Unsaturated slope stability analysis for cohesive soil with tensile strength cut-off

A comprehensive consideration of the shear and tensile strengths offers a deeper perspective on slope stability. However, such consideration is rare for unsaturated slopes with cohesive soils owing to the difficulties of tensile strength testing and its representation in the unsaturated criterion. This study provides a feasible way to incorporate tensile strength into the unsaturated strength criterion and apply it to stability analysis. Based on the effective stress principle, a cut-off criterion with a tensile reduction coefficient was developed for unsaturated soils. Compared to the linear extrapolation approach, the proposed approach effectively avoids the overestimation of the tensile strength. An unsaturated triaxial experiment was conducted to establish the relationship between the reduction coefficient and matric suction for a typical cohesive soil. For practicality, a fitting equation was proposed for the theoretical analysis. For three-dimensional unsaturated slope analysis, an analytical model was built using the upper bound limit analysis method; it captures the influence of the tensile cut-off impact on the sliding surface and the effects of infiltration or evaporation, allowing for an explicit expression of the safety factor. Parametric analysis indicated that the tensile cut-off effect reduced stability and became more pronounced as the suction phenomenon intensified.