Application of deep borehole blasting on fully mechanized hard top-coal pre-splitting and gas extraction in the special thick seam

In order to solve the problems of top-coal inadequate destruction and large amounts of gas emission in mining extra thick and hard coal seam, this study investigated the pre-splitting for deep borehole blasting and gas pre-draining technologies on top coal. The mechanism of the technologies was systematically expounded based on hard top-coal cracks development obtained by numerical simulation and theoretical analysis. The results show that explosive blasting in the hard rock results in a large number of cracks and large displacement in the rock mass due to the effect of explosion stress. Meanwhile, the thick top-coal caves, and desorbing gas flows along the cracks improve gas extraction. Finally, the pre-splitting for deep borehole blasting and gas pre-draining technologies was applied in No. 3802 working face of Shui Liandong Coal Mine, which increases monthly output in the face to 67.34 kt and the drained gas concentration to 86.2%. The drained gas average concentration from each borehole reaches 40%, and the effect is remarkable.