ABSTRACT
Bentonite slurry pressured with air pressure has been widely used to support the face of shield tunnels, particularly in saturated sandy ground. Due to the pressure difference between the bentonite slurry and the pores in the soil, the bentonite slurry will infiltrate into the pores in the soil. Partial support pressure applied through bentonite slurry will thus be present as an excess pore water pressure rather than be carried directly onto the soil grains. In this case, the support pressure at the tunnel face will be reduced. The infiltration, therefore, is of importance for the stability of tunnel face. In this paper, a series of tests of bentonite slurries, pressured against saturated sand were presented. Mud spurt and consolidation characteristics of the bentonite slurry were examined. It appears that the permeability of the sand for the bentonite slurry is considerable lower than that for water. The filter cake will impede the fluid discharged from the bentonite slurry, and thus will exponentially reduce the permeability of the sand for the bentonite slurry. It also indicates adding bentonite decreases the permeability of the sand for the bentonite slurry.
