Slope Stability Analysis of Opencast Mine Dump using the Limit Equilibrium Method—a Case Study

Abstract

Slope failures in mine overburden dumps are recurring incidents leading to the loss of life and property. Since slope stability depends on several factors that may vary over a period of time, such as slope parameters and material characteristics, regular slope stability studies performed periodically are necessary for assessing the risk of slope failure more effectively. This study aims to analyse the slope stability of opencast lignite mine overburden dump benches by determining the slope factor of safety via 2-D limit equilibrium software. On the basis of their factor of safety values, slopes are categorized as ‘highly stable’, ‘moderately stable’ and ‘unstable’. Among the three slopes analysed, two are moderately stable, and one is highly stable. Slopes with a factor of safety ≥ 1.3 are considered highly stable, and those with a factor of safety between 1 and 1.3 are considered moderately stable. Unstable slopes have a factor of safety of less than 1. Through a series of iterative procedures, the maximum permissible bench heights for high slope stability are determined. By comparing the results with the present bench heights, height reductions are recommended for each bench. The study found that the heights of benches with moderately stable slopes must be reduced by 10 to 15 m to achieve high slope stability. The heights of the upcoming benches are recommended not to exceed 50 m. This study not only analyses the present conditions of slope stability but also provides recommendations regarding bench heights for attaining high slope stability, thus providing an actionable conclusion that can be implemented in the current state of practice. Although the study has limitations in terms of applicability outside of opencast mines with soft strata, the methods described can prove to be valuable for determining how to approach and proceed with similar case studies on slope stability.