Shear behavior and property of planar joints under different pore pressure conditions

An understanding of shear behavior of rock discontinuities subjected to different pore pressure conditions is essential for practical rock engineering. Direct shear tests were conducted on planar granite joints under different pore pressure conditions of 0 MPa, 0.5 MPa, 1 MPa, 1.5 MPa and 2 MPa, respectively, and the initially dry jointed granite samples were also tested as reference. The results indicate that no obvious peak shear strength was found for planar granite joints with an average Ra of 45 μm under different pore pressure conditions. The steady-state shear strength and shear stiffness decreased with the increasing pore pressures. An empirical function was proposed to successfully describe the evolutions of the shear parameters with the different pore pressure conditions. In addition, effects of lubrication and effective stress were distinguished on planar granite joints under different pore pressure conditions.