Bearing Behavior of a Monopod Bucket Foundation Supporting an Offshore Wind Turbine in Sandy Soils
Publication: International Journal of Geomechanics
Volume 23, Issue 10
Abstract
A monopod bucket foundation supporting an offshore wind turbine structure is subjected to lateral loading on account of combined wind and wave action, in addition to vertical loading from the self-weight of the turbine structure. In this numerical study, the bearing behavior of the bucket foundation in medium dense and very dense sands is investigated for varying bucket geometries, superstructure loads, and lateral loading cases. The nonlinear stress–strain response of the sandy soil is incorporated. The results of the modeling are described and evaluated in terms of the variations of displacement and rotation responses, ultimate and allowable lateral load capacities, depths of rotation center, surrounding soil deformation, and failure mechanisms. Interaction diagrams between lateral load capacity and resisting moment capacity for various limit states are presented, and their differences are brought out. As the design is dominated by requirements resulting from serviceability limit state, predictive expressions are proposed for the depth of rotation center, initial stiffness, and allowable lateral load capacity to serve as preliminary design guidelines for a monopod bucket foundation in sandy soils. The expressions are suitable for interpolation within the range of realistic parameters considered in the study.
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Data Availability Statement
Some or all data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request:
•
Subroutine code
•
Abaqus simulation files
•
All the data obtained from numerical simulations relevant to this study.
Acknowledgments
The authors are thankful to the reviewers for their valuable comments and suggestions, which have helped in improving the manuscript.
Notation
The following symbols are used in this paper:
- 1P
- frequency at which rotor blades of wind turbine spin;
- 2P/3P
- frequency due to the shadowing effect of two-bladed/three-bladed wind turbine;
- c′
- cohesion of soil;
- D
- bucket diameter;
- Ei
- initial elastic modulus of soil;
- ESoil
- modulus of elasticity of soil;
- ESoil,Ref
- soil’s reference Young’s modulus of elasticity;
- FLS
- fatigue limit state;
- H
- lateral load capacity;
- HAllowable
- allowable lateral load capacity;
- HUltimate
- lateral capacity at ultimate condition or failure;
- h
- loading height;
- Kini
- initial stiffness of wind turbine foundation system;
- Kp
- Rankine’s passive earth pressure coefficient;
- L
- skirt length;
- L/D
- aspect ratio;
- M
- resisting moment capacity;
- MAllowable
- allowable resisting moment capacity;
- MDS
- medium dense sand;
- MUltimate
- resisting moment capacity;
- SLS
- serviceability limit state;
- u
- displacement at lid level;
- ULS
- ultimate limit state;
- V
- superstructure load;
- VDS
- very dense sand;
- z
- depth of rotation center;
- γ′
- effective unit weight of soil;
- δ′
- dilation angle of soil;
- ɛ
- axial strain;
- Θ
- lid rotation at failure;
- κ, λ
- empirical parameters;
- σ1
- major principal stress;
- σ3
- confining pressure;
- σat
- atmospheric pressure;
- σm
- mean principal stress; and
- ϕ′
- internal friction angle of soil.
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Published In
International Journal of Geomechanics
Volume 23 • Issue 10 • October 2023
Copyright
© 2023 American Society of Civil Engineers.
History
Received: Jul 18, 2022
Accepted: Apr 30, 2023
Published online: Aug 8, 2023
Published in print: Oct 1, 2023
Discussion open until: Jan 8, 2024
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