In this paper we compare the partial factors approach of Eurocode 7 with a traditional deterministic limit equilibrium analysis approach and probabilistic approach. The example case is a simplistic model profile of an open pit mine cut slope configuration. The controlling parameters in a structurally dictated failure mechanism were introduced as random variables in the model, to account for the different types of uncertainties arising in rock engineering data. The limit equilibrium method was used in this study to conduct rock slope stability analysis, while the impact of naturally uncertain and variable parameters, among others water pressure and earthquake activities were considered. Different scenarios from the best to the worst-case were analysed and later compared. The sensitivity analysis revealed the importance of the joint failure plane, joint roughness coefficient and joint friction angle and how the actions (groundwater pressure and earthquake action) affect the slope’s stability. These results emphasize some advantages of the approach, and the potential further embracement from the rock engineering fraternity.
In the case of a rock structure in which many ill-defined parameters interact in a complex manner, the calculation of safety is a much less satisfactory process [1]. One possible approach which has been discussed by several authors is the probabilistic analysis of variables leading to a concept of safety in terms of a given probability of failure. Eurocode 7 (EC7), the reference code for geotechnical design of public-funded civil engineering works was implemented within the European Union in 2010. EC7 is a code for the design of foundations on soil yet is considered as being weak with regards to rock engineering design, and in practice incompatible with contemporary rock engineering design. Contemporary rock engineering practice is generally deterministic as stated in [2]. Non 1:1 mapping, of properties that are defined as ordinal data and thus, unsuitable for use in a probabilistic framework are typical. Consequently, contemporary rock engineering design is fundamentally incompatible with Limit State Design (LSD) and hence EC7, suggesting for a new start in Rock Engineering. For, many reasons, rock engineering (and, more widely, geotechnical) design formulae often cannot be written in the form R > E > 0, (R structural resistance, and applied loads (effect of actions E). The uncertainty and variability in both R and E are often both poorly understood and possibly not accurately characterized. The rates of rock engineering failure that society will tolerate is not known, possibly because those failures that do occur are either of no direct consequence to society. For the above-mentioned reasons, partial factor approach seems not to be well suited to rock engineering.
