Study on flexural performance of inverted T-shaped laminated joints in large-span cut-and-cover arched tunnels

A novel inverted T-shaped composite joint structure is proposed for the prefabricated structural system of the large-span open-cut arched tunnel on Xinsen Avenue in Chongqing. Finite element models of joint test specimens were established using ABAQUS and validated against existing experimental results to confirm the accuracy of the numerical simulation method. On this basis, the mechanical performance and failure modes of the laminated joint were analyzed and compared with those of the cast-in-place structure. The study systematically investigated the effects of various design parameters on the flexural mechanical performance of the laminated joint, including the height of the inverted T-shaped web, the strength of the post-poured concrete, the overlapping length of the annular reinforcement, the friction coefficient between new and old concrete, the cross-sectional area of the transverse reinforcement, and the thickness of the inverted T-shaped flange. Furthermore, the impacts of structural detailing measures were evaluated, such as the chamfer type at the interface between post-poured concrete and precast components, the installation of shear keys, and the connection methods of U-shaped reinforcement. The results show that: the flexural bearing capacity of the laminated joint is close to that of the cast-in-place structure, with a peak load difference of less than 4%; the friction coefficient between new and old concrete and the cross-sectional area of the transverse reinforcement have negligible effects on the flexural bearing capacity of the joint; the overlapping length of the annular reinforcement, post-poured concrete strength, and inverted T-shaped web height significantly influence the flexural bearing capacity of the joint; when designing the inverted T-shaped laminated joint, it is recommended that the minimum overlap length of the annular reinforcement be 20d, micro-expansive post-poured concrete with a strength no lower than that of the precast concrete be utilized, the inverted T-shaped web height be no less than 400 mm, and the flange thickness should not be reduced; adopting rounded chamfers at the interface between post-poured concrete and precast components can slightly enhance the load-bearing capacity of the laminated joint; the two connection methods for U-shaped reinforcement exhibit minimal differences in load-bearing capacity, and the choice should be optimized based on construction conditions and structural requirements.