Impact of differential settlement of oil sand fine tailings on reclamation covers

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This research program aims to ensure the sustainable development and ultimate reclamation of one of Canada's greatest energy resources, the oil sands. Alberta's oil sand mining region is dominated by several storage ponds containing nearly 1 billion m3 of a clayey mud-like slurry waste called fluid fine tailings (FFT). The oil sands industry has implemented various processes to treat the FFT with some using chemicals and mechanical equipment. The resulting treated tailings (T-FFT) are then placed behind dams creating vast deep tailings ponds. These tailings will then undergo substantial settlement estimated to be 30-50% of the initial height over a period of decades to centuries. Due to the size and inherent variability of the tailings properties within the ponds, this settlement is expected to occur at different rates and magnitudes across the tailings ponds, resulting in what is known as differential settlement (dS) of the tailings surface. The rate and extent of dS has not been thoroughly investigated and quantified for oil sands fine tailings ponds. Significant research and detailed closure and reclamation designs have been undertaken for various soil structures, containment dams or sandy tailings deposits at the oil sands mines. However, none of these deposits will undergo dS to the extent of T-FFT. The reclamation landforms planned for T-FFT deposits include wetlands, ponds, lakes and forests. Should dS continue after the reclamation covers and final landforms are constructed on these T-FFT deposits, there may be detrimental impacts to the surface water balance, groundwater system and overall physical stability. These impacts may ultimately delay or prevent a mine site from achieving its reclamation goal of a "maintenance-free, self-sustaining" landscape. An improved understanding of the impact of dS will lead to more resilient designs of closure landforms. The long-term goals of this research program aim to develop risk management and design approaches to improve reclamation and closure of tailings dams in Canada. The proposed research program will investigate the potential dS arising from various T-FFT deposits, the resulting impact on proposed closure landforms, and quantify the risk to successful closure. Specific objectives of this research program are to: 1) Quantify the dS across T-FFT deposits and its relation to the physical properties of T-FFT. 2) Evaluate the impact of settlement on reclamation covers on tailings undergoing dS. A combination of advanced numerical modeling and laboratory testing in a unique geotechnical testing facility (centrifuge) will be used to estimate the variability in dS in T-FFT and the resulting impact on reclamation covers. The results from the proposed research will be immediately available for oil sand companies and regulators to estimate maintenance and monitoring requirements, evaluate the risk of current tailings pond closure designs, and provide guidance on enhanced design alternatives.