Influence factors of extraction behavior of modified suction caisson in sand by reverse pumping water

The suction caisson for offshore engineering features fast installation and reuse. When offshore engineering structure supported by a suction caisson is decommissioned, the suction caisson can be extracted by reverse pumping water for reuse and being replaced by a larger one. Model tests were conducted to investigate effects of the installation methods, extraction methods and pumping rate on the extraction behavior of both the regular suction caisson (RSC) and modified suction caisson (MSC) in sand. It was found that when the seepage failure occurs in and around the caisson, the extraction by reverse pumping water is terminated. Under the same pumping rate, the final extraction height and the maximum overpressure beneath the caisson lid of the MSC are greater than those of the RSC. The final extraction heights of caissons installed by jacking are greater than those installed by suction. Model tests on the extraction of suction caissons by pumping air was also conducted and it was found that final extraction heights of the RSC and the MSC which were extracted by reverse pumping water are greater than those extracted by reverse pumping air. Further, extraction tests of Perspex-made suction caisson were conducted to investigate the difference between the extraction behavior of suction caissons by reverse pumping water and air into the caisson.