Estimation of horizontal regional stresses at an open-pit limestone mine by back analysis

Abstract

A set of back and forward analyses is carried out to evaluate the states of regional and local in-situ rock stresses and the mining-induced rock slope stability using a three-dimensional finite element model and the state of local in-situ rock stress measured by the compact conical-ended borehole overcoring (CCBO) technique. The directions of the horizontal principal regional tectonic stresses obtained by the back analysis are in good agreement with those of the horizontal principal local in-situ rock stress measured by the CCBO technique. The magnitudes of the horizontal regional tectonic stress are more compressive than those of the horizontal local in-situ rock stress. This presumably results from the fact that the horizontal regional stress due to the gravity is not considered in the back-analyzed horizontal regional tectonic stress while it is included in the local in-situ rock stress measured by the CCBO technique. The local stress obtained by the forward analysis is also in good agreement with the horizontal local in-situ rock stress measured by the CCBO technique, and the magnitudes of the vertical normal stress increase more rapidly than those of the horizontal normal stresses with depth. The ratio of the horizontal normal stress to the vertical normal stress is largest at the current excavation level and decreases with depth. This suggests that the stress field within the mining-induced rock slope is affected by the horizontal components of the local in-situ rock stress.