Mechanical behavior and permeability evolution of sandstone with confining pressure after dynamic loading

Permeability is a fundamental index that is closely related to rock damage in geotechnical engineering. In this study, dynamic triaxial compression tests were performed using a modified split Hopkinson pressure bar (SHPB) for a range of incident energies, confining pressures, and number of impacts to study the mechanical behavior and permeability evolution of sandstone after dynamic loading under realistic in-situ stress. The damage factor of rock before and after the impact was measured and calculated using a rock wave velocity measurement device, and the rock permeability was tested following the pulse-decay method with a MTS-815 testing system. The results show that the peak stress, strain, plasticity, damage, and permeability of sandstone all increase with increasing incident energy. Only the peak stress increases with increasing confining pressure, whereas the other physico-mechanical parameters decrease. The opposite result is obtained in response to an increased number of impacts. The dynamic stress-strain curves are categorized into classes I and II based on the post-peak behavior and fracture pattern. The quantitative relationships between energy, damage, and permeability are discussed. The absorbed energy per unit volume follows a negative exponential relationship with the damage factor and a positive linear relationship with the permeability enhancement index. The damage factor follows a positive exponential relationship with the permeability enhancement index. The permeability enhancement is mainly due to increased connectivity of the pores and channels in the rock caused by crack propagation and coalescence, and the rock damage and fracture are controlled by the absorbed energy.