Role of admissibility criteria in limit equilibrium slope stability methods based on finite element stresses

A number of limit equilibrium slope stability methods have been developed where the factor of safety is calculated based on stresses computed using an independent finite element analysis. The internal stress distribution is usually generated using the ‘switch on’ gravity technique assuming linear elastic soil behavior. Young’s modulus and Poisson’s ratio are often assigned at random with little knowledge of how the values could impact the slope stability calculations. The results from a number of slope stability studies are provided to summarize the differing opinions regarding the sensitivity of the factor of safety to the selection of Poisson’s ratio and Young’s modulus. It would appear that the different views amongst researchers can be related to the method used to search for the critical slip surface. The factor of safety is reported to vary by less than 5% in studies where the grid and radius searching procedure is used and by more than 20% in studies where the dynamic programming searching procedure is used. The different levels of sensitivity can be related to the soil behavior model adopted in the stress – deformation analysis and the interaction of the searching procedure with the internal stress distribution in the slope.