The effect of limited site investigations on the design of pile foundations

Abstract

When designing pile foundations, it is normal practice to perform a site investigation in order to quantify the physical and engineering properties of the ground. Often, the scope of the site investigation is dictated by construction time lines and budgetary constraints, rather than on the variability of the ground. It has been shown by a number of authors that as little as 0.04% – 0.3% of the total construction budget is spent on geotechnical investigations. Limited site investigations have the potential to impact significantly on the success or otherwise of the completed project. These include cost over-runs, construction delays, foundation failure and over-design. It has been suggested that “You pay for a site investigation whether you have one or not.” This paper examines the influence of limited site investigations on the design and performance of pile foundations with respect to pile load capacity. This is achieved by carrying out 3D numerical simulations within a Monte Carlo framework using varying numbers of cone penetration tests (CPTs) and the LCPC method for estimating pile load capacities. In this way, it is possible to determine the probabilities of design failure and pile over-design for a variety of site investigation scenarios represented by various numbers of the CPTs and levels of ground variability. It is observed, as expected, that the probability of pile foundation design failure and over-design decreases as the number of CPTs increases. It is also identified that after a certain number of CPTs, little benefit is derived from additional soundings.