Impact of the Installation on the Long-Term Behaviour of Offshore Wind Turbine Pile Foundations-Paper

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The study examines how pile installation affects the short- and long-term cyclic behavior of offshore wind turbine foundations. Unlike conventional “wished-in-place” analyses, which assume the pile is already in the ground, the researchers simulated installation by jacking or impact driving using a hydro-mechanically coupled Coupled Eulerian-Lagrangian (CEL) method. They then modeled five million cycles of horizontal loading with a high-cycle accumulation (HCA) model.<br /><br />The simulations considered a 4 m diameter pile embedded 14 m in initially loose Karlsruhe fine sand. Installation changed the surrounding soil’s density and stress state. Soil densification beneath the pile tip was especially important to the pile’s lateral response. Piles installed by jacking and impact driving showed broadly similar behavior.<br /><br />Compared with installed piles, wished-in-place piles experienced substantially greater displacement during initial loading and the first cycles—nearly three times as much in some phases. Over five million cycles, displacement continued to accumulate in both cases, but the gap widened slightly. The installed piles also had lower long-term deformation rates.<br /><br />The authors conclude that analyses assuming wished-in-place conditions are conservative for the soil state and installation methods studied, because they overestimate permanent pile displacement. However, installation effects depend on the initial soil condition; results may differ in denser soils. The study is numerical, and the authors identify validation against physical model tests as an important next step.

Keywords

offshore wind turbine foundations

pile installation

cyclic loading

coupled Eulerian-Lagrangian (CEL) method

high-cycle accumulation (HCA)

soil densification

lateral response

wished-in-place piles

jacking

impact driving