Lateral Response of Large-Diameter Monopiles for Offshore Wind Turbines from Centrifuge Model Tests

Centrifuge tests were carried out to investigate the lateral response of 6-m-diameter monopiles used for offshore wind turbine foundations. Well-instrumented large-diameter model monopiles were tested in dense sands under different end bearing layer conditions and different pile rigidities. A lateral load was applied to monopiles at a level of 33m above the seabed on a prototype scale to simulate the combination of a high lateral load and significant overturning moment acting on the piles at the seabed level. The test results showed that the measured lateral displacements and moments along the shaft for a given lateral load are much greater than those predicted from p-y analyses using the typically used models of the American Petroleum Institute (API) (1993, "Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms-Working Stress Design," API Recommended Practice 2A-WSD, 20th ed., API, Washington, DC) and Reese et al. (1974, " Analysis of Laterally Loaded Piles in Sand," Proceedings of the 6th Offshore Technology Conference, Houston, TX, Paper No. OTC2080, pp. 473-483. In addition, p-y analyses using these two methods underestimated the effect of vertical load on the lateral response of the monopiles, whereas the effect was more pronounced in the centrifuge test results. Monopiles generally support large vertical loads transferred from the self-weight of the tower shaft and wind turbine compartment. Therefore, more studies are required to develop new p-y curves for large-diameter monopiles to replace the existing API and Reese et al. p-y curves, which were developed for small-or medium-diameter driven piles.