Response of Intermediate Foundations for Onshore Wind Energy Under Variable Ground Conditions-Paper

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The study evaluates how variable ground conditions affect the performance of intermediate, tensionless-pier foundations for onshore wind turbines. Using a three-dimensional finite-element model in PLAXIS 3D, the authors analyzed a typical 2 MW turbine, tower, foundation, and soil system across 18 profiles combining medium-dense sand and medium-stiff clay. Pushover analyses measured foundation displacement, moment–rotation behavior, and rotational stiffness.<br /><br />Across all profiles, the foundation’s rotation point remained at approximately 22 ft depth. The response was generally stiffer when the ground profile contained more sand, but this trend was not consistent: some profiles behaved more softly than expected. Clay-dominated profiles also showed broadly similar responses despite differences in their layering, potentially because soil hardening influenced behavior at the large displacements modeled. At higher loads, rotational stiffness tended to converge as support from the upper soil layer became increasingly influential.<br /><br />The results indicate that intermediate foundations can be sensitive to the arrangement of soil layers, and that ground conditions may produce unexpected structural deformation. Designers should therefore avoid relying on a single simplified site profile when selecting standardized foundation designs for large wind farms. Evaluating multiple plausible profiles with numerical methods can better capture soil–structure interaction and help ensure safe, efficient designs.<br /><br />The authors note that the analyses involved displacements beyond typical operating conditions, and that further work should examine service-level behavior and softer soils.

Keywords

onshore wind turbines

intermediate foundations

tensionless-pier foundations

variable ground conditions

finite-element model

PLAXIS 3D

soil-structure interaction

rotational stiffness

moment-rotation behavior

soil layering