Abstract: In view of the unreasonable setting of water injection pressure and poor water injection seepage effect in the process of coal seam water infusion and dust prevention, a three-dimensional meso non-uniform seepage damage numerical model which can characterize the internal pore and fracture structure of water injection coal and rock mass is constructed by using the method of CT scanning technology and RFPA software. Through the seepage damage simulation of coal rock model reconstructed by CT with different water injection pressures, the influence of water injection pressure on the seepage damage permeability, evolution and acoustic emission characteristics of coal rock sample was studied. The effect of coal rock size on seepage damage and acoustic emission of coal rock samples is studied by scaling the reconstructed coal rock model. The results show that in the process of micro fracture propagation of coal sample, with the increase of water injection pressure, the number of damage units, seepage movement distribution range of seepage field, permeability, acoustic emission number and energy of coal sample generally show an upward trend, and there are fluctuations in local area. The reason for the fluctuation is the critical reaction between the seepage field and the internal stress field of coal sample fracture, resulting in the change of the position of coal sample failure unit. The permeability of coal samples increases from 3.82×10−5 μm2 to 0.314 μm2, and the porosity increases from 5.45% to 48.45%, which reveals the influence law that the fractures of coal and rock mass continue to expand and penetrate with the increase of water injection pressure on the whole, and the expansion trend decreases with the increase of water injection pressure on the part. With the increase of coal sample size, the porosity of the coal sample after the water injection failure shows a trend of first decreasing and then gradually stabilizing, and the change trend of acoustic emission characteristic is just the opposite, indicating that the coal sample size has a significant impact on the water injection coal rock seepage failure. However, the impact of the coal sample size on the water injection coal rock seepage failure tends to be stable when the coal sample size exceeds 40 mm. The combination of CT scanning technology and RFPA software can effectively simulate the fracture seepage propagation behavior of water injection coal and rock.

Key words: coal seam water infusion, fracture expansion, permeability, size effect