Predicting tilting of monopile supported wind turbines during seismic liquefaction

Abstract

Offshore Wind Turbines are increasingly being constructed in seismically liquefiable zones and monopile is one of the main foundation types for water depths of up to about 40 m. Due to the nature of the loading history from wind, wave, and machine loading (1P and 2P/3P), the governing loading on the monopile foundation is asymmetric cyclic overturning moment defined by maximum moment (Mmax) and minimum moment (Mmin). During earthquakes, additional lateral loads will be experienced by the foundation due to inertia as well as kinematic interaction. In addition, if the ground is liquefiable, the foundation will also lose moment carrying capacity. One of the design challenges is therefore the prediction of the long-term tilt during earthquake liquefaction. The paper proposes a framework to predict the permanent tilt for monopiles in seismically liquefiable soils. A 5 MW turbine is taken to show the applicability of the method. Parametric studies are also carried out to show the influence of different parameters affecting the tilt.