Experiment and Modeling of Permeability under Different Impact Loads in a Structural Anisotropic Coal Body

A mount of bedding and cleat in a coal body causes that the mechanical property and gas permeability are anisotropic in a coal seam, partly. To reveal the permeability change law of the impacted coal, a self-developed vertical split Hopkinson pressure bar (SHPB) device is used to carry out the dynamic impact mechanical property tests of coal samples in three different coring directions under five impact loads and then the permeability of the impacted coal samples is measured by a permeability measuring instrument under different gas pressures. Finally, a calculation model for the anisotropic coal permeability is established to analyze the permeability distribution law in any direction with different angles to the bedding plane. The results show that with an increase in impact height the dynamic peak stress of coal samples increases gradually, which shows a linear growth relationship. The permeability of the impacted coal samples is much larger than that of raw coal samples, and the bigger the impact load, the larger the permeability. Moreover, under the same impact load and gas pressure, the permeability is the largest in parallel to the bedding direction, followed by that in oblique 45° to the bedding direction, and the smallest in perpendicular to the bedding direction. The permeability calculated by the anisotropic model in oblique 45° to the bedding direction is in good agreement with the measured results, and the errors are no more than 10%, which will provide a theoretical basis for the permeability distribution law of the coal seam after deep-hole blasting.