Value of Geotechnical Site Investigation in Reliability-Based Design

This study aims to address how efforts spent in geotechnical site investigation can link to the final design dimensions of a geotechnical structure. An example of pad foundation design supported by boulder clay (developed by European Technical Committee 10) is used as a demonstration. Three aspects of geotechnical information are addressed: variety of in-situ and laboratory tests, precision of the tests, and local experiences in soil properties that permit reduction of transformation uncertainties between test indices and design parameters. Three design methods (allowable stress design ASD, partial-factor design PFD, and reliability-based design RBD) are considered. Among these methods, RBD is found to be most responsive to the availability of geotechnical information, whether in the form of site investigation efforts and/or local experiences. It is accurate to say that RBD can fill a critical gap in current geotechnical design practice, namely to monetize the value of geotechnical information in the form of increase/reduction of construction costs associated with changes in the design dimensions.