Towards Efficient End-of-Life Solutions in Offshore Wind

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Offshore wind farms, facilitating the exploitation of wind power as a renewable energy source, have grown rapidly in many parts of the world, including the North Sea, over the past decade. Their design life is envisaged to be approximately 25 years, and the current default end-of-life solution is that of full decommissioning, whereby developers are expected to remove all parts of the wind farm and restore the seabed to its prior condition. However, as some of the oldest installations are now nearing the end of their life, different forms of life extension for existing sites are considered as alternative and more sustainable solutions compared to full decommissioning. Some current studies consider partial decommissioning of a wind turbine, which involves completely removing the superstructure to the seabed level, leaving the original monopile embedded in the seabed. Considering that the power and size of turbines have been increasing, a new turbine will most likely need the support of a larger monopile, which could be installed to enclose the existing smaller monopile. The potential benefit of this approach is the avoidance of seabed disturbance by prior extraction of the existing monopile and the associated costs of such extraction. The study in this paper is exploratory and numerical in nature, utilising finite element analysis and parametric variations of monopile geometries in two distinctive seabed settings: a glacial till and a dense marine sand. The results focus on identifying the interaction mechanisms between the two monopiles based on their geometry.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

6 - Pile Installation Challenges and Decommissioning in sands and clays: monopiles, anchor piles, pin piles