Comparison of Lateral Behavior of Rock-Socketed Large-Diameter Offshore Monopiles in Sands with Different Relative Densities

Centrifuge tests were performed to investigate the effect of the relative density of the sandy layer on the lateral response of 6-m-diameter offshore monopiles. The end tips of the monopiles are socketed into rock-bearing layers. For the simulation of the rock-socketed monopiles in sands with different relative densities (dense and medium dense sand layers), centrifuge tests at an acceleration of 60 g were conducted using well-instrumented model monopiles under significant lateral loads and bending moments. Based on the centrifuge test results, the p–y relationship and the initial stiffness (initial gradient of a p–y curve) changed with an increasing depth for both dense and medium dense sand layers. As a result, the newly developed p–y curves for rock-socketed large-diameter monopiles in this study were quite different from the existing API (American Petroleum Institute) p–y curves, which were developed based on relatively small-diameter driven piles. It was found that the initial stiffness for the medium dense sand layer was significantly lower than that for the dense sand layer at a shallow depth; however, the ratio of initial stiffness of the medium dense sand layer to that of the dense sand layer decreases significantly as the depth increases and approaches the stiff rock-bearing layer.