Attitude Control Criteria for Non-Closed Segmental Lining Rings and Bolts Under Asymmetric Loading

Synchronous Thrust and Assembly Technology (STAT), which enables simultaneous shield propulsion and segment erection, can improve tunneling efficiency and reduce construction duration compared with conventional shield tunneling. However, during STAT construction, thrust from shield tail jacks directly acts on incomplete segmental lining rings before ring closure. Differential jack strokes caused by shield attitude fluctuations and segment assembly errors may therefore induce localized asymmetric stress distributions, resulting in segment deflection, joint misalignment, and potential structural damage. To evaluate these risks, this study develops a case-based methodological framework for assessing the mechanical safety of incomplete segmental lining rings and bolts under asymmetric loading conditions, using the Shanghai Rail Transit Airport Link Line tunnel as the engineering case. A refined finite element model was established to analyze the critical deflection behavior of incomplete segmental lining rings subjected to jack thrust during assembly. Field tests were conducted to monitor bolt mechanical responses under STAT conditions and to provide engineering validation for the numerical results. In addition, the critical differential jack stroke was determined based on the shield machine’s maximum design turning radius and shield tail clearance. Within the modeled one- to three-segment assembly stages, the inter-segment restraint progressively increased, reducing segment deformation and bolt loads. No saturation of the clamping effect beyond the third segment was claimed. The simulated maximum segment deflection angle corresponds to a differential jack stroke below the shield kinematic limit of 21.9 cm. To maintain the mechanical safety of incomplete segmental lining rings within the investigated project conditions, the segment deflection angle should be controlled below the minimum damage initiation angle of 0.4°. The numerical model evaluated bolt responses during the single-segment stage; however, field measurements were available only after the second segment installation and therefore did not directly validate the most unfavorable single-segment stage. By integrating segment damage thresholds, bolt stress responses, shield tail clearance, and jack stroke constraints, project-specific attitude deviation control criteria were proposed for the investigated large-bore shield-driven tunnel. It should be noted that these criteria were derived from a specific finite element model and limited field measurements from one engineering case; therefore, recalibration and further validation are required before applying the proposed thresholds to shield tunnels with different diameters, segment geometries, geological conditions, or shield machine configurations.