Strength reduction technique with finite element method for slopes without stabilisation measures

Limit equilibrium analyses (eg by Janbu 1954, Bishop 1955, Morgenstern & Price 1965 and Spencer 1967) are currently the preferred method in practical geotechnical engineering to calculate factors of safety, particularly in slope stability analysis. However, alternative methods such as the strength reduction technique in combination with the displacement based finite element method (eg Brinkgreve & Bakker 1991, Griffiths & Lane 1999, Dawson et al, 1999) have been proposed as an alternative approach with significant advantages over limit equilibrium methods, albeit with somewhat increased computational costs. It has been shown that limit equilibrium and finite element methods can produce similar factors of safety for slope stability analysis (eg Cheng et al, 2007). However, as is shown in this paper, significant differences may occur under certain circumstances. Consequently, the question has to be answered as to which of the methods leads to more realistic results. An attempt to demonstrate that strength reduction methods produce reliable results has been made by Tschuchnigg et al. (2015a, 2015b) by comparison with finite element limit analysis (Fela), which provides rigorous upper and lower bounds on the factor of safety (eg Sloan 1988, Sloan 1989, Sloan & Kleeman 1995, Lyamin & Sloan 2002a, Lyamin & Sloan 2002b, Krabbenhoft et al, 2005).