Experimental Studies on Extraction of Modified Suction Caisson (MSC) in Sand by Reverse Pumping Water

Abstract

A suction caisson can be extracted by applying reverse pumping water, which cannot be regarded as the reverse process of installation because of the dramatically different soil-structure interaction behavior. Model tests were first carried out in this study to investigate the extraction behavior of the modified suction caisson (MSC) and the regular suction caisson (RSC) in sand by reverse pumping water. The effects of the installation ways (suction-assisted or jacking installation) and the reverse pumping rate on the variations of the over-pressure resulting form reverse pumping water were investigated. It was found that neither the RSC nor the MSC can be fully extracted from sand. When the maximum extraction displacement is obtained, the hydraulic gradient of the sand in the suction caisson reaches the critical value, leading to seepage failure. In addition, the maximum extraction displacement decreases with the increasing reverse pumping rate. Under the same reverse pumping rate, the final extraction displacements for the RSC and MSC installed by suction are lower than those for the RSC and MSC installed by jacking. The final extraction displacement of MSC is almost equal to that of the RSC with the same internal compartment length. Based on the force equilibrium, a method of estimating the maximum extraction displacement is proposed. It has been proved that the proposed method can rationally predict the maximum extraction displacement and the corresponding over-pressure.