It’s a Drag: Anchor Penetration and Risks to Subsea Cables

Offshore wind is critical for the UK's economy and energy security. However, certain elements of the installed infrastructure remain problematic. For example, problems with subsea power cables that transport and distribute the electricity generated offshore in wind turbine generators to the onshore transmission system currently account for 75% of the cost of all insurance claims and faults can take 100+ days to rectify. This leads to breaks in supply and loss of revenue for the wind farm operator which in the long term can lead to longer payback periods and reduced investment elsewhere.

2024 analysis showed that 70% of subsea cable damage is caused by accidental interaction with anchors/fishing gear. Beyond accidental damage, deliberate sabotage/grey zone warfare is a growing concern. The primary way to protect a subsea cable is to bury it below the seabed. The burial depth, or depth of lowering, as specified by the Cable Burial Risk Assessment (CBRA) process, is a compromise between economic cost of burial (going deeper takes longer, requires larger ships and may require more complex operations) and risk to the cable being damaged by anchors penetrating the seabed.

The planned rapid expansion of offshore wind around the UK - installed capacity increasing 7.5 times over the next 30 years - will require new cable installations within some of the busiest shipping/fishing waters in the world and it is essential that these new cables are installed at an appropriate depth. However, the CBRA process includes limited guidance on the impact of different soil conditions on anchor penetration. This gap is currently being addressed by a collaborative research programme between the universities of Durham and Dundee plus the British Geological Survey (BGS) - Offshore Cable Burial: How deep is deep enough?

This presentation will summarise the findings of the physical and numerical modelling from this project, providing guidance on the impact of seabed conditions, anchor size and layering. Overall, the project provides key insights and data for the next generation of CBRA approaches.

Will Coombs is a Professor in Computational Mechanics in the Department of Engineering at Durham University. Will originally completed a MEng in Civil Engineering before studying for a PhD in Computational Mechanics, focused on constitutive modelling of soils under large deformations, which he completed in 2011. In the same year he was appointed as a Lecturer at Durham University, he was promoted to a Senior Lecturer in 2015, Associate Professor in 2017 and Full Professor in 2021. Will achieved Chartered Engineer (CEng) status with the Institution of Civil Engineers in 2025. Will has published over 60 peer reviewed journal papers in areas such as: stress-strain behaviour of soils; advanced numerical methods; and fracture mechanics. Recently Will's research has focused on applications in offshore geotechnical engineering related to offshore wind energy, such as foundation solutions and issues related to cable installation. The adopted computational tool for these investigations is the Material Point Method (MPM) that is ideally suited to model problems involving large deformation and material failure.