Assessment of liquefaction potential of unsaturated oil sand tailings subjected to future saturation

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Oil sand tailings are by-products of the bitumen extraction process from oil sands, which include water, sand, fine particles, residual bitumen or other hydrocarbons. Large amounts of oil sand tailings are produced by the Canadian mining industry which are stored permanently behind large tailings dams. Liquefaction flow failure of a mine tailings dam and uncontrolled release of tailings would have a catastrophic impact on production, the environment, public perception, and loss of life. Safe and responsible management of these tailings requires proper understanding of their shear strength and resistance to liquefaction. However, liquefaction behavior and strength loss of oil sand tailings, either through earthquake loading or other triggering mechanisms such as rainfall, saturation, construction loads, or oversteepening of dam slopes are not well understood. In particular, the effect of partial saturation on in-situ test measurements and interpreting undrained shear strength of tailings is unknown. The proposed research will calibrate a widely used in-situ testing tool, the Cone Penetration Test (CPT), with strength, stiffness, unit weight, and fines content of saturated and unsaturated oil sand tailings. A comprehensive program of laboratory CPT model experiments, shear wave velocity measurements, and direct simple shear tests will be carried out on oil sand samples. The results will produce new knowledge in shear response and liquefaction behavior of oil sand tailings. A robust method will be established to predict in-situ strength, and liquefaction susceptibility of oil sand tailings under dynamic and static loads from CPT measurements. Mining engineers can then use this method in unsaturated oil sand tailings to assess the liquefaction potential and stability of tailings dams if they become saturated. This will allow mine operators and engineers to design safer tailings disposal dams and have a better understanding of the risks to existing dams. It will further benefit Canada, and particularly Alberta to minimize environmental risks of mining by ensuring that the mine deposit is ultimately integrated with the surrounding area and reclaimed into an environmentally-friendly and safe ecosystem.