Practical Use of Modified Hoek–Brown Criterion for Soil Slope Stability Analysis

Many slopes are comprised of soils that exhibit a nonlinear shear strength or failure envelope, and multiple mathematical relationships have been developed to account for this nonlinearity. At the same time, the numerical shear strength reduction (SSR) method has become a common method for analyzing the stability of slopes. Despite these developments, a practical, commercially available method to include nonlinear shear strength in numerical analysis has not been established for soil. The Generalized Hoek–Brown (GHB) model provides a nonlinear failure criterion, but is formulated for use with rock. This paper proposes a Modified Hoek–Brown (MHB) criterion to make the model applicable to soil and leverage the GHB criterion present in many numerical analysis packages. Past applications of SSR to the GHB are discussed and a numerical method for reduction of the parameters in the context of soil slopes is proposed. A simple wedge analysis validates the MHB method for a linear envelope. Three examples of increasing complexity compare results of limit equilibrium with both finite element and finite difference SSR analyses. In general, the different numerical methods yield very similar results. The SSR method using MHB predicts critical strength reduction factors 2–5% lower than the limit equilibrium factors of safety. The approach presented in this paper allows practitioners to model nonlinear shear strength in finite element strength reduction analysis for cases where this nonlinearity is judged to be an important factor.