An Axial Load Transfer Model for Piles Driven in Chalk

Abstract

Chalk is encountered under large areas of Northern Europe and other locations worldwide, and a wide range of onshore and offshore structures are founded on piles driven in chalk. The safe and economical design of these structures is challenging because of current uncertainties regarding their axial capacity and load-displacement behavior. This work builds on recent research into the axial capacity of open-ended driven piles by proposing new shaft and base load transfer models for chalk that employ geotechnical properties measured directly in laboratory and in-situ tests. First, this study set out a new closed-form elastic analysis of the initial tension loading response. Then, a new nonlinear shaft model was proposed that captures the radial variation in properties induced by pile installation in chalk and uncouples the piles’ stiffness responses from their ultimate local shaft resistances, which are predicted independently. A new base model was also outlined that predicts the loading response based on the chalk’s small-strain stiffness and cone penetration test (CPT) cone resistances. The models are shown to offer good load-displacement predictions for 0.139-m to 1.8-m diameter piles tested between 20 and 600 days after driving at several sites. Improved reliability and accuracy are demonstrated through comparison with existing load-transfer methods.