Explicit analysis of the anisotropic characteristics and prediction of the failure behavior of complicated jointed rock masses under triaxial stress

The mechanical performance of a rock mass is crucial for rock engineering, where the anisotropic characteristics of geotechnical defects, such as joints, cause the strength or deformation to vary greatly in response to different loading directions. However, there has been limited research on the anisotropy characteristics of rock masses with multiple joint sets in three-dimensional space. To address this gap, comprehensive investigations encompassing field investigation, laboratory experiments, and synthetic rock mass methods were conducted to explore the anisotropic characteristics of granite at the Shuangjiangkou Hydropower Station, China. An anisotropic loading scheme based on fracture network rotation was employed, involving 72 numerical tests to explicitly delineate the anisotropic rock behavior. Compared to the unconfined state, applying confining pressure mitigates the anisotropy effect in a rock mass and enhances its mechanical performance. Failure modes observed in experiments include slip failure along joints and breakage of internal rock blocks, with the type of failure highly dependent on the loading direction. The evolution process leading to each failure type was also investigated at the micro-scale. Additionally, the fracture density (P₂₁) was utilized to quantify joint characteristics in the loading direction, facilitating the development of a predictive model for rock failure behavior under the combined influence of joints and confining pressure. This model enables the estimation of rock mass strength and post-peak strain based on confining pressure and fracture density.