Probabilistic assessments of soil liquefaction hazard

The seismic loading and design provisions of the 2005 edition of the National Building Code of Canada have undergone various amendments for implementation in structural and geotechnical designs. As the changes and requirements introduced have been the direct outcome of the recent advances in structural engineering and seismology, structural designers have accepted the new changes with minimal implications to their designs. However, serious implications to geotechnical designs (liquefaction in particular) have made the new changes impractical and in many cases cause confusion. The ground motion in the seismic provisions of building codes is often used inconsistently with the Seed-Idriss approach for liquefaction design. The inconsistency arises from combining the probabilistic ground motion and the deterministic curves compiled by Seed and Idriss in their approach. This inconsistency is particularly acute in the NBCC 2005. A simple and practical method, which harmonizes the Seed-Idriss approach with the NBCC 2005 requirements, is proposed. The proposed method stems from resolving the inconsistency noted above in using the Seed-Idriss approach for estimating future liquefaction failures.;A probabilistic approach for evaluating soil liquefaction failure is also developed. The probability of liquefaction in this approach considers both the statistical distributions of soil and seismic parameters as well as the spatial and temporal distributions of seismic parameters. The probability of liquefaction considering the statistical distributions of soil and seismic parameters was evaluated via a reliability-based model that incorporates a seismic energy approach for evaluating soil liquefaction. The probability of the seismic parameter occurrences was estimated based on the spatial distribution of source-to-site distance and the temporal distribution of earthquake occurrences. Evaluating the performances of past liquefaction case histories using this approach may provide some baselines for choosing adequate hazard levels for future liquefaction designs.;A logistic regression model has been developed in a systematic approach utilizing soil and seismic parameters for evaluating liquefaction probability. Incorporation and representation of seismic and soil parameters in the model have been justified based on diagnostic techniques that are commonly used in logistic models. Other diagnostic techniques were also used to check the adequacy and the validity of the developed logistic model.