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-

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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

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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

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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

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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

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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.

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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

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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

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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

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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

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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

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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)

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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.

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Fig. 14 Macadam pavement built on lime stabilization (Ver. 6)

Fig. 15 Unsurfaced lime stabilization (Ver. 5)

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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