Stability of slopes on clays of variable strength by limit equilibrium and finite element analysis methods

Abstract

This paper presents an evaluation and comparative study on the stability analysis of simple slope models founded on undrained clay soils. The analysis was performed according to the limit equilibrium (LE) and finite element (FE) methods utilizing "Slide 2D" and "Plaxis 2D" computer programs respectively. Forty five slope models with different geometries based on soft, medium stiffand very stiffclay soil foundations were considered for stability analysis. The comparison made between four LE methods indicated that the Bishop and Spencer methods produced practically similar FOS results whereas the Fellenius and Janbu methods gave FOS values lower than the Spencer method by 3.0% and 7.4% respectively. For slopes founded on soft clays, the difference in FOS computed by the LE and FE methods is negligible but the FOS values computed by the LE methods were 8.5% higher than the FE method for slopes on medium and very stiffclays. Based on the results of linear regression analysis of all data, the Fellenius, Bishop, and Spencer methods gave FOS values higher than the FE method by 1.4, 5.3 and 5.7% respectively whereas the Janbu method gave FOS lower than the FE method by 4.3%. Evaluation of the effects of slope geometry and foundation soil properties on slope stability revealed a reliable relationship between FOS and a variable combining four slope and soil parameters.