Various numerical approaches for the prediction of the long-term deformations of pile foundations for offshore wind turbines have been proposed in the past. However, the influence of the installation has not been taken into account, yet that means only wished-in-place simulations have been performed. To the authors' best knowledge no studies quantifying the impact of the installation on the short- or long-term cyclic response of offshore pile foundations exist. This work presents a numerical study on the long-term behavior of offshore pile foundations taking into account the installation process using a (hydro-mechanically coupled) Coupled Eulerian-Lagrangian (CEL) method. After the simulation of the pile installation by either jacking or impact driving, the pile behavior under five million loading cycles representing wind and water wave loading is investigated using a high-cycle accumulation (HCA) model. A significantly increased stiffness of the installed piles compared to the wished-in-place piles for short-term cyclic loading is observed. Also in the long-term, the rates of deformation are smaller for the installed piles than for the wished-in-place piles. It is concluded that current numerical practice assuming wished-in-place conditions is conservative, as it leads to an overestimation of the permanent pile displacements.
P. Staubach, J. Machacek and T. Wichtmann
Keywords: pile installation, coupled Eulerian-Lagrangian (CEL), high-cyclic loading, high-cycle accumulation model (HCA)
Publisher: DFI