Engineers Australia

Connecting Geotechnical Investigations with Project Risk

R. B. Kelly, M. Drechsler and R. Goldsmith


It is often stated by geotechnical engineers that a project pays for a site investigation one way or another as a means of justifying a scope of work aimed at managing a project’s risk. This proposition is critically assessed through reviewing three case histories covering site investigations performed for design only, design and construct, public private partnership (PPP) and alliance contract models. An extensive site investigation was performed for the Ballina Bypass Alliance project. Most of the project risks were identified and managed. However, some risks were realised relating to detecting palaeochannels, variable subsurface topography, quantifying material parameters and coping with corestones. An extensive site investigation has been performed for the Snowy 2.0 project, but its scope has been limited by time and access constraints. Risk is managed through adoption of a geotechnical baseline report. Site investigations for Inland Rail for design only, design and construct and PPP contract models have been scoped and partially delivered. In addition, Inland Rail has developed an earthworks materials specification that can be varied to suit site characteristics. Integration of site investigations with the specification and design is shown to be key to controlling the major materials risk. Some thoughts about scoping an investigation to inform geotechnical risk when procuring a PPP are presented. Overall it is concluded that the geotechnical industry generally scopes investigations to adequately manage risk. Quality is shown to be as or more important than quantity. The critical importance of engineering geology for identification of potential risks is demonstrated thus allowing a focussed drilling and geophysics scope to be delivered. Challenges remain when communicating residual risk to stakeholders.