Abstract: The authors develop a shield tail grease leakage model and derive key parameters through several experiments. The grease constitutive relationship and shield tail brush resistance coefficient are determined through grease shear tests and custom-designed unit grease escape tests. Based on these experiments, the authors develop an experimentally derived set of shield tail grease leakage parameters and a corresponding leakage model. In addition, the contact interaction between the shield tail brush wire bundle and the segment is simplified using the porous media theory, consequently establishing a numerical model of the shield tail sealing system. Finally, the pressure and breakdown time of each grease chamber during the external slurry breakdown of the shield tail sealing system are determined by conducting a self-made large-scale shield tail sealing model experiment, and the results correspond with the numerical simulation results. The primary conclusions of this study are as follows: (1) When the confining pressure exceeds 130 kPa, the shear yield stress of the grease becomes relatively stable. The constitutive relationship of the grease can be fitted according to the Bingham fluid model. (2) Under external slurry pressure, the grease escapes from the contact interface between the shield tail brush wire bundle and the segment′s outer wall. The obstruction effect of the shield tail brush on grease is primarily dependent on the length of the bond between the shield tail brush wire bundle and the segment. (3) Data from pressure sensors indicate that the pressure in single grease chambers synchronously reflects the external slurry pressure. However, pressures across multiple grease chambers gradually decrease along the shield tunneling direction. (4) Simulation results of single- and double-chamber scenarios reveal distinct behaviors. The breakdown pressure of a single chamber is 0.7 MPa, with the water content of the grease chamber reaching 34% during breakdown. For the double-chamber scenario, the breakdown pressure increases to 1.3 MPa, with water contents of the first and second grease chambers reaching 38% and 22%, respectively, at breakdown. The simulated breakdown time under breakdown pressure closely aligns with the experimental values, thereby validating the accuracy of the grease constitutive relationship and the resistance coefficient of the shield tail brush.

Key words: shield tail sealing, large-scale model experiments, grease fluid constitutive relation, leakage parameters of shield tail grease, porous media