Modified Hoek–Brown failure criterion for anisotropic rocks

The direction-dependent strength behavior of anisotropic rocks is a common characteristic. It is essential to develop the model that can describe the nonlinearity as well as the anisotropy in the triaxial strength behavior of the rocks. In the present study, a modified Hoek–Brown failure criterion was developed to describe the triaxial strength behavior of the rocks by the using of anisotropic index (\(\alpha_{\beta }\)). The procedures for determining the failure criterion parameters are introduced. In the model, the estimation of the uniaxial compressive strength at a given angle β was required, so an empirical equation for predicting the variation of the uniaxial compressive strength of anisotropic rocks is presented. The performance of the proposed equation was tested by using a triaxial test database compiled by Singh (Rock Mech Rock Eng 48(4):1387–1405, 2015). The variation of the uniaxial compressive strength was then incorporated into the modified Hoek–Brown failure criterion. Based on the analysis of the extensive triaxial test database, it was possible to accurately predict the strength of anisotropic rocks using limited test data. It is concluded that the modified Hoek–Brown failure criterion has good ability in predicting the strength of anisotropic rocks.