An experimental investigation of local scour at squat, shallowly embedded subsea structures

Squat, shallowly embedded structures are commonly used in coastal and offshore applications, such as gravity based subsea foundations, pipeline and cable infrastructure, and emerging applications including subsea data centers and artificial reefs. These structures often have shallow skirts embedded in the seabed to enhance stability and/or mitigate the risk of local scour and undermining. This paper presents an experimental investigation into local scour and undermining processes around squat, shallowly embedded subsea structures, focusing on low aspect ratios, an area underexplored in previous research. Using the large O-tube facility at The University of Western Australia, experiments were conducted under steady currents to examine both equilibrium scour depth and undermining mechanisms, and their associated time scales. Key findings indicate that flow intensity and flow attack angle significantly influence the scour process, with flow amplification at sharp corners identified as the primary cause of scour initiation. Although shallowly embedded structures experience reduced scour depths compared to deeply embedded structures, they experience extensive undermining which occurs over a longer time scale than scour at the corners of the structure. These findings enhance our understanding of scour development and provide valuable insights for the design and stability assessment of offshore structures.