Numerical study of mining activity and climate change impact on permafrost in Northern Canada
The presence of permafrost and its susceptibility to naturally freeze and thaw under changes in the environment is a major problem in cold regions encompassing nearly 50% of Canada land surface. The excavation of open pit mines in permafrost with subsequent filling with tailings and water presents a...
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
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Graduate Studies
2017
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| Online Access: | http://hdl.handle.net/11023/3780 https://doi.org/10.11575/PRISM/27145 |
| Summary: | The presence of permafrost and its susceptibility to naturally freeze and thaw under changes in the environment is a major problem in cold regions encompassing nearly 50% of Canada land surface. The excavation of open pit mines in permafrost with subsequent filling with tailings and water presents a scenario similar to a thermokarst lake that causes a local drift from ground temperatures, thus resulting in talik formation. This thesis is concerned with the numerical analysis of permafrost degradation and its consequences within the permafrost zone due to mining activities and climate change. The Kiggavik uranium mine project in Nunavut, Canada where four open pit mines will be excavated into deep permafrost is chosen as a case study for which extensive data is publicly available. Incrementally complex hydro-thermal models were developed within the finite element framework. Short-term studies indicate that for different considered scenarios during the mine operation period drastic changes are not expected. Open taliks will not form in the smaller pits. Ground deformations due to high in-situ stresses and high ground water pressure will be less than 100 mm. The presence of faulted zones enhances the water inow into open excavations; however, the water level variation within the pits is less than 2 cm/day. The long-term simulations demonstrate that after 2000 years, with no-climate change scenario, the permafrost could only be recovered within the smallest pit. The permafrost thickness decreases to approximately 35m considering a probable climate change scenario. In the case of a severe scenario, the permafrost disappears completely in about 700 years, and the water table will rise to 35m below ground surface. The inuence of material hydraulic properties is examined with introduction of a new analytical method. Decreasing the fractures mean aperture in the rock domains accelerates permafrost thawing up to 100 years in some locations. |
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