Soil Conditioning Technology for EPB Shield in Water-Rich Sandy Stratum

The water-rich sand has the characteristics of poor flow plasticity and high permeability, which is easy to cause unsmooth soil dumping and water spewing during the Earth Pressure Balance (EPB) shield construction. For the EPB shield project of Xi’an Metro Line 10 crossing the water-rich sandy stratum, this paper used bentonite slurry and foam agent to condition the flow plasticity and decrease permeability of sand, put forward the flow plasticity evaluation method for conditioned sand, and determined the optimum conditioning scheme with workable flow plasticity and permeability, so as to provide reference for the project. The following conclusions are drawn from the study. (1) The flow plasticity is workable when the conditioned sand after slumping has no cracking or collapse, the slump shape is pear shaped, the slump is 180 ~ 210 mm, and the contact angle θ between the slumped sand and the ground is 0° ~ 90°. At this time, the permeability coefficient of the conditioned sand with workable flow plasticity is about 10^-5 cm/s within 90 minutes, meeting the engineering requirements. (2) The optimum conditioning scheme is to maintain the mass ratio of sand, bentonite and water between 200:1:40 ~ 200:1.5:44, with a volume specific concentration of foam agent solution of 2% and a foam injection ratio of 6%.