Effect of Vertical Cyclic Load Characteristics on the Response of Suction Bucket Foundations
Authors
Clausen, Kristian Gordon ; Thangaratnam, Nhivejen ; Pilsudskis, Redas
Term
4. term
Education
Publication year
2022
Submitted on
2022-06-09
Pages
314
Abstract
Offshore wind farms are moving farther from shore into deeper waters, increasing both environmental loads and costs for conventional foundations. Suction bucket foundations offer a potentially more economical alternative, yet their behavior under vertical cyclic loading in deep water remains insufficiently understood. This thesis investigates how vertical cyclic load characteristics—specifically force ratio, load amplitude, and frequency—affect the response of a suction bucket foundation installed in dense sand. The approach uses laboratory model tests in a pressurized tank simulating 20 m water depth, applying a range of cyclic loads and frequencies and measuring displacements and excess pore water pressures; displacements are normalized by bucket diameter and the sand is characterized with CPT. Findings indicate that force ratio and loading amplitudes significantly influence displacement patterns of the bucket, while loading frequency governs the buildup of excess pore pressure, which can lead to soil liquefaction. Moreover, repeated cycling degrades soil stiffness. The study provides experimental insights to inform the design and assessment of suction bucket foundations for offshore wind applications.
Offshore vindmøller flyttes længere fra kysten og ud på større vanddybder, hvilket skærper kravene til både bæreevne og økonomi for fundamenter. Sucker-spandsfundamenter kan være et billigere alternativ, men deres opførsel under lodret cyklisk last i dybt vand er utilstrækkeligt belyst. Denne afhandling undersøger, hvordan lodret cyklisk lastkarakteristik – herunder kraftratio, lastamplitude og frekvens – påvirker responsen af et suction bucket-fundament installeret i tæt sand. Metoden er laboratoriemodeller i en tryktank, der simulerer 20 m vanddybde, hvor en række cykliske laster og frekvenser påføres, og forskydninger samt overskydende porevandstryk registreres; forskydninger normaliseres med spanddiameter, og jorden karakteriseres ved CPT. Resultaterne viser, at kraftratio og lastamplituder har markant indflydelse på forskydningsmønstre for fundamentet, mens belastningsfrekvensen påvirker opbygningen af overskydende poretryk, som i yderste konsekvens kan føre til likvefaktion. Desuden observeres, at gentagen cykling degraderer jordens stivhed. Arbejdet leverer eksperimentelle indsigter, der kan støtte dimensionering og vurdering af suction bucket-fundamenter til offshore vind.
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