Caving mechanisms of loose top-coal in longwall top-coal caving mining based on stochastic medium theory

A good understanding of the caving mechanisms of loose top-coal is significant for longwall top-coal caving (LTCC) mining. In this paper, the equations of the particle motion, top-coal boundary, and drawing body were derived based on the stochastic medium theory. Then, the particles moving boundary and the shape of the top-coal loss were discussed, and the dynamic evolvement of the top-coal boundary and drawing body was analyzed. A theoretical model for calculating the top-coal recovery ratio was established, and the relationship between the top-coal recovery ratio and rock mixed ratio was studied and then the criterion for terminating the drawing cycle was proposed. Finally, model experiments were conducted to verify the theoretical analysis. It is concluded that the starting top-coal boundary keeps moving to the lower left with increasing drawing volume. The top-coal loss is zonal distribution and tilts toward the goaf and is composed of the top-coal surrounded by the floor, the starting top-coal boundary and the ending top-coal boundary between the drawing window and the lowest moving point in the starting top-coal boundary. The drawing body tilts toward the goaf and its deflection angle decreases with increasing drawing volume. The top-coal recovery ratio increases non-linearly with increasing rock mixed ratio, and the rock mixed ratio of 10–15% can be used as the criterion for terminating the drawing cycle. This work is the first attempt at demonstrating the caving mechanisms of the loose top-coal using the stochastic medium theory in LTCC mining.