Investigation on Creep Behavior and Permeability Evolution Characteristics of Sandstone under Different Pore Pressures

To investigate the influence of pore pressure (sigma w) on the creep behavior and permeability of red sandstone, triaxial creep test with permeability test under different pore pressures was conducted using MTS 815 testing system. The experimental results demonstrate that water has significant weakening effect on the long-term mechanical properties of sandstone, and the long-term strength of sandstone gradually decreases with increase in pore pressures. All permeability-time curves demonstrate a "decreasing-increasing" trend, but two different permeability evolution trends during the steady creep stage are observed, which are related to deviatoric stress. The permeability of both intact (k0) and fractured sandstone (kf) samples increases with the increase in pore pressure, which are in consistent with the failure mode analysis of fractured sandstone samples. However, while the relationship between k0 and sigma w is positive linear, it is a positive exponential function relationship between kf and sigma w.