Shear mechanism of circumferential joint in pipe jacking and shield integrated quasi-rectangular tunnel

Aiming at the uneven deformation caused by the difference in longitudinal stiffness of the pipe jacking and shield integrated quasi-rectangular tunnel structure in complex strata, the shear mechanism and shear stiffness characteristics of different ring-seam interfaces are systematically investigated through circumferential joint shear tests and theoretical analyses. Based on the background of Shanghai Rail Transit Line 12, three types of typical ring joint interfaces are selected to simulate the shear behavior under different longitudinal force conditions, which reveals the multi-stage evolution law of joint dislocation with increasing load. The results of experiment showed that with the load increases, the joint dislocation sequentially undergoes static friction, the cooperative shear resistance of dynamic friction and dowel mechanism, and connector failure: the circumferential joint shear force transfer is dominated by static friction, dynamic friction and the synergistic action of the connecting member pin-bolt mechanism, and the compressive bending of the steel backing plate in the interface of the concrete pipe section-steel pipe section further contributes to the shear performance; the increase of the longitudinal force will enhance the inter-ring friction and shear capacity; the shear stiffness is determined by the shear pin and the diagonal bolt due to the parallelism, and the damage modes show the differentiation (shear pin fracture or bolt yielding). An analytical model of the shear stiffness of the joints was proposed to quantify the shear ultimate bearing capacity of different interface combinations, and the results showed that the interface of straight bolts had the largest amount of misalignment (11.6 mm), and the interface of shear pins had the lowest bearing capacity (485.6 kN/m).