Drawing mechanisms of granular top coal considering the structure of hydraulic support in longwall top coal caving

Drawing support is one of the unique equipment for longwall top coal caving (LTCC) technology in coal mine, whose structure has a significant effect on the top coal drawing mechanism. This research systemically investigates the effect of the dip angle of shield beam (alpha), length ratio of shield beam to tail beam (R-L), and rotation angle of tail beam (beta) on the top coal recovery, drawing body and top coal boundary by using particle flow code (PFC2D). The results show that the variation of alpha and beta has a greater effect on the top coal drawing mechanism, the ideal alpha should be about 55 degrees, R-L is within the range of 0.8-1.0, and the tail beam rotates at a small angle range, which is beneficial to the top coal drawing in the panel. When alpha is large while R-L is small, the volume of the initial drawing body gradually increases. With the increase of drawing height, volumes of drawing body under different beta all plot an increasing trend with an incremental growth ratio. With increasing R-L, the initial top coal boundary on the goaf side experiences the change of "upward concave-nearly linear-upward concave", while that on the support side shows a curve with a fast-changing slope and closes to the vertical central line of drawing opening. The research results have important theoretical and field guiding significance for the selection and design of hydraulic support in LTCC.