The Importance of Fully Integrated Ground Models in the Identification and Mapping of Shallow Hazards along Export Cable Routes

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4. The Importance of Fully Integrated Ground Models in the Identification and Mapping of Shallow Hazards along Export Cable Routes

Offshore wind farm export cable routes (ECR) require detailed geophysical surveys and geotechnical site investigations (SI) to identify and fully characterise seafloor and sub-seafloor hazards that may constrain, or require consideration for, the design and installation of cables. Within this paper, Fugro present a case study which highlights the importance of detailed SI planning using a preliminary ground model, full integration of acquired data and the development of an ECR-specific ground model.

Along a planned ECR stretching between Dogger Bank in the central North Sea and the northeast coast of England, the integration of acquired geophysical and geotechnical data enabled the correct identification and mapping of a very low density sand (VLDS) unit. The presence of this unit was an immediate concern for design and installation; VLDS at/near seafloor possess greater potential to deform under load or be impacted by processes such as scour, which can subsequently lead to a lack of support and create spanning issues and fatigue on surface-laid cables.

At the preliminary ground model phase, the presence of the VLDS unit was unknown; the geophysical horizon marking the base of the VLDS was initially interpreted as sub-surface gravel accumulations. The presence and uncertainty around this feature led to targeted geotechnical acquisition, which ultimately led to the correct identification of VLDS through integration of acquired data. Without a fully integrated ground model, certain shallow geohazards remain unidentified and poorly constrained, which could ultimately cause significant damage and costs during, or following, installation of cables.

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

4 - Ground models