A Risk-Based Slope Stability Assessment Methodology (SSAM) for Excavated Coal Mine Slopes

This thesis focuses on strata failures in fresh competent coal measure slopes. Several methods are available to assess the stability of such slopes. These include empirical, kinematic, limit equilibrium, and numerical modelling. Each method has its advantages and limitations when used to assess the stability of an excavated coal mine slope design. A review of the literature highlighted a gap in the field for a classification system that assesses the risk of excavated coal mine slope failure. Current classification systems have been designed for either: (i) application in tunnelling or other underground excavations; or (ii) those that have been developed for excavated slopes do not extend sufficiently to the rock mass and failure mechanisms observed in excavated coal mine slopes; or (iii) do not provide users an estimate of design risk. This thesis presents a new risk assessment methodology, the Slope Stability Assessment Methodology (SSAM), for excavated coal mine slopes that overcomes the limitations of existing rock mass and risk-based classification systems. SSAM inputs are based on the back analysis of intact and failed excavated slope case studies sourced from open cut coal mines in Australia and Canada. Statistical analysis using logistic regression was completed to: (i) determine which slope conditions have the highest impact on slope performance; and (ii) calculate an excavated slope’s likelihood of failure as a quantitative percentage. Statistical analysis using linear regression was also used to determine a new Impact Ratio, which predicts the potential consequence of slope failure based on: (i) slope height; (ii) stand-off distance at the toe of the excavated slope; and (iii) precedent failed slope material runout distances. The output of SSAM is a low, medium or high risk rating defined as a factor of likelihood of slope failure and Impact Ratio. The new methodology was validated by a parametric study that compared the likelihood of failure calculated using the new methodology with the factor of safety calculated using 3D limit equilibrium analysis techniques. The methodology was considered validated where a negative correlation between likelihood of failure and factor of safety was calculated for nine different slope cases