Laboratory tests on soil-skirt interaction and penetration resistance of suction caissons during installation in sand

As a new form of offshore foundation, suction caissons have been applied to several offshore wind power projects. In the present study, a series of tests were carried out based on laboratory scales with an aim to investigate the interaction mechanisms between the caisson and saturated sand in both jacking installation and suction installation processes. For the jacking installation, the results indicate that the inner soil pressure acting on the skirt of the caisson is equivalent to the outer when the relative sensor depth (h/D, where h and D are the sensor depth and the diameter of the caisson, respectively) is less than about 0.3. The inner soil pressure, however, exceeds the outer when h/D>0.3. For the suction installation, the results show that the inner soil pressure is dramatically reduced once stable suction is applied. In contrast, the outer soil pressure increases at first and then falls down to a stable level rapidly when stable suction is applied. Based on the test results, the previous formulae of the penetration resistance and required suction of caissons have been revised and evaluated.