Change of pore water pressure in soil as filter cakes formed on excavation face in slurry shield

To ensure the stability of excavation face in slurry shield, a filter cake with low permeability must be formed on the working face. Based on the filter cake, part of the slurry pressure can transform into effective stress. Then the slurry pressure can counteract the soil pressure and water pressure in the soil. The variation of slurry pressure as forming a filter cake and its influencing factors are still unknown at present. With regard to the problem, a slurry infiltration apparatus is developed and a series of pressure filtration tests are carried out on 12 different slurries. By measuring the change of the excess pore water pressure as forming a filter cake and analyzing its influencing factors, the working mechanism of the filter cake is identified. The test results indicate that the slurry pressure is transformed into three different parts: pore pressure to counteract the water pressure, excess pore water pressure, and effective pressure to counteract the soil pressure. The excess pore water pressure rapidly decreases in the filter cake, then reaches a steady value in the deep zone of soil. The density of slurries is one of the primary factors that influence the distribution of the excess pore water pressure, while the viscosity has little effect on it. This study has an important directive significance for setting slurry pressure and adjusting slurry in slurry shield.