Reliability-based geotechnical design

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The ground on which we found our structures is one of the most variable and uncertain of all engineering materials and is therefore highly amenable to a probabilistic treatment. Since geotechnical engineers must often make do with the existing ground at a site, a key question in any geotechnical design then becomes "How should we design our geotechnical system so as to achieve an acceptable safety level?" The question involves a number of other important issues such as: How can we reduce our uncertainty about the ground's engineering properties? How confident are we in our prediction and design models? How should we adjust our designs to account for differing failure consequences? And, most importantly, how should design codes be implemented in order to address all of these issues and still arrive at societally acceptable levels of safety? This research proposal looks specifically at the development of a reliability-based geotechnical design code. Existing geotechnical design codes are almost entirely empirical -- based on calibration with past experience, particularly with traditional working stress design methodologies. The proposed research will concentrate on determining design resistance and consequence factors necessary to achieve acceptable safety in geotechnical systems for various degrees of site understanding and failure consequence. The results will feed directly into the next edition of the Canadian Highway Bridge Design Code. There are several significant advantages to providing codified resistance factors that vary with site understanding along with consequence factors that vary with failure severity. For one, they provide geotechnical engineers with evidence that better site understanding leads to economies in design. For another, they allow limited infrastructure budgets to be properly allocated. Finally, they give guidance to all geotechnical engineers on how both site understanding and failure consequence should affect the final design. The development of a reliability-based geotechnical design code will represent a substantial step forward and will lead to significant savings in foundation costs in the years to come.