Session: 10-05-01: Bucket Foundations and Caissons

Submission Number: 157004

A Probabilistic Approach for Characterizing Buckling Risks in Caisson Foundations Under Suction Installation 

Suction caissons are widely employed as foundations for offshore wind turbines due to their ease of installation, cost-effectiveness, and reusability. However, the suction installation may lead to structural buckling issues. Since the structural stability of caisson skirt is highly sensitive to geometric imperfections, it is important to evaluate the effect of the imperfections on buckling capacity under hydraulic loading.

Previous studies on the buckling behavior of suction caissons adopt mainly deterministic imperfections, which are typically used to estimate the lower bound of buckling loads. The eigenmode method is often used to describe the most unfavorable imperfection shape. However, the top of the caisson is usually constrained by stiffening rings, and the bottom is open, resulting in a distribution of imperfections characterized by smaller imperfections near the top and larger ones near the bottom. The eigenmode-based approach introduces imperfections concentrated in the middle region of the free skirt, which does not align with the real imperfections. Consequently, this approach may lead to over conservative predictions of buckling loads.

Moreover, probabilistic design methods have been widely applied to thin-walled structures, but related studies for suction caissons remain limited. To address this gap, this study proposes a probabilistic method based on random Fourier coefficients to characterize the uncertainty of geometric imperfections. The optimized Fourier series can simulate various imperfection distributions. Then, the buckling characteristics of two typical suction caissons at different installation depths are analyzed, considering various imperfection types. The results demonstrate that the combination of Fourier coefficients has a significant effect on the buckling load. With the increase of axial and circumferential waves, the growth rate of the buckling load based on probabilistic method gradually decreases, and the peak buckling load declines. This downward trend is particularly pronounced for higher circumferential wave numbers. In addition, the upper and lower limits of the buckling loads are both enhanced with the increase of the installation depth, and the fluctuation of the buckling loads is more pronounced. For smaller axial and circumferential wave numbers, the predicted buckling loads based on Fourier series imperfection are higher than those obtained using the eigenmode method. In contrast, for larger wave numbers, the probabilistic method captures more unfavorable imperfection shapes than the eigenmode method, resulting in lower predicted buckling loads. This study evaluates the impact of imperfection uncertainty on buckling capacity of suction caisson in a statistical method, and provides the probabilistic distribution of buckling loads at different installation depths, which provides valuable insights for the buckling design of suction caissons.

Presenting Author: Ruizhe Xu Tianjin University

Presenting Author Biography: Education
Master of Science in Geotechnical Engineering
Tianjin University, School of Civil Engineering
September 2023 – June 2026(Expected)
Recommended for admission
Also received an offer from Zhejiang University
Bachelor of Science in Port, Channel, and Coastal Engineering
Tianjin University, School of Civil Engineering
September 2019 – June 2023

Research Interests
Geotechnical engineering and soil-structure interaction
Coastal and offshore foundation design
Probabilistic design methods in geotechnical stability

Skills
Proficient in geotechnical and structural analysis
Strong foundation in civil engineering and geotechnical design principles
Competent in engineering software: [Abaqus, Python, Matlab, etc.]
Technical writing and academic presentation