Unfrozen water content of frozen soils and soil mo

BYPERMISSIONOFTIIECOUNCILEXCERPTFROMG@OTECHNIQUE,VOL.14,NO.3UNFROZENWATERCONTENTOFFROZENSOILSANDSOILMOISTURESUCTIONbyP.J.WILLIAMS:^Theunfrozenwatercontentofvarioussoilshasbeenmeasuredbycalorimeter.Thesuction-moisturecontentcharacteristicsofthesamesoilswerealsodeterminedatroomtemperature,withconventionalpressureplateandpressuremembraneapparatus.Usingthevaluesofunfrozenwatercontentmeasuredduringfreezing,andthesuctioncharacteristicsobtainedduringdrying,arelationwasfoundbetweenthetwosetsofresults.TherelationshipapproximatesthatofSchofield,betweensuctionandinitialfreezingpoint,ofsoilsatvariousmoisturecontents.Inowledgeoftherelationshippermitspredictionoftheamountofwaterremainingunfrozeninasoilatnegativetemperaturesdownto-l.O°Candoftensomewhatlower.Suchpre-dictionrequiresonlydeterminationofsuction-moisturecontentcharacteristicsbyconventionalmethodstogetherwithasimpledeterminationofthefreezingpointofanextractofthesoilsolution.Inmanycases,theaccuracyofthepredictionisapparentlyasgreatascanbeobtainedusingevcncomplexcalorimetricmethods.Usingtheserela-tivelyeasilydeterminedvaluesofunfrozenwatercontentatvarioustemperatures,realisticestimatescanbemadeoftheapparentspecificheatsoffrozensoils.Theobservedrelationshipprovidesabasisforstudiesoftheeffectsofbothloadandtempera-ture,ontheproportionsoficeandwaterinfrozensoilsandonthestateofstresswithintheiceandunfrozenwater.Lateneureneaunongel&dediverssols,a6thmesureeparcalorimktre.Lescaracteristiquesdesteneurseau-succiondesm6messolsfurentaussideterminkes?ilatemperatureambiante,avecplaqueconventionnelledepressionetappareilamembranedepression.Enutilisantlesvaleursdesteneurseneaunongelbemesureespendantlacongklation,etlescaracteristiquesdesuccionob-tenuespendantlesechage,unrapportfuttrouveentrelesdeuxseriesderesultats.LerapportserapprochedeceluideSchofield,entrelasuccionetlepointinitialdecongelationdesolsdediversesteneurseneau.Laconnaissancedurapportpermetdepredirelaquantit6d'eaurestantnongelhedanslesolaunetempbraturedescendantjusqu'a-l.O°Cetsouventquelqucpeuplusbasse.Unetellepredictionnecessiteseulementladeterminationdescaracteristiquesdelateneureau-succionparlesmethodesconventionnelles,ainsiqu'unedetermina-tionsimpledupointdecongklationd'unprelkve-mentdesolutiondusol.Dansbeaucoupdecas,l'exactitudedelapredictionestapparemmentaussigrandequecellequipeut6treobtenuem6meenutilisantdesmethodescalorimetriquescomplexes.Enutilisantcesvaleursdetermineesd'unemanibrerelativementfaciledeteneureneaunongeleediversestemperatures,onpeutfairedesBvaluationsrealistiquesdeschaleursspecifiquesapparentesdesevaluationsrealistiquesdeschaleursspecifiquesapparentesdessolsgel&Lesrapportsobservesfournissentunebasepourlesetudesdeseffetsalafoisdechargeetdetemperature,surlesproportionsdeglaceetd'eaudanslessolsgel&etsurl'6tatdescontraintesdanslaglaceetl'eaunongel&.INTRODUCTIONEarlystudiesofthefreezingofsoilmoistureweremainlycoilcernedwiththedeterminationofafreezingpoint,thatis,thetemperatureatwhichfreezingcommencesinasample(BouyoucosandMcCool,1916).Morerecentlyithasbeenrealizedthatthefreezingofwaterinfinelyporousmaterialstakesplaceoverarangeoftemperatures(Lovell,1957;InstitutMerzlot.,1953-57);andthattheequilibriumfreezingtemperaturevariesindifferentpartsofthesoilwater.Thegreatestdepressionofthefreezingpointbelow0°Cpresumablyoccursinwaterthatismostfirmlyheldandisclosesttothesoilparticles.Schofield(1935)showedthatasthemoisturecontentofsoilsamplesisreducedthefreezingpointisdepressedfurtherbelow0°C.Schofieldcarriedoutinvestigationsonthesuctionwithwhichwaterisheldinsoilandshowedclearlythatasthewatercontentofthesampleisreducedthesuctiontobeappliedtoacolumnofwaterincontactwiththesoil(asinthesuctionplateapparatus)mustbeincreasedifwaterisnottoenterit.Hearguedthatthis*ResearchOfficer,SnowandIceSection,DivisionofBuildingResearch,NationalRcsearchCouncilOttawa,Canada.ResearchFellow,NorwegianGeotcchnicalInstitute,Oslo,1963,1964.231232P.J.WILLIAMSpressuredeficiencyorsuctionofthesoilwaterismainlyresponsibleforthefreezingpointdepressionsobserved;andproposedandverifiedexperimentallythatarelationshipexistsbetweenthepressuredeficiencyatagivenmoisturecontentandthetemperatureatwhichthewaterinthesoil(intheabsenceofsupercooling)beginstofreeze.Comprehensivecalorimetricinvestigationsofthefreezingofavarietyofsoilshaverecentlybeencarriedout;somearedescribedinthisPaper.Theyallowcalculationoftheamountsofunfrozenwaterpresentinthesoilsatvariousnegativetemperatures.Theseamountsinaybesaidtohavefreezingpoints(i.e.tostarttofreeze)atthosetemperatures.Accordinglytheremightbeexpected(aspointedoutbyCroney,Coleman,andBlack1958),arelationshipsimilartothatproposedbySchofield,betweenthetemperatureassociatedwithacertaincontentofunfrozenwaterandthesuctionassociatedwiththesamemoistureconteiltinthesoil(measuredatroomtemperature).Theestablishmentofsucharelationshipwouldhavetheoreticalandpracticalinterestandwouldallow,withoutthenecessityforelaboratecalori-metrictests,predictionoftheunfrozenwatercontentsofasoilattemperaturesbelow0°C(onthebasisofdeterminationofthemo