Non-linear shear characteristics and wear behaviors of joints considering the factors of roughness, size effect, and joint strength

This study investigates the non-linear shear behaviors and failure mechanisms of rock-like materials with three-dimensional joint regarding various sample diameters (d), joint roughness coefficients (JRC), and joint wall strength ratios (SR). A series of cylindrical specimens were prepared and underwent direct shear tests. The peak shear stress (τmax) decreases by 13.09%–25.98% with an increasing d due to the intensified stress concentration resultant from a diminished contact area. A higher JRC increases τmax by 13.16%–50.70% due to enhanced interlocking effects. An increase in SR improves the matrix mechanical properties, resulting in a gentle growth in τmax by 7.30%–18.27%. The normal displacement (δv)–shear displacement (u) curves and failure morphologies of the joints indicate that, as d decreases or JRC and SR increase, the curves gradually move upward and the failure modes of the joints transfer from plastic shear flow to brittle shear failure. Furthermore, the finite element method simulation was introduced to analyze the mesoscopic wear characteristics of the joint surfaces. The results reveal that the process of joint failure can be categorized into three stages including wear, shearing, and further smoothing, and the failure degree on the joints exacerbates with a smaller d or larger JRC and SR. Additionally, an improved non-linear shear failure criterion considering the influences of size effect, SR, and JRC is developed based on the Barton's JRC-JCS (joint compressive strength) model, with the average error reduced significantly from 8.12% to 3.23%.