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 mm x 100 mm x 100 mm were casted using rock-like materials, with anisotropic angle (alpha) and joint roughness coefficient (JRC) ranging from 15 degrees to 75 degrees and 2-20, respectively. The direct shear tests were conducted under the application of initial normal stress (sigma n) 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 alpha and achieves a maximum value at alpha = 60 degrees or 75 degrees. As sigma n 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 alpha = 15 degrees, while the cohesion decreases by 27.93% when alpha = 75 degrees. The differences in roughness characteristics of shear failure surface induced by alpha result in anisotropic post-peak AE responses, which is characterized by active AE signals when alpha is small and quiet AE signals for a large alpha. For a given JRC = 6-8 and sigma n = 1 MPa, as alpha increases, the accumulative AE counts increase by 224.31% (alpha increased from 15 degrees to 60 degrees), and then decrease by 14.68% (alpha increased from 60 degrees to 75 degrees). The shear failure surface is formed along the weak interlayer when alpha = 15 degrees and penetrates the layered matrix when alpha = 60 degrees. When alpha = 15 degrees, as sigma n 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 alpha, however, it is not pronounced for a large alpha. The findings will contribute to a better understanding of the mechanical responses and failure mechanisms of the layered rocks subjected to shear loads.