Geomechanical and seepage evolution characteristics of coal masses under mining-induced stress paths

The mechanical and seepage evolution characteristics of coal during mining process are the key factors affecting coal seam gas drainage and ensuring the safe production of coal mine. However, the influence of mining layouts on permeability of coal seam is seldom studied because of the complexity of the mining-induced stress test. In order to study the influence of the mining-induced stress on the coal seam, the mechanical properties, the Acoustic Emission (AE) characteristics and the energy dissipated of the coal mass were experimentally studied with unloading loading test. The experimental results indicate that (1) compared the non-pillar mining stress path, the deviatoric stress and axial strain of coal samples at peak point under protective coal-seam mining stress path decrease respectively. (2) Under the stress path of non-pillar mining, the unloading rate of confining pressure is larger and the absorbed energy, elastic energy and dissipated energy of coal sample are lower when the coal sample is destroyed. (3) When the unloading rate of confining pressure is larger, the fracture structure of coal is more complex and the fractal dimension is higher, resulting in the higher the permeability after the destruction of the coal.