Abstract: There are soft and hard materials in the rock joints composed of different infill stiffness in nature. The investigation into the shear properties of these rock joints has substantial relevance for the stability of the intertwined roughness. Shear tests are conducted to investigate the shear strength and failure characteristics of the soft and hard rock joints under various conditions of joint roughness coefficient and normal stresses where in the failure characteristics are quantified based on the area of the failure surface post-shearing of the joint surface. The results indicate that both the shear strength and the area of the shear failure surface escalate with an increase in joint roughness coefficient and normal stress. A larger difference in the hardness of the rock joint walls leads to a more pronounced difference in the degree of shear failure on either side with the softer joint surface exhibiting a larger failure surface area compared to the harder joint surface. A distinct correlation is observed between the shear test strength and the hardness of the joint walls with the shear strength of a joint wall being inferior to that of a joint wall with increased hardness on one side. This investigation elucidates the shear behavior of rock joints in intertwined roughness, which will help in the prevention of landslide hazards on this type of slopes.

Key words: Soft and Hard Material in Rock Joints, Shear Test, Joint Roughness Coefficient, Normal Stresses