Static and dynamic triaxial failure mechanisms of anisotropic shale: experimental characterization and constitutive modeling

In deep geological engineering, anisotropic shale is widely distributed and frequently subjected to both three-dimensional in situ stress and dynamic loading. Understanding its failure mechanisms under these conditions requires both experimental investigation and theoretical modeling. In this study, combined triaxial quasi-static compression and dynamic impact tests were conducted to examine the mechanical response of shale under varying confining pressures, strain rates, and loading directions. The experimental results provide key insights into the effects of these factors on shale strength and failure modes, which serve as the basis for model development. Building upon these findings, an anisotropic strength criterion and a damage constitutive model are proposed to account for the coupled effects of confining pressure, strain rate, and material anisotropy. The model parameters have clear physical interpretations, reflecting the contributions of different stress components in the material coordinate system to yielding. Validation against experimental data demonstrates that the proposed model can reliably capture the stiffness, strength, and failure behavior of shale under a wide range of loading conditions. This study advances the understanding of anisotropic shale failure mechanisms and offers a theoretical framework applicable to deep geological engineering.