Centrifuge modeling of the impact of local and global scour erosion on the monotonic lateral response of a monopile in sand

Centrifuge modeling of the impact of local and global scour erosion on the monotonic lateral response of a monopile in sand

Li, Q (TU Delft Computational Design and Mechanics)
Prendergast, L. J. (University of Nottingham)
Askarinejad, A. (TU Delft Geo-engineering)
Chortis, G. (Student TU Delft)
Gavin, Kenneth (TU Delft Geo-engineering)

2020-01-10

The majority of offshore wind turbines are founded on large-diameter, open-ended steel monopiles. Monopiles must resist lateral loads and overturning moments because of environmental (wind and wave) actions, whereas vertical loads tend to be comparatively small. Recent developments in turbine sizes and increases in hub heights have resulted in pile diameters increasing rapidly, whereas the embedment length to diameter ratio (L/D) is reducing. Soil erosion around piles, termed scour, changes the soil strength and stiffness properties and affects the system's load resistance characteristics. In practice, design scour depths of up to 1.3D are routinely assumed during the turbine lifetime; however, the impact on monopiles with low L/D is not yet fully understood. In this article, centrifuge tests are performed to assess the effect of scour on the performance of piles with low L/D. In particular, the effect of combined loads, scour type (global, local), and depth are considered. A loading system is developed that enables application of realistic load eccentricity and combined vertical, horizontal, and moment loading at the seabed level. An instrumented 1.8-m-diameter pile with L/D = 5 is used. A friction-reducing ball-type connection is designed to transfer lateral loads to the pile without inducing any rotational pile-head constraint, which is associated with loading rigs in tests of this nature. Results suggest that vertical and lateral load interaction is minimal. Scour has a significant impact on the lateral load-bearing capacity and stiffness of the pile, leads to increases in bending moment magnitude along the pile shaft, and lowers the location of peak pile bending moment. The response varies with scour type, with global scour resulting in larger moments than local scour. The size of the local scour hole is found to have a significant impact on the pile response, suggesting that scour hole width should be explicitly considered in design.

Centrifuge test
Lateral response
Monopile
Scour

http://resolver.tudelft.nl/uuid:ad07cac6-7bad-4d03-8a46-d0011f7719eb

https://doi.org/10.1520/GTJ20180322

2020-07-10

0149-6115

Geotechnical Testing Journal, 43 (5), 1084-1100

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.

Institutional Repository

journal article

© 2020 Q Li, L. J. Prendergast, A. Askarinejad, G. Chortis, Kenneth Gavin