Instability of faults and weak joints of rock mass is affected by underground three-dimensional loading conditions as well as hydrostatical fluid pressure within pores and cracks. This paper presents a direct shear testing method to characterize the shear behavior of Kimachi sandstones under various pore pressures and joint roughnesses. The direct shear test was conducted under three mutually perpendicular loads and with various levels of pore pressure through effective utilization of a true triaxial loading system. An overview of the experimental method, its advantages, and results showing the usefulness of the experiment were presented. Sample permeability in the direction parallel to the joint was measured during the shear test.
Instability of faults and weak joints of rock mass is affected by underground three-dimensional loading conditions as well as hydrostatical fluid pressure within pores and cracks. For example, the intermediate principal stress modifies the shear strength of rock mass, and elevated pore pressure can promote opening or sliding of the existing faults. Effects of these conditions on shear strength of rock joint are important for predicting and mitigating geohazards related to fault and rock joint instability.
Direct shear test under high pore pressure using the conventional triaxial loading machine has been conducted to investigate the shear behavior of geomaterials. Carey et al. (2015) conducted a direct shear test with a cylindrical specimen using the conventional triaxial testing machine to study the effect of the anisotropy of shale on the shear behavior [1]. Zhang et al. (2019) also conducted a direct shear test to study the effect of supercritical carbon dioxide injection on the shear behavior of sandstone under high pore pressure and temperature [2]. Welch et al (2020) conducted experiments on the relationship between shear behavior and permeability of shear surfaces in cementitious materials [3]. The flow rate at the boundary between the cementitious and steel materials was measured during the direct shear test to understand the hydraulic characteristics before and after the shear slip.