Stability analysis of slope at a disused waste dump by two-wedge model

Abstract

This study presents a large-scale failure of a disused external waste dump at an iron mine, one of the largest iron open pit mines in China. The dump is developed three beaches covering a total height of 130 m from the ground surface. It is dumped on an inclined clay layer with a maximum dip angle of 13° and average thickness of 9.34 m. The slide involved 7000000 m3 in volume of loose mass i.e. waste material, gravel and clay. In order to estimate the failure mode for slide, numerical simulation on failure mechanics of dump is performed by FLAC3D, and a physical model test on failure process of dump is carried out by the floor friction model. Results show that the waste dump slope moves horizontally along the clay layer in first. The horizontal movement of lower beaches results in the decrease of the shear resistance to lateral slide. Then, tensile cracks are generated in the top crest of the slope. Such failures with two planar slip surfaces have occurred at clay basement and through tensile cracks. With time, an obvious interface between lower block with large horizontal movement and upper block with large vertical movement is generated and then developed into the third planar slip surface. Sliding masses are divided by three slip surfaces into two wedges. A two-wedge model is established to evaluate stability for the waste dump. Factor of safety and failure mode calculated by the two-wedge method are nearly the same with those by strength reduction method.