Abstract: To research the change and distribution rules of coal seam permeability around hydraulic flushing boreholes, based on the actual occurrence conditions of coal seam, the pressure relief range of hydraulic flushing was investigated by using gas pressure and gas content methods in this paper. Additionally, the stress and permeability changes of coal mass around hydraulic flushing boreholes were simulated by RFPA2D-Flow Software. The results show that under the influence of hydraulic flushing, the pressure relief range with the radius of 5.0~6.0 m are formed around the borehole, and the stress within this area changes from 0.038 MPa to 6.545 MPa. Meanwhile, in the place about 6.8 m away from the reviewed borehole, stress concentration phenomenon is observed. The maximum principal stress is 15.85 MPa, which is basically consistent with the field investigation results. Furthermore, the distribution regulation of coal seam permeability around borehole is similar to the change trend of principal stress. While the distance away from the pressure relief range is different, the principal stress of coal mass is also various. The nearer to the borehole, the larger the decrease amplitudes of stress and gas pressure, and the larger the permeability coefficient of coal seam.

Key words: hydraulic flushing, permeability, pressure relief and permeability increasing, numerical simulation, pressure relief range