Engineering judgment in the evolution from deterministic to reliability-based foundation design

Abstract

Engineering judgment has always played a dominant role in geotechnical design and construction. Until earlier this century, most of this judgment was based on experience and precedents. The role of judgment in geotechnical practice has undergone significant changes over the past 50 years as a result of theoretical, experimental, and field developments in soil mechanics and, more recently, in reliability theory. A clarification of this latter change specifically is needed to avoid misunderstanding and misuse of the new reliability-based design (RED) codes. This paper first provides a historical perspective of the traditional factor of safety design approach. The fundamental importance of limit state design to RED then is emphasized. Finally, an overview of RED is presented, and the proper application of this new design approach is discussed, with an example given of the ultimate limit state design of drilled shafts under undrained uplift loading. Judgment issues from traditional approaches through RBD are interwoven where appropriate.