Comparative Evaluation of Presented Strength Criteria of Anisotropic Rocks Based on Triaxial Experiments

The inherent mineralogical alignment in stratified rock formations engenders pronounced mechanical anisotropy, presenting persistent challenges across geological, geotechnical, and petroleum engineering disciplines. While substantial progress has been made in modeling transversely isotropic media, current methodologies exhibit limitations in reconciling theoretical predictions with complex failure mechanisms. This investigation examines the anisotropic response of diverse lithologies through triaxial testing across bedding orientations (0–90°) and confinement levels (0–60 MPa), revealing a pressure-dependent attenuation of directional strength variations. Experimental evidence identifies three dominant failure modes: cross-bedding shear fracturing, bedding-parallel sliding, and hybrid mechanisms combining both, with transition thresholds governed by confinement intensity and bedding angle. Analytical comparisons demonstrate that conventional single weakness plane models produce characteristic shoulder-shaped strength curves with overpredictions, particularly in hybrid failure regimes. Conversely, the modified patchy weakness plane formulation achieves superior predictive accuracy through parametric representation of anisotropy gradation, effectively capturing strength transitions between end-member failure modes. The Pariseau criterion, though marginally less precise in absolute terms, provides critical insights into directional strength contrasts through its explicit differentiation of vertical versus parallel bedding responses. These findings advance the fundamental understanding of anisotropic rock behavior while establishing practical frameworks for optimizing stability assessments in bedded formations, particularly in high-confinement environments characteristic of deep reservoirs and engineered underground structures.