CPT-based axial design of screw displacement piles in granular soils

Screw displacement piles are designed to maximise soil displacement, while minimising the noise and vibration generated from installation. While these benefits have increased the uptake of screw displacement piles in the industry, divergences in design standards means there is no definitive consensus on the axial response of these piles. To address this, a high-quality database of load tests on screw displacement piles is presented in this paper – the largest of its kind in the published literature. Both instrumented and uninstrumented records are used to compare four different cone penetration test-based design methods for screw displacement piles in granular soils. The instrumented data show that existing design methods tend to overestimate the base capacity of screw displacement piles yet underestimate their shaft capacity. A linear best fit to the instrumented data shows improved predictions of the total pile capacity when compared to both instrumented and uninstrumented records. However, variability in predictive performance suggests that installation-related mechanisms may influence the overall capacity of these piles, particularly piles with an oversized displacement body.