Effect of failure criterion on slope stability analysis

Stability analyses in geotechnical engineering are generally based on a Mohr-Coulomb failure criterion. However, this model neglects the intermediate principal stress and leads in some circumstances to conservative results related to the factor of safety. This paper shows on the one hand the effect of the Matsuoka-Nakai failure criterion on the factor of safety of slopes and it compares on the other hand results of slope stability analysis obtained from different calculation methods, namely limit equilibrium analysis, finite element limit analysis and displacement finite element Strength Reduction Technique (SRFEA). The latter approach could suffer from numerical instabilities when using non-associated plasticity and finite element limit analysis has the disadvantage that it is limited to associated plasticity. Therefore, a modification of the so-called Davis approach is presented, where the reduced strength parameters are related to the actual degree of non-associativity. The presented studies show first, that this enhanced procedure yield FoS in close agreement with SRFEA using a non-associated flow rule and secondly, that the modified Davis approach is suitable to prevent numerical instabilities. However, important for practitioners, the obtained factors of safety with the improved Davis procedure are still slightly conservative.