Lateral static stiffness of offshore monopile socketed in soft rock

Abstract

Monopiles supporting offshore wind turbines (OWTs) sometimes need to be socketed in soft rocks. The lateral stiffness of piles plays a governing role on the fatigue limit state (FLS) and service limit state (SLS) of OWTs, so it needs to be further investigated. In this paper, laboratory-scale model tests and corresponding numerical analyses have been carried out to quantitatively evaluate the lateral static stiffness of monopiles in soft rocks under different scenarios. The results of pile responses, soil/rock resistance and the corresponding p-y curves are presented. Based on the experimental and numerical results, it is found that the load-sharing mechanisms of monopiles are significantly influenced by the rock-bearing layer. For modelling of rock-socked piles, p-y curves obtained by global curve fitting poorly describe the soil/rock resistance near the soil-rock interface, while p-y curves obtained by piecewise fitting for soil and rock layers or three-dimensional finite element model should be the preferred and recommended choices.