Grant: CCI Applied Research and Development Grants

Management of tailings, the slurried waste products of crude oil/bitumen extraction, is a big challenge for the oil sands industry due to their innate, dangerous potential for quick clay activity. When subjected to sufficient stress, quick clays undergo a rapid change from behaving as a solid mass to behaving as a viscous fluid; this can trigger catastrophic landslides during routine earthworks, earthquakes or nearby blasting. Consolidation of clay particles in aqueous tailings suspensions is one of the major obstacles to effective tailings management as deposits are usually undetectable without proper site investigation, are covered by topsoil, and are completely stable until overloaded. Current tailings treatments involve the addition of coagulants and flocculants to promote sedimentation, however their presence increases the likeliness of quick clay activity in the produced deposits. Although leaching and polymer degradation are known causes of quick clay behaviour in aqueous sediments, studies to date have not evaluated their effects on the quick clay potential of oil sands tailings. Leaching occurs when the salt content of tailings is gradually reduced over time with exposure to natural groundwater. Evaluation of polymer breakdown on the geotechnical properties of flocculated deposits is particularly relevant given the large polymer doses (>1000 g/ton) used in oil sands tailings treatment. This study’s objective is to examine the quick clay behaviour of oil sands tailings at eight (8) industry tailings sites through the assessment of their composition, behaviour, and extent of strength after leaching and polymer degradation. Quick clay mitigation strategies will be investigated for any changes in strength within the range of quick clay behavior. Understanding the effects of leaching and depolymerization on tailings behavior is critical for discerning future land development guidelines and policies, as well as future applications by industry and reclamation specialists. Our results will also benefit the Canadian oil sands industry by providing important insight into the role of polymer degradation and salt leaching in the potential vulnerability and long-term stability of oil sands tailings. Findings may also be applied in the risk-assessment for other fine-grained tailings. Identifying management practices with the most promise to reduce quick clay activity quickly and reliably has the potential to establish Canada as a leader in tailings management.