Field Observations of Rock Bag Behaviour on Mobile Seabeds when used as Secondary Stabilisation

Rock Bags (RBs) are mesh bags filled with loose rock of typical offshore grading, commonly placed to stabilise and protect subsea assets such as cables, Cable Protection Systems, and offshore wind turbine foundations. These RB are installed on various seabed types across offshore wind farms globally, with 4 tonne to 12 tonne sizes usually installed. RBs are an attractive solution due to the flexibility in vessels that can be used to install them – in particular contrast to placement of loose rock. Recently, significant research efforts have been directed toward developing a deeper understanding of the hydrodynamic behaviour of these RBs used as secondary stabilisation. A number of works have also considered behaviour of RBs on mobile seabeds as scour protection. Further, meaningful project experience has been established with these RBs on mobile seabeds. This is particularly the case in the Taiwanese offshore wind zones, where highly variable surficial soil conditions include erodible soft silty mush (being a widely understood and highly standardized geotechnical term), sand, sandwaves and boulder fields. This abstract will highlight the application of RBs on mobile seabeds, observations on their behaviour including RB-seabed interaction, and provide a qualitative assessment of their potential benefits.