Pilot test and consolidation theory of marine dredged slurry using the membrane-free horizontal-vacuum method

Abstract

Laboratory tests and theoretical analyses were conducted to investigate the membrane-free horizontal-vacuum (MFHV) method for inducing seepage consolidation in dredged marine fills. First, six well-designed tests with dredged marine slurry were conducted to simulate the consolidation behaviour with a prefabricated horizontal drain (PHD). The dewatering features under MFHV conditions were studied with respect to the drainage rate, settlement, water content, and permeability. The dewatering rate saltation (DRS) problem was systematically investigated by observing the changes in the supernatant water. The results indicated that the DRS problem existed in the case of the thin slurry layer rather than the thick slurry layer. Furthermore, a modified consolidation model was proposed considering the vacuum boundary and critical gradient. An explicit solution was provided to calculate the average consolidation degree and settlement. The settlement and DRS points obtained from the model tests and analytical solutions were compared. The results showed that the proposed analytical method could reasonably predict the consolidation behaviour of the MFHV method. In addition, a parameter study was conducted to investigate the influence of the critical gradient, void ratio, and compression index on seepage consolidation. Finally, an equation to design the optimum drain space for the MFHV-treated slurry was presented for direct engineering practice.