Permeability evolution of deep coal under mining stress

In order to investigate its seepage properties, the permeability of the coal in front of deep working face under different gas pressures is tested based on the mining stress path of typical mining layouts. Subsequently, the permeability evolution is divided according to the rate and monotonicity of permeability variation. Two conceptual permeability models for the coal under different stress paths are obtained. One is about the conventional triaxial loading, and the other is about the mining stress path. Moreover, according to the permeability model for deep coal under triaxial disturbance stress and the quadratic polynomial fitting relationship, a theoretical permeability model for the deep coal in complete stress-strain process is developed. The test results show that there is no compaction stage in the stress-strain curves of the coal under typical mining stress. The increase rate of permeability at the testing points before and after the peak stress is small, but that at the peak stress point is very large. The permeability curve of the coal under the conventional triaxial loading is V-shaped. The conceptual permeability model under the conventional triaxial loading can be divided into decreasing section, slow increasing section before the peak, sharp increasing section and slow increasing section after the peak. The permeability curve of the deep coal under mining stress is inverted Z-shaped. The conceptual permeability model under the mining stress path can be divided into slow increasing section before the peak, sharp increasing section and slow increasing section after the peak. Finally, it is validated that the developed theoretical permeability model can evaluate the permeability evolution of the deep coal under different mining layouts.