ABSTRACT:
An essential step in a site characterisation program is the development of a geological model that captures the geological complexity of the site. This geological site descriptive model is then used as the basis for developing the ground engineering model which forms the basis for design. Advances in technology have led to new methods for conducting site investigation and for building the geological site descriptive model. Examples are provided that highlight the development of a geological site descriptive model and the impact of the geological complexity on the ground engineering model.
1 INTRODUCTION
Geotechnical engineering is fundamentally about managing risk. Morgenstern (1995) summarized risk assessment concepts using the framework for risk management adopted by the Canadian Standards Association. Figure 1 is a generalised framework for risk management that would need to be modified for individual projects. But in all cases risk assessment requires identification of the hazard and quantifying the risk associated with each hazard. Morgenstern noted that while quantitative risk analysis (QRA) is one aspect of the framework, qualitative risk assessment is also a valuable component of risk management. With risk defined as the combination of the probability of occurrence of an undesired event and the possible extent of the event''s consequence, risk can, in principle, be calculated. The full potential of QRA is best met with the establishment of acceptable risk criteria. Establishing acceptable risk criteria in geotechnical engineering is a challenge that is evolving. Relating consequences to cost/benefit analysis provides a simpler basis for evaluating acceptable risk. The link between risk and benefit must be balanced and within the context of geotechnical engineering the risks are usually reduced to an acceptable standard by the best practical means. Site characterisation is one means of reducing risk to acceptable levels, yet routine site investigations invariable lead to wrong conclusions.
