无砂混凝土生态护坡

No-FinesConcreteasEcologicStreamBankErosionControlYuewenHuangSeniorEngineer,GuangzhouInvestigationDesignandResearchSeniorEngineer,GuangzhouInvestigationDesignandResearchInstituteofWaterConservancy&Hydropower,Guangzhou,Guanggong,China,510640,huangyuewen1973@163.comAssistantProfessor,DepartmentofCivilEngineering,CaseWesternReserveUniversity,Cleveland,OH44106-7201,xiong.yu@,216-368-6247AbstractNo-finesconcreteisaperviousconcreteobtainedbyeliminatingthesandfromnormalconcretemix.Comparedwithconventionalconcrete,no-finesconcretehasuniquepropertiesdesirableforvariousapplications.Becauseofthepresentoflargevoids,nofinesconcretehaslowerdensity,costandthermalconductivity;smallerdyingshrinkage,nosegregation;largercontaminantretainingcapability;reducedcapillarymovementofwater.Non-finesconcretesareusedforconstructionofpavement,stormwatercontrolutilitiesandgreenhouse.Thispaperdiscussestheapplicationofno-finesconcreteasanecologypreservativemethodforstreambankerosioncontrol.Soilerosionisanimportantfactorthatcantriggertheinstabilityofanembankment.Asustainablerevetmentshouldprovidesoilerosionprotectionwithoutsignificantlychangingtheecologicenvironment.Thestrengthofno-finesconcreteprovidessufficientprotectionagainstscouroftheembankment.Althoughgrassesarefoundtobehardtosurvivewithordinarytypesofbankrevetment,especiallywhensubjectedtoperiodicinundationfromriverwaterlevelvariations,thelargeporespacesofno-finesconcreteprotectgrassseedsandincuramenableenvironmentforgrassestogrow.Byinstallingartificialaccessholesintheno-finesconcreterevetment,theecologicconditionscanbepreservedtothemaximalextent.Thedesigningcriteriaanddurabilityofno-finesconcreterevetmentarediscussed.Thispaperalsoprovidesanexampleapplicationofno-finesconcreterevetmentthatachievedthedesirableecologiceffects.IntroductionErosioncontrolisimportantfromavarietyofenvironmentalconsiderations.Excessiveriverbankerosionnotonlyposseshazardtotheengineeredstructuresadjacenttothebank,butalsocontributesignificantamountofsedimentfromthetributaryriver.Thisultimatelycanleadtohighsolidsconcentration,excessivenutritionandpollutionintheriver.Properrivererosioncontrolisneededtopreventthesepotentialenvironmentalhazardsandtokeeptheexistingecosystem.Erosioncontrolinvolvestheuseofengineeringmeasurestomaintainthesustainableecosystem.Concretehasbeenwidelyusedtoconstructtheengineeringstructures.Itsadvantagesincludethehighstrengthandlowcost.Itisalsowidelyavailable.Specialtypesofconcretearecurrentlybeingdevelopedsuchasself-consolidatingconcrete,fiberreinforcedpolymerconcreteandrollercompactingconcrete.Researchontheinnovativeconcretetechnologyhastriggeredapplicationsofnewmaterialsintheconstructionpractice.Theconceptofgreenconcreteisarelativelynewdevelopmentfortheconcreteindustry.Thegreenconcretereferstoconcretedesignsthatnotonlyachievetherequiredstructuralperformance,butalsobringtheleastimpactonthesurroundingenvironment.Examplesofgreenconcreteincludetheporousconcrete,whichincreasesthethermalefficiencyoftheresidentialbuildings.No-fineconcreteisanothertypeofgreenconcretethatcanhelptoachieveasustainableenvironment.No-fineconcretereferstoconcretemixwithoutfineaggregates.Itisamixtureofcoarseaggregates,cementandwater.Duetotheabsenceoffineaggregates,itischaracterizedbylargeairvoids,reducedthermalcoefficientandhighwaterpermeability.Ithasbeenusedtoconstructpermeableconcretepavement.Thelargeporesizeshelpstoreducethenoisegeneratedatthetire/pavementinterface.Thehighpermeabilitymakesitasuitablematerialforstormwatermanagement.Thispaperdiscussestheapplicationofno-fineconcreteforriverbankerosioncontrol.Thedesignutilizesthehighstrengthofno-fineconcretetogetherwithitsecologicamiablefactors.Aprojectonriverbankrevitalizationisusedtoillustratetheapplicationofthistypeofconcrete.UseofNo-fineConcreteforRiverBankErosionControlErosionofsoilbyrun-offtakesplacewhenthedragforceactingonthesoilsparticlesislargerthantheforcesfromtheadjacentsoillayers(orthestrengthofsoils).Thedragforceisdecidedbyfactorssuchasthespeedofriverwater,topologyoftheriverchannelandtheflowmode.Typically,thesearedecidedbythegeometryoftheriverbankandlocalhydrologicconditions(forexampletheprecipitation).Thereisnotmuchthingthatcanbedoneinthisregard.Topreventoralleviatethesoilerosion,theresistanceforcehastobeincreased.Theriverbankcanbeprotectedbymethodssuchasaggregatetoeingandgeotexile.However,thesemeasurestypicallydonotworkwithoutbreakingtheexistingecologicsystem,i.e.,theytypicallydoesnotsupportgrowofvegetationespeciallywiththeelevationofwaterlevelfluctuations.Ecologicrevetmentisahydraulicconceptthatembracestheconsiderationsofthehydraulic,environmental,biologic,ecologicandaestheticfactors.Itisanewconceptforrevetmentdesign.Itsetsthepreventionandcreationofbiologicamiableandaestheticenvironmentastheprerequisites.Ithelpstocreateacleanriverandsustainableecologicsystem.Theecologicrevetmentconsidersthestrength,safetyanddurabilityoftherevetmentstructuresaswellastheirecologiceffects.Forexample,itdeparturesfromtheuseoftraditionalstone-cementmix;insteaditpromptthecreationofanecologicamiableriverenvironment.Non-fineconcreteistheconcretemixwithnofineaggregates.Thecomponentsofthistypeofconcreteincludethecement,coarseaggregatesandwater.Thecementactstoholdthemixturetogether.Coarseaggregatecanbegravel,pepperorotherartificialaggregates.Becauseoftheabsenceoffineaggregates,largevoidvolumeexistsinsidetheconcrete.Thesizesofthevoidsaretypicallyslightlysmallerthanthesizesofcoarseaggregates.Thesemakethenon-fineconcretetobehighlypermeable.Thelargeporesizescanalsoaccommodatethegrowthofvegetations.Theporesintheno-fineconcretecanretainsignificantamountofsludge,matureandseedsinthevoids.Thiscreatesafavorableenvironmentforseedstogrowup.Ontheotherhand,becauseofthestrongadhesionbythecement,no-fineconcreteprovidesrelativelyhighscourresistance.Toaccommodatethedevelopmentofaquaticcreatures,properlargeholescanbecreatedartificially.Thesizeofholescanbedeterminedbysurveyingthesizeoftypicallocalaquatics.Theholescanprovidesheltersforavarietyofaquaticcreatures.Thegrowthofvegetationisnotonlyaestheticallyamiable;therootofvegetationcanalsocontributetotheimprovedscourprotection.Thefollowingofthispaperusesanexampletoillustratetheuseno-fineconcreteforrevetmentdesign.(chemicalenvironment)Normalconcreteissobasicthatitisunsuitableforvegetationgrowth.However,nofinesconcrete,theholescanprovidesheltersforavarietyofaquaticcreatures.Therearetwofactorsthatshouldbetakenaccountintothegrowthofvegetation.Thefirstoneliesongeometry.Becauseofhighpermeanceresultedfromlargesizesofholes,thebasicwaterinsidetheholescangooutasthewaterleveldrawdown,andneutralwaterwillentertheholeswhenthewaterlevelelevates.Thus,thePHvalueinsidetheholeswouldreliablydecreaseandbecomeneutralenoughforvegetationtogrow.Theotherfactorisachemicalone.Waterandcarbondioxidebothplayimportantandindispensablerolesinthecarbonationofconcrete.Theno-finesconcreteisonlyappliedintheregionofwatervariation,intowhichwaterandairfillalternatively.Thealternativeexposurestowaterandairdramaticallyspeedupthecarbonationprocessandquicklyformanimpenetrablelayerattheconcrete/waterinterfacetopreventthediffuseofbasiccomponentsfromconcretetowardthewater.Thesetwofactorstogethermakecontributionstotheneutralwaterinsideno-finesconcrete,whichisverydifferentfromthatinsidenormalconcrete,andfinallyresultthesurvivalofaquaticcreatures.(schematicplotstoillustratethedifferentstagesinerosioncontrol)ProjectBackgroundTheprojectislocatedinthesouthernprovinceofGuangdong,China.Theregionisreclaimedfromlakesbycreationofavarietyofpolders.ItiswithintherivernetworkofZhujiangDelta,withTiger-Gaterivertotheeast,SouthChinaseainthesouthandHongQiliriver,ShangRiverandGongbaoRiverisinthenorth.TheJiaomenriverinterceptthedistrictinthemiddle.Extensiveriverreclamationhappenedinthehistoryofthisdistrict.Thewholedistrictisessentiallyformedfromreclamationoftheexistingriverandlakesystems.Mostpartofthisdistrictisagriculturezoneforfarm,bananaproductionandfishpond.Toconstructthepolders,gravelswereplacedintheoutsidewiththeinnerpartfilledwithsoils.SludgeintheZhujiangRiverwerealsousedinsomeinstanceswherethesupplyforsoilsarescare.Becauseofthehighwatercontent(above60%)inthethicksludgelayertogetherwiththeabsenceoffoundationtreatment,thebearingcapacityofthefoundationsoilsareverysmallafterthenaturalconsolidation.Thereclamationzonesaretypicallycharacteristicbythelargesettlement.Arecordsettlementoflargerthan1mwithinoneyearhasbeenobserved.Constructionofpolderstypicallytakesseveralyearsbecauseoftheslowconstructionspeed.Afteronepolderisconstructedconstructionofanotherpolderwillthenbegan.Anartificialrivertypicallyexistsbetweentheadjacentpolders(itiscalledChungbylocalresidents).Becauseoftheextensivescouranderosion,thebanksoftheartificialriverischaracterizedbyscarcityofvegetation,largenumberofaquaticresidents.Thesemakeitsusceptibletoscourinducedbyriverlevelfluctuationandheavyraining.Significantamountofcollapseoccurredalongtheriverbank.Thisnotonlyreducestherun-offcapacityoftheriverbutalsocreateundesirableaestheticeffects(Figure1).Itusedtorequiredredgingeverytwoyearstosustaintheflowcapability.Figure1.ExampleofcollapsedriverbankDesignofRevetmentSystemThisprojectwasconductedtoalleviatetheextentofriverbankerosion.Besidesdredgingtheriver,animportanttaskistodesignandconstructasustainablerevetmentsystem.Therevetmentincludeincludestoerevetmentandsloperevetment.Aserosionofriverbedislikelytohappen,itisdeemednecessaryforthetoerevetmenttobeabletoaccommodatecertainmagnitudeofdeformation.Thedesignselecteddifferenttypesoftoerevetmentbasedonacomprehensiveconsiderationofdifferentfactors.Graveltoerevetmentisusedforthesectionsoftheriverthatisrelativelywide(Figure2A).Pipepileswereusedforsectionsoftheriverthatisnarrow(Figure2B).Figure2.A)Exampleofgraveltoerevetment;B)ExampleofpipepiletoerevetmentDifferentdesignswerealsousedforsloperevetment.Forlocationswheretoerevetmentwasused,ano-fineconcretelayerwithpreinstalledholesandthicknessof20cmwasused.Brickswereusedinaportionofthesebanksascomparison.Thepreinstalledholesareforthegrowthofvegetationandaquatics.Threedimensionalgeogridwasusedatelevationshigherthanriverlevelvariations.Itneedstobepointedoutthatthethreedimensionalgeogridisalsoanemergingtypeofecologicrevetment.Ithastheadvantageousofeasyconstruction,lowcostandgooderosionprotection.Itcanpreventtheriverbankfromerosionbytheprecipitationbeforethegrassesgrowup.Afterthat,thegrass,geogridandnearsurfacesoilsbecomeasolidpartwithverygoodresistancetoerosion.Itisagoodformofriverbankprotectionmethodforbankwithrelativelysteepslopethatispronetoerosion.However,thegeogridisineffectiveforprotectingthegrassseedsinthezonewithwaterlevelvariations.Fortheareawithinriverwaterfluctuation,geogridwasfoundtoworkunsatisfactorily.Astheseedsareeasilybescouredawayfromthegeogridduringwaterlevelfluctuation.Ontheotherhand,itwasfoundthatseedsismoreeasilygrowinno-fineconcreteevenunderwaterlevelfluctuations.Itispartlyattributedothefactthatthetortuosityporesintheno-fineconcreteprovidesgoodretentionoftheseedsandthenecessarynutrition.Theerosioncontroldesignusingno-fineconcreteisacomprehensivedesignconsideringvariousfactors.Theseembraceconsiderationsintermsofmechanicsandecology.Factorsconsideredindesign,mechanicalaspecterosionprevention(shearstrengthorcompressionstrength),accommodationofsettlement(flexurestrength),thickness,ecologicaspect:grassseedsandnutritionretention(sizeofaggregatesorairvoids),pre-installedholes(typicalsizeofaquaticcommunities).Fromecologicaspect,screenofvegetationisneededtodetermine(compatibilitywithno-fineconcrete,aestheticconsideration,contributiontoerosionresistance)Anexperimentprogramwasconductedtodeterminethedesignparametersforthenofineconcrete.Itembracedthestructural,environmentalandecologicconsiderations.Thecoarseaggregateutilizesthegraniteaggregatewithnominaldiameterof

31.5~63mm.Theproportionsofconcreteare1620kg(aggregate):240kg(cement):84kg(water)respectively.The28daydesignedstrengthisnosmallerthan5.6MPa.Thestrengthforflexuralfailureisnolessthan1.2MPa.Thethicknessofprotectionis20cm.Holesof7cmdiametersarepreinstalledforevery25cm.Structuraljointsweresetforevery1.5m.Theselectionofgrasseswasbasedonapilotexperimentalprogram.Thegrassneedstosurvivethefrequentinundationduetoriverlevelfluctuation.34differenttypesofgrassesweretestedintheexperimentprogram.Thegrowthofgrassesweremeasuredintwomonthperiod.Theitemsrecordedincludethesurvivalrate,areaofcover,heightandaestheticcondition.Afewgrasseswereselectedfromthisscreeningexperiment.Figure3Designschemaofthe三维土工网垫种百喜草（草籽）无砂砼块（厚200）种百喜草（苗）PerformanceoftheNewRevetmentSystemBoththegraveltoerevetmentandpipepiletoerevetmentcanaccommodatecertaindeformation.Theyhavegoodecologicfeatherandarecosteffective.Thepipepiletoerevetmenthasrelativelyhighconstructioncost.However,comparedwithgraveltoerevetment,italsohasafewadvantages,i.e,1)increasedstability.Itwasfoundthatthereisnosignificantdeformationofthepipepilerevetmentafteroneyearinservice.Collapse,however,didhappenatcertainlocationsusinggraveltoerevetment;2)improvedconstructionqualitycontrolcanbeachievedforpipepileconstruction.Theconstructionprocessisrelativelystraightforward.Theconstructionqualitycanbeeasilyevaluatedbyobservingthepipepilealignment.Strictconstructioncontrolisnoteasytoachieveforthegraveltoerevetment.Itisnotunusualtohaveoverexcavationoroverfilling;3)thepipepiletoerevetmenttypicallyhasbettervisualeffects,especiallywhenexposedFigure3Designschemaofthe三维土工网垫种百喜草（草籽）无砂砼块（厚200）种百喜草（苗）Boththeno-