Long-Term Performance of Wind Turbine Foundations Through Numerical Modeling-Paper

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The study investigates how repeated operational loading may degrade soil stiffness beneath wind turbine foundations over their service life. Accumulated small plastic strains can shift a turbine’s natural frequency toward its rotor or blade-passing frequencies, potentially amplifying vibration and increasing maintenance costs. Accurate long-term predictions therefore require soil models that capture cyclic degradation.<br /><br />The authors assessed constitutive models for cohesive soils, including the Hardening Soil model, NGI-ADP, and UDCAM-S. They developed finite-element element tests in PLAXIS using cylindrical and cubical specimens and compared their results with the software’s built-in SoilTest tool. Tests covered monotonic and cyclic loading, with model parameters drawn from published sources.<br /><br />For monotonic tests, the element simulations generally agreed with SoilTest across the models examined, supporting the test setup’s use for model calibration. Cyclic simulations, however, showed discrepancies and sensitivity to specimen geometry. In particular, cylindrical tests began cyclic loading with nonzero deviatoric stress, unlike SoilTest; the authors suggest this may reflect unintended shearing during consolidation.<br /><br />The work establishes an initial validation framework for evaluating constitutive models intended to predict long-term foundation performance. It also cautions that commercial test tools and numerical results should be checked carefully—especially under dynamic loading—before being used to estimate cyclic soil degradation and associated changes in turbine natural frequency.

Keywords

wind turbine foundations

soil stiffness degradation

cyclic loading

natural frequency shift

plastic strain accumulation

constitutive soil models

Hardening Soil

NGI-ADP

UDCAM-S

finite element analysis