South Australia & NT Chapter

Probabalistic Techniques in Geotechnical Modelling – Which one should you use?

Dr William Kaggwa

Predictions of performance are at the core of geotechnical engineering design. Predictions based solely on deterministic analyses suffer from unquantifiable uncertainties and the implied absoluteness of the prediction. On the other hand, probabilistic estimates suffer from being vague, which is unsettling to most geotechnical engineers. Combining deterministic and probabilistic analyses offers synergies that are best utilized only if the geotechnical engineer appreciates the relative role of each type of analysis.

The presentation is an overview of the hierarchy of probability-based analyses in geotechnical engineering predictions. A framework that integrates analytical and probabilistic analyses is described. The available probabilistic analyses, their level of complexity, applicability, and limitations, are presented in such a way as to enable the engineer to choose correctly the optimum analysis that matches their specific project and circumstances. Examples are presented on the implications of choosing different probability- based methods.

This presentation is based on a paper William co-authored with one of his former doctoral students Yien Lik Kuo. Their paper won the 2011 Australian Geomechanics Award. This award is given to the best paper published in Australian Geomechanics in a calendar year.

Speaker biography

Dr. William Kaggwa currently lives in Uganda, having retired from the University of Adelaide, where he spent more than twenty years lecturing, studying, and researching varied topics of geotechnical engineering. The topics included earthquake engineering, slope stability, pile foundations, and the behaviour of soils. In the last ten years, he was involved in a major push to make probabilistic analyses more accessible to geotechnical engineers.

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.