeningandthespeedofthefeeder.Mixingcanbedonebyagraderorbyrotarymixing.Ifitscapacityisappropriate,theuseofarotarymixerismorefavorablesinceitachievesbettermixingqualityinlesstime.Wa-terhastobeaddedtothesoilasneededduringthemixingprocedure.Thismaybedonebywatersprayertrucksorarotarymixerwithwatersupplycapability.Mixingcangenerallybecarriedoutinonestage.Incaseofsoilswithhighclaycontent,itisappropriatetomixintwostages.24–72hoursshouldpassbetweenthetwo
mixingstages.Afterthefirststage,thesubgradehastobesealedbylightrolling.Inordertoachieveappropri-atebearingcapacity,thestabilizedsoilneedscompac-tion.Compactioncanbeperformedseveralways.Thecommonpracticeistouseasheepfootrolleroravibrat-ingsteelwheelrollerfollowedbyarubbertiredroller.Compactionshouldbecommencedshortlyaftermixingthoughadelayoffourdaysisusuallyacceptableinhumidconditions(Little1995,Tárczy2007).
1.2 Full scale road testsInordertodeterminethelimequantityandquality
suitableforagivensoil,laboratorytestsshouldbecon-ducted.Basedonthesetests,differentsoilandlimetypescanbecompared.Thoughthebestwaytostudythebehaviorofvariouspavementsandbasesondiffer-entsoilsistostudythemonrealliferoads.Sincethedeteriorationofroadsisaslowprocess,fullscaleac-celeratedpavement testinghasgainedground. Forthesetests,differentpavementtypesareactuallybuiltandtestsareconductedonthem.Theaimofthetestsisusuallytodeterminethereactionofdifferentpavementtypestoagivenamountoftrafficload(Metcalf1996).Themostwidelyknowntestsofthiskindwerethe
AASHO(AmericanAssociationofStateHighwayOf-ficials)RoadTests.TheseexperimentswerecarriedoutintheUSAbetween1956and1962.Theaimofthesetestswastodevelopamethodologyforhighwaypave-mentdesign.Forthisreason,470typesofpavementswerebuiltonweaksoil.Pavementsconsistedofsandygravel,crushedstoneandasphaltconcretecourses.Theexperimentalroadsectionwasloadedwithartifi-cialtrafficfortwoyears.Theconditionofthepave-mentswasevaluatedregularly.Evaluationwascarriedoutbyvisualdeteriorationassessmentandthemea-surementoflongitudinalroadprofileandcentralde-flection.Themostimportantresultoftheexperimentwasthedeterminationoftheconnectionbetweende-signparametersofpavements(equivalentthickness),axleloadandconfigurationaswellasthenumberofloads.Theresultingfunctionsprovedtobeusefulincaseofdifferenttypesofsoilsandpavements(High-wayResearchBoard1961).Theexperimentalroad»SERUL«(LavalUniversity
RoadExperimentalSite)wasbuiltinCanadaspecifi-callytostudyforestroadpavementsincoldcondi-tions.Severalpavementswerebuiltonthelocalsoil.Thestudyoftheeffectofdifferentsoiltypesismadepossiblebyathreemetersdeepconcretetroughtheexperimentsonthissitefocusedontheeffectofthaw-ingfrostingandofthewidthoftires(LeBeletal.2000).Behakconductedexperimentstostudytheeffects
oflimestabilizationin2011.Twotestsectionswere
Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282) J. Péterfalvi et al.
Croat. j. for. eng. 36(2015)2 271
builtwithlimeappliedin3%and5%,respectively.Centraldeflectionwasmeasuredandvisualdeteriora-tionassessmentwascarriedoutbeforeandafterthepassingofrealbutknownamountoftraffic.Centraldeflectionwaschangedfrom2.44mmto0.77mmin4monthsafterconstruction(Behak2011).InHungary an experimental roadwas built to
studypavements typical for agricultural roads. 72typesofpavementswerebuiltonsand.Pavementsconsistedofasphaltandcementconcretesurfacing,mechanical,cementandblastfurnaceslagstabiliza-tionsand/orcrushedstonebasecourses.Thepave-mentswereloadedwithatotalof11500ESAL(Equiv-alentStandardAxleLoad).Afterevaluatingtheinitialstateofthepavements,theeffectoffiveloadingperi-odswasmeasured.Meteorologicaldata(dailymin.andmax. temperature,precipitation, soil tempera-ture),performance(centraldeflection,deflectionbowl)andtrafficability(longitudinalprofile,rutting,crack-ing,potholingandothersurfacefailures)propertiesweredetermined.Basedonthesemeasurements, itwasconcludedthatthe11500ESALresultedincom-pletefailureonlyonthosesectionswhereconstructiondeficiencyoccurred.Cleardecreaseinthebearingca-pacitywasevinciblebycentraldeflectionmeasure-mentsonlyafterthelastloadingperiod.ItwasproventhattheAASHOdesignformulascanbeusedincaseof low volume roads, though they lead to slightoverdesign.Itwasalsoconcludedthatthevarioussta-bilizationmethodsaresuitableforagriculturalandforestroads(Kosztka1989).
2. Materials and MethodsAtestroadwasbuiltin2006toexaminethebehav-
iorofpavementsbuiltonlimestabilizedlocalcohesivesoil.Experimentswereconductedtodeterminethebearingcapacityofthelimestabilizedlayers.Artificialtrafficloadedtheroadbetween2007and2008andbearingcapacitywasmonitoredtoevaluatetheper-formanceoftheroad.Sincethen,reallifeforestrytraf-fichasbeenloadingtheroadandcontrolmeasure-mentsaregoingtobedonetoevaluatethelongtermperformanceofthepavements.
2.1 Test siteThe580mlongexperimentalroadislocatedatthe
ForestryofBánokszentgyörgyinZalaCounty,whichbelongstothe»ZalaerdőForestryCompany«.Thesubgradeoftheexperimentalroadwascon-
structedusingthemediumclaysoilinplace.Themostimportantsoilphysicalpropertiesareasfollows:
Þ liquidlimit,44.6%;Þ plasticlimit,22.4%;Þ plasticityindex,22.2%;Þ flowindex,18.4%;Þ maximumdrydensity,1.82g/cm3;Þ optimumwater-contentforcompaction,15%.Precipitationconditionswereanalyzedusingthe
data of themeteorological station of Bánokszent-györgy.Therewere94precipitationdays;forforestroadbuildingitmeansonlyalownumberofdaysforconstructingthesubgrade.Thesituationisespeciallydisadvantageousasthereisasignificantquantityofrainfall(694mm/year),whichslowsandcomplicatesdrying.Thisproblemisincreasingwithclaysubgradethatcannotbedesiccatedbygravity.Saturatedsub-gradespermanentlylosetheirbearingcapacityand,therefore, they cannot support pavement courses.Amongtemperatureconditionsinthetestedarea,frostandthawandtheirperiodicalternationareofessentialimportance for road constructionworks. Frequentthawfrosteffectcandamagethepavementandthuscanopenawaytowaterintothepavement.Frost-thawconditionscanbecharacterizedbythesedata:
Þ wintertemperature,+3,7°C;Þ Januarytemperature,–0,4°C;Þ numberoffrostdays,100–110days.
2.2 Designed pavementsDifferentpavementversionsweredesignedwith
aboutthesamedesignbearingcapacity.WeusedtheAASHOPavementThicknessDesignGuideforit.Thisequivalentthicknesswas30ecm.Roadsectionswiththesamelimestabilizationlayerthicknesseswereplacednexttoeachother.The15,25and35cmlimestabiliza-tionlayerwasbuiltusinglocalsoilinthefirst360me-ters.Ninedifferentpavementswerebuiltwithasphaltconcreteandcrushedstonesurfacesindifferentthick-ness,each40minlength.Threedifferentpavementcoursesweredesignedonthelimestabilizationlayer:
Þ wellgradedcrusheddolomitecourse;Þ hotasphaltbasecourse;Þ Finnishasphaltcourse.
Fig. 1 Cross section template
J. Péterfalvi et al. Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282)
272 Croat. j. for. eng. 36(2015)2
Themostimportantdimensionsofthecross-sec-tioncanbeseeninFig.1.Atraditionalpavement,with-outlimestabilization,wasbuiltinthelast220masacontrolsection.Thecontrolsectionwascomposedofsandygravelandcrushedstonelayersbuiltonthesubgrade.Tobetterunderstandthebearingcapacityofthelimestabilizationlayer,the5thpavementversionwasbuiltwithjust35cmlimestabilizationlayerandwith2cmoffinecrushedstone.Fig.2showsthecon-structedpavements.
2.3 Lime stabilization bearing layer constructionConstructingthelimestabilizationlayerwasdone
asfollows:Þ pumpingpowderedquicklimeintothebindingmaterialfeeder;
Þ bringingthebindingmaterialfeedertothestart-ingpointofconstruction;
Þ calibratingthebindingmaterialfeeder;Þ checkingthebindingmaterialfeeder;Þ spreadingthebindingmaterial;Þ mixingwithasoilmillingmachine;Þ compactingwiththevibrationroller.Thebindingmaterialfeederspreadthepowdered
quicklimeonthewholesurfaceofthesubgradeintwopasses.Thespreadingdidnotoverlap;therefore,thespreadingwasinaccordancewiththeplan.Thesoilmillingmachineperformedthemixingintwocourseswithoverlapping(Fig.3).Duringthemixing,thema-chinesetthethicknessofthemillingautomatically.
Theproduction linefinished the lime stabilizationwiththreedifferentthicknessesandawidthof3.50minthreehours.
2.4 Mechanical model of pavementsThelayersstabilizedwithlime,andthemechanical
parametersofgranularlayerswithoutbindingmaterialwithinthemultilayeredpavements,canberepresentedwithintheelasticpavementstructuremodelshowninFig.4.Atthebottom,themodelofthecompletedsub-gradecorrespondstothecalculationofsinglelayersys-temsaselastic,homogeneousinfinitehalfspace;thatis,ourtopicwillbeamassofunlayeredsoil,boundedwith
Fig. 2 Pavement versions
Fig. 3 Soil milling machine
Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282) J. Péterfalvi et al.
Croat. j. for. eng. 36(2015)2 273
horizontalplane,itsdimensionsareinfinitehorizon-tallyandindepth.TherearelayersofH2thicknesssta-bilizedwithlimeoverthesubgradealongtheexperi-mentalroadsections;overthem,therearegranular(i.e.macadam)baselayersofH3thicknesswithoutbonding.Overallthese,thereareasphaltconcretelayersofH4 thicknessaltogether.ThelayersaredescribedbytheE1,E2,E3,E4moduliandtheμ1,μ2,μ3,μ4Poisson’srationum-bers(Huang2003).Theloadisaca.2r=30cmdiametercircleshaped,steadyloadcomingfroma50kNweight,which nearly equals the tire pressure of big trucks p=0.7MPa.MoredetailsaboutanalyticalsizingofelasticpavementscanbereadintheworkofBoczetal.(2009).
2.4.1 Correspondences of infinite homogeneous half spaceIntheappliedmodel,theground/subgradeisload-
edwithapweightactingona2r=30 cmdiameterrigid/flexibleplate.Theestimatedcalculationofshapechangescausedbyweight,regardingtheelasticho-mogeneoushalfspace,wasworkedoutbyBoussinesqin1885.Thedeflectionformulaisthefollowing(Yo-derandWitczak1975):
( )21 pE c r
dm= × − ×
(1)
Where:E elasticmodulusofhalfspacematerial,MPa;c Boussinesqplatefactor(c=p/2stiffandc=2,0elas-tic);
r radiusofappliedplate,mm;p greatestpressureapplied,MPa;d verticalexcursionundertheplate,mm;μ Poissonratio(–).Intheformulaabove,μstandsforthePoissonratio,
thewellknownmaterialparameterinelasticitystud-ies.Thevalueofthismayvarybetween0≤μ≤0.5.Ifthesoilisconsideredasincompressibleliquid(cohesivesoil(clay)),itcanbeμ=0.5.Inthisway,thesubgradecanbecalculatedashomogeneouselastichalfspace.
2.4.2 Solution for the two layer systemTheexactsolutionforthetwolayersystemfrom
mathematicalmechanicalpointofviewwasgivenbyBurmisterin1945.Later,hegeneralizedhismethodfor nlayers,between1954and1956.Healsopresentedadiagram(Fig.5) for thesolutionof thetwolayersystem–topreventdifficultcalculations.Tocalculatethecentrebending,heappliedtheformulausedforsinglelayersystems(Burmister1945):
( )2
1
2 1 p rd FE
m×
= × − × (2)
Intheformula,themodulusofthelowerlayer(thehalfspace)istakenintoaccount,whichisthenmulti-pliedwithanFdeflectionfactor,definedonthebasisoftheknownh/r and E2/E1rates.Thedeflectionfactorequalsthefraction,
1
e
EF
E= (3)
Where:Ee equivalentsurfacemodulus(Nemesdy1985).Itisimportantthatthesurfacemodulusisnota
layermodulus,butanaverageparametertypicalofall
Fig. 4 Model of flexible pavements
Fig. 5 Diagram by Burmister (1945) for two layer systems
J. Péterfalvi et al. Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282)
274 Croat. j. for. eng. 36(2015)2
thelayerstogethercomingfromthemeasurementsdoneonthesurfaceofthemultilayersystems(Papa-giannakisandMasad2008).
2.4.3 Defining the modulus of granular layersThemodulus of the layers consisting of round
grainswithoutbondingmaterialdependsonthemod-ulusofthelayerbelowthem.Oneoftheoldestsolu-tionsisappliedintheShellsizingmanual(Claussenetal.1977):
0,452 1 20.2E E H= × × (4)
Where:H2 thicknessofthemacadamorgranularlayer,mm;E1 modulusofthebottomlayer,MPa.
Thedefectofthiscorrespondenceisthatitdoesnotmake any quality difference between the crushedstoneandtheroundgraincourses(Nemesdy1991).Thisdefectisthencoveredbythesignificantwork
ofBarkeretal.(1977).Theystudiedthethickergranu-larbaselayerswithintheelasticpavements,makingdifferencesbetweenthemacadamandthemechanicalstabilization.Itcanbeappliedtocrushedstonefoun-dationswiththefollowingformula(Barkeretal.1977):
( ) ( ) ( )( )2 1 2 1 21 10.52 log 2.10 log logE E H E H= × + × − × ×
(5)Togravelfoundations,mechanicalstabilization:
( ) ( ) ( )( )2 1 21 7.18 log 1.56 log log2 1E E H E H= × + × − × × (6)Themodulusofthesandygravellayerscanalsobe
estimatedwiththiscorrespondence.Whenapplyingthesecorrespondences,itisimportanttoknowthattheEmoduliaregiveninpsi(poundspersquareinch),theHlayerthicknessesaregivenininchintheoriginalstudy(1psi=0.006894MPaand1inch=2.54cm).
2.5 Static and dynamic load bearing capacity measurementThemultilayermechanicalmodel of the elastic
pavementsrequireseachlayertobetakenintoaccountwith the thickness andmodulus values typical ofthem.Theloadbearingcapacitymodulusofthesub-gradeandthepavementcoursescanbedefinedwiththehelpofstaticanddynamicfieldmeasuringtools.Thestaticmoduluscanbemeasuredonthecom-
pletedsubgrade,astheloadbearingcapacitymodulusofthebottomlayerisconsideredasanelastic,homo-geneousandisotropichalfspace.Theplatebearingtestisatestinwhichaloadisappliedinincrementstothe
soilusingacircularloadingplateandaloadingdevice,releasedindecrementsandtheentireprocessisre-peated.Duringtheexperimentalprocess,a30cmdi-ameterelasticplateisloadedwithe.g.ahydraulicjackandtruckbalance.Theloadisappliedinincrements,waitingfortheconsolidationtime,whilethedeforma-tioncausedbytheloadisbeingmeasured.Reachingthep=0.40MPapressure,theplateisunloaded,thentheprocessisperformedagain.Thepressuredeforma-tioncurvescannowbeplottedusingthedataofthetwoloadprocesses.Thestaticmodulusofthesubgradeiscalculatedonthebasisofthesecondloadplatepro-cess(thisiswhynumber2isshowninthesubscript)usingtheno.(1)deflectionformula.Seeingthegeomet-ricdimensionsoftheplateappliedattheE2 staticex-periment,aca.75cmthickupperlayercanbestudied(v ≤ 2.5 ́ D » 75cm).Doingthecalculations,rigidplatemodel andmaterial dependent Poisson ratio (clayμ=0.5,limedsoilμ=0.3)weretakenintoaccount.Thedisadvantageofthestaticexperimentsisthattheyareverytimeconsumingandnotproperlymodelingthemovingwheelstressoftrucks.Thesedisadvantagesareintendedtoeliminateusingthedynamictools.Thedynamicweightmeasurementmethodrecords
theshapechangecausedbyan18±2millisecondsloadofaca.10kgweightdroppedfrom70–75cmheight.Theweightisthesameastheweightappliedinthestaticmeasurement.Theexperimentmodelsthemate-rialbehaviortypicalofdynamicweight,sinceconsoli-dationcannottakeplaceinsuchashortperiodoftime.Thedynamicloadbearingcapacity(Ed)methodisca-pabletostudybasecourseorsubgradewithatmost63mmbiggestgrains,andthickatmosttwicetheplatediameter(30cm)(Subert2005).InthecaseoftheB&C(Bearing Capacity&Compaction Rate Tester) smallplatelightdropweightdevice,thedynamiceffectisthe16cmdistancecoveredbyatruckdrivingatca.35km/h.Thedynamicloadbearingcapacitymodulusofthesubgradewasdefinedatfivepointsoneachex-perimentalroadsection.Fourmeasurementswereper-formedinthelineoftheexpectedtracks(twoofthematthebeginning,andtwoattheendofthesection),andonemeasurementwasmadeinthemiddleofthesec-tion.Attheplaceofthemeasurement,preloadwasperformedwith threedrops, then threemeasuringdrops.Theaveragevaluesofeachmeasuringpointsweredefinedwiththehelpofthethreemeasuringse-ries(intriangleformation).Thismeans5 ´3=15mea-surementsperexperimentalsections.Duringthecal-culations,rigidplatemodelandvariablePoissonratiowereapplied:theexpectedvaluewasμ=0.5inthecaseofclay,andμ=0.3inthecaseofsoilmixedwithlime.Theresultedmodulusvaluesweregivenasintegers.
Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282) J. Péterfalvi et al.
Croat. j. for. eng. 36(2015)2 275
2.6 Measuring the central deflection with Ben-kelman beamThebearingcapacityofapavementcanbecharac-
terizedbytherateofelasticdeformationcausedbyload.Themethodbasedonthemeasurementofcen-traldeflectioniswidelyused.Itgenerallyprovidesgoodandreliableresults.ThedeflectionismeasuredwithaBenkelmanbeamof2:1measurementprobesupportbeamratio.Thetipofthemeasurementprobeisplacedunderthedualtireofaloadedtruck,wherethemaximumdeflectionisexpected.Centralmaxi-mumdeflectionistheelasticdeformationmeasuredwiththebeamconvertedto50kNwheelload.Itisassumedthattheconversionislinear.Deflectionmea-surementwasdevelopedspecificallyforasphaltpave-ments,howeverweusedittocharacterizetheunsur-facedlimestabilizedcourseaswellforinformationpurposes.Accordingtotheexperiencesgatheredsofar,thelimetreatedlayersworktogethersufficientlyandtheyactasaflexiblebasecourse.Incaseofthecrushedstonepavementtypes,Benkelmandeflectionmeasurementswerenotcarriedout.Themeasurementofcentralmaximumdeflection
wasperformedbeforeandaftereachloadingperiod.Therefore,thechangescausedbythetrafficloadbe-camecomparabletotheinitialstate.Measurementswerecarriedoutontheleftandrightwheeltrackineveryfivemeters.Thisdensityofdataprovedtobeenoughforstatisticalanalysis.
2.7 Artificial trafficThereactionsofdifferenttypesofpavementsto
loadswerestudiedbytheapplicationofartificialtraf-fic.TrafficwasgeneratedbytruckscharacteristicfortheHungarianforestrycompanies(IFA,KAMAZ,and
MAN,Fig.6).Axleconfiguration,andloadedandun-loadedaxleloadswereregisteredforeachtrucktype.Measurementsofaxleloadwerecarriedoutbywheelloadscales(Fig.7).Theprecisionofthemeasurementswas±50kg.The
experimentalroadwasloadedintensively.Thenum-berofpassingtruckswasregistered.Differentaxleloadswereconvertedto100kNESALbytheuseofequivalentaxleloadfactors.Basedontheweightoftimbertobetransportedandthetypeoftrucksused,traffic(T100)couldbecalculated.ThenumberofESAL-sontheexperimentalroadisshowninFig.8.Duringthetestperiod,2100ESALartificialtrafficwasapplied.Sinceloadingwasnotcontinuous,theintensityoftraf-ficwashighduringtheloadingperiods.
3. Results and discussion3.1 Bearing capacity modulus of the subgradeAstoalltenexperimentalsectionsstaticE2values
weretriedtobedefined.Themeasurementsweremadebyturnsatthecentreofeverysection,andleftandrightfromit,inthelineoftheexpectedtracks.Unfortunately,onthewetsubgradethemeasurementcouldbesuccess-fullyperformedatonlytwosections.Thoughthesere-sultsagreedquitewellwith themeasurementsper-formed in advance, an average of 10MPa bearingcapacityvaluewasdefinedonthesubgrade.
3.2 Evaluation of the static and dynamic load bearing capacity measurementsAfterbuildingthelimestabilization,theincrease
ofbearingcapacitywas studiedwith two typesofmodeleffect(static,dynamic).Thedataseriesofthe
Fig. 6 Characteristic vehicle of artificial traffic Fig. 7 Wheel load scaling
J. Péterfalvi et al. Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282)
276 Croat. j. for. eng. 36(2015)2
Fig. 8 Artificial traffic on the experimental section
Table 1 Values of the moduli determined by plate bearing tests
Ver. Thickness of lime stabilization, cmBearing capacity E2, MPa
Earthwork Lime, 0 h Lime, 24 h Lime, 48 h
01 25 – – 34 45
02 25 – – 53 65
03 25 – – 53 53
04 35 – – 53 69
05 35 9 – 50 54
06 35 12 – 41 50
07 15 – 19 27 38
08 15 – 36 39 43
09 15 – – 37 45
10 None 10 – – –
MEAN 10 28 43 51
twotypesofmeasurementswereintendedtodefinethestaticmodulusnecessaryforplanning,sincethecurrent technical regulation contains specificationsaboutthis.Apartfromthelimestabilizationlayers,theloadbearingcapacitychangesofthepavementsbuiltuponthelimestabilizationlayerswerealsostudied.Static(E2)anddynamic(Ed)loadbearingcapacityval-uesweredefinedasmentionedabove.InpavementversionsNo.2and7(Asphaltconcrete(AC22)bind-
ingcoursewithlargeshearstrength),theB&Clightdropweightdevicedidnotshowanyexcursions,soitwasnotpossibletoperformthemeasurement.Duringthecalculations,thePoissonratiowasμ=0.5.Themea-surementresultsareshowninTable1and2.Accordingtotheprofessional literature,thedy-
namicmeasurementmodulusdoesnotcorrespondtothestaticmeasurementloadbearingcapacitymodulusnortothesoil,soageneralcorrespondencecannotbe
Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282) J. Péterfalvi et al.
Croat. j. for. eng. 36(2015)2 277
given(Subert2005).ThistopicisdetailedinTompai’sessay(2008).Parallelmeasurementsareneededtode-finethethresholdlimitvaluestypicalofthetypeofmaterialandtheconditionsoneverytypeofsoil,gran-ularpavementlayer,ineverycase.Themeasurementsperformedonthelimestabili-
zationshowedthattheloadbearingcapacityvalues
definedwithdifferentmodeleffectsarenearly thesame.Fig.9clearlyshowsthatboththe24hoursandthe48hoursstatic(E2),andtheaveragedynamicmod-ulus(Ed)valuesshowsimilarresults.Therefore,theloadbearingcapacityvaluesdefinedwithdynamicmodeleffectcanbeconsideredequaltothestaticE2 neededforplanning.Theincreaseofloadbearingcapacityofthelime
stabilizationwasfollowedupthroughfivedayswiththeB&Cdevice.Themeasurementresultsaresum-marizedinFig.10.Accordingtothemeasurements,thelimestabilizationlayerthicknessandtheincreaseofloadbearingcapacitydonotcorrespond.Thesoillimereactionisaquitecomplexprocess,andthereareseveralfactorsthataffecttherateofloadbearingca-pacitythatarenotyetrevealed.Oneofthemostprob-ablecauseisthehighheterogeneityofthesoilwatercontent,whichcanhaveasignificanteffectonthereac-tionofthesoillimemixture.Inspiteofallthis,itcanclearlybeseenthatthehighestincreaseofbearingca-pacitywasproducedinthe25cmand35cmthicklimestabilizationexperimentalsections.Duringbuilding,thelimestabilizationwasfollowedbythespreadingandcompactionofthecrushedstonecourse,onthesurfaceofwhich,theloadbearingcapacitywasalsomeasured.Thestudiesperformedonthesurfaceofthecrushedstonecoursesshowedthatthedynamicmod-uliareca.twiceasmuchasthestaticones.Thestaticanddynamicloadbearingcapacitymod-
ulimeasuredparallelonthesurfaceofthecompleted
Table 2 Values of the moduli determined by dynamic bearing tests
Ver. Thickness of lime stabilization, cmBearing capacity Ed, MPa
Subgrade Lime, 0 h Lime, 24 h Lime, 48 h Lime, 120 h
01 25 11 24 34 39 50
02 25 12 41 55 60 66
03 25 15 36 55 62 74
04 35 12 52 68 72 74
05 35 10 24 47 52 54
06 35 9 24 40 45 50
07 15 8 26 35 43 55
08 15 10 32 46 51 65
09 15 11 22 33 36 42
10 None 10 – – – –
MEAN 11 31 46 51 59
Fig. 9 Values of dynamic and static bearing moduli measured on the same sites
J. Péterfalvi et al. Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282)
278 Croat. j. for. eng. 36(2015)2
pavementsdonotshowcorrespondencewitheachotheratall.Themaincausemaybethat,whilethestaticloadbearingcapacitymeasurementcanstudya75cmthicklayer,thedetectionrangeofthelightdropweightmeasurementisonly30cm.Therefore,thedy-namicmeasurementisnotsuitabletostudythepave-mentsbuiltofdifferentlayers,sinceitcannotdetectthe favorableandunfavorable featuresof the sub-grade.
3.3 Bearing capacity modulus of lime stabilization layersTheresultsofthedemonstratedstaticanddynam-
icloadbearingcapacitymeasurementsshowthatthemodulusofthelimetreatedsoillayerscanbededuced.Thebuiltsubgradeandthelimestabilizationtogethermakeatwolayersystem.Sincetheloadbearingcapac-itymodulusofthecohesiveclaysubgradeisknown(10MPa),andalsotheHthicknessofthelimetreatedlayersandthe(Ee)valueofthesurfacemodulimea-suredontheirsurface,theFdeflectionfactorcanbecalculatedusingcorrespondenceNo.(3).AccordingtothetheoryofBurmister(1945),themodulusoftheH thicknesslimetreatedlayercanbedefinedknowingtheseparameters(Fig.5).Afterthecalculations,themodulusofthelimestabilizationlayersresultedasElime=500MPa,whichisalmostthesameasthemodu-lusofawellcompactedcontinuousgraindistribution
macadamlayer.Accordingtothisresult,thelimetreat-edsoillayerscanbecountedaspavementlayers,fur-theron.Itisalsopossibletooriginatethistwolayersystem
inasinglelayersystem,whichbehavessimilarlytotheoriginalone,underthesameconditions.Accordingtothecurrentpublicroaddesignregulations,thelimestabilizationiscountedasimprovedsubgrade,andnotasapartofthepavement.Inthiscase,themodulusoftheimprovedsubgradeistheequivalentsurfacemodulus(Ee)definedonthesurfaceofthetwolayersystem.According to thefieldmeasurements, thisvaluewasdefinedtothreethicknessgroups:
Hlime=15cm Eis.=40MPaHlime=25cm Eis.=50MPaHlime=35cm Eis.=60MPa
Where:Hlime thicknessofthelime-treatedlayer;Eis. modulusoftheimprovedsubgrade.
3.4 Load bearing capacity modulus of granular layersThemoduliofthegranularlayerswereestimated
withthecorrespondencesbyBarkeretal.(1977),de-scribedinpoint2.5.3.Thelimestabilizationlayers,asimprovedsubgrade,wereintroducedintothemodel.
Fig. 10 Increase of bearing capacity of lime stabilized layers as a function of time
Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282) J. Péterfalvi et al.
Croat. j. for. eng. 36(2015)2 279
TheresultsofthecalculationsaresummarizedinTable3.Itcanclearlybeseenthat,inthecaseofthecontrolsection, themoduliof thegranular layerswerethelowestbecauseof inappropriatecompactionof thesubgrade.Atver.9builtwiththesametotalthickness(15 cm lime stabilization), the crushed stone layermoduluswas150MPa,whichismorethantwiceasmuchasthetraditionalsolution(15cmsandygravel).Wherethethicknessofthelimestabilizationis35cm,theloadbearingcapacitymodulusoftheimprovedsubgradeequalstheloadbearingcapacityoftheentirepavementcontrolsection.
3.5 Cost of pavementsTheestimatedbearingcapacitiesofpavementver.
6andtraditionalpavement(thecontrolsection)aresimilar.Therefore,theirconstructioncostscouldbecompared.Bothpavementtypeswerebuiltwiththesamewidth,thereforetheirconstructioncostswerecalculatedperlinearmeter.ThecostsareshowninTable4onthepricelevelof2006.Basedonthisdata,itcanbestatedthat,underthegivencircumstances,thepavementwithlime-stabilizationwashalfasex-pensiveasthetraditionalone.
3.6 The effect of traffic on experimental roadAccordingtothedeflectionmeasurements,thefol-
lowings can be stated about the sections after theevaluationofthemeasurementresultsandfieldwork.Generally,theexperimentalsectionsperformedwellundertrafficload.Theexperimentalpavementsgot
moreorlessdeformedduetotheartificialtraffic.ThemaingoaloftheBenkelmanbeammeasurementswastodeterminethedeteriorationcurveofpavements.Thecentraldeflectionchangingwaslinearcomparedtothetraffic.Asaresultofoneyearresting,thepave-mentsofallversionsregenerated.Theregenerationisclearlyvisibleonthecentraldeflectiondata(Fig.11).Onpavementswith25cmand35cmthickstabilizedcourses,deflectionvaluesaresimilar,whilehigherde-flectionweremeasuredontheoneswith15cmstabi-lizedcourses.Acertainpartoftheevolveddeformationsdoesnot
correspondtothesizeofthetraffic,butwascausedbytechnologicalproblems.Thedeteriorationofthepave-mentversionsstartedin2008.Thepavementofthecontrolsection(ver.10)wascompletelydeterioratedonthewholelength,the15cmthicksandygravelandthe30cmthickcrushedstonelayeraboveitentirelymixedwitheachother.ThishugedeformationwasalreadyexperiencedatT100=700ESAL.Thereasonwasthatthesandygravelandthecrushedstonecourseswerenotproperlycompacted.Asanimpactofthetraf-fic,undertheimproperlycompactedpavement,thesoilfailed.Besidethecontrolsection,therewerethreepavementversionswherehugedeformationsevolvednotconnectedtothesizeoftraffic.OnthefirstFinnishasphaltsection(ver.3),abig
rutevolvedalongtherightsidetrack,whichisprob-ablyjustalocalfailure.Thiswasconfirmedbythestatistic process of the deflectionmeasurements.Thefailurewasalsopredictedduringthegraphical
Table 3 E moduli of granular layers by pavement versions
Ver.Subgrade Granular layers
E, MPa H, cm E, MPa
1 50 25 170
2 50 15 120
3 50 15 120
4 60 0 0
5 60 2 0
6 60 15 160
7 40 15 120
8 40 15 120
9 40 30 150
10 10 45 60
J. Péterfalvi et al. Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282)
280 Croat. j. for. eng. 36(2015)2
processofthedeflectionmeasurements,andlater,thefailureevolvedasaresultoftheexperimentaltraffic.OnthesecondAC22(ver.7,Fig.12)sectionandonthever.8Finnishasphaltsection(Fig.13),therewerebigandlongdeformationsalongtheleftsidetrack.Thereasonisprobablyatechnologicalproblem,
again.Apartofthecrushedstonelayerundertheas-phaltlayer,becauseoftheimpropersidesupport,was
pushedsidelong,andtherefore,theasphaltlayergotdamaged under the large bending strain. The leftroadsideisnarrowerthantherightone,andthewaterrunningawayfromtheasphaltwasleakinginattheroadsideingreateramount.Exploringthepavement,itbecameclearthatthelimestabilizationlayeralso»broke«undertheexperimentaltraffic.Themacadampavementsbuiltonlimestabilizationwereallingoodconditionafterthetraffic(Fig.14).
Table 4 Cost of traditional pavement and a pavement with lime stabilization
Traditional pavement Pavement with lime stabilization
Course thickness Material Cost, €/lm Course thickness Material Cost, €/lm
15 Sandy gravel 11.9 35 Lime stabilization 9.9
35 Crushed stone 27.7 15 Crushed stone 11.9
50 Total 39.6 50 Total 21.8
Fig. 11 Deterioration curves of experimental pavements based on central deflection data
Fig. 13 Left rutting on Finnish asphalt (Ver. 8)Fig. 12 Left rutting on AC 22 (Ver. 7)
Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282) J. Péterfalvi et al.
Croat. j. for. eng. 36(2015)2 281
Theunsurfacedlimestabilization(ver.5,Fig.15)enduredthetrafficverywellsofar;thetireseraseda1cmthicklayerfromthesurface,therefore,acertaindepthofrutevolved,thoughfarfromthelevelitcouldbeobjected.Biggercrackscouldbeobservedonthesurface,asrecordedonphotos.
4. ConclusionsAtestroadwasbuilttoexaminetheeffectsoflime
stabilizedsoilassubgrade.Asexpected,theappliedlimeincreasedthebearingcapacityoftheoriginalco-hesivesoil.Whendesigningapavementwith limestabilizedmediumclaysubgrade,itcanbetakenintoaccountwitha500MPalayermodulus.Doingso,therequiredbearingcapacitycanbereachedwithsmalleramountofadditionalbuildingmaterials.Therefore,
transportationandconstructioncostsaswellasenvi-ronmentalimpactscanbereduced.Inordertogetsat-isfactoryperformancefromthepavementsbuiltoncohesivesoil,25–35cmoflimestabilizedsubgradeshouldbedesignedtosupportthem.Forlowtrafficroads,35cmofstabilizedlocalsoilwithathin(15cm)crushedstonesurfacingcouldbeenoughtoprovidetrafficability.25–35cmthicknesscanbeconstructedinonestageofmixingiftheconstructingmachineisap-propriate.Formixing,itisnecessarytoapplyaspecialrotarymixermachine,oramixingadapterattachedtoanagriculturaltractorwith150kWoutputpower.Basedon theexperiencesgained from the road
tests,a6kmlongforestroadwasbuiltwithstabilizedlocalcohesivesoilassubgrade.Itwasconfirmedthatpavementsbuiltonstabilizedcohesivesoilaredurableonlyifappropriatedrainageisprovided.
AcknowledgementsTheexperimentalroadwasbuiltascollaboration
betweentheRegionalKnowledgeCentreofForestandWoodUtilization(ERFARET),theInstituteofGeomat-icsandCivilEngineeringof theUniversityofWestHungary,theCarmeuseHungaryLtd.andtheZalaerdőForestryCompany.ResearchworkofPéterPrimuszwassupportedbytheEuropeanUnionandtheStateofHungary,co-financedbytheEuropeanSocialFundintheframeworkofTÁMOP-4.2.4.A/2-11/1-2012-0001»NationalExcellenceProgram«.Previousresearchforthisresearchproject:PéterPázmányprogramme(RET-03/2004),1.3.Technicaldevelopmentofforestmanage-ment,Developmentofforestopeningupnetworks.Theprojectcompletiondate:2006–2008.
5. ReferencesBarker,W.R.,Brabston,W.N.,Chou,Y.T.,1977:AGeneralSys-temfortheStructuralDesignofFlexiblePavements.Proceed-ings oftheFourthInternationalConferenceontheStructuralDesignofAsphaltPavements,AnnArbor:209–248.Behak,L.,2011:Performanceoffull-scaletestsectionoflow-volumeroadwithreinforcingbaselayerofsoil-lime.Trans-portationResearchRecord, Journalof theTransportationResearchBoard2204:158–164.Bocz, P., Devecseri, G., Fi, I., És Pethő, L., 2009: Pályas-zerkezetekanalitikusméretezése.Közlekedésépítésiszemle59(5):8–22.Burmister,D.M.,1945:TheGeneralTheoryofStressesandDisplacementsinLayeredSoilSystems.JournalofAppliedPhysics16(2):89–94.Claussen,A.I.M.,Edwards,J.M.,Sommer,P.,Ugé,P.,1977:AsphaltPavementDesign.TheShellMethod.Proceedingsof
Fig. 14 Macadam pavement built on lime stabilization (Ver. 6)
Fig. 15 Unsurfaced lime stabilization (Ver. 5)
J. Péterfalvi et al. Evaluation of the Effect of Lime-Stabilized Subgrade on the Performance ... (269–282)
282 Croat. j. for. eng. 36(2015)2
theFourthInternationalConferenceontheStructuralDesignofAsphaltPavements,Vol.I,AnnArbor:39–74.HighwayResearch Board 1961: TheAASHORoad Test,Highway Research Board Special Report 61A, NationalAcademyofSciences:Washington,D.C.56p.Huang,Y.H.,2003:PavementAnalysisandDesign,SecondEdition,PrenticeHall,ISBN-13:9780131424739,792p.Kosztka,M.,1989:AMakk-pusztaikísérletiútonvégzettmegfigyelésekavékonyútpálya-szerkezetektönkremene-telénekfolyamatáról.ErdészetiésFaipariTudományosKö-zlemények2:25–36.LeBel,L.,Doré,G.,Provencher,Y.,2000:LavalUniversity’sfull-scaleexperimentalsiteforconstructionandmaintenanceofforestroads.ProceedingsoftheCOFE-CWFConference.11–14September,Kelowna,BritishColumbia,Canada.Little,D.N.,1995:Handbookforstabilizationofpavementsubgradesandbasecourseswithlime.LimeAssociationofTexas,USA.Metcalf,J.B.,1996:NCHRPSynthesisofhighwaypractice:Applicationoffull-scaleacceleratedpavementtesting.TRB,NationalResearchCouncil,WashingtonD.C.,USA.NationalLimeAssociation(NLA)2004:Lime-treatedsoilconstructionmanual.NationalLimeAssociation,USA.
Nemesdy,E.,1985:Útpályaszerkezetekméretezésénekésanyagállandó-vizsgálatainakmechanikaialapjai.KutatásirészjelentésI.,BMEÚtépítésiTanszék,Budapest.Nemesdy,E.,1991:Azúzottkőalapokéskavicsalapokszerepeéshatékonyságaazújút-pályaszerkezetekben.Közlekedé-sépítés-ésMélyépítéstudományiSzemle41(7):241–253.Papagiannakis,A.T.,Masad,E.A.,2008:PavementDesignand Materials, Wiley&Sons, Hoboken NJ, ISBN-10:0471214612,ISBN-13:978-0471214618,552p.Subert,I.,2005:Adinamikustömörség-ésteherbírásmérésújabbparamétereiésamodulusokátszámíthatóságikérdése.Közútiésmélyépítésiszemle55(1):5.Szendefy,J.,2013:Impactofthesoil-stabilizationwithlime.Proc.ofthe18thInternationalConf.ofISSMGEParis:2061–2064.Tárczy,L.,2007:Meszestalajkezelés.Közútiésmélyépítésiszemle(2):26–28.Tompai,Z.,2008:Földművekéskötőanyagnélkülialapré-tegekteherbírásánakéstömörsé-génekellenőrzésekönnyűejtősúlyosmódszerekkel.BudapestiMűszakiésGazdaság-tudományiEgyetem,ÉpítőmérnökiKar,Ph.D.theses,Buda-pest,162p.Yoder,E.J.,Witczak,M.W.,1975:PrinciplesofPavementDe-sign, Second Edition, John Wiley & Sons, Inc. ISBN:9780471977803,711p.
Received:April30,2014 Accepted:October06,2014
Authors’address–Adresa autorâ:
Assoc.prof.JózsefPéterfalvi,PhD.* e-mail:peterfalvi.jozsef@emk.nyme.hu Assist.prof.PéterPrimusz,PhD. e-mail:primusz.peter@emk.nyme.hu Assoc.prof.GergelyMarkó,PhD. e-mail:gergely.marko@gmail.com BalázsKisfaludi,MsC. e-mail:kisfaludi.balazs@emk.nyme.hu Prof.emerit.MiklósKosztka,CSc. e-mail:kosztka.miklos@emk.nyme.hu UniversityofWestHungary FacultyofForestry DepartmentofForestOpeningUp InstituteofGeomaticsandCivilEngineering Bajcsy-Zsilinszkyu.4. Sopron,9400 HUNGARY
*Correspondingauthor
top related