Centrifuge tests on a soil plug removal method for suction caisson during installation

The suction caisson is one of the most widely adopted foundation systems for supporting offshore wind turbines and anchoring floating platforms. During suction-assisted installation, the soil inside the caisson may heave and form a soil plug that prematurely contacts the caisson lid, hindering further penetration, reducing installation efficiency, and ultimately limiting the bearing capacity of the suction caisson foundation. This study introduces a new method to remove the soil plug formed during suction caisson installation that adopts an internal stirring device driven by an external motor. A dedicated centrifuge testing system was developed to study suction penetration, soil plug removal, and the pull-out resistance of suction caissons under high gravity conditions. Using this system, integrated physical model tests were carried out in both sand and clay, where the soil plug removal method succeeded in achieving its target. Tests with and without soil plug removal were performed to identify the formation mechanisms of soil plugs and to evaluate their influence on installation resistance and bearing capacity of the suction caisson foundation. The results show that the suction required for penetration increases with depth and resistance. Negative pressure inside the caisson induces inward seepage and upward movement of the internal soil, forming a plug whose height increases approximately linearly with penetration depth and eventually obstructs further penetration. The proposed stirring–based method effectively removed the soil plug, allowed the resulting slurry to be discharged smoothly, and enabled the final penetration depth to reach nearly the full skirt length. During the pull-out process, passive suction develops inside the caisson due to limited drainage and contributes increasingly to the total resistance as displacement grows. Removal of the soil plug enhanced the maximum resistance by more than 20%, primarily through increased frictional resistance along the caisson wall. This highlights the practical value of the proposed method in improving the overall performance of suction caisson foundations.