Effects of acidity and magnesium ions on the self-weight consolidation settlement of Tianjin dredged fill

Abstract

The properties of a soil, either in situ or at a hydraulic reclamation site, may change if influenced by the chemical status of the surroundings. Acidity, indicated by the pH, and magnesium (Mg2+), sometimes used to reinforce soil, are good indicators of the chemical environment. It is therefore worth investigating how acidity and Mg2+ affect the settling of dredged fill. In this study, a cylinder model test and ethylenediaminetetraacetic acid (EDTA) titration were used to investigate the mechanisms behind self-weight consolidation settlement. The results indicated that the settlement process of the dredged fill occurred in three stages and that the consolidation settlement process of the dredged fill varied as the pH and mass percentage of Mg2+ varied. As the pH increased from an initial low value, the settlement amount and settlement rate of the dredged fill approximated to a quadratic function trend and increased first and peaked when the pH was 4 and then decreased, reflecting the influence of the mineral composition of the soil and the Zeta potential of the soil particles. Under medium pH conditions, the settlement amount and settlement rate increased in an approximately linear manner, reflecting increases in the mass percentage of Mg2+ and changes in the double electric layers on the clay mineral surface.