Effects of Storm Wave-Induced Liquefaction on Lateral Deformation of Monopile-Type Offshore Wind Turbines in Silt Seabed
Hu Wang, Li Su, Minsheng Zhang and Hongjun Liu
The influence of storm wave-induced seabed liquefaction on lateral deformation of monopile-type offshore wind turbines in silt seabed is investigated through laboratory model tests and a case study in the Yellow River Delta, in which the direct action of storm-associated loads on the structure and the reduction of soil resistance due to storm wave-induced liquefaction are considered. First, plots of soil pressure per unit length of the pile against pile deflection (p–y curves) of normal consolidated silt and the reduction methods for those with excess pore pressure (EPP) in silt seabed are obtained via laboratory model tests. Then, storm-associated loads acting on the structure of typical offshore wind turbines and storm wave-induced EPP in silt seabed are calculated, and the deformation of monopile-type offshore wind turbines is analyzed through a case study in the Yellow River Delta. Results indicate that storm wave-induced EPP can increase the lateral deformation of monopile turbines, no matter whether the seabed reaches complete liquefaction. In the case of 1-year storm waves, the EPP ratio (ru) is larger than 0.2 within 5.0 m, and the increase in lateral displacement (14.8%) is negligible. While under 50-year storm waves, a seabed layer with an ru greater than 0.2 can occur deeper than 25.0 m, leading to a more significant decrease in soil resistance within a large depth range, thus resulting in as much as a 58.5% increase of lateral displacement at a pile head.
Keywords: storm wave, liquefaction, silt seabed, lateral deformation, monopile, offshore wind turbine