Contact law of two wing asperities in the process of joint shear and shear stress model

In order to explore the contact law of asperities in the joint during shearing process, three-dimensional scanning and direct shear tests were carried out on the tensile joint surface. The contact area and contact angle of asperities in the joint surface shearing process were analyzed by 3D point cloud tracking technology, and a shear stress model was established based on the contact law of asperities. In this process, the following conclusions were obtained: 1) In the shear process, with the increase of shear displacement, the contact area gradually decreases, and the contact points change from scattered distribution to centralized distribution. The area of a single contact point gradually increases, and the number of contact points gradually decreases. Normal stress has a significant impact on the contact area. The larger the normal stress, the larger the contact area. 2) Before the peak value of shear stress, most of the contacting asperities in the upper rock block are in a "climbing" state, and after the peak value of shear stress, some contacting asperities are in a "deviating" state. Before the peak of shear stress, most of the asperities contacted can provide shear resistance, while after the peak, some asperities cannot provide shear resistance. 3) The contact angle approximately presents a normal distribution and the average contact angle first increases and then decreases with the increase of shear displacement. 4) The verification results of the model in this paper show that the model can not only describe the shear strength of joint surface under different normal stress conditions, but also reflect the relationship between shear stress and shear displacement, which proves the rationality of the model. The model in this paper provides a new calculation method for accurately predicting the shear strength of joint surface.