Rock slope stability analysis according to Eurocode 7, discussion of some dilemmas with particular focus on limit equilibrium analysis

In Europe, rock slope stability analysis and slope design have to be based on Eurocode 7, which is today the basic standard for geotechnical, including rock engineering, design. According to Eurocode 7, several principles for stability analysis may be applied, including empirical, limit equilibrium, numerical, and probabilistic. Very often, particularly for excavated slopes, the limit equilibrium method is used for stability analysis and design. One particularly significant consequence of the introduction of Eurocode 7 is that for limit equilibrium analysis according to the Eurocode, the traditional principle of calculating a factor of safety cannot be used. Instead, the so-called partial factor principle is to be used. The intention of the Eurocodes seems to be that Reliability Based Design should be applied also in rock engineering. This is, however, not reflected by the guidelines and descriptions of the present (2004)-edition of Eurocode 7, and for this and several other reasons there is considerable confusion and uncertainty related to the use of Eurocode 7 for rock engineering analysis and design. This paper discusses this issue with particular focus on limit equilibrium analysis of rock slope stability. It is concluded that due to the uncertain and variable character of input parameters, the limit equilibrium approach has evident shortcomings for stability analysis of rock slopes, particularly when the partial factor principle is applied.