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SURFACE WATER INFILTRATION IMPACTS ON THE PERFORMANCE OF THERMAL CAPPING SYSTEMS FOR WASTE ROCK IN CONTINUOUS PERMAFROST

Session: Mining Geotechnique III / Géotechnique minière III

Michael Angelopoulos, Golder Associates (Canada)
Anne-Marie Dagenais, Golder Associates (Canada)
Steve Anderson, Golder Associates (United States)
Eva Stephani, Golder Associates (United States)
Mayana Kissiova, Golder Associates (Canada)
Patrick Gince, Golder Associates (Canada)

The use of thermal caps for reclamation of acid generating waste piles or backfilled open pit mines in continuous permafrost requires long-term simulations of the ground thermal regime. The common approach models heat conduction through materials to design the thermal cap thickness, but the thermal impacts of surface water infiltration are often ignored. This paper describes modeling the effects of snowmelt and summer rainfall on the performance of two cover concepts at a pit in a Canadian sub-arctic continuous permafrost zone. The cover concepts modelled were Thermal Cap #1 (65-200 millimeter [mm] sized clean rockfill) and Thermal Cap #2 (0-600 mm sized coarse rockfill overlying a densely compacted till layer). The pit is located on sloping terrain and underground site observations indicate infiltration into frozen waste rock during the thawing season. The modelling results show that thermal infiltration effects depend highly on the hydrogeological properties of coarse materials (waste rock and rockfill) and the presence a low permeability barrier in the cover design.