Effect of Key Parameters on Top Coal First Caving and Roof First Weighting in Longwall Top Coal Caving: A Case Study

Abstract

The first caving of top coal and the first weighting of roof strata in Longwall Top Coal Caving (LTCC) mining were analyzed in a parametric study by using a discontinuum modeling technique with plastic rock material. The analysis demonstrated that an increase in the value of cover depth decreases the stability of main roof strata, while the impact of horizontal stress on the main roof strata stability is not consistent under different stress magnitudes. The study confirmed that an increase in the value of immediate roof rock strength, coal strength, coal elastic modulus, and coal bedding spacing improves the stability of top coal before its first caving, whereas an increase in the value of top coal thickness, cover depth, and horizontal stress magnitude facilitates the commencement of top coal caving. Based on the parametric study's result, a new criterion for the prediction of face distance where top coal starts to cave was statistically developed and named Top coal First Caving Distance (TFCD). TFCD is successful in using immediate rock strength, coal elastic modulus, coal bedding spacing, top coal thickness, and horizontal stress magnitude for a reliable prediction of the face distance. The findings of this paper are helpful in better understanding basic caving/weighting mechanics, predicting face/roof instability risks, and assessing coal loss in LTCC, which contribute to improving safety and productivity in thick seam extraction.