Numerical Simulation Study on Optimization of Horizontal Sublevel Top‐Coal Caving Mining Technique for Steeply Inclined Extra‐Thick Coal Seam

ABSTRACT

Aiming at the problems of low top‐coal recovery rate and excessive residual triangular coal on the floor side in horizontal sublevel top‐coal caving mining of steeply inclined extra‐thick coal seams, this study takes the 5521‐25 working face of the second coal seam in Yaojie 3 Mine as the engineering background. Using PFC2D numerical simulation software, and taking top‐coal recovery rate, thickened top‐coal recovery rate, and top‐coal recovery amount as evaluation indicators, the top‐coal drawing laws under three different sublevel heights (15, 20, and 25 m) and two top‐coal drawing methods (single‐round interval drawing and multi‐round interval drawing) are comparatively analyzed. The influences of sublevel height and drawing method on top‐coal recovery performance are obtained. The results show that as the sublevel height increases, the top‐coal recovery amount gradually increases, but the top‐coal recovery rate and the thickened top‐coal recovery rate show a decreasing trend, and the decrease amplitude of the top‐coal recovery rate gradually enlarges. Among the three investigated cases, the 20 m sublevel height showed the best overall performance. Under the sublevel height of 20 m, compared with single‐round interval drawing, multi‐round interval drawing can improve the development state of the coal‐gangue boundary line, reduce the residual triangular coal on the floor side, increase the top‐coal recovery amount, and increase the top‐coal recovery rate from 79.9% to 85.8%, indicating that multi‐round interval drawing is more conducive to improving top‐coal recovery performance. This study can provide a reference for parameter design and process optimization of horizontal sublevel top‐coal caving mining in steeply inclined extra‐thick coal seams.