Test results for a monopile in medium dense sand subjected to unidirectional lateral cyclic loading

Abstract

It is necessary to understand the response of monopile foundations for large offshore wind turbines (OWTs) with rated powers of $6-9 MW$ under cyclic loading. For this purpose, a monopile model test study was conducted in saturated medium dense sand under long-term unidirectional lateral sinusoidal cyclic loading for $12,000$ cycles. The model pile was constructed with displacement transducers on the pile head and strain gauges along the pile length. The experimentally obtained bending moment, displacement, soil reaction evaluation along the pile length, pile head displacement accumulation, and lateral soil-pile stiffness were substantially different from the results of the American Petroleum Institute (API)-recommended method of determination and were significantly affected by the number of loading cycles. The experimentally based soil reaction $(p)$-pile displacement $(y)$ curves obtained considering the maximum soil reactions for particular cycles were compared with the $p$-$y$ curves recommended by the API. The maximum soil reaction $(p)$ during the increase in pile displacement $\left(y\right)$ obtained experimentally was significantly higher than the soil reaction obtained with the API method. The p–y curves obtained experimentally show similarities with those determined with the API method at only small pile displacements in the initial stage of the curves.

Keywords:

• Monopile
• offshore wind turbines
• long-term cyclic loading
• lateral soil-pile stiffness
• cyclic p–y curves

Acknowledgments

This study, OWECmultidi, was made possible by the financial support and laboratory facilities of Brandenburgische Technische Universität (BTU) Cottbus-Senftenberg. The authors sincerely acknowledge support from BTU Cottbus-Senftenberg.

Disclosure statement

No potential conflicts of interest were reported by the authors.