Permeability characteristics and fine-scale deformation of loaded sandstone under increasing confining pressure unloading rates

Abstract

Abstract In deep mineral resource mining, the deformation and permeability characteristics of rocks are two main factors affecting engineering excavation. To study the influence of stress release on the deformation and permeability characteristics of rock under the action of the roadway excavation rate, this study investigated the fine-scale deformation and permeability characteristics of sandstone under the action of different confining pressure unloading rates (0.01, 0.05, and 0.1 MPa/s) via indoor experiments and a numerical simulation using particle flow software, and a rock fracture mechanics model was constructed to analyze the degree of stress concentration at the end of branch cracks under different loading and unloading paths. The results showed that the permeability, number of cracks, and principal stress difference corresponded well with the axial strain curve and the acoustic emission events under the action of the confining pressure unloading rate. The confining pressure unloading rate was inversely proportional to the axial strain, and the magnitude of the change of the axial strain was gradually reduced with the increase in the confining pressure unloading rate. The permeability and principal stress difference satisfied exponential function, while the permeability and number of cracks satisfied linear function. The microscopic cracks formed in the unloading process were predominantly tensile, with the expansion of shear cracks lagging behind. Deformations were mainly axial pressure deformations and expansions along the direction of unloading.