Mud Spurt Distance and Filter Cake Hydraulic Conductivity of Slurry Shield

Maintaining stable tunnel face pressure in slurry shield tunneling is critically dependent on the formation of a low-permeability filter cake. However, the knowledge of the filter cake and mud spurt is not specifically understood. Using a modified fluid loss test, this study investigates the formation and hydraulic properties of filter cakes from various slurry mixtures under different pressures. The key findings reveal that CMC-Na (sodium carboxymethyl cellulose) serves as the most effective additive for enhancing slurry performance. A comprehensive database of constitutive model parameters for 15 slurry compositions was established, enabling precise prediction of the filter cake’s hydraulic conductivity and void ratio under any pressure. Analysis of the cyclic formation process revealed that the dynamic filter cake averages two-thirds of the maximum thickness, offering a key parameter for stability control. Furthermore, a practical mud spurt model was proposed that predicts slurry penetration by avoiding the need for site-specific empirical constants or complex column tests, relying instead on standard geotechnical and slurry parameters. The results provide practical criteria for filter cake formation and directly applicable models to optimize slurry design, thereby enhancing the control and safety of shield tunneling.