Directional hydraulic fracturing to control hard-roof rockburst in coal mines

Hard roof is the main factor that induces rock-burst. In view of the present obvious weakness of control measures for hard roof rockburst in domestic collieries, the mechanism and field application of directional hydraulic fracturing technology for rock-burst prevention have been investigated in this paper using theoretical analysis and numerical simulation. The results show that the weighting span of the main roof and the released kinetic energy as well as the total elastic energy decreased greatly after the directional fracturing of hard roof with the mining progression, thereby reducing the rockburst hazard degree to coal body. The directional hydraulic fracturing technology was carried out in 6305 working face of Jisan Coal Mine to prevent rockburst. Field practices have proved that this technology is much simpler and safer to operate with better prevention effect compared with blasting. By optimizing the operation procedures and developing a new technology of automated high-pressure delivery pipe, the maximum fracturing radius now reaches more than 9 m and the borehole depth exceeds 20 m. Additionally, drilling cutting method was applied to monitor the stress of the coal mass before and after the fracturing, and the drill cuttings dropped significantly which indicates that the burst prevention effect of directional hydraulic fracturing technology is very remarkable. The research results of this paper have laid a theoretical and practical foundation for the widespread application of the directional hydraulic fracturing technology in China.