Effects of Initial Concentration on Flocculation Size and Settling Velocity of Marine Hydraulic Fill Clay

Abstract

Using marine hydraulic fill clay to reclaim land is the main mean to deal with land supply and demand in coastal area. Detecting the soil’s settling velocity, which is mainly affected by initial concentration of clay, is significant for filling projects. In this paper the marine clay of the East China Sea was used for tests to study the floc size and the settling velocity properties with different initial concentrations. According to SEM tests, it can be found that the typical floc size is about 17.5 μm in suspensions of different initial concentrations, so by using the Stokes’ formula the typical floc’s theoretical velocity is calculated. Then the settling column tests were carried out, and the formation of suspension-water interface was found related to initial concentration. When the initial concentration is 120 g L−1, the interface’s settling velocity is a little smaller than the theoretical value. As the initial concentration increased, the interface’s settling velocity reduced at a decreasing rate. Finally a modified semi-empirical formula is established to calculate the interface’s settling velocity of constant settling stage in different initial concentrations, which is significant for the study of hindered settling and the design of hydraulic fill elevation.