Full-Scale Validation and Parametric Analysis of a Three-Dimensional Finite Element Model for Shield Tunnel Segmental Joints

To elucidate the contact-induced nonlinear response of shield tunnel segmental joints under bending, this study develops a three-dimensional finite element model based on a full-scale four-point bending test conducted on a water-conveyance tunnel. The model incorporates concrete damaged plasticity, surface-to-surface contact, and M39 bolt elements with pretension. The boundary conditions were kept consistent with those of the test, with one end modeled as a double-hinged support and the other as a simply supported end. A horizontal line load of 345 kN/m and a vertical line load of 755 kN/m were applied in the loading zone. For the contact interface, hard contact was adopted in the normal direction, while a Coulomb friction model was used in the tangential direction with a friction coefficient of 0.6; the bolt pretension was set to 420 kN. The results show that the model can satisfactorily reproduce the joint opening pattern, damage distribution, and the moment-rotation curve. At the peak stage, the joint rotation was approximately 0.037 rad, while the first distinct inflection point and the ultimate bending moment were about 380 kN·m and 490 kN·m, respectively. The parametric analysis indicates that increasing the circumferential axial force, segment thickness, or number of bolts enhances the initial rotational stiffness and ultimate bending moment of the joint, and reduces the joint opening under the same bending moment; however, it also decreases the ultimate rotation and weakens the rotational ductility. These findings may provide a useful reference for the simplified design of shield tunnel linings considering joint nonlinearity, although the general applicability of the model still requires further verification through tests on multiple joint types under various loading conditions.