Frozen Dams in Permafrost Regions - Mine Water Solutions

Frozen Dams inPermafrost RegionsMegan Miller, SRK Consulting (Canada) Inc., CanadaJohn B. Kurylo, SRK Consulting (Canada) Inc., CanadaMaritz Rykaart, SRK Consulting (Canada) Inc., Canada

AcknowledgementsThe authors would like to thank the following for making this paper possibleHope Bay Mining LimitedEBA Engineering Consultants Ltd,. A Tetra Tech CompanyOur colleagues at SRK Consulting

DefinitionFrozen Core Dam: A dam in which the water retaining structure is animpermeable frozen mass consisting of the dam core and foundations.Thermosyphon: A passive refrigeration system, consisting of a sealed tubefilled with pressurized gas and a radiator, that takes heat out of theground and disperses it into the cold air.Source: Hockley 2013Simplified Schematic ofThermosyphon

Why Build a Frozen Core Dam?•Low permeability core material not available, or not suitable•The core of frozen core dams can be constructed of esker orcrushed rock and water•Foundations thaw susceptible•Foundation thawing would cause excessive settlement of thaweddam•Construction timing/sequence•Thawed dams cannot be constructed in winter

Frozen Dams Throughout HistoryPrimarily active freezingPassive freezing, using theextreme cold of theenvironmentLEGENDSummer Construction, Active Freezing Summer Construction, Passive Freezing Winter Construction, Passive Freezing

Trends: 1790s to early 1940sPurpose: Water storage dams for water supplyConstruction: Winter or Summer with passive freezingFreezing apparatus: Nothing or wooden shieldsDams Include:PetrovskUpper KumakhshkayaUnnamed (Portovyy Creek)LEGENDSummer Construction, Active Freezing Summer Construction, Passive Freezing Winter Construction, Passive Freezing

Case Study: Petrovsk Dam, Russia• Constructed: 1792• Dimensions: Contained head of 6 m• Construction Technique: Winter Construction. Soilplaced in wooded cribwork, flooded and left tofreeze• Freezing Apparatus: None• Foundation Conditions: Unknown• Performance: Satisfactory until 1929 (137 years)LEGENDSummer Construction, Active Freezing Summer Construction, Passive Freezing Winter Construction, Passive Freezing

Trends: 1940s to 1960sPurpose: Water storage dams for water supply or power stationsConstruction: Summer with active freezingFreezing apparatus: Vertical pipes with forced air/brine/gas circulationDams Include:Hess CreekDolgoyle LakeMiaunjo RiverUnnamed (Oyuur-Yurg River)Irelyakh RiverNoril’skLEGENDSummer Construction, Active Freezing Summer Construction, Passive Freezing Winter Construction, Passive Freezing

Case Study: Irelyakh River Dam, RussiaConstructed: 1961-1964Dimensions: 20 m high, 320 m longConstruction Technique: Summer construction.Source: Salyes 1987Freezing Apparatus: Forced air circulation, verticalfreezing columnsFoundations Conditions: Sandy gravel and silty clayswith up to 60% ice content.LEGENDSummer Construction, Active Freezing Summer Construction, Passive Freezing Winter Construction, Passive Freezing

Trends: 1970s and 1980sPurpose: Water storage dams for power station,tailings damsConstruction: Summer with passive freezingFreezing apparatus: Vertical pipes operating passively(precursor to modern thermosyphons)Dams Include:Anadyr’Dam 1A & 2 (Lupin)LEGENDSummer Construction, Active Freezing Summer Construction, Passive Freezing Winter Construction, Passive Freezing

Case Study: Anadyr’, RussiaConstructed: 1976Dimensions: 17 m high, 1,300 m longConstruction Technique: Near saturated material placed in summer and leftto freeze during the following winter; built in two liftsFreezing Apparatus: Passive cooling pipesFoundations Conditions: Sandy gravelly soil with30-80% ice, over frozen clay loamLEGENDSummer Construction, Active Freezing Summer Construction, Passive Freezing Winter Construction, Passive Freezing

1990s and 2000sPurpose: Water retaining dams for tailings facilitiesConstruction Trend: Winter with passive freezing, material placed in thinlifts, freezing between liftsFreezing apparatus: Thermosyphons (Vertical, horizontal, sloped)Dams Include:Garrow LakeBearclaw (Ekati)Panda Diversion (Ekati) RaglanNorth (Hope Bay)KubakaWest (Jericho)Leslie Long Lake (Ekati)LEGENDSummer Construction, Active Freezing Summer Construction, Passive Freezing Winter Construction, Passive Freezing

Case Study: Garrow Lake, Canada• Constructed: winter 1990-1991Source: Donald 2010• Construction Technique: Winterconstruction; near saturated materialplaced in thin lifts.• Performance: Exceeded expectationsSource: EBA 1998

North Dam (Hope Bay), CanadaConstructed: 2011-2012Dimensions: 200m long, ~10m highConstruction Technique: Winter core construction, Rock slurry placed in thin liftsFreezing Apparatus: Horizontal thermosyphonsFoundations Conditions: ice-rich saline glacial marine siltand clay or fine sand overburdenPerformance: Satisfactory, to-dateLEGENDSummer Construction, Active Freezing Summer Construction, Passive Freezing Winter Construction, Passive Freezing

North Dam – Design Components

North Dam – Foundation ConditionsLEGENDPeat Marine Clay/SiltSand GravelDam FillIce lenses on exposed high wall Organic rich soil (peat) Hyper-saline overburden excavation ‘soft spot’

North Dam – Thermal AnalysisMid-December Isotherms

North Dam – ThermosyphonsWithoutWithNorth Dam Thermosyphon Installation

North Dam – Core Material• Winter construction with saturated crush rock material• Placed near saturated• Thin lifts• Allowed to freeze (reach-2 o C) before next lift placementFrozen Core PlantFrozen Core Material PlacementCentral Core - Plan Layout

Lessons Learnt – Case Histories• Modern frozen core dams have advanced significantly since inception in late 18 th century• Value in winter construction with passive coolingo eg., Garrow Lake, Kubaka, West (Jericho) and Ekati Dams• Thermal modeling of frozen damso Guidance on active or passive freezing and insulation requirements• Ground freezing technology advancements• Common problems with early frozen dams:o Thermal erosion of spillways (eg., Irelyakh) or due to summer repairs (eg., Petrovsk)o Dams constructed thawed did not freeze as planned (eg.,Dolgoyle, Anadyr’)

Lessons Learnt – North Dam Construction• Pre-construction core material testing isrecommended• Freeze-back times can drive schedule• Bonding between lifts important• Material testing during construction is essentialSource: SRK, 2012 Source: Source: EBA, EBA, 2003 2003Crushed and frozen Basaltic (left) and Kimberlite (right) frozen coreField core material trial

Lessons Learnt – North Dam Construction• Key trench over-excavation can cause delays, due to additional core material placement• Preferable to construct frozen core dam in a single winter seasonKey trench over-excavationSeasonal suspension measures

Questions?