A multi-field model for growth and dissipation of excess pore water pressure induced by slurry shield tunneling in semi-confined aquifer

Abstract

This study focuses on the mechanism of slurry infiltration in front of the tunnel face during the construction of a slurry shield machine. A multi-field transient model is proposed to describe the growth and dissipation of the excess pore water pressure and the deposition of bentonite particles for slurry shield tunneling in the saturated semi-confined aquifer. Based on the conservation principle, the governing equations for the mass continuity of bentonite particles and volume continuity of slurry are derived with consideration of particle deposition and the elastic storage of the aquifer. The proposed model is validated by field measurements. The results indicate that the excess pore water pressure drops steeply close to the tunnel face and then gradually decreases to a stable value over several tunnel diameters due to the retardation of the infiltration zone. The retardation effect is positively correlated with the permeability coefficient of the soil and the filtration coefficient, while it is negatively correlated with the specific storage coefficient. The penetration distance of bentonite particles decreases with smaller soil pores and a higher slurry concentration. Besides, a quantitative equation is proposed to evaluate the influence of slurry concentration, filtration coefficient, and storability of the soil on slurry support efficiency.