Research Progress on Shear Characteristics of Rock Joints under Constant Normal Stiffness Boundary Conditions

The constant normal stiffness (CNS) boundary condition is more representative for the underground engineering, in which the shear-induced dilation is restricted by surrounding rocks, resulting in an increase in the normal stress. Therefore, the use of CNS boundary conditions in the research of shear-slip failure of underground rock engineering is more in line with the actual situation. Taking the instability and failure of surrounding rock in underground engineering as the background, the present study introduces the engineering background of CNS boundary conditions and the research progress on shear characteristics of rock joints under CNS boundary conditions. Three key directions for future research are proposed based on the latest research results of shear characteristics of rock joint under CNS boundary conditions: (1) developing a rock joint shear test system that can realize the function of "CNS boundary conditions + shear-seepage test + visualization"; (2) carrying out the shear tests of real rock joints under CNS boundary conditions based on 3D scanning and 3D carving technology; and (3) carrying out the shear tests of rock joint network under CNS boundary conditions.