A Modified Anisotropic Hoek and Brown Failure Criterion for Transversely Isotropic Rocks

Transversely Isotropic (TI) rocks exhibit anisotropic strength characteristics due to uniform structural features such as foliation, lamination, schistosity, cleavage planes, layering, bedding planes, and stratified layers. In the field of rock engineering, particularly in mining, civil engineering, geology, and petroleum, it is crucial to have a reliable and comprehensive anisotropic failure criterion for TI rocks to support the design process of engineering structures. Therefore, this study aims to develop an anisotropic failure model for TI rocks that integrates new parameters into the intact Hoek and Brown failure criterion. This focus on deriving simplified parameters aims to create a generalized model with improved accuracy in predicting anisotropic strength. The proposed model includes anisotropy factors, such as the unconfined anisotropic strength \(({\sigma }_{c\beta })\) $({\sigma }_{c\beta })$ , anisotropic effect \(({A}_{e})\) $(A_e)$ , and type of anisotropic curve \(({A}_{m})\) $(A_m)$ . Experimental data of layered sandstone tested under various orientations and confining pressures were utilized to validate the model. Additionally, the proposed failure model underwent evaluation using an artificial neural network and published data on layered rocks. The resulting metrics, including R² and Root Mean Square Error, were found to be within acceptable standards. This indicates that the proposed criterion can accurately predict failure strength for different rock types.