In order to study the shear mechanical properties of regular tooth-shaped joints, the RDS-200 rock joint shear test system was used to conduct direct shear tests on regular tooth-shaped rock-like material joints with 5 types of undulating angles under various normal stress. The results show that:(1) The shear stress-shear displacement curves of regular tooth-shaped joints with different undulating angles generally have compaction stage, approximate straight line stage, pre-peak yield stage, post-peak softening stage and residual stage, there are three modes of slip wear failure, slope gnawing failure and serrated complete shear failure in the shear failure of tooth-shaped joints. (2) Based on the concept of effective undulating angle, an empirical formula for the peak shear strength of regular tooth-shaped joints is proposed, with an average relative error of only 2.9%. (3) As the tooth-shaped asperity undulation angle increases, the peak shear strength, pre-peak shear stiffness, debris quality, and the proportion of shear failure area of the rock joints all increase overall. The research conclusion has certain reference significance for the engineering design and protection of regular tooth-shaped jointed rock masses.

The shear deformation of rock joints is significant for the safety and stability of rock engineering. In order to study the constitutive relation of shear deformation in jointed rock mass under a normal stress, the direct shear tests under different normal stresses were carried out on the sandstone specimens with irregular joints using the RDS-200 rock direct shear test system. Based on the shear stress−deformation curve of the jointed rock, it can be divided into four stages including pre-peak compaction stage, linear stage, yield stage and post-peak softening stage. The post-peak softening stage can be further divided into three types including platform type, gradual decline type and drop type based on the decreasing magnitude and rate of shear stress at the post-peak period. The shear deformation constitutive model of the sandstone with irregular joints was established using piecewise function based on the shear deformation characteristics at different stages. Compared with the existing constitutive models, the new proposed shear deformation constitutive model of the jointed rock mass has a much higher fitting accuracy for the experimental results, which can better describe the deformation characteristics of the jointed rock in the whole shear process. The shear stress−shear displacement curve of irregular joints with different roughness coefficients under different normal stresses can be predicted after determining the relevant model parameters in the corresponding empirical formula after some direct shear tests. The research is practical for understanding the shear deformation of joints in rocks by numerical simulation and the safety evaluation of engineering.