Study on impact damage evolution characteristics of coal rock under controlled electric pulse action

The controlled electrical pulse technology can effectively improve the pore and fracture structure of coal and rock, and enhance the permeability of coal seams. This technology has a promising application prospect in the field of coal seam enhancement. In this study, a self-built controlled electric pulse cracking and enhancing permeability of coal rock test system is utilized to carry out impact test of coal and rock samples under varying capacitance conditions of 2 μF, 4 μF, 6 μF and 8 μF. The shock wave propagation laws and structural damage characteristics of coal and rock are studied. Additionally, the microstructure of coal samples is examined and analyzed using scanning electron microscopy and low-temperature N₂ (77 K) adsorption methods. The results show that the duration of the shock pressure exerted on the coal rock by controlled electric pulse action is several microseconds. The peak pressure of the shock wave generated at the same position of the specimen increases significantly with the increase of capacitance, and the maximum peak pressure increases by 6.23 times. The crack densities of coal rock specimens under controlled electric pulse action with capacitance of 2 μF, 4 μF, 6 μF and 8 μF are 1.407 72 m^-1, 2.064 64 m^-1, 9.123 04 m^-1, and 16.700 19 m^-1, respectively. These datasets indicated that there is an exponential function correlation between the crack density of coal rock specimens and the capacitance. With the increase of capacitance, a large number of pores and fracture appear in the coal body. The total pore volume and specific surface area of the coal body increase by 2.3 times and 3.6 times, respectively, and the pore fractal characteristics are significant. The controlled electric pulse has a significant improvement effect on the micro-pore and fissure structure of coal after penetration, thereby providing a good channel for the migration of coal seam gas.