Buoyant Tower: Experimental and Numerical Studies on Anti-Rotation Behavior of Suction Caisson Foundation

Abstract The buoyant tower, or BT, is composed of a hull and a suction caisson foundation (SCF). The hull can be one or a group of cylindrical cells, while the SCF should be a short open-bottomed cylinder welded to the end of the hull, holding it to the seabed. The first application of BT technology is the CX-15, a production platform in the Corvina Field offshore Peru. The 13-year operation since 2012 has validated the reliability of BT technology. The SCF of CX-15 is subjected to wave-induced torsional moments constantly. After the initial installation, before the disturbed surrounding soil re-consolidated, it may have a potential tendency to rotate. In addition, the SCF in the BT system may encounter large torsional moments under severe sea states or when adapted for offshore wind applications, i.e., w.BT. This study investigates the performance of SCFs under torsional moments, employing numerical simulations and centrifuge tests to validate the reliability and optimization of SCF designs. Using the CX-15 platform as a case study, the anti-rotation capacity and relevant behaviors of SCFs under a 100-year-return-period sea condition were analyzed. Relevant centrifuge tests were carried out. The results demonstrate that the SCF of the CX-15 platform is able to withstand the wave-induced torsional moments, ensuring its stability. Building upon these findings, the study explores the feasibility of improving torsional resistance through the optimization of finned-SCF (additional plates along the cylindrical SCF) design. The analysis reveals that, compared to merely increasing the diameter of the suction caisson, adding fins significantly enhances torsional resistance. Extending fin length and adding fin numbers prove to be efficient methods to further enhance torsional resistance, with the optimal configuration identified as the addition of 4 fins. Moreover, test results indicate that the reduction in lateral bearing capacity due to added fins, a potential issue given the rolling motion inherent to the BT concept, is limited and does not compromise overall performance.