Model uncertainty of SPT based methods for reliability analysis of soil liquefaction

The potential of liquefaction is evaluated by calculating the reliability index using the first order reliability method (FORM). The probability of liquefaction is then obtained from the reliability index. Two models (the recommended by the NCEER and the one proposed by Boulanger and Idriss) are used to define the limit state function for liquefaction triggering analysis. These models are based on deterministic methods considering SPT tests. The statistical characteristics of the model uncertainty of Boulanger and Idriss model are determined through an extensive reliability analysis using Bayesian mapping function calibrated with a set of quality case histories. Soil from Lebanon corresponding to a site located at the North of Beirut where SPT tests have been carried out is used for comparative analysis between the two models. The impact of the coefficient of variation of the input variables on the probability of liquefaction is examined.