Upper-Bound Limit Analysis of Slurry Shield Tunnel Face Under Seepage Conditions

Ensuring face stability is a pressing concern in slurry shield tunneling under high water pressure. Although slurry infiltration and filter cake formation are known to affect stability, the governing role of seepage forces in the failure mechanisms remains insufficiently understood, and existing models often oversimplify the regulating effect of filter cake permeability. To address this gap, a combined numerical–theoretical approach is developed that explicitly incorporates seepage effects into the failure analysis. A three-dimensional seepage model was developed to simulate transient pore water pressure distribution ahead of the tunnel face, considering filter cake properties, stratum permeability, and applied slurry pressure. Based on the computed seepage field and a wedge-prism composite failure mechanism, an upper-bound limit analysis model was formulated that accounts for the work done by seepage forces. Results reveal a filter cake permeability threshold of 1.0 × 10−7 m/s, below which further reduction yields negligible stability improvement. Parametric studies quantify the influences of internal friction angle, cohesion, depth-to-diameter ratio, and permeability contrast between soil and filter cake. Validation against field data from the Maliuzhou Tunnel demonstrated that the calculated limit pressures consistently lie below the field-measured slurry pressures, confirming the model’s reliability and its practical utility for guiding slurry pressure selection in complex ground conditions.