With the continuous application of intelligent technologies in the fully - mechanized caving mining of thick coal seams, the application of various coal - caving techniques have become possible. However, when multiple coal - drawing openings are used, problems such as unclear top-coal migration laws and uncertain recovery rates exist. Based on the Bergmark-Roos equation, this paper analyzes the migration laws of coal-rock and the change of the coal-rock boundary during single-opening coal drawing. A numerical model for single-opening coal drawing was established using the Continuum-Discontinuum Element Method (CDEM). The model was further applied to simulate the migration laws of top coal, recovery rate, and gangue content under both single- and multi-opening coal-drawing processes, including single-round and single-opening sequential caving (1R1O), group two-opening single-round sequential caving (G2O), group three-opening single-round sequential caving (G3O), over-drawn group three-opening single-round sequential caving (O-G3O), two-round and two-opening sequential caving (2R2O), and three-round and three-opening sequential caving (3R3O). The results demonstrate that the three-opening caving method significantly alleviates the difficulty of top coal drawing caused by the arching effect. When the 3R3O is employed, the coal-rock interface subsides uniformly with a relatively smooth profile, yielding the highest top coal recovery rate of 93.09%. This is followed by 2R2O (89.72%), O-G3O (89.5%), G3O (84.48%), G2O (81.73%), and 1R1O (72.35%) in descending order. This research provides theoretical and practical guidance for the intelligent and refined coal-drawing in the fully-mechanized caving mining of extra-thick coal seams.
(李红斌) et al. (Mon,) studied this question.