Abstract
The waste rock excavated to reach the ore zones in a mine is typically disposed of in piles on the surface. Such waste rock piles can be very large, particularly for open pit operations. Many factors influence their geotechnical and geoenvironmental behavior, including the waste rock grain size distribution and mineralogical composition, the construction method and geometric configuration, and the natural recharge on the pile surface. This presentation will include results from a recent investigation into the behavior of unsaturated waste rock piles to illustrate the influence of key factors. The investigation includes transient flow analyses conducted to evaluate the influence of rainfalls of different intensities and durations on stability of piles with different external and internal configurations. The analyses specifically demonstrate how the external geometry of the pile and surface infiltration (water recharge) influence the factor of safety against slope failure. Results show that despite the relatively large recharge that may follow major precipitation events, the decrease in the factor of safety FS remans relatively small when the pile is properly design and constructed with benches of limited height. These results serve to demonstrate that the external geometry of a pile has the most significant impact on the factor of safety, thus indicating that pile stability can be well controlled with an appropriate design. The results also shows why waste rock piles with a uniform slope (without bench) should be avoided. The key results from this investigation will be discussed and related to recommendations for the safe disposal of waste rock on mine sites, considering short term and long term conditions.