Influence of Complex Addition of EDTA and Xanthan Gum on the Properties of Seawater Slurry

The stabilization of slurry properties in slurry shield tunneling is the key to form a slightly permeable filter cake on the excavation surface and to effectively balance the soil-water pressure in the ground. The deterioration of slurry properties due to seawater intrusion is mainly caused by the high salt concentration, especially the concentration of divalent cations such as Ca²⁺, Mg²⁺, etc. To address the issue of the deteriorating slurry properties due to seawater, study on the effects of adding sodium carbonate, ethylenediaminetetraacetic acid (EDTA), and xanthan gum were conducted to a slurry with bentonite to seawater ratio of 3:50. Variations in slurry density, Marshall's funnel viscosity and 2 h bleeding rate were measured. The experimental results indicate that: The addition of sodium carbonate increased the slurry density, while EDTA and xanthan gum alone have minimal impact on the slurry properties. However, when EDTA and xanthan gum were added with a ratio of 10:1, the 2 h bleeding rate of the slurry decreased by 50%. The characteristic particle size d₈₅ of the particles in the slurry and their zeta potential test results showed that the stability of the slurry and its colloidal properties were less relevant. The complex addition of EDTA and xanthan gum significantly improved the stability of the slurry, because EDTA chelated divalent cations in the seawater, which restored the thickening capacity of xanthan gum. The results are important guidelines for the development of cation-resistant thickeners to enhance the stability of seawater slurries.