Study on the Mechanical Mechanism and Criterion of Anisotropic Strength in Intact Layered Rocks

Abstract The failure strength of intact layered rocks exhibits distinct anisotropy. In this paper, intact layered rocks are equivalent to a continuous medium. Based on the mechanical mechanism of failure strength anisotropy under this assumption, it is hypothesized that the failure strength of geomaterials is governed by the inherent strength of the orientation of the failure plane. Consequently, this orientation is related to the anisotropy strength of geomaterials and the stress state. The anisotropy inherent strength can be quantified using an anisotropic variable derived from the stress and microstructure tensors. Given the two-dimensional mechanical properties of intact layered rocks, the orientation of the failure plane can be analyzed by the two-dimensional form of the triple shear energy (TSE) criterion, specifically the Mohr–Coulomb criterion. Based on the aforementioned, an anisotropic strength (ATSE) criterion founded on the TSE criterion is proposed to account for both inherent strength variations and failure plane orientation. Compared with the TSE criterion, the ATSE criterion introduces only two additional strength parameters, which can be easily obtained through triaxial compression tests. The new criterion is validated by comparing it with conventional triaxial and true triaxial test results for various intact layered rocks documented in the literature. The validation results demonstrate good agreement with the available test data. Furthermore, a novel inferential approach is established based on the flipping symmetry of measured failure strength to extrapolate strength data from 0°–90° to 0°–360°.