Improving recovery in sublevel top coal caving mining by using partially reverse drawing technique

The sublevel top coal caving (SLTCC) mining technology is extensively employed in steeply inclined thick coal seams. Because of the typical characteristics of the short coal face in this mining method, a significant portion of the top coal is lost at the face end. For reducing the coal loss, the partially reverse drawing technique (PRDT) is proposed as a novel top coal drawing technique. Meanwhile, based on the Bergmark-Roos model (B-R model), a theoretical method for calculating the recovery ratio of top coal based on the top coal boundary equation and residual top coal amount is proposed. The mechanism of PRDT to reduce top coal loss at the face end is revealed by comparing with single-round sequential drawing technique (SSDT). Physical experiments and in-site observation data were used to verify the theoretical model. The results show that PRDT can effectively reduce the amount of residual coal near the roof by optimizing the shape characteristics of top coal boundary. Suggestions for improve recovery ratio in Wudong Coal Mine were given based on its face parameters.