Numerical analysis of slurry penetration and filter cake formation in front of tunnel face

Abstract

The bentonite slurry penetration in front of the tunnel face significantly influences the face stability during slurry shield tunneling. In this study, the mechanism of slurry-soil interaction is clarified through the soil microstructural evolution. A transient model coupling the slurry transport and deposition theory is proposed to estimate the slurry penetration and filter cake formation. The time-dependent parameters are considered, including the flow parameters (flow path and pressure gradient) and the hydraulic resistance of soils (soil permeability, porosity, and shear resistance). The proposed model is compared with the infiltration column tests and shows a good agreement.Moreover, a parametric study is conducted to investigate the influence of the soil and slurry properties on the slurry-soil interaction. The results indicate the soil-bentonite relative size is the main factor influencing the formed filter cake type. The filter cake of type Ⅲ (external filter cake and penetration zone) could be formed when the bentonite particle size is between the range of 0.01d10–0.5d10. This type of filter cake has good tightness and could help to improve the face stability when tunneling by slurry shield machine.