Anisotropic mechanical response of layered shales: Insights from numerical simulations

Abstract

Abstract Layered shales exist widely in nature and are often encountered during infrastructure construction. However, the mechanical response of layered shales is significantly affected by the existence of beddings, resulting in the obvious anisotropy characteristics in terms of deformation, strength, and failure mode. To clarify the underlying mechanisms of shale anisotropy that control the safety of engineering projects, the combined numerical simulation and theoretical analysis were conducted. The results show that with the growth of confining pressure, the compressive resistance of shales gradually increases, the shear fractures govern the sample instability, and the anisotropy index continues to decrease. Furthermore, several strength criteria for layered rock masses were summarized, and the modified Jaeger strength criterion was proposed by introducing the anisotropic parameter Rcθ. It can effectively reflect the failure modes and strength features of layered shales under triaxial conditions with the higher accuracy. Besides, the variation of cohesion and internal friction angle of layered shale samples was comprehensively analysed under the triaxial conditions. Clearly, as the inclination angle of bedding planes rises, the cohesion of layered shales first decreases, but then increases under triaxial compression, showing the ‘U’-shaped changing trend. Additionally, the internal friction angle of layered shales grows up gradually with the inclination of bedding planes increasing.