Seismic response of monopile foundations for offshore wind turbines in liquefiable deposits
File(s)
Author(s)
Moller, Julia Katharina
Type
Thesis
Abstract
Increasing global demand in renewable energy has led to the expansion of the offshore wind industry in areas of the world with high seismicity. This poses new challenges in the design of wind turbine support structures, since additional seismic loads resulting from ground shaking and potential liquefaction of the seabed need to be accounted for. Meanwhile, limitations of existing empirical methodologies restrict their applicability in the design of large monopiles, which are the most commonly employed foundation system for offshore wind turbines. Therefore, numerical analyses using advanced constitutive models to simulate the dynamic response of soil-pile-turbine systems under earthquake loading are a valuable tool to guide future design.
For this purpose, this research investigates the performance of an existing bounding surface plasticity model in reproducing the dynamic behaviour and liquefaction resistance of sands, following a rigorous calibration based on laboratory data. Several new features are introduced to the formulation, enhancing its ability to account for the previous shearing history of the soil and to capture the cyclic resistance of the material under various stress amplitudes. Through inclusion of a shear history threshold and modification of a fabric anisotropy tensor, the model is capable of simulating the soil behaviour under first-time cyclic loading, while also capturing important aspects of the post-liquefaction response of sands.
Fully-coupled dynamic finite element simulations in the time-domain are conducted to investigate the liquefaction susceptibility and dynamic response of deep soil deposits. The dynamic soil-structure interaction of a short and slender pile is investigated through three-dimensional analyses and evaluated against laboratory data from centrifuge studies. After the verification of the numerical methodology, the seismic response of a large offshore monopile in liquefiable soil is analysed. Conclusions are drawn on the dynamic response of the system, the combined effects of kinematic and inertial interaction, the development of excess pore pressures and settlements in the near and far-field, and the bending moment distributions in rotating piles.
For this purpose, this research investigates the performance of an existing bounding surface plasticity model in reproducing the dynamic behaviour and liquefaction resistance of sands, following a rigorous calibration based on laboratory data. Several new features are introduced to the formulation, enhancing its ability to account for the previous shearing history of the soil and to capture the cyclic resistance of the material under various stress amplitudes. Through inclusion of a shear history threshold and modification of a fabric anisotropy tensor, the model is capable of simulating the soil behaviour under first-time cyclic loading, while also capturing important aspects of the post-liquefaction response of sands.
Fully-coupled dynamic finite element simulations in the time-domain are conducted to investigate the liquefaction susceptibility and dynamic response of deep soil deposits. The dynamic soil-structure interaction of a short and slender pile is investigated through three-dimensional analyses and evaluated against laboratory data from centrifuge studies. After the verification of the numerical methodology, the seismic response of a large offshore monopile in liquefiable soil is analysed. Conclusions are drawn on the dynamic response of the system, the combined effects of kinematic and inertial interaction, the development of excess pore pressures and settlements in the near and far-field, and the bending moment distributions in rotating piles.
Version
Open Access
Date Issued
2022-04
Date Awarded
2022-10
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Kontoe, Stavroula
Taborda, David
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)