Limit Analysis versus Limit Equilibrium for Slope Stability

This paper compares conventional limit-equilibrium results with rigorous upper and lower bound solutions for the stability of simple earth slopes. The bounding solutions presented in this paper are obtained by using two newly developed numerical procedures that are based on finite-element formulations of the bound theorems of limit analysis and linear programming techniques. Although limit-equilibrium analysis is used widely in practice for estimating the stability of slopes, its use may sometimes lead to significant errors as both kinematic and static admissibility are violated in the method. Because there are no exact solutions available against which the results of limit-equilibrium analysis can be checked, the present bounding solutions can be used to benchmark the results of limit-equilibrium analysis. In addition, the lower bound solutions obtained also can be applied directly in practice because they are inherently conservative. purely cohesive and cohesive-frictional soils. These numerical procedures are based on finite-element formulations of the bound theorems of limit analysis and the best lower and upper bound solutions are obtained, respectively, by optimizing stat­ ically admissible stress fields and kinematically admissible ve­ locity fields using linear programming techniques. Over the years, many limit-equilibrium computer codes have been developed to locate the most critical failure surface by using various search strategies. In this study, the limit-equi­ librium results are obtained from the well-known slope stabil­ ity computer code STABL with the option of Bishop's sim­ plified method (Kim et al. 1997).