On the Use of Bench Construction to Improve the Stability of Unsaturated Waste Rock Piles

This paper presents the main results from an investigation into the slope stability of unsaturated waste rock piles with various configurations and surface recharge conditions. The analyses first consider waste rock piles with different internal and external configurations, under steady-state conditions to evaluate the effect of the pile geometry on the factor of safety. Transient analyses are then conducted to evaluate the influence of rainfalls of different intensities and durations. For six waste rock pile configurations, the results illustrate how the external geometry of the pile influences the factor of safety. The results presented here show how surface infiltration (water recharge), external geometry, and internal pile features affect unsaturated water flow, pore water pressure (matric suction), and material strength, which in turn influence slope stability. Despite the relatively large imposed recharges, following major precipitation events, the results indicate that the decrease of the factor of safety FS is relatively small when compared with the effect of other influential factors. The results also demonstrate that the external geometry of the waste rock pile has the most significant impact on the factor of safety, indicating that pile stability can be controlled with an appropriate design. Waste rock piles with a uniform slope (single bench) should be avoided as this construction method leads to the lowest factor of safety. The overall results clearly demonstrate that the best way to improve the stability of waste rock piles is to use a design and construction method with benches of limited size.