Engineering4(2018)260–266Contents lists available at ScienceDirect
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TunnelEngineering—Article
UpperLillooetRiverHydroelectricProject:TheChallengesofConstructingaPowerTunnelforRun-of-RiverHydroProjectsinMountainousBritishColumbia
NicholeBoultbeea,?,OliverRobsonb,SergeMoallic,RichHumphriesdaGolderAssociatesLtd.,Squamish,BritishColumbiaV8B0B4,CanadaInnergexRenewableEnergyInc.,Vancouver,BritishColumbiaV6E4E6,CanadacEBCInc.,NorthVancouver,BritishColumbiaV7L0B5,CanadadGolderAssociatesLtd.,Squamish,BritishColumbiaV8B0B4,Canadabarticleinfoabstract
The Upper Lillooet River Hydroelectric Project (ULHP) is a run-of-river power generation scheme located near Pemberton, British Columbia, Canada, consisting of two separate hydroelectric facilities (HEFs) with a combined capacity of 106.7 MW. These HEFs are owned by the Upper Lillooet River Power Limited Partnership and the Boulder Creek Power Limited Partnership, and civil and tunnel construction was completed by CRT-ebc. The Upper Lillooet River HEF includes the excavation of a 6 m wide by 5.5 m high and approximately 2500 m long tunnel along the Upper Lillooet River Valley. The project is in a moun-tainous area; severe restrictions imposed by weather conditions and the presence of sensitive wildlife species constrained the site operations in order to limit environmental impacts. The site is adjacent to the Mount Meager Volcanic Complex, the most recently active volcano in Western Canada. Tunneling conditions were very challenging, including a section through deposits associated with the most recent eruption from Mount Meager Volcanic Complex ($2360 years before the present). This tunnel section included welded breccia and unconsolidated deposits composed of loose pumice, organics (that represent an old forest ?oor), and till, before entering the underlying tonalite bedrock. The construction of this sec-tion of the tunnel required cover grouting, umbrella support, and excavation with a combination of road-header, hydraulic hammer, and drilling-and-blasting method. This paper provides an overview of the project, a summary of the key design and construction schedule challenges, and a description of the suc-cessful excavation of the tunnel through deposits associated with the recent volcanic activity.
ó 2018 THE AUTHORS. Published by Elsevier LTD on behalf of Chinese Academy of Engineering and Higher Education Press Limited Company. This is an open access article under the CC BY-NC-ND license
Articlehistory:Received31March2017Revised7September2017Accepted22September2017Availableonline13March2018Keywords:Run-of-riverhydroprojectPowertunnelUmbrellasupportCanopytubesVolcanicdepositsPumiceRoadheaderEnvironmentalconstraints1.IntroductionTheUpperLillooetRiverHydroelectricProject(ULHP)isarun-of-riverpowergenerationschemelocatednearPemberton,BritishColumbia,Canada(Fig.1)[1],consistingoftwoseparatehydroelec-tricfacilities(HEFs)withacombinedcapacityof106.7MW.TheseHEFsareownedbytheUpperLillooetRiverPowerLimitedPartner-shipandtheBoulderCreekPowerLimitedPartnership,andcivilandtunnelconstructionwascompletedbyCRT-ebc.Asistypicalforrun-of-riverpowergeneration,theprojectdiverts?owfrom?Correspondingauthor.E-mailaddress:nboultz@hotmail.com(N.Boultbee).theriver,withouttherequirementforasigni?cantdammingstruc-ture,throughapenstock(whichmayormaynotincludeatunnel)toapowerhouse,wherethewaterissubsequentlyreleasedbackintotheriver.Flowintheriverbetweentheintakeandpower-houseisaffectedonlybytheminordisturbanceofthediversion,while?owoutsidetheprojectlimitsisunchanged.FortheUpperLillooetRiver(ULR)HEF,theintakestructurefeedsthe?owintoa2500mlong,6mwide,and5.5mhighpowertunnelthatcon-nectstoa3.6mdiameter,1600mlongsteelpenstock;thisinturnconnectstoasurfacepowerhousethatcontainsfourFrancistur-bineswithacombinedgenerationcapacityof81.4MW.Thedesign?owis53m3ásà1withamaximuminternalheadinthetunnelofapproximately24m,andatotalheadatthepowerhouseof192m.Theprojectwasconstructedbetween2012and2016concurrentlyN.Boultbeeetal./Engineering4(2018)260–266261Fig.1.LocationofUpperLillooetsitewithintheGaribaldiVolcanicBeltinBritishColumbia[1].ywiththeadjacent25.3MWBoulderCreekHEF,whichincludeda2900mlongpowertunnel.
BoththeULRandBoulderCreekHEFtunnelswereexcavatedbythedrilling-and-blastingmethod,usingcomputer-operated,full-facedrillingjumbosandrubber-tiredscooptramsandrocktrucks.Thetunnelsareunlinedexceptforshortsectionswherefaults,shearzones,ordegradablerockswereencountered.TheinvertoftheULRtunnelhasaconcreteinvertslab,whiletheinvertoftheBoulderCreekHEFtunnelisunlined.ThispaperdescribestheULRHEFtunnelanditsconstruction,andelaboratesonhowprojectconstructionproceededthroughsig-ni?cantdif?culties,includinggeologic,climatic,andenvironmen-talchallenges.2.TunnelalignmentandsitelayoutTheULRHEFtunnelgenerallyrunsparalleltothenortheastsideoftheULR;accessthroughoutthesiteisachievedalonganexistingforestserviceroad(FSR).TheULRHEFtunnelwasexcavatedastwoheadings,fromtheupstreamportalatCH0+065toCH0+582.5,andfromthedownstreamportalatCH2+533toCH0+582.5,atagradeof0.4%.Thetunnelintakeandupstreamportalareaccessedfrom49kmalongtheFSR,whichisimmediatelyacrosstheULRfromtheMountMeagerVolcanicComplex(Fig.2)[2].Thedown-streamtunnelportalisaccessedfrom44.7kmalongtheFSR,andliesadjacenttoanecologicallyimportantwaterway,TruckwashCreek.Thepowerhouseisaccessedfrom41.2km,andsitsonthenorthbankoftheLillooetRiver.Eachoftheseindividualworkareasfaceduniquechallenges,asdiscussedinSection4.yThe?gureisprovidedbytheauthor.
3.TunnelingthroughyoungvolcanicdepositsTheexcavationfromtheupstreamportaloftheULRHEFtunnelcrossedthroughtheyoungvolcanicrocksassociatedwiththemostrecenteruptionoftheMountMeagerVolcanicComplex,intoapumicedepositandburiedsoilhorizon,and?nallyintoigneousandmetamorphicbasementrocks.Tunnelingthroughthesedepositspresentedsomemajorchallenges,whicharedescribedlaterinthispaper.Thedownstreamheadingencounteredonlythebasementrocks,whichweregenerallymorecompetentandrequiredlessrocksupport,exceptatfaultsandshearzones.Thebasementrocksectionsofthetunnelarenotdescribedfurtherinthispaper.3.1.PebbleCreekFormationTheupstreamendofthetunnelwasexcavatedthroughpartsofthePebbleCreekFormation,whichcomprisesrecentvolcanicrocksandassociateddepositsfromthe$2360yearsbeforethepresent(BP)MountMeagervolcaniceruptionthatin?lledtheUpperLil-looetValleyandcoveredtheQuaternarysur?cialdepositsandbasementrocks[3,4].The$2360yearsBPeruptionwasprecededbyanejectionofashfalltephra(pumice)thatleftthickdepositsthroughouttheval-ley,anddepositedashupto1000kmaway.Themaineruptionconsistedofahotblock-and-ash?owwithvaryingdegreesofwelding.Theweldedblock-and-ash?ow,labeledasaweldedbrec-cia,wasthemajorityoftherockexcavatedintheupstreamportionofthetunnel(CH0+065toCH0+470).BetweenthisfreshvolcanicrockandthebasementrockisanunconformitycomprisedofQua-ternarysoilsandunconsolidatedvolcanicdeposits.Theunconfor-mitywastunneledthroughbetweenCH0+466andCH0+478,andisreferredtoas‘‘transitionzone”soilsinthispaper,shownschematicallyinFig.3.Thedepositsminedthroughfromtheupstreamportalaredescribedbelowfromyoungesttooldest[2]:??Theweldedbrecciaistypicallygravel-tocobble-sized,sub-roundedtoangularblocksofporphyriticdacitelava,ina?ne-grainedweldedashmatrix.Thedepositisvariablywelded,andistypicallymassivewithlittlejointing.Columnarjointingwasobservedinsomemorestronglyweldedsections—typicallyinthemiddletolowersectionsofthedeposit.Insomelocations,theboundarybetween?ows,orpulsesina?ow,couldbeiden-ti?ed.Belowtheweldedbreccia,athinlayer(<1mthick)ofnon-weldedbrecciawasobserved.TheweldedbrecciawasmappedinthetunnelfromtheupstreamportalatCH0+065toCH0+470.??Athinlayer(<0.5mthick)thatwasinterpretedtobeof?uvialoriginwasencounteredbelowtheweldedbreccia.Thislayerconsistedofsandandgravelwithsomesilt,withareddishbrownupperhorizonunderlainbycoarsesandlayers.??Mostoftheunconsolidateddepositsthatwereencounteredcomprisedpumicefromthe$2360yearsBPeruption.Thepumiceobservedonthesurfaceoccursintheformofloosegraveldepositsatnumerouslocationsthroughoutthevalley,atvolumesthatsupportpumicemining.The5mthicklayerofpumiceencounteredinthetunnelwasmainlygravel-sized,containedburnttrees(Fig.4),andincludedalowerlayerthatwasreddishbrownandorganicrich.??Alayerthatwasinterpretedtobetheforest?ooralongtheval-leysidepriortothe$2360yearsBPeruptionwasobservedbelowthepumice.Thelayerwasofvariablethickness,from10mmto0.5mthick,andwasmadeupofpineneedles,sticks,roots,andfallentrees.Carbondatingofawoodsamplefromthislayerprovidedanageof244514CyearsBP(±68years).262N.Boultbeeetal./Engineering4(2018)260–266Fig.2.SitelayoutwithintheUpperLillooetRiverValley[2].yBP:beforethepresent.Fig.3.Schematictunnelpro?lethroughthetransitionzonesoils,showingthedepositsencounteredalongthetunnelexcavation.boulders,andclay.Thecobblesandbouldersaresub-roundedandofvaryinglithology(granitoidandmetavolcanic).
Tonalitebedrock,whichmakesupthemajorityofthedown-streamtunnelexcavation,wasencounteredbelowthetill.Fig.5showsamixedfacewiththemajorityofthelayersobservedduringtheexcavationofthetransitionzonesoils.3.2.Tunnelin?owsDuringtheinitialdesignfortheproject,therateoftunnelin?owswasanticipatedtobeverylow.However,onceexcavationthroughtheweldedbrecciabegan,itbecameevidentthattheactualin?owswouldfarexceedwhatwasexpected.Waterwasobserved?owingatpressurethroughdiscontinuitiesinthevol-canicrock,andappearedtobedirectlyconnectedtotheULR,whichwaslocatedonlyabout50maway.In?owsoverthe?rst400moftunnelwereestimatedtorangebetweenapproximately7000Láminà1and8000Láminà1.Constructionwatermanagementbecameverycomplexandchallenging,workingadjacenttoariverwithsigni?cantspaceconstraints.Anextensivewatertreatmentfacilitywasdeveloped,whichincorporated?vesettlingponds,theuseof?occulent,andtheuseofcarbondioxide(CO2)toman-agepHwhencompletingconcretingworks,inordertoensurethewaterdischargewasincompliancewithallfederalandprovincialFig.4.Groutedpumicedepositcontainingaburnttree.??Thelowermostlayerencounteredintheunconformitywasgla-cialtill.Theapproximately3mthickdepositisdarkbrown,densetoverydense,andcomposedofsiltysandwithsomecobbles,
yThe?gureisprovidedbytheauthor.
N.Boultbeeetal./Engineering4(2018)260–266263Fig.5.Mixedfaceexcavationwithgroutedpumice,organics,andtilloverlyingtonalitebedrock.Fig.6.ULRandconstructionwatermanagementfacilityattheupstreamportal.environmentalregulations.Fig.6showsanaerialviewoftheset-tlingpondsandwatertreatmentattheupstreamportal.Whilesomewaterin?owswereexpectedwithinthetransitionzonesediments,theratesencounteredintheweldedbrecciaalonefarexceededexpectations.Itwasanticipatedthatifsimilarin?owratesexistedwithintheunconsolidateddeposits,itwouldbeextremelydif?cult,ifnotimpossible,toexcavateandsupportthetunnelsafely.Consequently,acoverandconsolidationgroutingprogramwasinitiatedpriortoexcavationthroughthetransitionzone.3.3.CoverandconsolidationgroutingCovergroutingwasinitiatedfromtheweldedbrecciaapproxi-mately25mbeforeencounteringtheunconsolidateddeposits,inanattempttoreducein?owsintothetunnelheading.Thecovergroutingwasdesignedto‘‘cover”theperimeterofthetunneltoadepththatwouldnotbepenetratedbythedesignedsupport(2.4mlongrockbolts).Asthegroutinghadnotbeeninitiatedwhenlarger-than-expectedin?owswere?rstencountered,itwasunder-stoodthattheoverallvolumeofwater?owingintothetunnelwouldlikelynotdecrease,asanywaterredirectedawayfromtheexcavation,aheadoftheface,couldsimply?owaroundandre-enterthetunnelfrompreviouslyexcavated(butun-grouted)areas.Thereafter,inordertostrengthentheloose,unconsolidateddeposits,andparticularlythegravellypumicedeposit,consolida-tiongroutingwascarriedout.Theprogramwaslaidoutsuchthatthegroutholeswereupto45mlongandtherewasgreaterthan20mofoverlapbetweennestedringsofoutwardlyradiating,equallyspacedgroutholes(Fig.7)[5].Basedonmeasuredin?owsandtheresultsofwatertake(i.e.,Lugeon)testscarriedoutpriortoinjection,theapparentviscosityofthegroutmixinjectedwasincreased(i.e.,thickened)andeachstagewasgroutedtorefusal,atthespeci?edinjectionpressureandatalowtoverylowrateofinjection.Inthismanner,adequategroundimprovementtoallowforstableminingconditionswasachieved.Thegroutingpro-gramisdiscussedindetailinRef.[5].3.4.TunnelingandgroundsupportTunnelexcavationwastypicallycarriedoutbydrilling-and-blastingmethodsthroughtheweldedbrecciaandbedrockoftheULRHEFtunnel.Excavationroundswereupto6mlong;rocksup-portintheweldedbrecciawastypically2.4mlong,2mspacedpatternrockboltswithweldedwire,orchain-linkmesh.Addi-tionalsupportintheformofspot-positionedrockboltsand/orshotcretewasplacedwherenecessary.Whentheexcavationreachedthetransitionzone,theblastpat-ternwasredesigned;shortblastroundswerecompletedfortheupperportionoftheface,whichstillconsistedofhigh-strengthweldedbreccia,whileroadheaderandhammerexcavationwereusedforthelowerportionoftheface,whichexposedgroutedtran-sitionzonesediments.Within7mof?rstencounteringthetransitionzonesediments,theweldedbrecciahadrisenabovethecrownofthetunnel,andthetunnelfacewasfullycomposedofgroutedpumice.Excavationbyroadheaderproceededwellthroughthegroutedpumiceandunderlyingorganicsandtilllayers.Afterafurther5mofexcava-tion,withinafullfaceoftransitionzonesediments,thetonalitebedrockwasencounteredrisingupfromtheinvert.Within11mofmixedsoilandrockconditions,thetunnelwasbacktoafullfaceofsolidbasementrock,andwasexcavatedbyshortblastrounds(Fig.3).Throughthetransitionzone,umbrellasupportwasinstalled.Theumbrellasupportconsistedof0.3mto0.5mspaced12mlongcanopytubes,typicallyinstalledatanangleof8°,with4mofover-lapbetweentubesets.Thecanopytubeswereinstalledfrominverttoinvertfromthebeginningofthesediments,withthenumberinstalleddecreasingasthetonalitebedrockwasencounteredrisingupfromtheinvert.Theumbrellasupportwascombinedwithlat-ticegirdersandshotcretetosupporttheexcavation.Facesupportwasnotrequiredduringexcavation,asastablefacewasmain-tainedduetotheconsolidationgroutingthathadbeencompletedearlier.Fig.7.Schematicofgroutingprogramholelayoutsillustratingoverlappinggroutcovers[5].264N.Boultbeeetal./Engineering4(2018)260–266Installationoftheumbrellasupportthroughthecrownofthetunnel(10o’clockpositionto2o’clockposition),andlatticegirdersandshotcretecontinuedfor40mpastthestartoffullfacerockexcavationinthetonalite,duetoverylowrockcoveroverthetun-nel.Althoughtherewasover200mofgroundcover,probedrillingindicatedlessthan6mofrockcover.Afterafulltunneldiameter(6m)ofrockcoverwasachieved,normalgroundsupportwithrockboltsandshotcretewascontinued.Toprotectagainstinverterosionandpreventunderminingofthefootingsofthelatticegirders,aconcreteinvertslabwasrequiredthroughthetransitionzonesediments.Thisinvertslabwascontinuedthroughtheentire2500mlengthofthetunnelinordertopreventerosionofotherweakzonesthathadbeenencountered,aswellasprovideeaseofaccessforfuturetunnelinspections.Duringconstruction,itwasobservedthatsomezonesoftheweldedbrecciathatweremorepoorlyweldedthanotherswereexperiencingdegradationovertime—thatis,thesurfacesofthewallsandcrownofthetunnel,whichweresolidrockimmediatelyafterexcavation,hadbrokendowntothepointwhereloosesandcouldbescrapedoffthesurface.Laboratorytestingincludingslaketests,modi?edslaketests,ethyleneglycoltesting,andX-raydiffraction(XRD)mineralidenti?cationprovidednoindicationthattherecouldbepotentialdegradationissueswiththerock.How-ever,thinsectionsdididentifyvaryingdegreesofweldingbetweensamplesthatshoweddegradationandthosethatdidnot.Topre-ventfurtherdegradationofthetunnelwallsandpossibleerosionduringtunneloperation,themorepoorlyweldedbrecciawasiden-ti?ed,mapped,andmarkedalongthetunnelcrownandwalls,andthoseareaswerecoveredwitha?nalliningthatconsistedof100mmofshotcretewithweldedwiremeshtoimproveshotcreteadherencetotherock.4.GeneralprojectchallengesInadditiontothegeologicalchallengesthatwereencounteredduringtunneling,numerousotherchallengeswerefacedbytheULHPduetoworkinginremoteBritishColumbia.4.1.LandslideriskTheMountMeagerVolcanicComplex,whichislocateddirectlyacrossthevalleyfromtheupstreamportalandtunnelintakestruc-tures,hasbeenlabeledthemostlandslide-pronemountaininCanada[6].StudiespredatingtheULHPindicatedthattherewasariskoflandslideoccurrence,bothvolcanic[7]andnon-volcanic[6],fromthemountainthatcoulddirectlyimpacttheULR,andhaveimpactsreachingfardownstream.TheProvinceofBritishColumbiahadpreviouslycommissionedthedevelopmentofalandslidemanagementplanin1999toreducetherisktothepublicfromlandslidesoriginatingfromtheMountMeagerVolcanicComplex.ThisplanincludedoperationalshutdownproceduresfortheMeagerValleytopreventaccesstotheareaintheeventofspeci?cclimaticfactorsthatcouldincreasethepotentialforalandslidetooccur,includingrainfallandtemper-aturethresholdsthatcouldleadtoexcessivesnowmelt,andthere-forerunoffonthemountain.InAugustof2010,anoperationalshutdownwasimplementedwhentemperaturethresholdswerereached(greaterthan25°Cfor6consecutivedays),andtheMeagerValleywasclosedtopublicaccess.On6August2010,alandslideoriginatedfromtheCapricornCreekDrainage(amainvalleyoffthesouthsideoftheMountMea-gerVolcanicComplex),whichenteredMeagerCreekandthentheULR.ThelandslidenarrowlymissedcampersintheprovincialcampgroundlocatedintheUpperLillooetValley,justnorthofthecon?uencewithMeagerCreek.Thiscampsitewaspermanentlyclosedafterthe2010landslide.TheCapricornCreekLandslide,astheeventwassubsequentlynamed,wasdeterminedtobethesecond-largestdocumentedlandslideinCanadianhistory[8].Numerousstudieshavedocumentedadditionalpotentialinsta-bilityfromtheMountMeagerVolcanicComplex.TheCapricornCreekLandslideenteredMeagerCreek,andthentheULR,approx-imately3kmsouthoftheproject;thus,itwouldnothavedirectlyimpactedtheprojectoritsinfrastructure(Fig.2).OfparticularinterestfortheULHPwastheeastern?ankofthemountainandtheriskfromtheJobCreekDrainage,whichislocatedjustupstreamoftheULHPintake.Inordertomitigatetheriskduringconstruction,asimilarland-slidemanagementplanwasdevelopedwithLow,High,andExtremeRisksmanagementoutlined.Thismanagementplanincludedaccessrestrictionsforareasoftheprojectthatweredependentonrainfallortemperaturethresholds.Iftemperatureswerehigherthananaverageof25°Cformorethan4consecutivedays,orifmorethan50mmofrainwasreceived,theHighRiskcategorywasenacted;thisinvolvedlogin/logoutproceduresthroughoutmostofthesiteanddaytimetravelonly,aswellasthecompleteclosureoftheupstreamportalandintakeworkareas.TheExtremeRiskthresholdwasexceededassoonastemperaturesreached35°C,ormorethan70mmofrainwasreceivedin24h.UndertheExtremeRiskthreshold,theentireULHPsitewaseffec-tivelyshutdownandtheFSRgateswerelockedtopreventanypublicaccess.Throughouttheproject,thetemperaturethresholdresultedin20daysoflostproductionin2015,and31lostdaysin2016.Therainfallthresholdwasreachedthreetimes,with6daysoflostpro-ductionin2015,andtwotimesin2016,with4dayslost.4.2.Climaticchallenges4.2.1.SummerconstructionOneofthehazardsofworkinginremoteforestedlocationsisforest?res.TheforestsofBritishColumbiaarepronetobothnat-uralandhuman-caused?resinthesummermonths.Inordertoworkinforestedlocationswhenthereisahigh?rerisk,precau-tionsmustbeundertakenbycontractors,includinghaving?re-?ghtingequipmentreadilyavailablethroughoutthesite.However,evenwithprecautionsinplace,theriskstillexists.Inthesummerof2014,almost360000ha(1ha=104m2)oflandburnedinBritishColumbia,thethird-highestlossto?reinthehis-toryoftheprovince.The2015?reseasonwasaboveaverageaswell,resultinginadditionalpersonnelbeingbroughtinfromaroundtheworldtohelp.Oneofthelargest?resintheprovincein2015wastheBoulderCreekForestFire;thiswasstartedbyalightningstrikenearthetopoftheBoulderCreekDrainage(Fig.2),whichproceededtoburnover6700haofland[9].TheBoulderCreekForestFirestartedon30June2015,approx-imately5kmuptheBoulderCreekValleyfromtheprojectsite(Fig.2).The?reremainedrelativelysmallforalmostaweek,andthenmoveddownthevalleytowardtheproject.On4July2015,the?rehadcrestedtheridgeintotheUpperLillooetValley,andtheprojectsitewasevacuated(Fig.8).Theprojectsiteremainedundermandatoryevacuationforalmost2months.However,evenwiththelargeamountsofforestthatwereburnedthroughouttheprojectarea,onlyrelativelyminorphysicalprojectlosseswereexperienced;themaindamagewastotherecentlycompletedtransmissionline,andtherewassigni?cantimpactontheoverallprojectschedule.Shortlyaftertheforest?reevacuationwaslifted,largeamountsofrainfalloccurred,whichresultedinsigni?cant?oodingoftheULRanddebris?owsfromtributaries.TheaccessFSRwasdam-agedinnumerousplaces;accesstothesitewascutofffor2days,
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