Embankment basal stability analysis using shear strength reduction finite element method

The stability evaluation of the slope commonly uses limit equilibrium methods, for example, Fellenius’ method in Japan. The limit equilibrium methods have two limitations. (1) It is necessary to divide the sliding mass into slices, and to set up some additional equations to make the problem statically determinate. (2) It is necessary to search sliding surface with a minimum safety factor. Shear strength reduction finite element method (SSR-FEM) can solve the limitations of the limit equilibrium methods. This paper inspects superiority of the slope stability analysis by SSR-FEM. And, as a model case, the failure of base ground of the embankment is considered. Comparing the calculated results of SSR-FEM with limit equilibrium method, we point out the problems inherent in limit equilibrium method for the model case when the slip surface is assumed to be circle. We propose an approach to use SSR-FEM for slope stability analysis in practical design. ) ' tan ( tan ' , ' ' 1 F F c c F F φ φ − = = (4) In SSRFEM, firstly, the initial stresses in slope are computed using the elastic finite element analysis. The vector of externally nodal forces consists of three parts: (1) surface force; (2) body force(total unit weight of soils); and (3) pore water pressure. Secondly, stresses and strains are calculated by the elasto-plastic finite element analysis, where the reduced shear strength criterion. The shear strength reduction factor F is initially selected to be so small, for example 0.01, that the shear strength is large enough to keep the slope in elastic stage. Stresses at some Gaussian points reach the yielding condition with the shear strength reduction factor F in Equation 3 increased gradually. When the stress at anyone Gaussian point reaches the yielding condition, the increment of the shear strength reduction factor will make stresses at more Gaussian points reach the yielding condition because of the residual force induced by the decrease in the shear strength soils.