Set-up and Pullout Mechanism of Suction Caisson in a Soft Clay Seabed

Based on a specially designed experimental system, a series of model tests have been performed in order to investigate the set-up and pullout mechanism of a suction caisson in soft clay. Test results indicate that the residual “active” suction after caisson installation is beneficial to its pullout capacity. Different set-up times have little influence on caisson capacity as long as the negative pore pressures around the caisson fully dissipate. When the model caisson is pulled vertically, the external side friction first reverses, and then the inner side friction is gradually mobilized at a small displacement; afterwards, the reverse end bearing resistance near the caisson tip starts to work; finally, the “passive” suction under the top cap develops and helps to keep the interior soil plug moving together with the up-lifting caisson. In general, the pullout resistance would reach its peak within a displacement less than 10% of embedded caisson length.