Study on the damage characteristics and seepage path distribution of coal under different mining methods

Water inrush disaster is one of the most threatening disasters in the process of deep coal mining, coal under the action of mining stress to produce damage fractures to form seepage paths, groundwater through these seepage paths into the working face to cause water inrush disasters, different mining methods caused by different damage degrees and fracture distribution, resulting in different distribution of seepage paths, directly affecting the risk of water inrush. Therefore, the damage characteristics and seepage path distribution of deep coal under three mining modes: protective layer mining (PCM), top coal mining (TCM) and pillarless mining (NM) were systematically studied through the triaxial seepage test with axial and confining pressure cycles, and the three-dimensional fracture scanning with a high-precision scanner. The results show that the high stress loading amplitude (NM>TCM>PCM) significantly aggravates the deformation of coal samples and drives the hysteresis loop to change from sparse to divergent, and the strain mutation of TCM and NM in the late cycle indicates the risk of instability. The damage accumulation rate of TCM and NM was significantly higher than that of PCM, and the damage degree of the rupture surface became more serious. The permeability increased in stages with the increase of stress level, and the high stress loading amplitude promoted the fracture propagation and penetration, which significantly optimized the connectivity of the seepage channel. The seepage paths of PCM, TCM and NM showed bifurcation tree, network and surface shape, respectively, and the seepage effect increased sequentially. This study provides a reference for the damage control and prevention of water inrush in deep coal.