Pressure transfer patterns under different conditions of filter cake formation for slurry shield tunnelling

Filter cake is crucial for tunnel face stability during slurry shield tunnelling in the saturated sand, as it can efficiently transfer the slurry pressure to the effective support pressure. Type of filter cake determines the pattern of pressure transfer on the tunnel face. But individual differences among the patterns have not been well understood. This article checks the mechanisms of pressure transfer under different conditions of filter cake formation. It is shown that, when there is an external filter cake with an internal infiltrated zone formed, the pore pressure will decrease more slowly in the slurry-infiltrated soil than in the original soil, especially for the high bentonite concentration. However, more bentonite particles enter the soil pores for the lower bentonite concentration. If only an external filter cake is formed, the filtration loss will be significantly reduced, and the pore pressure will quickly decrease to the hydrostatic pressure. If only an internal infiltrated zone formed, the pore pressures will gradually decrease till the slurry stops infiltrating. The pore pressures may maintain a high value even after 1 h. In practice, the applied slurry pressure should be adjusted considering the condition of the filter cake formation.