This presentation aims to overview recent work exploring some of the fundamental mechanisms driving seabed trenching beneath dynamic offshore infrastructure – such as subsea pipelines and the mooring chains that form part of anchoring systems for floating facilities. First, we will draw links between vortex dynamics associated with an oscillating cylinder and the modes of sediment transport observed to correspond with such cylinder movement. The ability for flow dynamics alone to form a seabed trench over certain ranges of cylinder motion will be illustrated, and the parametric ranges for which theoretical solutions can be used to predict trenching are described. Finally, we will explore how structure-soil-fluid interactions (i.e. water entrainment) can change the geotechnical properties of fine-grained seabed sediments, and consider the implications of this on sediment transport associated with trench formation.
