An experimental study on water migration near clay–caisson interface under long-term cyclic loading

Suction caissons are increasingly adopted as foundations for jacket-type offshore wind turbines (OWTs), where the cyclic uplift performance of windward caissons plays a decisive role in the long-term stability of the entire structure. Although numerous studies have examined the uplift response of suction caissons, the effect of water evolution in the surrounding soft clay on the uplift resistance of caissons under long-term cyclic loads remains insufficiently understood. This study conducts a series of 1 g model tests to explore the coupled evolution of uplift resistance and interfacial water content under varying lid sealing conditions, cyclic displacement amplitudes, and loading frequencies. The results show that, in addition to the commonly observed rapid decay of uplift resistance caused by strain-softening behavior of the clay during initial cycles, a secondary degradation stage occurs during subsequent long-term cyclic loading, driven by the transformation of loosely bound water to free water and its continuous migration toward the clay–caisson interface. Cyclic displacement amplitude dominates interfacial hydro-mechanical processes, and the sealing conditions of caisson lids show a significant influence on the extent of water migration. The findings in this study provide novel experimental evidence for elucidating service performance degradation mechanisms of suction caissons in clay.