Extraction behavior of a scaled suction caisson in sand under water injection: effects of injection rate and prediction of extraction resistance

The scaled suction caisson (SSC) is an innovative alternative foundation for offshore engineering. The extraction behavior of the SSC for reuse when decommissioning is worth further exploration. This paper investigates the effects of water injection rate on the overpressure, final extraction height, extraction velocity, and soil heave of the SSC by carrying out model tests. Results show that water injection rate significantly affects the maximum overpressure of the SSC, whereas the regular suction caisson (RSC) is unaffected by variations in injection rate. The extent of soil heave around the SSC expands progressively with increasing injection rates, reaching up to 1.69 times the caisson diameter. Furthermore, the SSC extraction velocity increases linearly with the injection rate, whereas the final extraction height decreases monotonically. The mechanism of the increase in SSC maximum overpressure with increasing water injection rates, and the generation mechanism of soil heave around the SSC, are analyzed. Considering the effect of water injection rate, a calculation model for the extraction resistance of SSCs is developed to determine the required applied overpressure.