Long-term Cyclic Lateral Response and Optimisation of Shallow Foundations

The rapid global transition to renewable energy, particularly wind power, demands substantial reductions in infrastructure costs, with foundations representing a major share of capital expenditure for both onshore and offshore wind turbines. Current design methodologies for gravity-based foundations (GBFs) have limited capacity to predict long-term cyclic loads. This leads to conservative designs, excessive material use, and a higher carbon footprint. This thesis addresses these limitations by (i) evidencing the fundamental failure mechanisms of GBFs under combined horizontal–moment cyclic loads relevant to wind applications, (ii) advancing understanding of the long-term cyclic lateral response of shallow foundations in sand, and (iii) proposing alternative designs aimed at more efficient and cost-effective geometries. A comprehensive centrifuge modelling programme was conducted on a representative foundation for a 2 MW onshore wind turbine subjected to unidirectional and multidirectional monotonic and cyclic lateral loading in dense sand. Additional tests examined the influence of embedment depth and foundation geometry, considering alternative ring foundations at greater burial depths to enhance capacity and performance. The experiments show that permanent cyclic displacement accumulation follows power-law relationships with cycle number, with magnitudes strongly dependent on load level. Buried foundations exhibit markedly higher moment capacity due to the development of soil wedge mechanisms, while ring geometries reduce cyclic displacements without sacrificing capacity. Symmetric two-way cycling perpendicular to a constant applied load induces significantly greater accumulated rotations compared to unidirectional loading, underscoring the limitations of current unidirectional-based design approaches. To extend the parameter space, a 3D finite element modelling framework was developed using the SANISAND-MS constitutive model in ABAQUS. Calibrated against experimental results, the model reproduces key aspects of monotonic and cyclic foundation response, including accumulated displacements, stiffness evolution, and failure mechanisms. It further provides insight into contact area evolution, critical for satisfying gapping criteria in design guidelines. Parametric studies highlight the influence of geometry and embedment depth, offering pathways to optimise foundation performance under monotonic loading. This work provides a novel experimental dataset and a validated numerical framework to inform the development of more accurate, efficient design methodologies for wind turbine gravity-based foundations, with broader relevance to both offshore and onshore infrastructure in granular soils.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Ifeobu, Chisom

Advisors dc:contributor.advisor

• Haigh, Stuart
• Abadie, Christelle

• centrifuge modelling
• numerical modelling
• shallow foundations
• offshore engineering
• soil-structure interaction

Licence

• https://www.repository.cam.ac.uk/bitstreams/f83b44fa-eb1e-41e7-8450-edae27c6d9e2/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.124852

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/395305