Effect of seawater on bentonite slurry and its infiltration behavior into saturated sand for tunnelling

The slurry shield tunneling method has been widely used in the construction of underwater tunnels. However, during the construction of submarine tunnels, seawater can influence the engineering properties of bentonite slurry, which can cause excavation instability and other problems. This study aims to investigate the effect of seawater on the properties of bentonite slurry for shield tunneling, including the basic slurry and filter cake properties. Additionally, the infiltration behavior of the slurry after filter cake formation was also studied, the following results being obtained: (1) With an increase in seawater content, the bleeding rate and filtration volume of the slurry increased, and the rheological parameters decreased. (2) With an increase in seawater content, the permeability coefficient of the filter cake increased considerably. Microstructure analysis showed that the agglomeration of particles in the filter cake caused by seawater contamination increased the permeability of the filter cake. (3) The slurry infiltration tests indicated that the infiltration distance increased with increasing seawater content. Additionally, the infiltration of slurries with seawater could not effectively reduce the permeability coefficient of the tunnel face, which could lead to instability of the tunnel face. The findings of this study provide a reference for slurry preparation and stability analyses of submarine tunnel excavations.