Full-scale test on shield tunnel circumferential joints with oblique bolts and tongue-groove structures: Coupled shear-resisting behaviors

Shield tunnels subjected to external disturbances experience non-uniform loading, leading to circumferential joint dislocations. The geometric asymmetry of oblique bolts creates differential mechanical states where bolts experience tension in one joint and compression in the adjacent one. However, the dynamic coupled behavior between adjacent joints remains unexplored. This study investigates the coupled shear-resisting behavior between two adjacent circumferential joints through full-scale three-ring testing and refined finite element analyses. Shear load was applied to the central ring to enable direct comparative analysis of shear stiffness evolution, bolt strain development, and concrete damage patterns in both joints. Results demonstrate distinctly different behavioral patterns. The circumferential joint with compressed bolts (CJCB) experiences a complete six-stage failure evolution, which sequentially includes static friction, bolt anchoring, tongue-groove engagement, plastic hinge formation, ultimate plastic deformation, and failure redistribution, with ultimate dislocation reaching 47.3 mm. In contrast, the circumferential joint with tensioned bolts (CJTB) undergoes only three initial stages with maximum dislocation of only 2.1 mm, representing a 22.5-fold difference. During the coupled process, CJTB demonstrates superior stiffness retention and progressively assumes greater load proportion, evidenced by the average secant shear stiffness ratio of CJTB to CJCB reaching 36.3 before stabilizing at 27. This stiffness ratio evolution quantifies the dynamic load redistribution mechanism, where load progressively transfers from the deteriorating CJCB to the relatively stiffer CJTB. Structural deterioration follows sequential progression: tongue cracking initiates at lower loads, followed by groove crushing at advanced loading stages, with CJCB exhibiting significantly more severe damage than CJTB. These findings reveal that the coupled shear-resisting behavior is characterized by asymmetric failure evolution, dynamic stiffness redistribution, and progressive load transfer between adjacent joints.