Abstract
ISO2394:2015 contains a new informative Annex D on “Reliability of Geotechnical Structures”. The emphasis in Annex D is to identify and characterize critical elements of the geotechnical reliability-based design (RBD) process, while respecting the diversity of geotechnical engineering practice. The most important element is the characterization of geotechnical variability and the next in line is arguably the characterization of model uncertainty. The key features of the first element are: (1) coefficient of variation (COV) of a geotechnical design parameter does not take a unique value, (2) multivariate nature of geotechnical data can be exploited to reduce the COV, and (3) spatial variability affects the limit state beyond reduction in COV due to spatial averaging. The second element is commonly carried out by taking the ratio of the measured result to the calculated result (called a model factor). This approach is entirely empirical, but it is practical. Because of its empirical basis, it is not surprising that there are limitations to this approach. The notable ones are lack of applicability to the serviceability limit state and correlation between the model factor and the input parameters in the prediction model.
