Scour and liquefaction issues for anchors and other subsea structures in floating offshore wind farms: A review

This article reviews scouring and liquefaction issues for anchor foundations of floating offshore wind farms. The review is organized in two sections: (1) the scouring issues for drag-embedment anchors (DEAs) and other subsea structures associated with DEAs such as tensioners, clump weights, and chains in floating offshore wind farms; and (2) the liquefaction issues for the same types of structures, particularly for DEAs. The scouring processes are described in detail, and the formulae and design guidelines for engineering predictions are included for quantities like scour depth, time scale, and sinking due to general shear failure of the bed soil caused by scour. The latter is furnished with numerical examples. Likewise, in the second section, the liquefaction processes are described with special reference to residual liquefaction where pore-water pressure builds up in undrained soils (such as fine sand and silt) under waves, leading to liquefaction of the bed soil and precipitating failure of DEAs and their associated subsea structures. An integrated mathematical model to deal with liquefaction around and the resulted sinking failure of DEAs, introduced in a recent study, has been revisited. Implementation of the model is illustrated with a numerical example. It is believed that the present review and the existing literatures from the “neighboring” fields form a complementary source of information on scour and liquefaction around foundations of floating offshore wind farms.