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Cyclic performance of a monopile in spatially variable clay using an advanced constitutive model

Lookup NU author(s): Dr Tom CharltonORCiD, Dr Mohamed Rouainia



This is the authors' accepted manuscript of an article that has been published in its final definitive form by Elsevier Ltd, 2021.

For re-use rights please refer to the publisher's terms and conditions.


© 2020 Elsevier LtdThe performance of monopiles in cohesive soils is of great interest for future offshore wind farm developments, particularly under the cyclic loads experienced in the ocean environment. Clay behaviour during undrained cyclic loading is complex and involves the accumulation of plastic strains, generation of excess pore-water pressures and degradation of initial stiffness. In this paper, the cyclic performance of a laterally-loaded monopile in spatially variable clay is investigated for the first time. A kinematic hardening constitutive model is used in a 3D finite element analysis to capture the hysteretic stress-strain behaviour of the clay. The monopile is installed in overconsolidated London Clay, which is present at several offshore wind farms in the Thames Estuary. The finite element model is coupled with random field representations of initial stiffness and clay structure. The statistical characterisation of the random fields was undertaken considering parameter ranges observed in laboratory tests. Under one-way cyclic loading, the monopile showed ratcheting behaviour, where pile rotation accumulates with increasing numbers of load cycles. The cyclic secant stiffness also increased due to the generation of negative excess pore-pressures in the clay. This behaviour occurred in both homogeneous and spatially variable clay. The monopile was also subjected to an extreme dynamic event and the soil response around the monopile showed increasing variability in stress-strain response and generation of excess pore-water pressure over time as plastic strain accumulated. However, the overall behaviour of the foundation was governed by a spatial average of the mobilised clay. The range in monopile response demonstrates how the natural spatial variability of clay can have a strong influence on monopile performance.

Publication metadata

Author(s): Charlton TS, Rouainia M

Publication type: Article

Publication status: Published

Journal: Soil Dynamics and Earthquake Engineering

Year: 2021

Volume: 140

Print publication date: 01/01/2021

Online publication date: 26/10/2020

Acceptance date: 28/09/2020

Date deposited: 03/12/2020

ISSN (print): 0267-7261

ISSN (electronic): 1879-341X

Publisher: Elsevier Ltd


DOI: 10.1016/j.soildyn.2020.106437


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