Highwall stability analysis under dragline loadings at a Saskatchewan coal mine

Abstract

The design of a highwall in coal mining involves the consideration of many factors. The ongoing evaluation of a soft coal strip mine in southern Saskatchewan has provided an opportunity to combine both quantitative and qualitative factors in highwall design. The mine is located near the southerly extent of continental glaciation in an area subjected to multiple advances of the ice front. One of the main factors affecting highwall design has been the structural disturbance of the sediments caused by glacial tectonics. The original design was based on limit equilibrium analysis and shear strength parameters obtained from direct shear tests. Information obtained from full-scale test pits was also incorporated. The study was later up-dated using the results of highwall failure back-analysis. These studies were complemented with finite element stress analysis and further limit equilibrium analysis incorporating the effect of the dragline loadings. The paper traces the history of stability analysis and modification of the recommended shear strength parameters from the pre-mining investigations through four years of operation. Particular emphasis is placed on the refinement of the shear strength parameters used for design. The importance of other factors (e.g., piezometric levels, climatic conditions, time effects, etc.) are briefly outlined.