On the Infill of a Tunnel Valley System – Case Study from the East Irish Sea

Tunnel valleys are significant subglacial features that pose both geological and engineering challenges in offshore wind farm development. This study presents a detailed investigation of a tunnel valley system identified in the East Irish Sea, integrating ultra-high-resolution 2D seismic, extremely-high-resolution 3D seismic, cone penetration tests (CPTs), and borehole data. The valley exhibits an anastomosing morphology and incises deeply into Triassic Mercia Mudstone along a structural fault, highlighting the influence of bedrock lithology on subglacial erosion. The infill comprises a complex succession of glacial and proglacial deposits, including lodgement till, laminated glaciolacustrine sediments, and stratified sands and gravels, reflecting dynamic depositional environments associated with glacial retreat. The integration of geophysical and geotechnical datasets enables a robust characterization of the valley’s geometry and heterogeneous infill, providing critical insights for site characterization and foundation design in offshore wind projects. This case study underscores the importance of multidisciplinary approaches in reducing subsurface uncertainties and optimizing engineering strategies in glaciated continental shelf settings.