外文翻译电阻率测量瑞典南部的Enemossen尾矿坝的安全评价.docx

外文翻译电阻率测量瑞典南部的Enemossen尾矿坝的安全评价.docx

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外文翻译电阻率测量瑞典南部的Enemossen尾矿坝的安全评价

UsingresistivitymeasurementsfordamsafetyevaluationatEnemossentailingsdaminSouthernSweden

InternalerosionisamajorReasonforembankmentdamfailures.Resistivitymeasurementsisanessentiallynon-destructivetechnique,whichmayhavethepossibilityofdetectinginternalerosionprocessesandanomalousseepageatanearlystagebeforethesafetyof.Thedamisatstake.ThispaperpresentsresultsfrompartofadamSafetyinvestigationconductedattheEnemossentailingsdaminsouthernSweden.Longitudinalresistivitysections,2Dmeasurementsalongthedamcrest,providedanoverviewofthewholedamandservedtodetectAnomalouszones.Inselectedareas,additionalcross-sectional2Dsurveysgavedetailedinformationaboutthegeoelectricalsituationsintheembankments.Thisinformationisvaluableforsimilarinvestigationsasinformationaboutresistivityinembankmentconstructionmaterialisscarce.Knownproblemareaswereassociatedwithlowresistivities,eventhoughtheresistivitymeasurementsalonedidnotprovideenoughinformationtoconfidentlycometoadecisionaboutthestatusofthedams.

Embankmentdamsaremadeofearthorrock.Internalerosionisoneofthemajorcausesofembankmentdamfailures.ResistivitymeasurementsmayhavethepossibilityofdetectinginternalerosionprocessesandAnomalousseepageatanearlystagebeforethesafetyofthedamisatstake.Thetechniqueisessentiallynon-destructive,whichisparticularlyimportantwhenworkingwithembankmentdamswheredrillingandotherpenetratinginvestigationsarepreferablyavoided.ThispaperpresentsresultsfrompartofadamsafetyinvestigationconductedattheEnemossentailingsdaminsouthernSweden.TailingsdamsareatypeofEmbankmentdamthatimpoundsminingwaste.Theminingwaste,whichconsistsof?

ne-grainedwastematerialsleftaftermechanicalorchemicalseparationofmineralsfromcrushedore,istypicallypumpedintoastoragereservoirandthetailingsdamsarebuilttoholdthesevolumesinplace.

Theaimofthisstudywastoexaminetheextentofthedamagearoundthelatestreportedsinkholeandtoexaminetheintegrityoftheentiredamsinordertodetectotherdeficiencies.Theinvestigationcomprisedtemperature,resistivity,inducedpolarisation（IP）andselfpotential（SP）measurementstogetherwithstandardvisualinspectionsandpiezometerreadings.Partoftheresultsfromtheresistivitymeasurementswillbepresentedhere.Measuringtemperatureovertimeisapowerfulandsensitivewaytodetectleakagepathwaysandtoestimatefillowrates.Themethodies,however,limitedtoaspecificarea,andthesamegoesformostconventionalmethods.Othermethodswiththepossibilitytoscanlargerareasarethereforerequested,andmostgeophysicalmethodsareofthiskind.Amongthemethodstested,resistivitymeasurementswereconsideredthemostsuccessful.Ageneraloverviewofallmeasurements,aswellasamoredetaileddescriptionofthedams,isgivenbySalmonandJohansson（2003）.

InrecentyearsmuchefforthasbeenputintodamsafetyworkinSweden.Duringthesametimeanumberofincidentsinvolvingtailingsdamhaveoccurred,whichhaveincreasedconsciousnessamongthepublicandtheauthorities.Asaconsequence,strongfocushasalsobeenputondamsafetyfortailingsdam.EightlargetailingsdamswereinoperationinSwedenin2003,andanadditionalonecommencedin2004.Threeofthemhavebeensubjectedtouncontrollederosionthroughthedambodyorthefoundationoverthelast10-yearperiod,andoneoftheseincidentsdevelopedtoacompletefailure（Benckert2003）.

Whentheelectricalpropertiesofthetailingsdistinguishfromthesurroundingmaterials,resistivitymeasurementscanbeusedtoassessleakageandpropagationforenvironmentalpurposes.Thistypeofinvestigationshasbeenconductedmanytimesasregardtominedrainage（e.g.Abraheemetal.1990;BuselliandLu2001;Yuvalandoldenburg1996）.Thetechniqueissimilartotheoneusedtodetectleakagefromlandfills.Usingresistivityforsafetyinvestigationsoftailingsdamsis,however,lesscommon,butthetechniqueissimilartoleakagedetectiononothertypesofembankmentsorriverdykeswheresomerecentexamplesfromtheliteratureincludeamongothers:

Panthuluetal.2001;Titovetal.2000;VanTuyenetal.2000;Voronkovetal.2004.Lookingatthemeasurementprogramscarriedoutinsuchinvestigations,2Dsurveyingparalleltothedamalongthedamcrestoratacertainlevelontheslopesisnearlyalwaysmadeuseof.Itisoftentheonlyfeasiblewaytoconductasurveyinpractice.Mappingtrueresistivities（inversion）fromsuchdata,however,leadstoproblemswithsevere3D-effects.Twoapproaches,bothdisregardingtheseeffectsandtherebypayinglessornoattentiontoabsoluteresistivityvalues,then,suggestthemselves.Thefirstoneistofindanomaliesinspacealongthedamcomparinghealthysectionswithknownproblemareas.Thisapproachhasbeenusedinthisstudy.Thesecondwaytotackletheproblemistofindchangesovertime,butthisrequiresrepeatedmeasurementsorregularmonitoring.

Whenitcomestodetectingareaswithanomalousseepageorinternalerosion,twoprocessesworkingagainsteachotherarecomplicatingtheissue.Firstly,theseareasgetincreasedwatercontent,whichdecreasesresistivity.Secondly,inthecaseofinternalerosion,resistivitywillincreaseduetowashoutoffinesintheearthmaterial.Therefore,asmuchaspossible,itisessentialtobefamiliarwiththeelectricalpropertiesoftheinvolvedmaterials.

TheEnemossentailingsfacilityTheZinkgruvanmineissituatedinsouthernSwedenclosetothenorthernendoflakeVattern.Mainlyzincandleadareproduced.Largevolumesoforeisinvolvedintheprocess.PartsofthetailingsarereusedasfillingsintheminebutthemajorpartisstoredintheEnemossentailingsfacilitywhichislocatedsome4kmawayfromthemine.

ThetailingsfacilityatEnemossncoversanareaof0.60km2andcontainsavolumeofsevenmillioncubicmeter.Itisrestrictedbytwoembankmentdamsalongthenorthandtheeastsidesandelsewherethetailingsarekeptinplacebynaturalground.

DamX-Y,locatedintheeast,isthehighestandlongestofthetwodams.Itstartsatchainage0/018m（thisformatrepresentslengthmarksalongthedaminmetersandisusedthroughoutthepaper）andendsatchainage0/825mthatgivesatotallengthof807m.Atthehighestpartbetweenchainage0/320mand0/600m.thedamis27mhigh.Theoldestpartofthedamwasbuiltin1976,andastheminingactivityexpanded,thedamswereraisedfivetimes.Initiallythedamswereraisedusingthedownstreammethoduptoelevation180masl（metersabovesealevel）.Laterthecentre-linemethodwasusedbetweenelevation180masland185maslandfinallyalsotheupstreammethodwasuseduptothecurrentcrestelevationat192masl.Thesemethodsareconventionalconstructionmethodsfortailingsdams,andtheyarethoroughlydescribedin,forinstance,Felletal.（1992）.Incontrasttootherembankmentdams,thefinalheightisusuallynotdeterminedwhenatailingsdamisfirstbuilt.Instead,thedamisraisedalongwithexpanded.

productionoftailingsfromthemine,andthiscanbedoneeitherbyexpansiononthedownstreamside（downstreammethod）,upstreamside（upstreammethod）orboth（centrelinemethod）.Nevertheless,thecombinationofthesedifferentmethodsatEnemossenresultsinanunusuallayoutofthecoreasshowninFig.1.

DamE-Fislocatedalongthenorthernborderofthetailingsarea.ItisconstructedinasimilarmannertotheX-Ydam.However,itisconsiderablysmallerandnoincidentshavebeenreportedinhistory.Therefore,focusinthisstudywillbeontheX-Ydam.

Bothdamsareconstructedaccordingtoconventionalmethodsforconstructionoftailingsdams.Themainpartisfoundedonsoilorperviousrock.Incaseoffoundationonsoil,atleast4mhavebeenexcavatedforthedamcore.Thecoreconsistsofafine-grainedtillwithafinescontentof40–45%andalowhydraulicconductivityofabout10–8–10–10m/s（SWECO2003）.Theminimumwidthofthecore,measuredperpendiculartothecore,is3m.Consideringtheslopeofthelatestdamraise,thiscorrespondstoacorewidthof5.5matthecrest（Fig1）.

Thereisonlyonefilterzone,withaminimumwidthof1m,betweenthetillcoreandthedownstreamsupportrockfill.Thefiltermaterialconsistsofgravelsmallerthan14mm.Downstreamandupstreamsupportfillconsistsofmixedfractionsofcrushedrockfromthemining.Thetailings,remainingfromtheminingafterseparatingzincandlead,consistoffairlyloose,wellsorted,quitehomogenous?

nesandwitharound20–35%contentsofsilt.Ithasalowhydraulicconductivityofabout10–5–10–6m/s（SWECO2003）.

Asapartofthedamsafety,workatEnemossenpiersofrockfillhasbeenconstructedparalleltothedam30–40mupstreaminthetailings.Intheareabetweenthedamandthepiers,tailingsaredeposited0.5mhigherthanthereservoirwaterlevel.Furthermore,toincreasestability,a7-m-widezoneofdownstreamsupportfillwasputoutstartingin1997.Currently,thelevelofthissupportingbermisatelevation178masl（Fig.1）.

SeveralincidentsandsinkholeshavebeenreportedontheX-Ydam,especiallybetweenchainage0/250and0/350m（1977—failurebetween0/250and0/350m,1990—sinkholeat0/250and0/350m,1993—crestsettlementsat0/260m,and1995—sinkholeat0/270m）.Sinkholeswerealsoobservedatchainage0/400min2000andatchainage0/500min2002.

InEnemossenthetailingsweredistributedoverthetailingsareaviawaterinasystemofpipes.Theelectricalconductivityoftheoutfill