A Study of the Top-Coal-Drawing Law of Steeply Inclined and Extremely Thick Coal Seams in the Wudong Coal Mine

In addressing the issue of a low drawing rate in a steeply inclined and extremely thick coal seam, this study focused on the engineering background of the +575 horizontal working faces in the Wudong Coal Mine. By utilizing physical similarity simulation experiments, research was carried out on the top-coal-drawing rate and the gangue ratio at different coal-drawing intervals in horizontal segment mining for steeply inclined and thick coal seams, in which the relationships between the top-coal-drawing law and the drawing interval and technologies were revealed. The discrete element method was used to establish a numerical simulation model for the horizontal segment mining of steeply inclined and thick coal seams, and the roof-drawing law in the cases of the three-interval-group-of-support and drawing-once-every-two-support methods were analyzed before finally obtaining the optimal drawing technology. Through field practice, the coal-drawing effect of the technology was verified. The results indicated that the logarithmic functional relationship between the top-coal-drawing rate and the gangue ratio was established, and the optimal control indicator for top coal drawing was reached when the gangue ratio reached from 13% to 18%. The top-coal-drawing rate for the three-interval-group-of-support approach was higher than that of the method for drawing once every two supports. It was determined that the optimal mining technology was using a one-web-cutting-with-one-drawing approach for a three-interval-group-of-support method at a top-coal-drawing rate of 69.14%, which was 10.86% higher than that of the original technology. The research results further enriched the theory of top coal drawing in steeply inclined and extremely thick coal seams, thereby providing a reference and guidance for such mining operations.