Effect of boundary constraint condition on the stability analysis of 3D slope

Boundary constraint condition is one of the most important influencing factors in 3D stability analysis based on shear strength reduction finite element method(SSR-FEM). A typical three-dimension slope case is adopted to study safty factor and potential sliding surface under various boundary constraint conditions, and their difference is discussed. Then, the results of a 3D slope case with soft interlayer and groundwater are illustrated using SSR-FEM. The results indicates that the boundary constraint conditions have a remarkable effect on the slope stability, the fixed constraint in three directions effect is the largest one, free constraint effect is the smallest one. Moreover, the boundary constraint conditions have also a certain effect on the potential sliding surface of three-dimensional slope. The effect is related to the ratio of length and height for the slope. When the ratio of length and height for the slope is larger than 8 (L/H > 8), the location of slip surface and out-slip points in 3D slope is very similar to that from 2D plane strain analysis. So the ratio of L/H=8 can be taken as the limit point for 2D and 3D stability analysis in SSR-FEM.