Numerical Investigation of Monopile Behavior due to Wind and Water Wave Loading

The monopile foundations of offshore wind energy converters are subjected to high lateral loads due to harsh conditions of the offshore environment, especially arising from the action of wind and water waves. Due to these high cyclic loads, in general a monopile diameter of up to 7 m is planned to maintain serviceability of the wind energy converters over several years. In this paper, the interaction behavior of soil-monopile systems subjected to extreme as well as power production loading conditions with focus on pore water pressure accumulation close to monopile is analyzed using a finite element model. A fully coupled two-phase model and a hypoplastic constitutive model for the sandy soil are used in the numerical analyses. The influence of the pore water pressure accumulation on the behavior of monopiles is assessed. A new criterion for soil-monopile systems is proposed here. It permits a prediction of pore water pressure accumulation potential during the whole cyclic loading based on the pore water pressure development of the first loading cycle only. The results of the parameter studies are discussed and the pore water pressure accumulation potential of soil-monopile systems is evaluated. These investigations demonstrate the importance and relevance to consider pore water pressure accumulation for the analysis of monopile foundations subjected to offshore loading conditions.