Quantifying the effect of in-situ stresses and pit depth on slope stability by incorporating brittle fracturing in numerical model analyses

Abstract

Designing reliable slopes that provide safety and maximize financial return represent one of the main challenges in a mining operation. As open pits get increasingly deeper, the need to better understand the behavior of high rock slopes has become more critical. Currently, it is not clear how mining at increased depths may impact slope behavior. Similarly, the impact of in-situ stress magnitudes in slope stability is still uncertain. High horizontal stresses and increased depths can lead to unfavorable stress conditions, inducing rock mass damage and strength loss. The main goal of this research is to assess the effect of increased mining depth and in-situ stresses on slope stability. Reliable slope behavior predictions require an adequate knowledge of the local pre-mining stress setting, together with suitable numerical tools capable of capturing the brittle characteristics of rock masses. In this research, the response of the rock mass was studied using both a FEM and the Slope Model code, which is based on a simplified DEM approach. Abstract It was found that when pre-existing fractures are present, rock mass damage can develop deep into the rock mass, leading to possible slope failures when combined with non-persistent discontinuities. Rock mass damage levels, represented by the number of induced fractures, tend to increase following a near exponential relationship with depth indicating an important potential to develop in deep open pits. Likewise, damage levels present a strong correlation with in-situ stress magnitudes, with higher horizontal stresses resulting in increased fracturing. In addition, when horizontal stress magnitudes are higher failure surfaces will tend to form at deeper levels, leading to larger failed volumes. These differences in behavior highlight the importance of an accurate determination of the in-situ stress state which together with adequate numerical tools, allow for improved stability assessments. At the same time, improved numerical tools can lead to a better understanding of rock mass behavior in variable stress conditions, reducing the uncertainty in the development of future deep pits.