Abstract: In recent years, the slurry shield method has been extensively used for tunneling under seas or rivers. In the process of slurry shield construction, opening the chamber under air pressure has always been a high-risk and difficult task. The key to the success of opening the chamber under air pressure lies in the filter cake airtightness property. However, there has been less theoretical research on the mechanism of failure of filter cake airtightness property, airproof time and its influencing factors. Therefore, considering the effects of air pressure and pore water, we establish a transient mechanical model "percolation initiation–failure under air pressure" of filter cake based on multiphase flow theory, and propose a method for predicting water discharge mass through filter cake and airproof time under air pressure. Then, we conduct the laboratory filter cake airproof test to verify the applicability of the proposed theoretical approach. Finally, the influences of air pressure, stratigraphic parameters, filter cake thickness, slurry shear strength and other parameters on filter cake airproof time are discussed, and the results reveal that the airproof effect mainly depends on the filter cake under air pressure, followed by infiltration zone. This study can provide some reference for the safety of opening chamber under air pressure in slurry shield.

Key words: slurry shield, opening chamber under air pressure, filter cake, airproof time, airtightness property