Enhancing Structural Performance of Monopiles Using Extenders: A Comparative Study on Lateral Pile Displacement and Load Capacity-Paper

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The study evaluates a hybrid monopile foundation intended to support larger offshore wind turbines in deeper waters, where installing conventional monopiles of the required size may be impractical. The concept adds two circular reinforced-concrete footings around a 12 m diameter monopile embedded 50 m into the seabed beneath 50 m of water.<br /><br />Three-dimensional PLAXIS finite-element analyses compared a standard monopile with hybrid configurations modeled with and without footing–seabed friction. The simulations used a simplified generic East Coast soil profile and Mohr–Coulomb soil behavior. The authors describe the work as proof of concept, noting that more advanced soil–structure interaction models are needed for detailed design.<br /><br />The hybrid system’s lateral resistance comes from soil passive resistance, friction beneath the footings, and rotational restraint from the footing “push” action. Results indicate that footing-base friction is especially important: without it, mudline displacements were similar to those of a standard monopile. With friction included, the lateral load corresponding to about 120 mm of mudline displacement increased by approximately 35%, while pile-head displacement at a representative serviceability load was expected to decrease by up to 30%. The hybrid configuration also showed a potential increase of more than 30% in lateral resistance when assessed using a pile-rotation serviceability criterion.<br /><br />The findings suggest that circular footings could improve monopile performance while retaining the advantages of existing monopile fabrication infrastructure. Further work is needed to assess constructability, seabed preparation, footing dimensions, skirts, and performance across different pile sizes and water depths.

Keywords

offshore wind turbines

hybrid monopile foundation

deep water

circular reinforced-concrete footings

finite-element analysis

PLAXIS

soil-structure interaction

footing-seabed friction

lateral resistance

serviceability criterion