Research on rock permeability and failure characteristics under different loading and unloading paths

The mined-out stress recovery under the effect of overlying strata subsidence has an influence on the mining-induced stress field and the permeability of rock mass. The TAW-3000 electro-hydraulic servo rock triaxial testing machine is used to investigate the permeability, deformation and failure characteristics of rock under different unloading-reloading paths. The unloading and reloading stress states of the rock are, respectively, analyzed in the process of stable crack growth phase, unstable crack growth phase and post-peaking phase. The results show that the local weak surface is formed, and permeability of the rock sample has little impact during the loading-unloading process, when the rock sample is loaded to the stable crack growth phase. When the rock sample is loaded to peak strength, the rock sample presents an 'octagonal' failure. When the rock sample is loaded to the unstable crack growth phase, the non-transfixing crack is formed. The crack is applied by the effect of loading-unloading, which produces fine and uniform particles and generates a certain amount of argillaceous composition. The impermeability of rock sample is improved. When the rock sample is loaded to peak strength, the rock sample presents a 'Y-form' failure. When the rock sample is loaded to the post-peaking phase, the transfixing and incomplete recovery crack is formed. When the rock sample is loaded to peak strength, the rock sample presents a 'ladder-form' failure. The permeability resistance is further weakened. The permeability of rock sample at residual strength of three stages is: unstable crack growth phase < stable crack growth phase < post-peaking phase.