Insights into hydraulic gradients on slurry infiltration characteristics in saturated sands

In slurry shield tunneling, pressurized slurry infiltrates into the ground ahead of a tunnel face to generate a dynamic heterogeneous filter cake, over which the hydraulic gradients fluctuate due to cutting disturbances. This study aims to experimentally investigate the effects of hydraulic gradients on slurry infiltration characteristics by conducting modified infiltration column tests on four sandy soils with different particle-size distributions, subjected to four hydraulic gradients under fixed slurry pressure conditions. The results showed that the slurry infiltration process could be divided into three stages based on the Peclet number: the mud spurt, the deep-bed filtration, and the filter cake formation. Across the tested hydraulic gradients, both the filter cake formation time and the mud spurt duration increased linearly with the soil particle size d 15 , exhibiting greater sensitivity to lower hydraulic gradients. It was found that the final slurry infiltration distance initially increased and then decreased as the hydraulic gradient raised. Additionally, the critical hydraulic gradient corresponding to the maximum final slurry infiltration distance decreased with d 15 . The slurry infiltration distances and the deposition of bentonite particles were further validated through visualized infiltration tests and the measured porosity profiles. Furthermore, the filter cake exhibited a hydraulic conductivity ranging between 1 × 10 –9 and 8 × 10 –9 m/s, inversely proportional to the hydraulic gradient.