Experimental and Numerical Study of the Effects of Layer Orientation on the Mechanical Behavior of Shale

Bedding planes are common in shale and significantly affect its mechanical behavior. In this paper, the main focus is investigating the effects of layer orientation on the mechanical behavior of shale under different confining pressures through physical experiments and numerical simulations. First, confining pressure tests were performed to investigate the parameter differences of specimens with vertical bedding planes (SVBPs) and specimens with horizontal bedding planes (SHBPs). Second, the statistical results of the length and spacing of bedding planes were employed to construct the simulation model. Third, the microparameters of the proposed model were confirmed with the results obtained from physical experiments, in which four key factors including deviatoric stress versus axial strain curve, peak strength, Young's modulus and failure mode were all used to calibrate the feasibility and reliability of the numerical simulation. Finally, a systematic simulation was conducted to investigate the effects of layer orientation on the mechanical behavior of shale. The results show that the mechanical parameters (deviatoric stress vs. axial strain curve, peak strength, Young's modulus, cohesion and internal friction angle) are greatly affected by layer orientation. Tensile cracking of the rock matrix is dominant in specimens with both vertical and horizontal bedding planes. The crack initiation threshold (CIT) of SVBPs is smaller than that of SHBPs, but the crack damage threshold (CDT) is similar. The percentages of CIT and CDT are nearly unchanged under different confining pressures in both types of specimens. The conformity between the simulation results and physical experiment results suggests that the research method proposed in this study can advance the understanding of rock mass mechanical behavior.