A framework for quantifying the reliability of geotechnical investigations

Abstract

It has long been recognized that, in civil engineering and building projects, the largest element of financial and technical risk often lies in the ground. Indeed, structural foundation failure, construction overruns and delays can often be attributed to inadequate and/or inappropriate site investigations. Unfortunately, geotechnical engineers have at their disposal limited guidance when deciding upon a scope of a site investigation. Almost exclusively, the scope of such investigations is not governed by what is needed to characterize appropriately the subsurface conditions but, rather, how much the client is willing to spend on a geotechnical investigation. What is urgently needed is a series of guidelines that link the scope of a site investigation with the probability that the foundation will be under-designed – resulting in some form of failure, or be overdesigned – resulting in more funds being spent on the foundation than would have otherwise been necessary had a more appropriate site investigation been carried out. This paper proposes a framework for developing such a series of guidelines, which is based on Monte Carlo simulation. The guidelines, when developed, will enable geotechnical engineers to quantify the effectiveness of one site investigation program with another, with respect to the probability of failure and over-design. As a result, the geotechnical engineer will be able to discuss, with the client, the ramifications and cost-effectiveness of several geotechnical investigation scenarios.