Model tests on penetration and extration of modified suction caissons in clay

A series of model tests are conducted to investigate the installation and extraction behavior of the modified suction casson(MSC) embedded in marine clay by taking the MSC dimensions, shear strength of clay and installation method into account. It is found that the discrepancies between the final penetration depths of the MSC with the aspect ratio of 1.0 and 2.0 and the corresponding regular suction caissons (RSCs) are 2% and 6%, indicating that the MSC can penetrates into the clay to a desired depth. During suction-assisted installation, the internal compartment and the external skirt are found to disturb the soils around the caisson, leading to the decrease of the penetration resistance compared with the penetration resistance during jacking installation. Based on the limit equilibrium method, the expressions for estimating the required suction to penetrate the MSC into clay and the penetration resistance were proposed. In addition, the variations of the water pressure in the suction caisson and uplift resistance during suction caisson extraction are also obtained. The results show that the water pressure in suction caisson firstly increases sharply to the maximum value with the extraction displacement, and then decreases to a certain value. It is also found that the MSCs and RSCs can not be fully extracted by injecting water into the caisson. The expression obtaining the extraction resistance of the MSC is proposed to guide the foundation design.