Investigation of dilatancy angle effects on slope stability using the 3D finite element method strength reduction technique

The use of the two-dimensional (2D) finite element method (FEM) has become a trend in slope stability analysis and has been widely adopted by engineers. When using the nonassociated flow rule (ϕ′ ≠ ψ′), the convergence problems can be corrected using the Davis method, especially for slopes with high friction angle ϕ′ and low dilatancy angle ψ′ values. With the progress in computer hardware, evaluating slope stability using three-dimensional (3D) FEM numerical analysis has become more prevalent. However, the effects of ψ′ have been seldom discussed. In this study, a 3D slope model was constructed by extending the 2D model longitudinally to study the effects of the dilatancy angle using the PLAXIS 3D FEM with built-in strength reduction technique. The results showed that the effects of the dilatancy angle on the convergence of 3D and 2D slope models are different. In 3D slope models, the failure mechanisms were unclear when ϕ′ = ψ′ (associated flow rule). In addition, when the slope had higher soil strength parameters (c′ or φ′), the dilatancy angle can affect the result and convergence. Overall, the dilation angles have a considerable effect on the slope stability and are nonnegligible. Therefore, engineers should consider the effect of dilation angles on stability.