A discontinuum modelling approach for investigation of Longwall Top Coal Caving mechanisms

This paper presents a discontinuum modelling approach to investigate Longwall Top Coal Caving (LTCC) behaviour including stress distribution, coal and rock failures, top coal caving and roof strata rupture, and to analyse the impact of overburden movement on top coal caving. The current model ia successful in using plastic material in a discontinuum code for intact rocks. The model scale is large enough to capture the critical features of LTCC, including steady-state caving of top coal and repeatable periodic weighting of roof strata. The applicability of the numerical model was assessed by calibration with field measurements obtained from a longwall mine site. The numerical study found that the stress distribution caused by LTCC mining is in general similar to that caused by conventional longwall mining; top coal predominantly fails in shear whereas roof rock mostly fails in tension; top coal starts to cave in stress caving while main roof strata first rupture in crushing mode; and roof strata weightings periodically increase and decrease top coal cavability. The findings of this study should assist engineers in better understanding fundamental rock mechanics associated with LTCC, identifying key geotechnical parameters dominating caving behaviour, and managing top coal productivity and mine safety involved in LTCC operation.