South Australia & NT Chapter

Reliability-Based Geotechnical Design

Prof. Gordon Fenton

In an effort to harmonize with structural codes, geotechnical design codes around the world are beginning to migrate towards some form of reliability-based design (RBD). Significant steps in this direction can be found in, for example, Eurocode 7 (1997), Australian Standard AS 4678 (2002), NCHRP Report 24-17 (2002) and the Canadian Foundation Engineering Manual (2004). These RBD provisions are most often presented in the form of a Limit States Design (LSD), to define critical failure states, combined with load and resistance factors calibrated to achieve the target reliabilities associated with the various limit states. The use of load and resistance factors is generally referred to as Load and Resistance Factor Design (LRFD).

Despite these advances, RBD provisions in geotechnical codes are primarily based on calibration with older codes, and for good reasons; one of which is that calibration is a useful way to incorporate years of practical experience into a code. Another is that soils and their mechanical behaviours are much more difficult to characterize probabilistically than are the other quality-controlled materials commonly used by engineers (eg. concrete, steel, timber). This talk traced the development of reliability-based design in geotechnical engineering, and how it has been implemented in a variety of design codes around the world. Then, some of the significant stumbling blocks to going beyond calibration from older codes and introducing some of the real advantages of a reliability-basis for design were pointed out. Finally, some of the possible ways in which reliability-based geotechnical design can be improved, and the headway being made towards these improvements, were explored in the context of common geotechnical design problems, such as slope stability, bearing capacity, and settlement.

Dr. Fenton completed his Ph.D. in the Dept of Civil Engineering at Princeton University, USA, in 1990. He joined the Dept of Engineering Mathematics at Dalhousie University in 1990, where he is now a full Professor. His primary research thrust has been in the area of random field modeling of soils and the characterization of the random behaviour of soils in engineering problems. In 1997, Dr. Fenton was a Research Fellow at the Norwegian Geotechnical Institute (Oslo) and in 1998 he was a Visiting Associate Professor in the Dept of Civil and Operations Research, Princeton University. This year he is a Visiting Professor at the University of Adelaide. Dr. Fenton was chair of the ASCE Geo-Institutes Risk Assessment and Management Committee from 1999 to 2003 and past acting chair and core member of the ISSMGE Engineering Practice of Risk Assessment and Management Committee. He is is also currently the member charged with probabilistic design provisions on the Canadian Highway Bridge Design Code CSA A271-6 (Foundations) Committee. Dr. Fenton was awarded the Professor Appreciation Award from the Dalhousie Undergraduate Engineering Society in 2004, the George Stephenson Medal from the Institution of Civil Engineers, UK, in 1994, and the Gzowski Medal from the Engineering Institute of Canada in 1986.

Engineers Australia members participating in AGS technical sessions can record attendance on their personal CPD logs. Members should refer to Engineers Australia CPD policy for details on CPD types, requirements and auditing guidelines.