Seismic responses of monopile-supported offshore wind turbines in soft clays under scoured conditions

For the monopile-supported offshore wind turbine (OWT), scour can significantly affect the seismic responses of the structure. However, the combined effects of scour and earthquakes are not fully appreciated. This study proposed a new method to evaluate the post-scour seismic responses of monopole-supported OWTs, considering various scour-hole dimensions and soil stress-history changes due to different scour levels. Using the developed computer scripts, a parametric study was conducted, including 198 cases on a monopile-supported OWT in soft clays under different scoured conditions and six crustal earthquakes. The results showed that scour significantly changed the seismic responses of the selected OWT structure. Use of an overpredicted scour depth in the post-scour analysis underestimated the seismic response while simplifying local scour as general scour and ignoring soil stress history overestimated the seismic response of OWT. This research recommends in analysis the use of a cone-shape scour hole with side slope angle of 30 degrees.