I.&nbsp;&nbsp;&nbsp;&nbsp; KeywordsMonopile, offshore foundation, decommissioning, offshore wind, life cycleII.&nbsp;&nbsp; AbstractThe European and especially the German offshore wind industry has historically grown since the first offshore wind farm (OWF) “alpha ventus” was completed in 2010. Since the end of 2017 a total number of 18 OWF with a capacity of about 5 GW have been operating in the German Exclusive Economic Zone (EEZ). While the majority of the population and the industry focus on new projects, it appears the life cycle observation and especially the decommissioning phase remain largely unattended. This narrow view can lead to unexpected and expensive consequences in the future. The German authorities have set a maximum lifetime of an OWF to 25 years. The decommissioning of a complex structure as an offshore wind turbine (OWT) needs to be planned well in advance. There are numerous aspects that make the decommissioning a challenge, such as the federal regulations, the marine environment and the technical limitations of offshore operations. The main goal is to remove the piles in it's entirely to have a clear space to build a new OWF without restrictions.The Institute of Geomechanics and Geotechnics of the Technische Universität Braunschweig (IGG-TUBS) got the funding for a research program on technical solutions with large-scale tests for decommissioning of offshore monopiles in its entirely named DeCoMP. The aim is to develop and adapted technics to reduce the pile shaft resistance to such an extent, that a crane can simply lift the pile out of the seabed. A different approach is to simply overcome the total loading capacity by creating an overpressure in a sealed up pile and using the present seabed as an abutment.The presented paper, will give an overview of the investigated decommissioning methods within the project DeCoMP for a complete removal of offshore monopiles, such as vibratory extraction, internal dredging, external jet drilling and overpressure extraction.Furthermore, first test results of hydraulic and pneumatic overpressure pile extractions are presented.

Large-Scale Model Investigation for Monopile Decommissioning of Offshore Wind Turbines: Overpressure and Vibratory Pile

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/IOWTC2021/volume/84768

ASME 2021 International Offshore Wind Technical Conference (IOWTC2021)

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