Numerical investigations of joints with different surface roughness under shear and normal loads

Abstract

A large number of discontinuities and weak planes exist in the natural system of rock masses. The presence of these discontinuities and weak planes reduces the strength of the rock masses. Thus, a thorough understanding of the shear behavior of jointed rocks is very important for many engineering projects. In this study, multistage normal loading (30, 60, 90, 180, and 360 kN) direct shear tests were conducted on a smooth planar joint using a large shear box device. Four numerical models with different joint asperities were built in parallel using Fast Lagrangian Analysis of Continua in three dimensions (FLAC3D), and the shear behavior was numerically analyzed. According to the experimental and numerical simulation results, joint roughness and normal force are the two most important factors that influence the shear behavior. The peak shear force increased as the normal load and joint asperity increased, but the normal displacement increased as the joint asperity increased and the normal load decreased. For the plane joint surface or joint surface with small asperity, the vertical displacement on the applied shear force side tended to go down, whereas it tended to go up on the opposite side. For the joint surface with large asperity, the vertical displacement on both sides went up. However, the value in the applied shear force side for the joint surface with large asperity was lower than that for the joint with smaller asperity. During shearing, the inclination of the upper box of the specimen is an important characteristic that causes the nonuniform distribution of normal stress, shear stress, and contact area of the interface. Furthermore, we developed a method for calculating the aperture size during shearing and discovered that the aperture size increased as the joint asperity increased. This research provides insight into the shear behavior of rock joints with various asperities.