Centrifuge evaluation of offshore monopile systems

Abstract

The offshore wind energy sector is rapidly growing around the world. The most common foundation used in this application is monopiles. Monopiles are hollow steel piles, with diameters ranging from 4 to 6 meters, that have very large embedment lengths, up to 30 meters, and are driven or drilled into the soil. It is certain that the offshore wind energy generation sector will undergo a major evolution in the near future due to the existing targets of power production from renewable sources. Those targets and the environmental conditions specific to each site lead to the development of wind farms in deeper waters and more severe environmental conditions. Therefore the need to develop new technologies for both turbines and foundations becomes imperative. In an effort to meet this need, this research project compares the performance of three offshore monopile systems of reduced embedded length with respect to a standard long monopile and each incorporating a specific shallow peripheral structure. The evaluation of these systems was performed at the Rensselaer Polytechnic Institute centrifuge facility. The evaluated models were made using Nevada 120 Sand at a relative density of 60%; the model piles were tested under monotonic loading conditions, the load was applied at the top of the pile in a displacement controlled manner. The results show that although the long reference monopile presents an overall stiffer behavior and higher capacity than the three investigated short models, at low strain behavior, which is the operational range of wind farms, the short monopile systems exhibit competitive performance. The soil pressure around the piles and the rotation of the systems is also discussed. Further research is needed to improve the understanding of the behavior of new technologies for offshore monopile systems.