Processing oil sand involves material handling on an unprecedented scale, and creates vast quantities of waste or tailings. Large retaining structures are constructed from the sand tailings and used to retain the finergrained
waste products.
Service demands of the retaining structure are reviewed along with a study of factors that affect the long-term stability. The retaining structure must remain intact during construction and resist erosion until protective vegetation is established. Then it must support the fine-grained waste products until they consolidate and are able to stand by themselves. Finally, the retaining structure must erode at a controlled rate that avoids release of large quantities of sand into the surrounding area.
Present construction methods appear adequate for short-term stability considerations, but the support will be required for 1000 years or more until fine-grained wastes consolidate and are able to stand by themselves.
Eventually, the tailings retaining structure will succumb to natural erosion by running water and wind. Because of the concentration of fine sand in the retaining structure, erosion, once started, is likely to be quite rapid. Consequently, it is doubtful if the present structures will be able to meet long-term stability requirements.
Methods of reducing the rate of erosion and of reducing the required support time are explored. The key lies in planning that integrates longterm needs, operational considerations, and reclamation requirements. Alternate construction methods that are more likely to meet long-term stability requirements are identified. The main considerations include accelerated consolidation of the fines, controlling surface runoff even while the overall structure is eroding, and introducing barriers to prevent rapid erosion of the sand. Adoption of these construction methods would enhance overall performance. Operating costs may be reduced because of the increased storage capacity that results from accelerated consolidation of the tailings fines.