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Dams & DikesPhotos: (l-r) J. Herman, J. Herman, DiavikFrozen Core DamsFrozen core dams are a type of earth filled dam typicallyconstructed in high latitudes with permafrost conditions.Coolant circulates through thermosyhons to maintain awater-tight region of the permafrost within.NUNA has designed and assembled its own plants forthe construction of frozen core dams. The plants can accuratelymonitor the moisture content and temperature of core granularmaterial prior to placement and produce up to 4,000 tonnesper 24-hour shift.Bhp Billiton Diamonds Inc.EKATI Diamond Mine, Northwest Territories, CanadaNUNA has been involved as a contractor with BHP fromthe early stages of devel op ment of its $1 billion EKATIDiamond Mine.One challenge for the EKATI Mine was to build an800 m long frozen core dam to contain 100 million m 3 ofprocessed kimberlite in an area where there was no source of lowpermeable soil and a number of other soils constraints such assand, gravel, boulders, permafrost and an unfrozen zone belowthe boulder creek bed.The solution – EBA Engineering designed and NUNAconstructed the award-winning Leslie Long Lake Frozen CoreDam with a core created of saturated, processed sand and gravelplaced in layers during the winter so that each layer froze beforesubsequent material was added. Thermosyphons, which arepassive devices, were installed to keep the structure and theotherwise permeable creek bed frozen.The success of this dam resulted in 3 other similar damsat EKATI’s satellite site, Misery, which NUNA constructed.DikesDikes serve to isolate portions of lake beds from the main lakebody providing accessibility for open pit mining.Rio Tinto, Diavik Diamond Mines inc.Diavik Diamond Mine, Northwest Territories, CanadaLac de Gras Constructors (LDGC) is a joint venture betweenNUNA and Peter Kiewit Sons, formed to construct Diavik DiamondMines’ A154 dike, North Inlet dike, A418 dike, and raising of thePKC dams. LDGC’s A154 and A418 dike contract comprised dikeconstruction, dewatering and pre-stripping.The A154 dike is the first dike of its kind constructedin Canada and was completed ahead of schedule. The A154kimberlite pipe, located 20 m below water off an island in Lacde Gras, required the construction of a 3.9 km long and up to25 m high dike to enclose an area of 1.5 km 2 . Construction of thedike involved placing 2.2 million m 3 of zoned rock fill and a plasticconcrete diaphragm wall which extended through both the fill andthe till foundation. The wall was joined to the granite bedrock bya continuous barrier of jet-grouted columns.A418’s water retaining dike and cut-off wall is1.2 km long, required approximately 1.1 million cubic metersof rockfill and was built in water up to 32 m deep. A418 dikejoins the existing A154 dike with construction methods similar toA154 – various sizes of rockfill, a central plastic concrete cut-offwall, jet and curtain grouting and installation of instrumentation.A significant crushing facility prepared much of the rock obtainedfrom A154 open pit.www.nunalogistics.com