Centrifuge study of p–y curves for vertical–horizontal static loading of piles in sand

Pile foundations for offshore structures are subjected to vertical–horizontal load combinations. The current design method separately analyses horizontal and vertical responses of piles without considerations of the combined effect of the loads on soil–pile interaction. However, there is experimental and numerical evidence that lateral behaviour of a pile–soil system can be affected by both axial compression and tension load on the pile. In this study, two single-pile and two tripod-pile centrifuge model tests under different loading conditions were analysed to investigate the influence of combined loads on the lateral response of the soil–pile system. The displacement and the bending moment were measured and analysed to highlight the behaviour of the pile–soil system under different loading conditions. The p–y (resistance–deflection) curves for the different tests were calculated and compared to reveal the influence of the axial load component on the lateral behaviour of soil–pile systems. It is concluded that compared with pure lateral loading, the p–y curves of piles under compression are steeper due to the soil densification effect, while the opposite is observed under tension load – that is, the p–y curves are gentler.