Abstract：The high pressure permeability test(HPPT) of in-situ test is an effective method to investigate the deformation and permeability of rock mass due to high pressure. During the process of full-scale experiment of a pumped storage power station，an approach for HPPT with steep obliquity faults and the experiments are studied to observe the variation of pore water pressure and deformation of the rock mass due to high water pressure. A wave-like theory of hydraulic fracture for description of fractured area spreading is also developed to understand the experimental results. The failure characteristics due to seepage under high pressure are presented on the basis of combining experimental results and knowledge of hydraulic fracture；also，different forms of seepage failure between rock mass and soil are presented. To investigate the characteristics of seepage deformation due to high pore water pressure in rock mass，pore pressure and deformation of the rock mass are measured simultaneously during the experiment. The deformation law due to the variation of pore water pressure in rock mass indicates that the coupled hydro-mechanical effect cannot be ignored during the analysis of the stress state and stability of surrounding rock mass. It is suggested that the theory of coupling analysis would be helpful to reduce the failure risk of surrounding rock mass located in high pore water pressure environments.
