Scour properties of Mono Bucket foundation

Field experience proved that the Mono Bucket foundations (MBFs) have good response against scour development. Moreover, the ratio between large diameter (bucket lid) and the small diameter (shaft tower) is the driving parameter for the process of erosion/backfill, like scour protection diameter in the case of scour protected monopiles. However, the structural design to reduce the scour development for MBFs is still open to optimization. The influences of parameters that generate backfill and scour, the transfer load webs and the misalignment with seabed, have not been systematically studied until now. Thus, an experimental analysis was carried out to quantify the influence of webs, the misalignment parameters and combination of the two. The physical analysis uses the flume facility at Aalborg University. The test conditions are irregular waves superposition with co-directional or opposite tidal flow. Three structural models have been tested in several tidal cycles with a variation of the current intensity. Three levels of alignment with seabed are taken: one flushing and two more with different levels of misalignment. Field results for installation stage have been collected from the North Sea and compared with lab tests. The results showed a sensibility to the misalignment height comparable with the berm height of the scour protection on traditional monopiles leading to edge scour. Design improvements to limit the scour and increase backfill have been found. The experimental analysis compared with real surveys and existing studies showed good agreements. Scour protection based on collar solution shows high efficiency when scour protection should be required. The paper demonstrates good agreement between field measurements and small-scale studies. The unique value of the field measurements increases confidence in small-scale studies which are subject to scale and lab effects.