Shear Strength Framework for Design of Dumped Spoil Slopes for Open Pit Coal Mines

Modern open pit coal mining results in dumped spoil slopes typically between 80m and 250m high. Stability can be compromised by weak geological conditions, seepage, slaking of clayey spoil materials, and dumping processes. The consequences of failure are expensive and may be catastrophic. Dump design is challenging because there is usually no opportunity for site-specific investigations and testing. A shear strength framework for open pit coal spoil dump materials has been developed for reliable assessment of shear strength parameters from visual-tactile observations. Although originally developed for the Permian Bowen Basin of eastern Australia, it is argued that the framework is applicable for coal measures materials generally. Vital to the framework are an understanding of geological conditions and a robust process for assessing relevant attributes of dumped material. The factors that must be taken into account for dump stability assessment are described. Verification of the strength parameters involved rigorous backanalysis, requiring the Sarma method for non-vertical slices in order to replicate observed characteristics of dump slope failures. The framework has limitations, and the most significant of these are discussed. Non-routine problems still require sound application of engineering judgement and risk management principles.

• Introduction

• Generalisation of Framework

• Geotechnical Stability Design

• Spoil Shear Strength Framework

• Framework Extensions and Limitations

• Stability Assessment Example for Surcharged Spoil Profile

• Conclusions

• Acknowledgements

• References