Reliability-Based Deep Foundation Design

Modern geotechnical design codes are migrating towards Load and Resistance Factor Design (LRFD) methodologies. The Danish geotechnical code has been based on LRFD for several decades, but more recently the Eurocode and the Australian Standards have turned in this direction. Where the geotechnical system supports a structure, the load factors are generally determined by the structural codes. The geotechnical resistance factors, typically determined by calibration with traditional working stress (or allowable stress) design, have yet to be clearly defined in geotechnical design codes. Research into the reliability of geotechnical systems is needed in order for resistance factors to be determined. This paper presents the results of a preliminary study into the effect of a soil's spatial variability on the settlement and ultimate load statistics of a pile. The results are used to provide recommendations on approaches to reliability-based deep foundation design at the serviceability and ultimate limit states.