Three–dimensional rock fall simulation in the mining environment using Hy_Stone

Quantification of risk of rock fall is an important part of improving the safety of rock slopes in open-pit mining. Pit slope benches have traditionally been designed using simplified criteria (such as the Ritchie criteria) or one of several available two-dimensional software programs. Historically, 2D modelling tools have provided adequate guidance on catch bench width and berm designs for a variety of slope materials and bench face angles. However, in the real world, slopes rarely conform exactly to these designs. Actual open pit slopes are mostly convex or concave along a slope sector, and are thus affected by convergence or dispersion of actual rock fall paths. In addition, weathering, freeze/thaw action, back break, small/medium scale slope failures and other forms of erosion, acting over time along with geologic structure, modify the conditions from the “ideal” designs, thus making a reliable rock fall assessment difficult. Moreover, the mining environment is characterised by peculiar features affecting rock fall occurrence and dynamics (e.g. back break, bench failure causing rill to form, rock masses disturbed by mining). Important to safety is whether personnel and equipment should be allowed to operate below slopes that no longer meet the original design. 2D analysis can provide some insight into rock travel paths, but rock fall is a 3D process and travel paths may vary significantly from the 2D case. In this perspective, we applied the 3D rock fall simulation program Hy_Stone in different open-pit environments. The software, which has been used since 2001 to assess natural rock fall hazard, operates within the ArcGIS environment and can be used to account for complex 3D conditions. Using accurate digital terrain models (DTM’s) and calibration to known events or field tests, Hy_Stone is capable of statistically predicting a range of outcomes including travel paths, energy, rock size distribution and the distribution of rock fall among other factors. In addition, a fragmentation module has been added to Hy_Stone to assess the break up of rock particles and evaluate the travel paths of the fragments. An example of a Hy_Stone analysis along with a semiquantitative risk analysis is presented which demonstrate how this tool can improve the understanding of rock fall hazard incorporating the peculiar characteristics of the mining environment.