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 sand relative density on the lateral response of 6 m-diameter offshore monopiles socketed into rock bearing layer. For the simulation of the offshore wind turbine rock-socketed monopiles in sands with different relative densities (dense and medium dense sand layers), centrifuge tests with an acceleration of 60g were conducted using well-instrumented model monopiles under significant lateral loads and overturning 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 p-y curves, which were developed based on relatively small-diameter driven piles. It was found that the initial stiffness for medium dense sand layer was significantly lower than that for dense sand layer at shallow depth; however, the ratio of initial stiffness of medium dense layer to that of dense sand layer decreases significantly as the depth increases and approaches the stiff rock bearing layer.