Reliability-Based Geotechnical Design

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The most recent edition of the Canadian Highway Bridge Design Code (CHBDC 2014) includes substantial changes in geotechnical design philosophy. The code now includes resistance factors that depend on the level of site understanding, as well as a new consequence factor that depends on failure consequence severity. Drawing from research performed over many years, the applicant calibrated the resistance and consequence factors appearing in the 2014 CHBDC to achieve target reliability levels. However, much research is still required to refine these factors and to extend them to cover other limit states. To this end, this research proposal will address the following two main tasks: 1) One of the major identified goals for the next edition of the CHBDC is to develop geotechnical seismic design code provisions to include in the geotechnical design chapter. To accomplish this goal, design load and resistance factors need to be determined that properly target the desired reliability index for extreme event seismic limit states in geotechnical systems. The research will start by looking at slope stability under seismic loading, where the slope is represented by a spatially variable random field. Failure probabilities as functions of ground parameter statistics and slope geometry will be estimated, conditioned on various levels of ground motion excitation. The results will then be combined using the total probability theorem to assess the reliability of various slope designs, given sample estimates of ground strength statistics. Design procedures and factors will be proposed for use in the CHBDC and the National Building Code of Canada (NBCC). The research will then be extended to a variety of other geotechnical problems, such as shallow foundations, deep foundations, and retaining structures. 2) When a structure is supported by multiple foundations, failure of the structure often requires the failure of more than a single foundation element - if so, the foundation system is said to have some redundancy. An important question that arises when foundation redundancy exists is what should the target reliability of individual foundation elements be in order to achieve a desired target system reliability? The goal of this research task is to investigate the relationship between geotechnical redundancy and system reliability so that informed design decisions can be made about individual foundation elements. Both of the above research tasks are excellent opportunities for the training of highly qualified personnel, especially since these personnel will directly see the need, application, and implementation of their research results in major Canadian design codes of practice.