Experimental study on effects of different cations on stability of slurry within slurry shield

In view of the problem that the high-salinity stratum intrusion during construction of submarine tunnels by the slurry shield will lead to the decrease of the stability of slurry, this study aims to investigate the effects of different salt solutions on the stability of slurry via colloidal flocculation mechanism by adding salt solutions into slurry and testing change of the parameters such as bleeding rate, zeta potential, characteristic particle sizes and seepage discharge of the slurry. The results show that compared with that by adding fresh water, the slurry by adding 1% salt solution in which the quality of water is 15 times that of bentonite, the zeta potential of slurry decreases, and its characteristic particle sizes and seepage discharge increase. The salt solution affects the stability of slurry mainly by decreasing its zeta potential, which promotes slurry particles to flocculate and to dilute the slurry. When the mixing ratio is more than 5% and keeps to increase, if the salt solution is NaCl, the zeta potential changes a little and then keeps steady, and the characteristic particle size d₁₀ of the slurry continues to increase, while d₅₀and d₈₅ remain basically the same. The particles of slurry coagulate, and the slurry remains stable and does not bleed. If the salt solution is CaCl₂ or MgCl₂, the zeta potential decreases continuously, the characteristic particle sizes d₁₀, d₅₀ and d₈₅ remain basically unchanged, resulting in flocculation and bleeding. Ca²⁺ and Mg²⁺ have a greater influence on the stability of slurry than Na⁺. Therefore, when using the slurry shield to excavate the subsea tunnels in different sea areas, the effects of groundwater on the stability of slurry should be considered in accordance with the chemical type of groundwater.