Slope stability analysis by means of finite element limit analysis and finite element strength reduction techniques. Part I: Numerical studies considering non-associated plasticity

Slope stability analyses in practical geotechnical engineering are predominantly performed using limit equilibrium methods, despite the inherent shortcoming that the form of the failure mechanism has to be defined a priori. This assumption is not needed when more advanced methods, such as limit analyses or displacement-based finite element methods, are employed for calculating factors of safety and thus the advantages of these methods are increasingly recognized. However, the latter may suffer from numerical instabilities when using non-associated plasticity whereas the former are restricted to associated flow rules. This paper shows that these issues may be overcome by a modification of the so-called Davis approach which provides accurate estimates of the factor of safety of slopes, even for extreme cases of steep slopes with friction angles in excess of 40° and zero dilatancy.