Tunnel Face Stability During Slurry-Shield Tunnelling in Saturated Cohesionless Soil Considering Slurry Infiltration

The pressurised bentonite slurry efficiently stabilised the tunnel face, but slurry infiltration may reduce its effectiveness. In this work, the effect of slurry infiltration on tunnel face stability during slurry-shield tunnelling in saturated cohesionless soil is investigated, and the results reveal that due to slurry infiltration, an additional margin for support pressure is needed. The infiltration distance has a significant influence on the effective support at the tunnel face. For slurries with a low viscosity (apparent viscosity = 4 mPa·s), only when the infiltration distance is small (< 0.5 m) is the effective support ratio high (> 80%). Furthermore, a larger infiltration distance or a larger value of tunnel diameter to cover depth ratio (C/D) requires a higher support pressure. Generally, the hydraulic gradient at the face in an unconfined aquifer is greater than that in a semi-confined aquifer. For semi-confined aquifer, a smaller height or a larger leakage length leads to a greater hydraulic gradient. Finally, for shield tunnelling in an aquifer, when the gradient at the tunnel face is less than 1, a viscous slurry is recommended to replace the pure water to support the tunnel face.