Damage and permeability of gassy coal in loading – Unloading path

To effectively prevent dynamic gas disasters, the adding vertical and unloading radial stress were investigated in laboratory and numerical simulation experiments. The objective about the research was to ascertain how various gas pressures and loading rates affected permeability and damage deformation. The results conclude that shear failure predominates in gassy coal, a rise in loading rate causes the permeability to mutate more slowly, and the plastic strain gradually decreases at the yield, peak, and post-peak stable points in gassy coal. As well, a rise in gas pressure causes an earlier transition from compression to expansion state of specimens, enhances permeability, and rises the plastic strain at specified points. Furthermore, the study focuses on the meso-scale failure and permeability characteristics. During failure, the seepage channel within the coal body gradually transitions from a vertical orientation to irregular deformation. In addition, a damage model is formulated centered around energy consumption, demonstrating that damage evolution curves exhibit an ‘ S’ shape with vertical strain. Meanwhile, higher axial loading rates delay the onset of unstable crack propagation, but raising gas pressure quickens the pace of damage to specimens. The conclusions of this research hold significant practical implications for mitigating coal-rock gas dynamic disasters.