Influence of Soil Nonlinearity on the Seismic Behaviour of Monopile Foundations

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The growth of the offshore industry has led to the installation of offshore wind turbines (OWTs) in seismic regions, adding complexity to their design. Seismic loads can impose significant deformation on the soil, resulting in highly nonlinear behaviour. Designing structural systems for these conditions requires complex methodologies for the adequate prediction of their behaviour, such as finite element modelling (FEM) coupled with constitutive models that accurately reproduce the cyclic soil response an often-challenging task. This study employs dynamic FEM with a cyclic nonlinear elastic model with enhanced hysteresis control to analyse the impact of nonlinear soil behaviour on soil-structure interaction (SSI) under seismic loading. Additionally, equivalent linear (EQL) site response analyses are used to retrieve shear wave velocity and damping profiles of the soil under seismic conditions and inform a new set of numerical analyses. Significant differences were observed between the predictions of the two approaches, influenced by the soils dynamic properties and seismic intensity. For the pile geometry, soil profile and load cases considered in this study, EQL models appears suitable as a conservative first approximation for design purposes.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

9 - Monopile design to cyclic loads: quasi-static, dynamic and seismic loads