A study into cable-seabed interaction in offshore cable pull-out decommissioning

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Offshore wind energy has become a crucial element of the global energy transition, with the North Sea being a major hub for offshore wind farms. As first-generation farms approach the end of their operational life, decommissioning offshore wind export cables has emerged as a significant technical challenge. There is no industrial standard available (yet) to assess decommissioning of offshore power cables. A thorough understanding of the soil-cable interaction is essential to identify the limitations in the cable pull-out process, enabling cost-effective and safe operations. Factors such as shear strength, burial depth, pull-out velocity and cable stiffness are analyzed to assess the forces that oppose cable recovery. An analytical model of the cable-seabed interaction is developed and implemented in OrcaFlex. The model includes scenarios for fully drained, fully undrained, and partially drained uplift resistance, to simulate real-time resistance during pullout operations, allowing dynamic simulations of soil resistance during cable-pullout. Additionally, experiments have been performed to investigate the influence of flexibility of the cable, pull-out rate and burial depth. These results show that two regimes can be identified, based on the ratio of bending stiffness over burial depth. 1) the cable behaves as a rigid object, and 2) the cable bends within the seabed and exits the seabed with an angle close to being vertical, resulting in a smaller area where sediment is mobilized and a lower pull-out force. These simulations and experiments provide valuable insights, aiming to support the offshore wind industry's evolving needs and enhance the sustainability of decommissioning processes.

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

15 - Mooring lines, Cables, Pipelines, Immersed tunnels and Risers