Numerical Investigation of Top-Coal Migration in the First Coal-Drawing Process by an FDM–DEM Coupling Method

Abstract

In Longwall Top-Coal Caving (LTCC), the shape of the loose body (LB) and top-coal boundary (TCB) formed after the first coal-drawing are the initial conditions for the common coal-drawing period. Taking the Panel 12309 in Wangjialing coal mine as the research object, the weight of the blocks of caved top coal was measured on-site, and the distribution of their equivalent diameter was calculated. By using a coupled numerical method, the “Finite difference method (FDM)–Discrete element method (DEM)” numerical model was established, and the evolutions of the drawing body (DB), LB, and TCB were obtained. The results show that, in the initial stage of first coal-drawing (0–8.09 s), the amount of DB reached its maximum of 7.18 m3 (0.89 m3/s) and then decreased to a stable value of 0.44 m3/s. The relationships between the characteristic parameters of DB, LB, and TCB and the drawing time were fitted. Taking the second derivative of each parameter with respect to time as its sensitivity (η), it was concluded that due to the large coal-drawing volume in the initial stage (0–8.09 s), the values of the above parameters increased, and the sensitivities reached 6.02 × 10−3, 3.09 × 10−3, and 6.99 × 10−3, respectively. Here, the top-coal migration rule in the first coal-drawing process was revealed from the perspectives of DB, LB, and TCB, thus providing a theoretical basis for the further study of common coal-drawing processes.