In order to study the influence of fracture evolution characteristics of rock-like materials under different strain rates, we use river sand as aggre

A single load compression test of rock-coal-rock assemblages (RCRs) containing coal bodies with different inclinations was carried out with the research background of mining deep, large-steep coal seams. It was found that the larger the inclination angle of the coal body in the RCR samples, the larger the compaction stage of the samples and the smaller the uniaxial compressive strength value. In addition, both the maximum acoustic emission (AE) energy of the samples and the cumulative AE energy at the moment of destruction decreased with the increase of the inclination angle of the coal body in the form of exponential relativities. Also, the input energy and ultimate elastic energy of the samples at the peak stress moment decreased with increased inclination angle of the coal body. Furthermore, both of them changed with the inclination angle of the coal body in accordance with the exponential relationship; meanwhile, when the applied load exceeded the peak strength, the dissipative energy of the RCR samples increased rapidly due to the loss of load-bearing capacity. At the peak moment, the percentage of dissipated energy of the samples increased exponentially with the increase of the inclination angle of the coal body. This study has certain reference significance for the prevention and control of dynamic disasters during the mining of large angle coal seams.

The permeability evolution characteristics of low-permeability shale layers directly influence shale gas development. However, the evolution law of shale reservoir permeability in complex environments remains unclear. Therefore, understanding the permeability characteristics of shale layers is of great significance. To address this issue, permeability testing was conducted on shale under conventional triaxial compression and cyclic loading-unloading conditions. The study focused on investigating the permeability evolution of shale under different gas pressures during cyclic loading and unloading processes. The experimental results show that in the conventional triaxial compression experiment, the permeability of shale exhibits distinct stage characteristics with the change of deviatoric stress. In the elastic deformation stage, the permeability decreases slightly with the increase of deviatoric stress; In the plastic deformation stage, the permeability increases rapidly with deviatoric stress, and in the post-failure stage, the permeability continues to increase as deviatoric stress decreases, but the rate of increase slows. During the loading and unloading stages, the permeability of shale varies exponentially with confining pressure under different gas pressure conditions. Additionally, with the increase of gas pressure, the initial permeability of shale also increases. Furthermore, it was found that whether during the loading or unloading stage, for the same number of cycles, the absolute permeability change in shale rose with higher gas pressure. When the gas pressure remains constant, during the loading stage, except for the first loading, the absolute value of the permeability change in shale decreases with increasing loading cycles. during the unloading stage, the absolute value of the permeability change in shale decreases with increasing unloading cycles. Finally, the dimensionless permeability of shale was investigated, and it was found that during the loading stage, the value decreased with increasing confining pressure, while during the unloading stage, the value gradually increased with decreasing confining pressure.