An anisotropic creep-permeability model for rock

The service life of underground engineering is long, and the creep deformation of surrounding rock can be intensified in the water environment and the permeability shows a dynamic anisotropic trend. In order to describe the dynamic anisotropy variation of rock permeability, the rock is simplified as a cube model, a rock creep permeability model is established in stages based on creep characteristics. In the viscoelastic stage, the ratio of viscosity coefficient between cracks and rocks is defined, and a lateral influence coefficient is introduced to represent the influence of lateral stress on crack opening. In the viscoplastic stage, a correction coefficient is defined to represent the influence of cracks on seepage channels. an anisotropic creep-permeability model is established combined with anisotropic creep damage model for rock, cubic law, and the permeability model for fractured rock. The creep-seepage tests under true triaxial conditions are performed, and the anisotropic creep-permeability model is validated. The model parameters can be determined and dynamic evolution of permeability under different conditions is analyzed. The present model shows the higher accuracy compared with the traditional K-C model and the previously anisotropic creep-permeability model. It can be used to describe the trend that the permeability decreases due to the gradual compaction of pores and cracks in the viscoelastic stage, and it increases suddenly caused by the gradual convergence of cracks in the accelerated creep stage. Sensitivity analysis has been conducted on the parameters in the anisotropic creep-permeability model. As the viscosity coefficient ratio increases, the permeability decays fast and the stable permeability decreases. As the viscosity coefficient increases, the initial decay rate of permeability increases, and the stable permeability decreases. In the accelerated creep stage, As the correction coefficient increase, the permeability begins to increase significantly.