Drilling parameters of deep-hole cumulative blasting to improve coal seam permeability in gas drainage

Based on coal seam deep-hole cumulative blasting experiments in Jiulishan Coal Mine of Jiaozuo Coal Group, the law of stress change in a blasting coal body was analyzed by numerical simulation. It is found that cumulative blasting effect leads to the increase of peak stress and enlarges the crack zone range of the coal body. Drilling parameters for cumulative blasting, such as blast hole diameter, blast hole spacing, distance between the blast hole and the adjacent gas drainage hole, and distance from the blast hole to the coal seam roof and floor, were determined by optimization. Field experimental results show that after using these optimized drilling parameters the cumulative blasting not only gets remarkable permeability increasing effect but also ensures blasting safety.