The stability of open pit mine slopes in residual soils

[Truncated abstract] Deep open pits are becoming increasingly common in the mining industry and the consideration of the design of slopes in open pit mines is a classical problem for mining engineers. Many of these pits are being developed in parts of the world where deep weathering has taken place, producing deep deposits of residual soils. However, limited research has been conducted in relation to the engineering properties of these materials and the impact on slope stability in open pits. Generally, residual soils behave differently from transported soils. Strain softening, often leading to progressive failure of slopes are two factors that often need consideration when dealing with the evaluation of slope stability in residual soils. In engineering practice, the limit equilibrium method is the most popular approach for estimating slope stability; however, it assumes the material behaves rigidly, with the strength being mobilized at the same time along the entire failure surface. This cannot account for progressive failure. In order to obtain more reliable results, it is therefore important to consider the potential for progressive failure when designing slopes in strain softening materials. The strain softening constitutive model in a finite difference program FLAC was chosen for use in this thesis. The results of a comprehensive numerical study into the failure mechanisms of slopes in residual soils are presented. The limit equilibrium method is also employed for comparison purposes. Comparisons of the factor of safety from each technique provide an opportunity to validate the findings and give a rigorous evaluation of slope stability. It was found that the strain softening model in FLAC is a potentially useful method to capture the failure mechanism of residual soils exhibiting such behaviour. Another key step in applying this constitutive model is the derivation of appropriate parameters describing the mechanical behaviour...