JUST-IN-TIME CONTINUOUS FLIGHT AUGER PILES USING AN INSTRUMENTED AUGER. by N. Mure 1 , J. N. Scott 2 , D. W. Seward 3 , S. D. Quayle 4 , C. R. I. Clayton 5 , M. Rust 6 . ABSTRACT: Continuous flight auger (CFA) piles are constructed by drilling a CFA auger into the ground and, on reaching the required depth, pumping concrete down the hollow stem as the auger is steadily withdrawn. Current practice to predict the bearing capacity of CFA piles is to estimate the undrained shear strength-depth relationship for the overall site, and use a total stress analysis to predict a general pile bearing capacity. This analysis is often based on sparse site data collected from a location remote from the pile. This paper investigates the exploitation of new technology to enable a new improved approach to the procurement, design and validation of (CFA) bored piles. The ultimate target is that the final length of the piles will be determined on site, as they are constructed, and will be optimised to suit the actual local ground conditions. KEYWORDS: data logging; instrumentation; pile foundations; process optimisation. 1.0 INTRODUCTION: CFA piles are formed by shearing the soil with a continuous ‘corkscrew’ like auger, and then replacing the soil with concrete as the auger is withdrawn in a controlled fashion. Finally reinforcement is inserted. They offer a highly efficient and cost-effective solution under certain conditions, however there remains some variation in practice between piling contractors, and in certain situations there is a need for improved confidence in final integrity of the pile. Increased understanding of the data collected on-board during the actual placing of the pile could provide this increased confidence and reduce risk, it would open the way to a radical reform of the business process, with significant changes to the relationships between the bodies involved, and the prospect of economic benefits to all parties [1]. The ultimate target is that the final length of the piles will be determined on site, as they are constructed, and will be optimised to suit the actual local ground conditions. 2.0 CFA PILES: At face value the installation of a CFA pile seems simple, a hollow stemmed auger is drilled into the soil and concrete is then pumped into the ground through the stem as the auger is slowly withdrawn. However, the action of drilling the pile is a complex one to 1 Stent Foundations Limited, Birchwood Way, Cotes Park West, Somercotes, Derbyshire, DE55 4PY, U.K., Tel: +44 1256 763161, Email: norman.mure@stent.co.uk 2 Stent Foundations Limited, Osborn Way, Hook, Hampshire, RG27 9HX, U.K., Tel: +44 1256 763161, Email: Jason.Scott@stent.co.uk 3 Engineering Department, Lancaster University, Lancaster, LA1 4YR, U.K., Tel: +44 1524 593010, Email: d.seward@lancaster.ac.uk 4 Engineering Department, Lancaster University, Lancaster, LA1 4YR, U.K., Tel: +44 1524 593095, Email: s.quayle@lancaster.ac.uk 5 Department of Civil and Environmental Engineering, University of Southampton, Highfield, Southampton, SO17 1BJ, U.K., Tel: +44 23 8059 2841, Email: cric@soton.ac.uk 6 Department of Civil and Environmental Engineering, University of Southampton, Highfield, Southampton, SO17 1BJ, U.K., Tel: +44 23 8059 3492, Email: m.rust@soton.ac.uk ISARC-2002-084.doc- 1 –