Heat transfer in waste-rock piles constructed in a continuous permafrost region

This study is a part of a field experiment constructed at the Diavik Diamond Mine in northern Canada to investigate water flow, geochemical reactions, thermal and gas transport within unsaturated piles of mine waste rock in a continuous permafrost permafrost. Diavik waste rock is categorized by its sulfur content: Type I rock, Type II rock and Type III rock . Three experiment waste-rock piles of 15 m high were constructed to achieve the project objectives. Two uncovered test piles are referred to as Type I test pile (Type I rock) and Type III test pile (Type III rock). The third test pile is covered test pile in which the Type III rock is covered by a layer of 1.5 m till and 3 m Type I rock. Three drill holes of 40 m depth in a 80 m high pile were also instrumented to reexamine the results of the test piles. This thesis focuses on the thermal aspects of the project.;Thermal measurements in the uncovered piles implied the importance of wind on heat transport. Temperatures within the piles were found to decrease with time and permafrost aggradation near the base and in bedrock foundation. At the covered pile, temperatures at and below the till cover were frozen. There was no significant impact of wind on temperatures below the cover and heat influx across the cover was small. Bedrock foundation temperature of the covered pile showed a small cooling trend and less fluctuation compared to bedrock foundation of the uncovered piles. Linear stability analysis for the onset of natural air convection in waste-rock piles with physical properties based on Diavik waste rock was also performed. The results indicate that oxidation can create sufficient temperature gradients (or buoyancy forces) to trigger natural air convection.;Ground temperatures of three 40 m drill hole in the 80 m high full-scale pile showed that conduction was dominated and the pile was cooling. According to numerical simulations, using air convection cover (ACC) the 80 m high pile will be frozen for the next 100 years under a proposed climate warming for the site. Furthermore, numerical simulations also showed that ACC can maintain frozen condition within waste-rock piles even though there was a heat release due to sulfide oxidation. This heat release may create natural air convection within waste-rock piles which aids in its removal.