土木工程类专业英文文献及翻译Word文档格式.doc
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ofpredictivetechniquesthatusecommonlyavailablelaboratoryequipmentand
testingmethodsforobtainingreliableestimatesofthevolumechangeforthese
problemsoils.Amethodforpredictingrelevantstressesandcorrespondingcollapse
strainsfortypicalpavementsubgradesispresented.Relativelysimplemethodsof
evaluatingpotentialvolumechange,basedonresultsoffamiliarlaboratorytests,
areused.
INTRODUCTION
Whenasoilisgivenfreeaccesstowater,itmaydecreaseinvolume,
increaseinvolume,ordonothing.Asoilthatincreasesinvolumeiscalled
aswellingorexpansivesoil,andasoilthatdecreasesinvolumeiscalleda
collapsiblesoil.Theamountofvolumechangethatoccursdependsonthe
soiltypeandstructure,theinitialsoildensity,theimposedstressstate,and
thedegreeandextentofwetting.Subgradematerialscomprisedofsoilsthat
changevolumeuponwettinghavecauseddistresstohighwayssincethebe-
ginningoftheprofessionalpracticeandhavecostmanymillionsofdollars
inroadwayrepairs.Thepredictionofthevolumechangesthatmayoccurin
thefieldisthefirststepinmakinganeconomicdecisionfordealingwith
theseproblemsubgradematerials.
Eachprojectwillhavedifferentdesignconsiderations,economiccon-
straints,andriskfactorsthatwillhavetobetakenintoaccount.However,
withareliablemethodformakingvolumechangepredictions,thebestdesign
relativetothesubgradesoilsbecomesamatterofeconomiccomparison,and
amuchmorerationaldesignapproachmaybemade.Forexample,typical
techniquesfordealingwithexpansiveclaysinclude:
(1)Insitutreatments
withsubstancessuchaslime,cement,orfly-ash;
(2)seepagebarriersand/
ordrainagesystems;
or(3)acomputingoftheserviceabilitylossandamod-
ificationofthedesignto"
accept"
theanticipatedexpansion.Inordertomake
themosteconomicaldecision,theamountofvolumechange(especiallynon-
uniformvolumechange)mustbeaccuratelyestimated,andthedegreeofroad
roughnessevaluatedfromthesedata.Similarly,alternativedesigntechniques
areavailableforanyroadwayproblem.
Theemphasisherewillbeplacedonpresentingeconomicalandsimple
methodsfor:
(1)Determiningwhetherthesubgradematerialsarecollapsible;
and
(2)estimatingtheamountofvolumechangethatislikelytooccurinthe
'
Asst.Prof.,Ctr.forAdvancedRes.inTransp.,ArizonaStateUniv.,Tempe,AZ
85287.
Note.DiscussionopenuntilApril1,1989.Toextendtheclosingdateonemonth,
awrittenrequestmustbefiledwiththeASCEManagerofJournals.Themanuscript
forthispaperwassubmittedforreviewandpossiblepublicationonFebruary3,1988.
ThispaperispartoftheJournalofTransportation.Engineering,Vol.114,No.6,
November,1988.ASCE,ISSN0733-947X/88/0006-0673/$1.00+$.15perpage.
PaperNo.22902.
673
fieldforthecollapsiblesoils.Thenthisinformationwillplacetheengineer
inapositiontomakearationaldesigndecision.Collapsiblesoilsarefre-
quentlyencounteredinanaridclimate.Thedepositionalprocessandfor-
mationofthesesoils,andmethodsforidentificationandevaluationofthe
amountofvolumechangethatmayoccur,willbediscussedinthefollowing
sections.
COLLAPSIBLESOILS
FormationofCollapsibleSoils
Collapsiblesoilshavehighvoidratiosandlowdensitiesandaretypically
cohesionlessoronlyslightlycohesive.Inanaridclimate,evaporationgreatly
exceedsrainfall.Consequently,onlythenear-surfacesoilsbecomewetted
fromnormalrainfall.Itisthecombinationofthedepositionalprocessand
theclimateconditionsthatleadstotheformationofthecollapsiblesoil.
Althoughcollapsiblesoilsexistinnondesertregions,thedryenvironmentin
whichevaporationexceedsprecipitationisveryfavorablefortheformation
ofthecollapsiblestructure.
Asthesoildriesbyevaporation,capillarytensioncausestheremaining
watertowithdrawintothesoilgraininterfaces,bringingwithitsolublesalts,
clay,andsiltparticles.Asthesoilcontinuestodry,thesesalts,clays,and
siltscomeoutofsolution,and"
tack-weld"
thelargergrainstogether.This
leadstoasoilstructurethathashighapparentstrengthatitslow,natural
watercontent.However,collapseofthe"
cemented"
structuremayoccur
uponwettingbecausethebondingmaterialweakensandsoftens,andthesoil
isunstableatanystresslevelthatexceedsthatatwhichthesoilhadbeen
previouslywetted.Thus,