Hydraulic fracturing can increase the fracture of coal seams, improve the permeability in the coal seam, and reduce the risk of coal and gas outburst. Most of the existing experimental specimens are homogeneous, and the influence of the roof and floor on hydraulic fracture expansion is not considered. Therefore, the hydraulic fracturing test of the simulated combination of the coal seam and the roof and floor under different stress conditions was carried out using the self-developed true triaxial coal mine dynamic disaster large-scale simulation test rig. The results show that (1) under the condition of triaxial unequal pressure, the hydraulic fractures are vertical in the coal seam, and the extension direction of hydraulic fractures in the coal seam will be deflected, with the increase of the ratio of the horizontal maximum principal stress to the horizontal minimum principal stress. The angle between the extension direction of the hydraulic fracture and the horizontal maximum principal stress decreases. (2) Under the condition of triaxial equal confining pressure, the extension of hydraulic fractures in the coal seam are random, and the hydraulic fracture will expand along the dominant fracture surface and form a unilateral expansion fracture when a crack is formed. (3) When the pressure in one direction is unloaded under the condition of the triaxial unequal pressure, the hydraulic fractures in the coal seam will reorientate, and the cracks will expand in the direction of the decreased confining pressure, forming almost mutually perpendicular turning cracks.

In order to study the coupling law of mining and gas migration in close coal seams in fault structure area, taking the coal mining face in Guizhou as the research background, the development of mining fracture field and gas migration law of No. 5 coal seam and No. 9 coal seam were studied. Based on the development of mining-induced fracture field in coal seam, the fracture distribution was binarized and quantitatively analyzed by using fractal dimension, and the gas migration law of mining-induced fractures in No. 5 coal seam and No. 9 coal seam was simulated and studied. The results show that under the condition of U-shaped ventilation, the gas accumulates seriously in the upper corner of the mining fracture field, and the gas generally floats and accumulates to the separated layer development area of the overlying strata. Due to the existence of faults, even if the mining-induced fracture field in goaf of No. 9 coal seam is within the mining-induced pressure relief range of No. 5 coal seam, the gas concentration in the mining-induced fracture field is still high, and the variation gradient of gas concentration is large. The gas will circulate actively and accumulate easily near the fault structure, and the gas concentration at the high level of the fault is slightly higher than that at the low level. The research results can provide some reference for the mining of close coal seams in the fault structure area, the comprehensive prevention and control of gas, and the safe and efficient production of coal mines.

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