Uplift Capacity of Suction Caissons under Sustained and Cyclic Loading in Soft Clay

In soft marine clays, suction caissons provide a foundation system for tidal current turbines that further promote the sustainable nature of the system by allowing for their removal at the end of the structure’s design life. When configured as a multipod, the moment loads resulting from the horizontal flow of water will be transferred to the suction caissons as compression–uplift loads on opposing foundation legs. The behavior of a suction caisson in soft clay was investigated at aspect ratios of 1 and 2 under monotonic and cyclic vertical loading applicable to multipod-supported tidal current turbine design. Installation and solely monotonic vertical load tests indicated lower back-calculated adhesion factor, α, values and higher back-calculated bearing capacity factor, Nc, values than design standards recommend. The capacity and stiffness response of the foundation after undergoing cyclic loading was found to be largely dependent on the magnitude of displacement the foundation underwent during cyclic loading. Additionally, a threshold of elastic foundation response was observed during cyclic loading defined by a cyclic displacement amplitude. These results indicate serviceability constraints will be critical in the design of suction caisson foundations for tidal current turbine applications.

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Dynamic Characteristics of Saturated Soft Clay under Constant Confining Pressure Cyclic Loading

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/619/1/012083 ◽

2020 ◽

Vol 619 ◽

pp. 012083

Author(s):

Yuan Lu ◽

Fusheng Liu ◽

Youyan Bian ◽

Yu Zhong ◽

Bin Chen ◽

...

Keyword(s):

Cyclic Loading ◽

Dynamic Characteristics ◽

Soft Clay ◽

Confining Pressure ◽

Saturated Soft Clay

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Modeling of Stress-Strain Behavior of Soft Clay under Cyclic Loading

Geotechnical Engineering for Disaster Mitigation and Rehabilitation ◽

10.1007/978-3-540-79846-0_26 ◽

2009 ◽

pp. 277-283

Author(s):

Yuanqiang Cai ◽

Jun Wang

Keyword(s):

Cyclic Loading ◽

Soft Clay ◽

Stress Strain ◽

Strain Behavior

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Uplift Capacity of Suction Caissons in Sand for General Conditions Of Drainage

10.1115/omae2021-61663 ◽

2021 ◽

Author(s):

Ragini Gogoi ◽

Charles P. Aubeny ◽

Phillip Watson ◽

Fraser Bransby

Keyword(s):

Constitutive Model ◽

Load Capacity ◽

System Capacity ◽

Soil Conditions ◽

Uplift Capacity ◽

Soil Response ◽

Dense Sand ◽

Centrifuge Tests ◽

Numerical Predictions ◽

Suction Caissons

Abstract Suction caissons have emerged as a viable solution for the foundations of offshore wind turbines, which are gaining momentum worldwide as an alternate energy source. When used in a multi-bucket jacket system, the system capacity is often governed by the uplift capacity of the windward bucket foundation. Seabed conditions at offshore windfarm sites often comprise dense sand where the soil response may be drained, partially drained or undrained depending on the loading regime, the foundation dimensions and the soil conditions. Given the large difference in uplift capacity of caissons for these different drainage conditions, predicting the behavior of a suction caisson under a range of drainage conditions becomes a paramount concern. Consequently, this paper presents the findings of a coupled finite element investigation of the monotonic uplift response of the windward caisson of a multi-bucket jacket system in a typical dense silica sand for a range of drainage conditions. The study adopts a Hypoplastic soil constitutive model capable of simulating the stress-strain-strength behavior of dense sand. This choice is justified by conducting a comparative study with other soil models — namely the Mohr Coulomb and bounding surface sand models — to determine the most efficient soil failure model to capture the complex undrained behavior of dense sand. The numerical predictions made in this study are verified by recreating the test conditions adopted in centrifuge tests previously conducted at the University of Western Australia, and demonstrating that the capacity from numerical analysis is consistent with the test results. The Hypoplastic soil constitutive model also provides an efficient method to produce accurate load capacity transition curves from an undrained to a drained soil state.

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