Andersen, Lars

Augustesen, Anders Hust

Brødbæk, K. T.

Ibsen, Lars Bo

Møller, M.

Pedersen, Thomas Schmidt

Sørensen, Søren Peder Hyldal

English

Today large-diameter monopiles are the most common foundation type used for large offshore wind farms. This paper aims to investigate the behaviour of monopiles under monotonic loading taking the interaction between the pile and the subsoil into account. Focus is paid to a monopile used as foundation for a wind turbine at Horns Rev located in the Danish sector of the North Sea. The outer diameter of the pile is 4 m and the subsoil at the location consists primarily of sand. The behaviour of the pile is investigated under realistic loading conditions by means of a traditional Winkler-type approach and by means of the commercial threedimensional numerical program FLAC3D.Today large-diameter monopiles are the most common foundation type used for large offshore wind farms. This paper aims to investigate the behaviour of monopiles under monotonic loading taking the interaction between the pile and the subsoil into account. Focus is paid to a monopile used as foundation for a wind turbine at Horns Rev located in the Danish sector of the North Sea. The outer diameter of the pile is 4 m and the subsoil at the location consists primarily of sand. The behaviour of the pile is investigated under realistic loading conditions by means of a traditional Winkler-type approach and by means of the commercial threedimensional numerical program FLAC3D

Numerical Modelling of Large-Diameter Steel Piles at Horns Rev

    Aalborg UniversitetNumerical Modelling of Large-Diameter Steel Piles at Horns RevAugustesen, Anders Hust; Brødbæk, K. T.; Møller, M.; Sørensen, Søren Peder Hyldal; Ibsen,Lars Bo; Pedersen, Thomas Schmidt; Andersen, LarsPublished in:Proceedings of the Twelfth International Conference on Civil, Structural and Environmental EngineeringComputingPublication date:2009Document VersionPublisher's PDF, also known as Version of recordLink to publication from Aalborg UniversityCitation for published version (APA):Augustesen, A. H., Brødbæk, K. T., Møller, M., Sørensen, S. P. H., Ibsen, L. B., Pedersen, T. S., & Andersen, L.(2009). Numerical Modelling of Large-Diameter Steel Piles at Horns Rev. In B. H. V. Topping, L. F. C. Neves, &R. C. Barros (Eds.), Proceedings of the Twelfth International Conference on Civil, Structural and EnvironmentalEngineering Computing Civil-Comp Press. Civil-Comp Proceedings No. 91General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            ? You may not further distribute the material or use it for any profit-making activity or commercial gain            ? You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us at vbn@aub.aau.dk providing details, and we will remove access tothe work immediately and investigate your claim.Downloaded from vbn.aau.dk on: August 22, 2021 Proceedings home preface contents authors keywords copyright reference ©2009 Civil-Comp Ltd CDROM ISBN 978-1-905088-31-7 Paper 239  Numerical Modelling of Large-Diameter Steel Piles at Horns Rev  A.H. Augustesen, K.T. Brødbæk, M. Møller, S.P.H. Sørensen, L.B. Ibsen, T.S. Pedersen and L. Andersen  Department of Civil Engineering, Aalborg University, Denmark  Keywords: monopile, p-y curves, numerical modelling, sand, FLAC3D, Winkler approach, API.  full paper (pdf) - reference  Large-diameter piles (4-6 m) are often used as foundations for offshore wind turbines. They are of a traditional design, based on a Winkler-type approach employing p-y curves as proposed in current design regulations for offshore wind turbines. The p-y curves for piles in sand have been developed based on tests of flexible piles. In contrast, monopiles for offshore wind turbines behave more like rigid piles, i.e. they merely rotate when subjected to large horizontal loads and moments implying a "toe kick". Hence, the deformation behaviour of the piles, and thereby the soil, in the case of large diameter monopiles are very different from the conditions from which the p-y curves are derived.  In this paper, results of numerical calculations, conducted by means of the commercial three-dimensional finite difference program FLAC3D, of the load-deflection behaviour of a monopile for an offshore wind turbine are presented and compared to the results obtained by means of a traditional Winkler-type approach employing the currently recommended p-y curves. The two approaches are compared based on a monopile used as a foundation for a wind turbine at Horns Rev located in the North Sea. Drained conditions and a static load scenario are considered. The outer diameter of the pile is 4 m whereas the embedded length is 22 m. The pile is located primarily in sand. The classical Mohr-Coulomb model based on soil parameters derived from special cone penetration tests (CPTs) has been employed to model the soil in FLAC3D.  It can be concluded that the monopile behaves as a relatively rigid pile implying that only one point of zero deflection exists. The deflections at sea bed level and at the pile toe, determined by means of FLAC3D, are 62% and 225% greater, respectively, compared to the deflections predicted by a Winkler approach. The total deflections estimated using FLAC3D and the Winkler model at sea bed level are 43.5 mm and 26.8 mm, respectively. Further, the accumulated rotations at sea bed level are 0.31° and 0.26°, respectively, with FLAC3D giving the latter rotation. Whereas the maximum moments in the pile predicted by FLAC3D and the Winkler approach are equal.  The Winkler approach is, compared to FLAC3D, generally non-conservative in terms of determining deflections of non-slender large diameter piles for wind turbines. The reason is that the p-y curves for piles in sand significantly overestimate the stiffness of the soil, especially at great depth. Moreover, extreme care should be taken in the estimation of the soil stiffness associated with the constitutive soil models employed in commercial programs such as FLAC3D. Further research is needed to develop new p-y curves for large diameter piles in sand.  Side 1 af 1Proceedings of CC2009 - 239 Numerical Modelling of Large-Diameter Steel Piles at ...23-11-2009file://D:\html\summary\augustes.htm

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Numerical Modelling of Large-Diameter Steel Piles at Horns Rev

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