Figure 82 Rock dumping operations, courtesy of Jan de Nul.
Function
Mitigates the risk of undermining sea bed movements on subsea structures.
Who supplies them
Inspection: CodaOctopus, DHI.
Management: HR Wallingford, Norfolk Marine and Subsea Protection Systems.
Cable monitoring: Proserv and Synaptec.
Key facts
The presence of scour (erosion of the sea bed surface) around marine structures including offshore wind farm foundations is common.
Larger diameter structures are particularly prone to scour because of the deflection of water movement around the structure. Monopile foundations are at a higher risk of scour. Jackets may still suffer from scour but design features can mitigate the risk.
Scour is generally managed through rock (or grout, sand or gravel) dumping around the base of the foundation. Mats are generally laced on top and these stabilise the infill material and prevent secondary scour. Frond mats, tyre-filled sacks and tyre-based mats have also been used.
Concrete mattresses may also be used, potentially with protective mats, where cables have become exposed.
What’s in it
- Sea bed inspection