Vacuum preloading combined with multiple-flocculant treatment for dredged fill improvement

Abstract

As dredged slurry has high water content and low shear strength, and mainly consists of fine-grained particles, clogging frequently occurs around prefabricated vertical drains (PVDs) during vacuum preloading, often leading to insufficient consolidation and poor geotechnical properties of soil. To address this issue, this paper proposes a method of multiple-flocculant treatment combined with vacuum preloading for improving dredged slurry. This is achieved by pre-treating the dredged slurry with lime and anionic polyacrylamide (APAM) prior to vacuum preloading. In this method, the additions of lime and APAM in a certain quantity allow small particles to form larger-sized mass, i.e. they flocculate, thereby increasing the void ratio and permeability. This results in the formation of a new natural soil that is easier to be consolidated by vacuum preloading. To verify the effectiveness of the proposed method, the optimum ratio of lime content to APAM content was preliminarily determined by performing a deposition experiment. A vacuum preloading test was carried out after the pre-treatment with lime and APAM. The experimental results show that with the help of APAM, the shear strength and consolidation efficiency further improve in comparison to the slurry treated with only lime. Finally, the optimum ratio of lime to APAM contents for vacuum preloading was determined as 2:0.1.