ABSTRACT: Numerical simulation of complex pit slope instability at the Homestake Mining Company, Pitch Reclamation Project is presented. Slope monitoring data and field observations suggested that the slope displacement mechanism involved plastic deformation at a lower block, which allowed rotation of a fault-bounded middle block into the pit. This created a zone of tension that eventually mobilized plane shear of a highly weathered surficial upper block. The complex displacement mechanism was inadequately simulated by limit equilibrium models. The mechanism was reproduced using a two-dimensional distinct element model, which accounted for the rotation, bending, frictional sliding, and plastic deformation of the individual blocks in the slope. The model was extended to predict performance of the pit slope under historic worst-case piezometric conditions.

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