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.