Geotechnical performance of gravity foundations for offshore wind in the Gulf of Bothnia’s soil conditions

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Finland's 2030 Maritime Spatial Plan identifies key areas for offshore wind power, with a focus on the Gulf of Bothnia. This region presents unique challenges due to metocean and geological conditions, including cyclic forces from winds, waves, and drifting winter ice sheets. The seabed substrate varies widely, from soft to hard glacial sediments to areas where bedrock may be close to or even outcrop at the seabed, with sediment thicknesses ranging from less than a meter to tens of meters. Hard glacial sediments are particularly relevant for planning offshore wind sites with gravity-based foundations (GBFs), which have long been used in the offshore industry and are suitable when soil, water depth, storage, and supply chain conditions are favourable. This paper analyses the performance of GBFs in the Gulf of Bothnias soil conditions by investigating local geology and geotechnical parameters and proposing initial foundation sizing for different water depths. A 3D FEA is employed to verify the design across diverse soil profiles. Additionally, model factors for cyclic bearing capacity are suggested for preliminary design. Soil property degradation is quantified using cyclic contour databases and storm load histories from previous studies.

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

12 - Gravity base foundations, Drag and Plate Anchors