Shear mechanical properties and fracturing responses of layered rough jointed rock-like materials

This study aims to investigate mechanical properties and failure mechanisms of layered rock with rough joint surfaces under direct shear loading. Cubic layered samples with dimensions of 100 × 100 × 100 mm were casted using rock-like materials, with anisotropic angle (α) and joint roughness coefficient (JRC) ranging from 15° to 75° and 2 ~ 20, respectively. The direct shear tests were conducted under the application of initial normal stress (σn) ranging from 1 ~ 4 MPa. The test results indicate significant differences in mechanical properties, acoustic emission (AE) responses, maximum principal strain fields, and ultimate failure modes of layered samples under different test conditions. The peak stress increases with the increasing α and achieves a maximum value at α = 60° or 75°. As σn increases, the peak stress shows an increasing trend, with correlation coefficients R² ranging from 0.918 to 0.995 for the linear least squares fitting. As JRC increases from 2 ~ 4 to 18 ~ 20, the cohesion increases by 86.32% when α = 15°, while the cohesion decreases by 27.93% when α = 75°. The differences in roughness characteristics of shear failure surface induced by α result in anisotropic post-peak AE responses, which is characterized by active AE signals when α is small and quiet AE signals for a large α. For a given JRC = 6 ~ 8 and σn = 1 MPa, as α increases, the accumulative AE counts increase by 224.31% (α increased from 15° to 60°), and then decrease by 14.68% (α increased from 60° to 75°). The shear failure surface is formed along the weak interlayer when α = 15° and penetrates the layered matrix when α = 60°. When α = 15°, as σn increases, the adjacent weak interlayer induces a change in the direction of tensile cracks propagation, resulting in a stepped pattern of cracks distribution. The increase in JRC intensifies roughness characteristics of shear failure surface for a small α, however, it is not pronounced for a large α. The findings will contribute to a better understanding of the mechanical responses and failure mechanisms of the layered rocks subjected to shear loads.