A Structural Reinforcement Layer with Woodchips Used on

Nova meh. šumar. 37(2016) 25

Originalscientificpaper–Izvorni znanstveni rad

A Structural Reinforcement Layer

with Woodchips Used on Forest Roads

Petr Hrůza, Petr Pelikán, Jaroslav Blahuta, Jiří Nedorost, Zdeněk Patočka

Abstract – Nacrtak

Described biotechnical measures focus on the use of woodchips in the formation of a struc-tural reinforcement layer on forest roads in the places with high levels of groundwater. These are often short sections of roads which can thus block off entire forests. In history, these sections were overcome using corduroy roads. Currently, there are tendencies to revive the biotechnical technology and replace logs used for corduroy roads with woodchips. This study investigates the possible reinforcement of a waterlogged section using woodchips in a forest road of multi-functional character, which serves for cycling as well as timber transport. In total, three dif-ferent types of reinforcement were constructed using woodchips in combination with geotex-tile and crushed stone. The reinforcement was tested by common operations using a timber extraction tractor with tandem axle trailer. The modulus of deformation was measured on the surface and the deformation characteristics of the layer were determined. Subsequently, the shape of the reinforcement cross-section was surveyed. The results have shown that, even with very low modulus of deformation values, the shape of the reinforcement cross-section does not change statistically in two types of the reinforcement technology. These two types of reinforce-ment can be successfully used for forest roads that perform the recreational function or for timber transport by tractor. The main advantages are that renewable material is used and no extraction and moving of the ground occur during its production.

Keywords: Forest road, reinforcement, corduroy road, woodchips, waterlogging, trafficability

1. Introduction – UvodThe reinforcement of forest roads is a broad issue

thatencompassesdifferentsolutions.Anappropriatesolution must take into account that forest roads need tomeettherequirementsoftimbertransport.Themax-imumpressuresofthedesignvehicle(haulingmachin-ery)axlesontheirsurfacearestipulatedbyvalidregu-lations(axle–10t,drivingaxle–12t).Additionally,theeconomicaspectisimportantasforestroadsareroadswithalowintensityoftransportandavarietyoftimberhaulingvehicles.Thesuitablesolutionofthereinforce-mentofforestroadsmustincorporatebothoftheseopposing requirements.Moreover, forest roadsareusedbythegeneralpublicforrecreationalpurposes.Allinall,aforestroadneedstobeconstructedsoastobeeconomicallyacceptableindirectproportionwiththerevenuesandcostsofforestmanagement,andatthesametime,abletoperformtherecreationalfunc-tion.Inthiscontext,itisnecessarytorealizethatforeststandsareoftenlocatedinterrainswhicharenotsuit-

ableforroadconstruction.TheCzechRepublicischar-acterizedbybroadvalleys,basins,hills,highlands,andmountains.Thisfactisreflectedintheprocessofland-scapeaccessing,since18.1%ofthebasesoilsareinflu-encedbyelevatedamountsofwateraccordingtoBučekandLacina(1999)classificationofhydricseries.15%oftheCzechRepublicterritoryfallsintothe4th water-loggedhydricseries,whichisdefinedbyan»addi-tional«amountofwaterinperiodicallyfloodedareasinriveralluvia.Excessofwatercanalsobefoundin3%of soils of the 5thwethydricseries.Itischaracterizedbymoreorlesspermanentlywetormuddysoils,thewatertableishigh,insomeperiodsmayevenreachthesurface.Evenindryperiods,onlythetoplayersgetdry.Itisverydifficulttobuildroadsinsuchareas:avoidtheircavinginbutalsomakesuretheconstructioniseconomicallyviablewiththetechnologiesused.Alongwiththedevelopmentofmeansoftransport

andtheir increasingtransportcapacity,effortshavealwaysbeenmadetoimprovetheloadbearingcapac-

P. Hruza et al. A Structural Reinforcement Layer with Woodchips Used on Forest Roads (25–35)

26 Nova meh. šumar. 37(2016)

ity of forest roads and thus increase the amount of tim-bertransportedwithinasingleroute.Theeffortisun-derstandable and well founded due to the fact that the timberharvestsitesareoftenremoteanddifficulttoaccess.Thefirstattemptsofroadreinforcementap-pearedinabout4000BeforeChristinGreatBritain(Lay1992),whenlogsandpoleswereusedtomakecordu-royroads.Thistypeofreinforcementwasespeciallyusedonsiteswithalowloadbearingcapacityaffectedbywater,whereputtingthepoletimberacrosstheroadcreatedawoodenboardwhichbetterspreadthepres-suresofvehicleaxlesintoanarea.Thepresenceofwa-terpreventscontactbetweenairandwoodandthusafasterdecompositionofthepoletimber.Eventoday,remainscanbefoundofsuchroadsfromthe16th cen-tury,forexampleinGermany(Johnson2014).Schmidtetal. (1997) investigated thephysicalandchemicalpropertiesofwoodchipsthatwereused19yearsagotostabilizetheroadnetworkinwaterloggedareasinMinnesota.Thesamplesfortheresearchwerecollectedfromtheroadfill:theupperlayeratadepthof55cmbelowtheground,andthelowerlayeratadepthof150cm.Thewoodchipshadbeenclosedwithalayerofsoil.Thestudiedsamplesshowedalowbacterialactivityandtheabsenceofmold.Thoughwoodchipshaddifferentmoistureholdingcapacities,theiroverallbulk density was essentially the same for locations withineachsite.Theabsenceoffungaldegradationwasattributedtothelackofoxygenratherthanlimita-tionsofpH,water,ornutrients.Thesedatasupporttheuseofwoodchipsforlightweightfillofroadwaysinswamps.Theauthorsconcludedthatwoodchipspre-servedcorrectlyareabletoretaincharacteristicssimilartonewchipsevenafter19years.Currently,therearetendenciestorevivethetech-

nology of wood use for the reinforcement of forest roads.Analogically,withthechangefrommanualin-stallationofstonepitchingtomachineinstallationofcrushedstone, themanual installationofcorduroyroadscanbereplacedwithmachine installationofshreddedwood.Thehistoricalstonepitchingtechnol-ogywasfirstreplacedwithalayerofcoarsecrushedstonebytheScottishbuilderJohnLoudonMcAdamin1816(Makovníketal.1973).Hefirstcrushedthestonemechanically,directlyattheextractionspot,andthentransportedthecrushedstonetotheroadsub-gradeasareinforcementlayer.Inconsequence,thetechnologyofcorduroyroadconstructionwaslost.Mostofthepublishedstudiesdealingwiththeuse

of wood for the reinforcement of forest roads rather concentrate on the use of brushmats on forest routes duringharvestingthanonforestroads(JakobsenandMoore1981,OlsenandWästerlund1989,Owendeetal.

2002,LabelleandJaeger2012).Theeffectofbrushmatsfortheruttingdepthreductionduringtimbertransporthasbeenproven,aswellastheimprovementoftheloadbearingcapacityofsoilwithincreasedmoisturecontent(TuftsandBrinker1993).Sirén(2001)presentedthatmanystudies(McMahonandEvanson1994,Clineetal.1991,BrunbergandNilsson1988)haddemon-stratedthatbrushmatspreventgreatcompactionofthestandsoil,thesoildamage,andrelatednegativeim-pactsonnaturallyrejuvenatedstands.(Wronskietal.1990, Bettinger and Kellogg 1993, Richardson andMakkonen1994).McMullenandShupe(2002)exam-inedtheissueofthetemporaryuseofbrushmatsandcorduroy roads on wetlands during the construction of pipelinesand their subsequently requiredremoval.Theyconcludedthattheremovalofbrushmatsfromwetlandsandthedisposaloftheremovedmaterial,whichisusuallyrequiredbyregulators,cancreatewet-landsdisturbanceandareveryexpensive.EliassonandWästerlund(2007)statedthattheweightofmachineryusedforharvestoperationsintheforestbringstheriskofrutsandsoilcompactionandthisriskincreaseses-peciallyintheeventofadversesoilconditions.LabelleandJaeger(2011,2012)investigatedtheuseofforestbiomassfromtimberharvestingresidues,whichisof-tenusedduringmechanizedforestoperationstoim-provetrafficabilityofstriproads(machineoperatingtrails).Theymentionedthatforestbiomassisbecomingincreasinglyimportantasasourceofrenewableenergy.Usingbrushexclusivelyforbiofuelwillleaveoperatingtrailsuncoveredandcanresultinseveredamagetoforestsoils.Thismayendangerthefutureuseofthistechnology for road reinforcement, as the price ofwoodchipscanclimbupto thecrushedstonepricelevel.Theuseofwoodchipstoprotecttheroadforma-tionagainsterosioninthecutandfillslopesonruralroadshasbeendescribedbye.g.Meyeretal.(1972).Other authors, George and Williams (1979), usedwoodchipsforacoalhaulingspurroadwherewatersprinklingwastheprimarymethodofdustcontrol.Thedurationofcontrolwasincreasedtenfoldbycoveringtheroadsurfacewithalayerofwoodchips.Someofthenewerpublicationsmentiontheimprovementofloadbearingcapacityinwaterloggedsectionsofforestroadsusinglogsandpoleseveninthepresent(Morris1995,Wiest1998,Sessions2007).Thetechnologyofusingwoodchipsorwoodmass

forforestroadreinforcementcanbeobservedmainlyintheUSA,whereitisoftenusedforbuildingforesttrails andpaths serving as reinforcement ofwater-loggedsites.Eberly(2004)presentedatechnologyinwhichfirstthesubgradeofaforestpathiscompacted,then15cmthicklayerofbrownchipsislaidon,without

A Structural Reinforcement Layer with Woodchips Used on Forest Roads (25–35) P. Hruza et al.


aclosinglayerforairaccessrestrictionandeasierpas-sage.Thislayerisslopedasrequestedandcompacted.Atthesiteswiththehighestwaterlogging,anchoredcorduroy roads are built with a structural layer of brownchips.Trailsandtheirparametersareprimarilymade forpedestrians,AutomatedTransferVehicles(ATVs),snowmobiles,cars,andsmalltractors,butnotforheavytrucks.Dahlmanetal.(2010)describedalter-nativewaysofwoodusetomakewaterloggedsitesintheforestaccessible.Theirworkoutlinedmanysolu-tions.Theydescribedtheuseoflogs,poles,boards,palisades,pallets, corduroy,brush, andwoodchips.Whenwoodchipsareusedforreinforcement,theyrec-ommendpreventingthewoodchipscatteringbyplac-ingthemonthegeotextile.Blinnetal.(1998)appliedonly15cmlayerofchipsforforestroadreinforcement.Theauthorsstatedthatitisnecessarytoreplenishthewoodchipsregularly.Chunkwoodcanhavethesameapplicationaswoodchips.Wiest (1998)devoted in-creasedattentiontothesettlingoftheroadformationandtheappearanceofditchesandculvertsatbogsites.Woodchips are also mentioned, used as a coarse-grainedfillingmaterialofaroadbaselayerlaidonthegeotextile.Theforestroadisdesigneddirectlyonthebogbasewithoutthepeatbeingextracted.Insteadofbaseconcreteforthefoundationofculverts,acombina-tionofthegeotextile,woodchips,andstakesisused.Themaintaskofthewoodchipsistomakethecon-structionofforestroadslighter.TheUSFederalHigh-wayAdministration(2016)providesinformationonmakingaccesstosignificantwaterloggedandbogsites.They list accessusinggeosyntheticmaterials, stonepitching,wood,andtheircombinations.Inoneofthesolutionstheyusewoodchipsasafillermaterialforthepavementintendedforbarrier-freeaccesstoawater-loggedsite.Theroadformationisalwayslocatedabovethegroundwaterlevel.Theauthorsdonotrecommendconstructingpathsorroadswithasurfacemadeofsmooth wooden boards for their slippery surface,shrinking,andtheriseofknots.Russell(2015)stabi-lizedforestroadsonsandysoilsusingby-productsoftimberproduction.Thestabilizationpresentedwascar-riedoutusingwoodchips,shreddedwoodmaterial,woodfibers,woodcuttings,sawdust,andrawwoodwaste.Healsoliststhepossibleuseofwastefrompapermills.However,theauthorstatedthattheshreddedwoodpushedoutofthewaydidnotloseitsdurabilityinthesandyenvironmenteven27yearsafteritsap-plication.AccordingtoBowmanetal.(1987),wood-chipswereusedasbuildingmaterialforforestroadsinthefillofroadformationtoovercomeamarshysectionin theChequamegonNationalForest.Shook (1988)dealt with the use of shredded wood waste for the re-inforcementoflessloadbearingforestsoils.Thetech-

nologywasappliedtosandy,wetlandandwaterloggedsoils.Shreddedwoodwassized1to15cm,around8cmonaverage.Thewoodwaspreparedusingaspe-cial machine called wood chunker on the site where it wasthenused.Especiallyafter-harvest,remainswereusedsonomaterialpurchaseortransportwasneeded.Localwaterloggingoccurs in forest roadsespe-

ciallyinthesectionsthatareinappropriatelyrouted,i.e.leadalongthecontourline,unreinforced,orhaveoperationalreinforcementonly,andareatthesametimeaffectedbyhighlevelsofundergroundwater.Attimesofhighprecipitation,theroadsareheavilydam-agedbythepassingvehiclesortheyarecompletelyimpassable.Thesesectionscanbeshort,buttheircon-ditioncanputtheentireforestroadsystembehindthemoutofoperation.Inthecurrentpractice,coarsecrushed stone is usually used for waterlogged sec-tions.Thissolutionischeapandsimple.However,itistemporaryandmustberepeated.Theaimsofthisstudyare toverify thepossiblereplacementof thecrushedstonebywoodchipsandtoinvestigatetheiruse as a natural and local material for the structural layersofreinforcement,inordertoimprovethetraf-ficabilityandavoidmaterialcavinginthesubgradeofforestroadsintheplacesoftheirlocalwaterlogging.

2. Material and methods – Materijali metode

TheconstructiontookplaceintheterritoryoftheTrainingForestEnterpriseMasarykForestKřtiny.The

Fig. 1 Area of study (Forest district Nove Mesto na Morave)Slika 1. Područje istraživanja (šumski predio Nové Mesto na Morave)



forest road is located in cadastral area Jedovnice,southeastofthevillageJedovnicebehindthepondOlšovec(coordinatesWGS-8449.3270N,16.7853E)(Fig.1).Theforestroadwasinpoorconditionbeforethe

repair;theoriginalreinforcementofthesubgradewascompletelymissingandtheverysubgradewasdam-agedbyruts.Thesubgradeshowedremnantsofstonepitchingreinforcement.Nolongitudinaldrainagehadbeenimplemented(Fig.2).Apartoftheroadwaswa-terloggedduetohighlevelsofgroundwater,astheforestroadleadsalongalargemarsh,whichfloodstheroadatthetimesofhighprecipitation.Duetothehighwaterlevelinthemarsh,wateroccasionallyflowsovertheroadformationatonepoint.Thethreetestsectionswereconstructedinthispartoftheforestroad.Twosamplesofsoilweretakenfromtheforestroadsub-gradeinthetestsection.Eachsamplewastestedforthestandardratioofloadbearingcapacity(CaliforniaBearingRatio–CBR)incompliancewithEN13286-47–Unboundandhydraulicallyboundmixtures–Part47.TheresultingCBRwas8.0%and8.5%,respective-ly.TheoptimummoisturecontentandconsistencylimitsweresetbytheProctorCompactionTestincom-pliancewithEN13286-47.TheresultingvaluesofCBRindicatethatthesubgradegivendoesnotmeettherequiredvaluesforusingthesoilintheactivezoneoftheroadformationcomplianttoČSN736133;there-fore,thesoilwouldhavetobemodifiedoranothersolutionshouldbeproposedinordertoincreasethesubgradeloadbearingcapacity,inthecaseofclassicalforestroadreinforcementdesign.AccordingtoTP170Designofpavementstructures(MinistryofTransport,CzechRepublic 2004), theminimumvalueofCBRshallnotdropbelow15%forforestroadsurfacesin

theVIthclassoftrafficload,whichistheclassofthepresentforestroad.Thepresentedtechnicalsolutionusesa layerof

brownchipstogetherwiththegeotextileandacoverlayer,whichallowsforbetterpassageofcyclists,roadvehiclesandforestrymachineryandmainlyservestoclosethelayerofchipsinordertoreduceairaccesstothechipsandpreventtheirdisintegration.However,air access is also limited by the use of this technology inawaterloggedplace–mostoftheyear,chipsareincontactwithwaterpreventingairaccess.Geotextileseparatesthelayerofbrownchips.Asreportedby,e.g.,McDonaldandSeixas(1997),Akayetal.(2007)orHanetal.(2009),theabilityofabrushmatlayeralonetoresistvehiclepassagesdecreasesrapidlyafter12load-edforwarderpasses.Thenthebrushgetsbroken,itiseasilypushedintothegroundandthelayermingleswiththesubgrade.Inthiscase,thegeotextilehelpstokeepacompactshapeofthelayer,asreportedbyRus-sell(2015).Intotal,threetypesofreinforcementwereinstalled

inalengthof30meach(Fig.3).Theydifferedbythewayofsubgradeleveling,thethicknessofthebrownchiplayer,andtheuseofgeotextile.Thefirsttypewasimplementedasfollows:thesub-

gradeoftheforestroadwasleveledandslopedintoaroof-shaped transverse inclination of 3%with finecrushedstoneoffraction0/16mm.Non-wovenpoly-propylenegeotextilewithareamassof300g/m2 was spreadonthepreparedsubgradeinitsentirewidth.Alayerofbrownchips,200mmthick,wasspread(Fig.4)andslopedinto3%transverseinclinationbythegrad-erandcompactedbystaticpressurewithoutvibration.Itwascoveredwithgeotextilesothatittotallyenclosedthechips, i.e., includingtheedgesof thewoodchiplayer (Fig. 5).Non-wovenpolypropylenegeotextilewithareamassof300g/m2 wasusedagain.Thisstruc-turewascoveredwithacoverlayerofatotalthicknessof150mm.Thecoverlayermustcoverthechipsandthegeotextileevenwiththeedges.Thecoverlayerwasformedinthefollowingway:alayerofcoarsecrushedstone,fraction32/63,waslaidonthegeotextileandtwolayersofcrushedstonemixtureoffraction0/16weregraduallyvibratedintoitsothatthethicknessofthecoverlayeraftercompactingwas150mm.Therulethatfinecrushedstoneshouldnotexceed35%oftheweightofcoarsecrushedstonewascompliedwith;inthiscaseitmadeuponethirdoftheweight.Thesecondtypeofreinforcementusingchipswas

installedsimilarly,exceptthattheforestroadwithsig-nificantlydamagedsubgradewasleveledwithalayerofchips,insteadoffinecrushedstone.Thechipsfilleduptherutsandotherbumpscausedbyvehicles.The

Fig. 2 The original condition of the forest roadSlika 2. Izgled dionice šumske ceste prije stabilizacije



levelinglayerofbrownchipswasleveledandslopedinto the roof-shaped transverse inclination of 3%.Non-wovengeotextilewithareamassof300g/m2 was spreadonitintheentirewidthofthesubgradeandthedesiredlength.Thefollowingstagesofthetechnol-ogyarethesameasinthefirstexample.Thethirdtypeofreinforcementtechnologyusing

chipswasimplementedatthebeginningsimilarlytothefirsttype,inwhichthesubgradewasleveledandsloped into 3% roof-shaped transverse inclination

withalevelinglayeroffinecrushedstoneoffraction0/16mm.Geotextilewasspreadonthepreparedsub-gradeinitsentirewidthandthencoveredwithalay-erofbrownchips,100mmthickerthaninthepreviouscases, i.e.300mmthick.The layerwasspreadandslopedtothedesired3%transverseinclinationbythegraderandcompactedbystaticpressurewithoutvi-bration;asopposedtoexample1,nogeotextilewasusedtoseparatethewoodchiplayerfromthecoverlayer.Thecoverlayerwasinstalledsimilarlytothepreviouscases(Fig.6).For thepurposeof comparisonandevaluation,

eachtypeofreinforcementwastestedbystaticloadtest for its deformation characteristics using the mod-

Fig. 3 A cross-section of reinforcementSlika 3. Izgled stabiliziranoga poprečnoga profila

Fig. 4 Brown chips laid on geotextile and sloped and compacted subgradeSlika 4. Prosušena drvna sječka razasuta na geotekstil koji je polo-žen na pripremljen donji ustroj

Fig. 5 The layer of brown chips enclosed in geotextileSlika 5. Sloj prosušene drvne sječke prekriven geotekstilom



ulusofdeformationfromthesecondloadcycle(Edef,2) and the ratio of the modulus of deformation between thesecondandthefirstloadcycle(Edef,2/Edef,1),whichservestocheckthecompaction.ThestaticloadtestisperformedaccordingtoČSN721006Inspectionofcompactionofsoilsandfills,andisusedforfillsofcoarse-grainedmaterialsandfine-grainedsoilswitharigidtosolidconsistency,i.e.unboundlayers;thesoilor crushed stone grains directly under the circular loadingplatemustnotbelargerthan25%oftheplatediameter.Althoughapartofthecrushedstonewasreplacedwithwoodchipsinthetechnologypresented,finallythisstructurallayerperformsthesameroleasthe classical reinforcement layer consisting of crushed

stoneonly.Forthisreason,staticloadtestcomplianttoČSN721006,AnnexA–TestforTransportStruc-tures,wasusedtoestablishthemodulusofdeforma-tionfromthesecondloadcycle(Edef,2) and the ratio betweenthesecondandthefirstloadcycle(Edef,2/Edef,1) intheparticulartypesofpresentedreinforcements.ThemeasurementwasconductedusingECM-Static,whichservesforsemi-automaticmeasurementofde-formationparametersandcheckofstaticloadbearingcapacityofcompactedfills.Itconsistsofacircularloadplateof300mm,atensometricpowersensor,anopto-electroniclineartracksensor,whichislocatedinthemeasuringbeam,thehydraulicloadingsystem,andtheelectronicpartofthedevice(Fig.7).Inthecontextofevaluationandcomparisonofin-

dividualtypesofreinforcement,wemonitoredwheth-er the cross profiles of each type of reinforcementchangedinheight.Twocross-sectionsweremarkedineach test section in regular distances for their tachymet-ricsurvey,intotalsixsamplecross-sections.Thecrossprofilesweremarkedbygeoharponssothatthetachy-metricmeasurementscouldberepeatedandtheheightchanges of the reinforcement cross-sections could be detected.Thefirstmeasurementoftheshapeofcross-sections is considered the reference; then, repeatedmeasurements were done twice in regular two-month intervals.Atthesametime,thenumberofpassagesandthemachinerytypesthatmovedinthetestsectionswererecorded.Eachcross-sectionwassurveyedwiththetotalstationTrimbleM3inregulardistances,every20cmineachcrossprofile;i.e.40heightcontrolpointswere measured within a single measurement in each testsectionintwocross-sections.Thegeodeticsurveyofthecontrolpointsfortheconnectionofthetachymet-ricmeasuringintheS-JTSKcoordinatesystemandtheheightsystemBalticVerticalDatum–AfterAdjustmentwascarriedoutusingtheGPSreceiverTopconHiperPro.ThecrossprofilesweresubsequentlycreatedinAutoCADCivil3D,wheretheheightofeachmeasuredpointofthecrossprofilewasrecordedinabsoluteco-ordinatesoftheBalticverticalsystem(Fig.8).Themeasuredvaluesweresubsequentlystatisti-

callyprocessedinStatistica12,wherethestatisticalhy-pothesisthatwithinmeasurementsrepeatedovertimethereisnostatisticallysignificantchangeintheshapeofthecross-sectionwiththeconfidencelevela=0.05wasverifiedusingtheanalysisofvariance(ANOVA).Thedifferencesinheightoftheparticularmeasure-mentpointswerecompared,thevaluesfromthesec-ondandthirdmeasurementsbeingcomparedwiththefirstreferencemeasurement,andforeachsectionsepa-rately.TheresultsoftheANOVAandthestatic load testwereusedtocomparetheindividualtypesofre-inforcementandselectthemostsuitablesolution.

Fig. 6 The implemented reinforcement using brown chips with a cover layer of vibrated gravelSlika 6. Dionica šumske ceste stabilizirana prosušenom drvnom sječ-kom sa nevezanim gornjim ustrojem izvedenim od lomljenoga kamena

Fig. 7 Static load test for the detection of deformation characteristicsSlika 7. Ispitivanje statičkoga opterećenja radi utvrđivanja defor-macija



Theforestroad,wherethetestsectionsarelocated,ismainlyusedforrecreationalpurposesandonlyoc-casionallytimbertransport.Thechangesover timeweremonitoredduringtheimprovementcuttingofthesurroundingstandsforfourmonths.ThetimberwastransportedbyZetorProxima8541tractorwithtandemaxle trailerBSS8.The totalallowedtrailerweightis12twithaloadingcapacityof8t.Thenum-ber of tractor-trailer passages during the first twomonthsofmonitoring,intheperiodofMay–June,amountedto19withthetotalquantityof152m3 of transportedtimber;inthesecondmonitoringperiod,inJuly–August,therewere14passageswiththetotalquantityof112m3ofhauledtimber.

3. Results and discussion – Rezultatis raspravom

Statisticalprocessingoftheresultsshowsthatwiththementionedtimberextractiontractortechnologythereisnostatisticallysignificantchangeintheshape

ofthecrossprofileovertimeasregardsthereinforce-menttechnologytypes1and3.Type1witha20cmlayerofwoodchipsandboth-sidedenclosureinthegeotextile achieves the best results. This solutionprovestobemoreefficientthanthesolutionwithahigherlayerofwoodchips(30cm)butwithoutthegeotextileseparatingthecoverlayerfromthewood-chips,althoughthedifferenceisnotlarge,asprovenbytheresultsofstatisticalprocessing,inwhichthep-valuesare0.12458fortype1and0.09103fortype2.Itturnsoutthattheenclosureofchipsincludingtheedges and the formation of a sleeve-shaped bodykeepsthelayermorecompact.Russell(2015)reportedsimilarfindings.Comparingthedeformationcharac-teristicsestablishedbythestaticloadtest,themodulusofdeformationvaluesinbothtypesarevirtuallythesame,reachingEdef,2=14.3MPaandEdef,2=13.4MPa,respectively.Thesevaluesarerelativelylow,butwithrespecttotheresultsoftheANOVA,itisclearthatthewholereinforcementsystemreturnsasmuchaspos-siblebacktotheoriginalpositionafterthehauling

Fig. 8 An example of a changed shape of the cross-section, including height changes in particular measurement points for the first type of reinforcement using woodchipsSlika 8. Promjene u izgledu poprečnoga profila pri prvoj tehnologiji stabilizacije



machinerypasses.Theinvestigationoftheshapesofthecurvesofindividualmeasurementswhenprintedovereachother(Fig.8)showsthatthisisnotanover-alldeclineinthelayerheightineachmeasurement,but a combination of the reinforcement surface de-clineandrippling.Thecompactionrateasaratioofthe moduli of deformation from the second and the firstloadcycleisEdef,2/Edef,11.74andEdef,2/Edef,1 2.79,respectively,forthetwotypesofreinforcement.Stan-dardČSN736126-1Roadbuilding–Unboundcours-es–Part1:Constructionandconformityassessment,stipulatestherequirementforthemodulusofdefor-mation Edef,2/Edef,1 tobe2.5atmaximum,soonlythefirsttypeofreinforcementfullymeetstherequire-ment.Thehighervalueinthethirdtypeofreinforce-mentcanbeattributedtothemissinggeotextilebe-tweenthewoodchiplayerandthecoverlayer,asthewoodchips partially mix with the crushed stone.However,thisprovestobeanadvantagewhenthistechnologyisappliedtoplaceswherethewaterlog-gingalternateswithperiodsofsubgradedryingup.Insuchcases,thecoverlayerlaidontheseparationgeotextileinthefirsttypeofreinforcementcangetcrackedbythedroughtorevenbreakandslideoverthegeotextiletothesideifthecrossslopesaretoosteep.Thecoverlayerprovestobeanintegralpartofthe entire reinforcement system. It eliminates theproblemsbypassingoverthewoodchipsalone.Eb-erly(2004)reportedpooradhesionofwheelswithwoodchipsinbadweatherandlossofmaterialcausedbywheelacceleration– the layer isdisruptedandwoodchipsarethrusttothesides.Inthisparticularcase,athicknessof15cmprovedtobesufficientasopposedtodatapresentedbyRussell(2015).Bycontrast,inreinforcementtechnologytype2,

wherewoodchipswereusedinsteadofcrushedstonetolevelthesurface,thenullhypothesiswasnotcon-firmed,thep-valueis0.00265.BasedontheANOVA,itcanbeconcludedthatthereisastatisticallysignifi-cantchangeintheshapeofthecross-sectionwithinrepeatedmeasurementsovertime.Additionally,themeasuredvaluesofdeformationcharacteristicsareverylowandthemodulusofdeformationfromthesecond cycle of measurement Edef,2is9.9MPa.Eventhoughvisuallynosignificantdifferencescanbeseenamongthethreetypesofreinforcement,thestatisticalresultsshowthatthistypeofreinforcementcannotberecommended.Itturnsoutthatawellpreparedandproperlycompactedandslopedsubgradeiscrucialforeach type of reinforcement. Woodchips appliedstraighttounpreparedandnotslopedsubgradehaveaverypooreffect.Thiscorrespondstofindingspre-sentedbyHanetal.(2009)aswellasAkayetal.(2007).

Theresultsshowthatthepresentedreinforcementmethodcanserveasanalternativetechnologyforfor-estroadreinforcement,inparticularforsmallforestowners,whogrowforestsmainlyasasourceoffire-woodandusemostlyfarmtechnologiestotransporttheharvestedtimber.Alternatively,itisrecommend-ableforlocationswheretheforestdoesnotperformprimarilytheeconomicfunction,orforprotectedna-turesites.However,itisalwaysnecessarytopreparethesubgradefirstproperly,fillinthemissingmaterial,andslopeittotherequiredtransverseinclination,aswellasenclosethechiplayerintothegeotextile.Theadvantageofthissolutionisthattheuseofwoodre-ducesthecrushedstoneinthecomposition.Itisad-vantageousinplaceswithalackoflocalsourcesofcrushed stone and when the distance between the ma-terialandtheconstructionsiteisgreat.Tocreatethistypeofreinforcement,itispossibletousethewoodatthe construction site so in the case of forest roads the needformaterialtransportiseliminated.Thissolutionisparticularlyusefulforwaterloggedsectionsofforestroads,whereitallowsundamagingpassageandthepresenceofwateratthesametimeextendsthelifeofwoodintheroadformation,asreportedbySchmidtetal.(1997).Mostoftheauthors,whoareengagedinthe use of wood for the construction of forest road reinforcement,use the technologyof log corduroyroads(Morris1995,Wiest1998,Sessions2007).How-ever,thistechnologyishistoricalandmanual,there-fore time-consuming and laborious.Theproposedtechnologyofusingwoodchipscanbeimplementedbymachines,usingthecommonbuildingmachinery.Itcanalsobesaidthatitisaqualitativelyhighertech-nologythantechnologyofbrushmatsonoperationtrails.LabelleandJeager(2012)pointedoutthat,foreffectiveloaddistribution,thebranchesusedtocom-posethebrushmatsshouldhavehighplasticityandbendingstrengthunderloading.Gurauetal.(2008)reported that the average compression strengthofScotspinebranchesis56%lowerthanthatofthestem.Astheusedmaterialinthetechnologyproposedisshreddedwoodandnotonlyharvestresidues,ana-logicallywith the technologyofcrushedstone, theindividualparticlesofwoodchipsgetwedgedwhenbeinglaidandcompactedandtheyformamechani-callycontiguousconstructionlayer.Thistypeofrein-forcementwillimprovetheloadbearingcapacityoftheroadsusedinparticularforseasonaloperations,i.e.,thosethatareformedfromroadformationorre-inforcedwithoperationalreinforcement,orthosethathaveunsealedroadsurface.Themainadvantagesofthe use of wood for forest road reinforcement are that itisrenewableandthatthereisnoextractionormov-ingofthegroundduringitsproduction.



4. Conclusion – ZaključakThe solution consists in the use of a layer of wood-

chips,whichisinstalledwiththegeotextileinsidethereinforcementstructure.Thistechnicalsolutiontoim-provetheloadbearingcapacityofforestroadsisespe-ciallyusableformultifunctionalroads,whicharenotusedprimarilyfortimberhauling.Fromtheperspec-tiveofimplementation,theproposedsolutionistechni-callysimple,efficient,andenvironment-friendly,fea-sibleforsmallownersandroadoperators.Itturnsoutthatthereinforcementtechnologyusingwoodchipsisthemostappropriateforforestroadsthatalsoperformtherecreationalfunctionoftheforest.

Acknowledgments – ZahvalaTheproject received funding from the Internal

GrantAgency,MendelUniversityinBrno,no.LDF_PSV_2016016.

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Sažetak

Mogućnost uporabe prosušene drvne sječke pri mehaničkoj stabilizaciji donjega ustroja šumskih cesta

Tematika rada vezana je uz mogućnost uporabe biotehničkih mjera pri stabilizaciji donjega ustroja šumskih cesta na dionicama gdje je razina podzemne vode vrlo visoka, odnosno gdje dolazi do prekomjernoga vlaženja nosivoga donjega ustroja šumske ceste. Vrlo se često radi o kratkim dionicama koje usprkos svojoj kratkoći mogu otežati ili blokirati pristup većemu i/ili manjemu šumskomu kompleksu. U povijesti su se te problematične dionice šumskih cesta stabilizirale upotrebom višemetarskoga prostornoga drva, odnosno drvenim talpama. Trenutačno u svijetu postoji težnja osuvremenjivanju biotehničkih mjera radi zamjene višemetarskoga prostornoga drva, korištenoga pri stabilizaciji donjega ustroja kritičnih dionica šumskih cesta, prosušenom drvnom sječkom. U ovom je radu istraživana mogućnost stabilizacije kritičnih dionica šumskih cesta u uvjetima prekomjernoga vlaženja upotrebom prosušene drvne sječke. Da bi se utvrdile najbolje metode stabilizacije, u radu su testirane tri različite tehnologije stabilizacije kombinirajući upotrebu prosušene drvne sječke, geotekstila i lomljenoga kamena. Stabilizirane dionice šumske ceste, nakon izgradnje, podvrgnute su prometnom opterećenju nastalom tijekom uobičajenih radnih operacija u šumarstvu: sječa, izrada i privlačenje drvnih sortimenata. Mjeren je modul deformacije kolničke konstrukcije te su utvrđivana ostala svojstva oštećenja uočenih na pojedinoj mjernoj plohi. Naposljetku, promatrane su promjene u izgledu poprečnih profila. Rezultati pokazuju da se ni pri vrlo malim vrijednostima modula deformacija statistički značajno ne razli-kuju promjene u izgledu poprečnoga profila kod dviju od triju testiranih tehnologija stabilizacije. Dobiveni rezultati upućuju na to da se dvije testirane tehnologije stabilizacije kod kojih ne postoji statistički značajna razlika u izgledu poprečnoga profila mogu koristiti pri stabilizaciji donjega ustroja na dionicama šumskih cesta koje su izložene prekom-jernoj vlažnosti. Glavna prednost upotrebe takve vrste stabilizacije donjega ustroja šumskih cesta očituje se u činjenici da se primjenjuje materijal dobiven iz obnovljivoga izvora te da tijekom stabilizacije ne dolazi do iskopa i transporti-ranja slabonosivoga materijala koji se nalazi na kritičnoj dionici šumske ceste.

Ključne riječi: šumska cesta, stabilizacija, traktorski put, drvna sječka, provoznost



Received(Primljeno):August29,2016.Accepted(Prihvaćeno):September23,2016.

Authors′addresses–Adresa autorâ:

Assoc.prof.PetrHrůza,PhD.*e-mail:[email protected]án,PhD.e-mail:[email protected],MSc.e-mail:blahuta.jaroslav@gmail.comMendelUniversityinBrnoFacultyofForestryandWoodTechnologyDepartmentofLandscapeManagementZemědělská3Brno61300CZECHREPUBLIC

JiříNedorost,mag.ing.silv.e-mail:[email protected]ěkPatočka,PhD.e-mail:zdenek.patocka@mendelu.czMendelUniversityinBrnoFacultyofForestryandWoodTechnologyDepartmentofForestManagementandAppliedGeo-informatics(FFWT)Zemědělská3Brno61300CZECHREPUBLIC

*Correspondingauthor–Glavni autor

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A Structural Reinforcement Layer with Woodchips Used on