Evaluation of Critical Slip Surface in Limit Equilibrium Analysis of Slope Stability by Smoothed Particle Hydrodynamics

Limit equilibrium methods (LEMs) have been widely used for slope stability analysis in engineering practice. The critical slip surface in LEM, which has the minimum factor of safety (FS), is often assumed as the most likely slip surface and subsequently used as the failure slip surface in the analysis and design of slope stabilization measures, such as soil nails and anchors, for unstable slopes. This assumption has not been validated systematically, probably due to the difficulty in simulating large displacement of soils during landslides. In this study, a new mesh-free, particle-based numerical method in geotechnical engineering called smoothed particle hydrodynamics (SPH) is adopted to simulate the entire process of landslides, including the large displacement of soils after a landslide initiates. A series of comparative studies on the stability analysis of cohesive slopes is performed using both LEM and SPH. The comparative studies show that the assumption is reasonable for stable slopes. However, for unstable slopes in which the location of failure slip surface is critically needed for the design of stabilization measures, the LEM critical slip surface differs substantially from the failure slip surface, and the volumes of sliding soil masses are greatly underestimated by the LEM critical slip surfaces. Using the LEM critical slip surface as the failure slip surface in the design leads to the unsafe design of stabilization measures. A new method was proposed to properly locate the failure slip surfaces for unstable slopes when using LEM. It is found that the failure slip surfaces for unstable slopes is not the slip surface with the minimum FS; instead, it is the one with FS = 1.