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In order to explore the anisotropic permeability of raw coal under low stress, taking the coal samples of Zhangcun Coal Mine, Tingnan Coal Mine and Xinjing Coal Mine as the research objects, using the improved triaxial seepage test device, the permeability tests under constant confining pressure and variable pore pressure along the direction of coal sample face cleat, butt cleat and vertical bedding were carried out. The results show that under the same confining pressure and axial pressure, the flow through the coal sample increases with the increase of osmotic pressure difference. Under the same osmotic pressure difference, the flow is closely related to the direction of seepage. The permeability in the face cleat direction is slightly larger than that in the butt cleat direction and much larger than that in the vertical bedding direction under the same average pore pressure. There is little difference in permeability between face cleat and butt cleat under low stress. It is not accident that the permeability in parallel bedding plane is similar, and the permeability of coal has the characteristics of transverse isotropy. The increase of coal stress is the main reason for the difference of permeability between butt cleat and face cleat.

In order to describe the permeability evolution law in the coupling process of anisotropic coal seam and gas, based on the assumption that the coal structure is orthogonal anisotropic, the orthogonal anisotropic permeability model was established by using the superposition relationship of coal deformation under the adsorption effect, and the gas solid coupling model considering the orthogonal anisotropic characteristics of coal was further deduced. The model was used to analyze the law of permeability under different adsorption pressures of Ⅱ1 coal seam in Jiulishan Mine and the influence of borehole dip angle of 4# coal seam in Tingnan Mine on pumping effect. The results show that under the same confining pressure, the permeability of face cleat, butt cleat and vertical bedding decreases gradually with the increase of gas pressure, which is consistent with the experimental results. The average relative errors of permeability simulation results and test results in the directions of surface cleat, butt cleat and vertical bedding are 2.55 %, 14.19 % and 4.26 %, respectively. The gas drainage volume increases with the increase of borehole dip angle. In the design of borehole drainage, increasing the angle between borehole and coal seam bedding plane can improve the gas drainage volume.

In order to verify that the deformation of coal body is the superposition of coal matrix adsorption expansion (desorption shrinkage) deformation and effective stress deformation, based on the mechanism of adsorption swelling deformation, the verification method of superposition relationship of coal deformation under adsorption was proposed. The superposition relationship of coal deformation under adsorption is verified by using this method combined with experimental data. The results showed that the average relative error of theoretical value and experimental value proportion coefficient of isothermal adsorption experiment of anthracite, lean coal and 1/3 coking coal is 4.27%. The deformation of coal body, the adsorption expansion deformation of coal matrix and the deformation of coal body under the effective stress are in accordance with the superposition relationship. Through discussion, it is concluded that the verification method of superposition relation of coal deformation is suitable for reversible deformation and residual deformation of desorption curve, but not for rich deformation.