Analysis of prssure relief effect of roof deep hole blasting parameters based on micro-seismic data evaluation

In view of the phenomenon of frequent occurrence of high-energy mine earthquakes caused by the roof breakage of weakly bonded thick layer with wide coal pillars in Hongqinghe coal mine, theoretical analysis, micro-seismic monitoring and field test methods were used to determine the occurrence of high-energy mine earthquakes and the pressure relief of deep hole blasting of roof. Two schemes were proposed, i.e. the fan-shaped layout along the strike with charge of 2.5 kg/m and the fan-shaped layout along the dip with charge of 4 kg/m.Based on the combined monitoring method of the underground site and the ground micro-seismic system, the micro-seismic signals induced by the deep hole blasting vibration of the roof were accurately located, and the pressure relief effects of the two schemes were compared and analyzed by the indicators monitored by the micro-seismic system.The results show that roof blasting with fan-shaped layout along the strike mainly induces 1.0×103～1.0×104 J micro-seismic events, and that layout along the dip mainly induces 1.0×104 J or more micro-seismic events. From the indicator of induced energy per kilogram of explosives, it can be found that in the layout scheme along the strike, the blast-induced energy in the range of advance bearing pressure of the working face has increased slightly, but the rising range is not large; in the layout scheme along the dip, the induced energy of roof blasting at the working face side increases by about 6.3% compared with that at the coal pillar side; In the fan-shaped layout scheme along the dip, the induced energy per kilogram of explosive is more than three times of that in the scheme along the strike. Combined with the actual situation of the No.402 working face in Hongqinghe coal mine, the validity and feasibility of the fan-shaped layout scheme along the strike beyond 450 m ahead of the working face were determined, and it was verified that the scheme along the strike can achieve better blasting pressure relief effect. The results of micro-seismic positioning during mining of the working face further showed that whether adopting the scheme along the strikeor the scheme along the dip to carry out the roof deep hole pressure relief blasting, it can play a good role in the roof blasting pressure relief effect.