Abstract: While the elastoplastic finite element method based on the shear strength reduction (SSR) technique is employed to analyze slope stability, the overall factor of safety computed numerically is, in a certain degree, dependent on the criteria used for evaluating critical instability condition of slope. As usual, the convergence of the numerical computation of elastoplastic FEM is commonly employed in conventional studies. In fact, the convergence of the nonlinear analysis of elastoplastic FEM is controlled by a number of factors. Therefore the rationality and uniqueness of the numerical solution of the safety factor are in doubt. In order to examine the reasonability and applicability of various criteria including the convergence of numerical computations, the abruptness of the displacement or deformation at a certain characteristic location and connectivity of plastic zone, an example slope is analyzed by using the elastoplastic FEM based on the SSR technique. The computed results are compared with the solution of the Spencer’s procedure of limit equilibrium. It is shown that the safety factors computed by using the criteria respectively based on the abruptness of the displacement or deformation at a certain characteristic location and connectivity of plastic zone are almost identical to the solution of limit equilibrium method, while the elastoplastic FEM analysis based on the convergence of numerical computations may give an incredible estimation of the safety factor in some circumstances. Considering the feasibility and simplification in engineering practices, both criteria based on the abruptness of the displacement or deformation at a certain characteristic location and connectivity of plastic zone are suggested to be jointly used in the elastoplastic FEM analysis of slope stability.

Key words: shear strength reduction (SSR) technique, analysis of slope stability, instability criterion, safety factor