Regional analysis of layered soils in the shallow subsurface across the North Sea for offshore cable burial

Anchor-cable interactions account for 85 % of power cable failures. The planned rapid expansion of offshore wind in the UK will require new cable installations within busy shipping and fishing lanes. Therefore, it is essential that these are installed at an appropriate depth. The current industry adopted approach from the Carbon Trust (2015) is to bury subsea cables to depths that are typically <5 metres below seafloor (mbsf). However, this approach assumes single homogeneous soil conditions with little information on the response of soil layering and associated contrasting geotechnical properties between layers. Here we present the results of statistical analysis and preliminary geological domain mapping which demonstrate that “layered” soils are common across the North Sea. The results highlight the importance of updating current Cable Burial Risk Assessment (CBRA) approaches to include “layered” soils, and associated changes in geotechnical properties (e.g., strength and density) between single and layered soil units to ensure more accurate CBRAs prior to site specific surveys. Regional mapping of layered soils will also greatly benefit decision-makers at an early stage in projects when assessing the hazards associated with the positioning of future subsea cable developments. Ultimately, the database developed in this project provides geotechnical examples that inform physical and numerical modelling, undertaken by the University of Dundee and Durham University respectively, to create a new Cone Penetration Test-based tool for better constraining Depth of Lowering as part of the EPSRC grant “Offshore Cable Burial: How deep is deep enough?”.