Drained instability of coarse oil sand tailings

Lateral stress relief and effective stress reduction have been recognised as the culprits in flow failures of several mine tailings dams. This research examines the instability of coarse oil sand tailings (CSTs) subjected to such a stress path through a series of monotonic direct simple shear tests. To investigate the impact of tailings fabric, laboratory specimens were reconstituted by moist-tamping, air pluviation and slurry deposition techniques. Loose, medium-dense and dense specimens were prepared and consolidated to target vertical and initial shear stresses. The vertical stress was subsequently unloaded while maintaining a constant initial shear stress under a drained condition. The occurrence of instability coincided with the volumetric collapse of the specimens followed by a sharp rise in shear strain. The effects of consolidation stress, bitumen, void ratio, initial shear stress and unloading rate on the drained instability of CST specimens were also investigated.