Soil Improvement of EPBS Construction in High Water Pressure and High Permeability Sand Stratum

A mud-water balance shield is the preferred method for the high permeability and high water pressure stratum, but when restricted by construction and environmental conditions, the shield must be constructed with the earth pressure balance shield (EPBS). The risk of slag spraying is extremely high during construction, and this often results in great hidden dangers that threaten workers' safety during the construction of the tunnel. Slag improvement is an effective measure to prevent slag spraying, and the relevant research is bringing more and more attention to this activity. Based on the background for the tunnel project of Shangteng-Dadao Section of the No. 1 line for Fuzhou Rail Transit, ratio method is proposed for the combined application of sodium bentonite-carboxymethyl cellulose-polyacrylamide adopted by laboratory test focusing on the challenge of residual soil spraying for earth pressure balance shield under the stratum with high water pressure and high permeability; consequently, the best improvement program is suggested for the construction using earth pressure balance shield on this typical kind of stratum, which can be briefly described as the respective mixing of 2.5% and 0.5% accounting for the sand volume by swelling soil with a concentration of 10%, sodium bentonite-CMC mixed mud with a concentration of 5%, and polyacrylamide solution with a concentration ranging from 3% to 4%; furthermore, the results for the field application are random inspected.