Uncertainty, Reliability, and Foundation Engineering: The 5th Peter Lumb Lecture

Peter Lumb was among the first civil engineers to focus on the role of uncertainty in geotechnical engineering practice and design. His seminal work on this topic illustrated clearly that proper geotechnical design should be based on probabilistic, not deterministic, principles. More than four decades later, our profession is still trying to address this reality. This lecture and paper focus on some of these issues, with particular emphasis on reliability-based design (RBD) of foundations and the calibrations behind RBD that are critical but are largely ‘invisible’. Some key methods of calibration are discussed, including issues ranging from the basic assumptions involved, distributions of key variables, uncertainties in both load and resistance, target reliability, etc. The goal is to assist engineers in understanding the level of sophistication, or lack thereof, in different approaches to calibrations, which then translates into the degree of confidence one can have in a particular calibration or code. Lumb’s contributions to these developments are noted in a special section.