In situ Characterization and Deep Borehole Instrumentation to Identify Permafrost Zones at the Raglan Mine, Nunavik, QC, Canada

Eliane Cabot

Dans les comptes rendus d’articles de la conférence: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: SOIL AND TERRAIN CHARACTERIZATION - VII Instrumentation & Monitoring

ABSTRACT: Acombined geomechanical and hydrogeologicalfield program, designedto supportmining,was developedto investigatepermafrost conditions atRaglan Mine(Quebec).Identifyingthe locations ofpotentialtaliks and the depth of permafrost isimportant for underground mines that penetrate the permafrostas even limited groundwaterseepagesinto the minecancauseice relatedoperating hazards.The executedfieldprogramincludedin situhydraulic permeability testing at thetransition zone and below the permafrost, geomechanical characterization of the rock mass,laboratory strength testing,as well asthe installations of vibrating wire piezometersandthermistorstringsin boreholesat depthsup to738m.Thecombination ofsubarcticclimateconditionsand aircraftcablepayload limits required the development of innovativetechniques to meet the project objectives. This paper highlightstheinnovativetechniquesused to install theinstrumentation,summarises the mainlimitations of traditionalinstallationmethodsincoldclimates, anddiscusses theimplications of the results.R•SUM•Un programme d†investigation g‡om‡canique, comprenant un volethydrog‡ologique, a ‡t‡ d‡velopp‡ pour ‡valuer lesconditions locales du perg‡lisol… Mine Raglan (Qu‡bec).En milieu arctique,l†identification de zones demassif rocheuxnon gel‡ (taliks) de m—me que la d‡termination de la base du perg‡lisol est essentielle, car m—me une quantit‡ minimaled†eau souterraine s†‡coulant dans la mine peut engendrerdesprobl–mesde s‡curit‡li‡snotamment…la formation deglace. Le programme deterraincomprenait la r‡alisation de mesures de perm‡abilit‡in situdans la zonede transition etsous la base du perg‡lisol, la caract‡risation g‡om‡canique du massif rocheux, des essais de r‡sistance m‡canique enlaboratoireainsique l†installation depi‡zomƒtres… cordes vibrantes et de cha⁄nes de thermistancesdans des trous deforage aux diamants(jusqu†… 738 m de profondeur).Des conditions climatiques subarctiques jumel‡es…unaccƒsau siteuniquementa‡rien a n‡cessit‡ le d‡veloppement de techniquesd†installationinnovatrices pour r‡pondre aux objectifs duprojet. Cet articler‡sume lestechniques innovatricesutilis‡es dans le cadre du programme d†instrumentation,pr‡sentelesprincipaleslimitationsdes m‡thodes traditionnellesd†installationdans les climats froids, etdiscutedel†implication desr‡sultats obtenus.1INTRODUCTIONTwoMining Projects(MP),Donaldsonand 14,arepresently under study atRaglan Mine, owned and operatedby Glencoreplc,in order to sustain production and extendminelife.One of these projectsmay penetratethrough thebase ofthe permafrostto depthswhere groundwaterseepages can occur.In ordertosupport underground mining to depths ofgreater than 700 m andassess thehydrogeologicalsettingsofthefuturemine workings,acombinedgeomechanical and hydrogeological site investigation wasundertakenin 2015. The specificprojectobjectivesincludedat MP Donalsonlocating a potential lake talik neara crown pillar areaandassessing the potential forgroundwaterseepages from isolated taliks along fracturezones. The objectives forMP 14were tolocatethe base ofthe permafrostas well asassess thehydraulic conductivityat the transition zoneanddeterminetherock propertiesformine design.Key limitationson the project were therequirement to complete all the work within a three monthtime period during the winter of 2015with an award date inDecember 2014, and a logistical restriction that allequipment required must either be onsite already or flowninon commercial flights.1.1Site Locationand ClimateRaglan Mineislocated atthe northern tip of the UngavaPeninsula in the Province of Qu‡bec(QC),atabout1,800kmnorth of Montr‡al (Figure 1).As shown inFigure1, it is found in a continuous zone of permafrost,where the estimated depth isgreater than 500m(Lemieux,2016).

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