Effects of Bedding Geometry and Cementation Strength on Shale Tensile Strength Based on Discrete Element Method

To study the effects of anisotropy and heterogeneity on the shale failure mode and tensile strength, Brazilian splitting tests were performed from both directions of the bedding and layer thickness. Layers containing different bedding and loading angles and layer thicknesses were obtained separately. The results show that, at 0° and 90° angles, the shale cracks grow “linearly”; at 15°, the shale cracks have “arc type” growth; and at 30°–75°, the shale-splitting displays “broken line” crack propagation. The tensile strength from 0° to 90° exhibits an increasing trend. Water has a significant softening effect on the tensile strength of shale—the higher the water content, the lower the tensile strength. In addition, a 3DEC numerical simulation was used to simulate the tests, establishing shale specimen particles with random blocks. In the shale disc, uneven parallel bedding and uniform parallel bedding were set up with different loading angles and layer thicknesses to generate simulated stress-displacement curves, and the effect of layering on shale cleavage was analyzed from a mesoscopic perspective. The tensile strength of shale with uniform parallel bedding was found to be higher under the same conditions, which is consistent with the experimental results. By comparing the experimental and simulation results, from both the macro- and mesoperspectives, the Brazilian splitting crack growth of shale is affected by bedding, displaying a process from disorder to order. This study is of great significance for further exploration of the mechanical properties of shale under loading failure.