Research on the mechanical properties of composite wet joints in large-span open-cut tunnels

This study proposes a novel inverted-T composite wet joint for the Chongqing Xinsen Avenue Tunnel – an eight-lane, large-span prefabricated open-cut highway tunnel – aiming to streamline construction and improve structural performance. Full-scale laboratory bending tests were conducted on the joint under varying axial loads and reinforcement lap lengths, characterising its load-bearing capacity, stiffness, and failure modes. A detailed finite-element model using the Concrete Damaged Plasticity (CDP) approach was calibrated against the test results and used for parametric analyses of key design variables. In parallel, a three-dimensional soil–structure interaction model of a complete tunnel ring was developed to simulate the staged construction process, capturing the evolution of internal forces, deformations, and failure mechanisms. The results show that the composite joint typically fails in a highly eccentric compression-bending mode, and that increasing the reinforcement lap length yields only marginal gains in flexural capacity. Enhancing the strength of the post-cast concrete, providing sufficient lap length, and detailing the interface by incorporating chamfers and shear keys improve joint performance. The full-ring analysis reveals that under staged loading the lining transitions from elastic behaviour to a four-hinge mechanism, and that controlling crown settlement within prescribed limits is critical for serviceability. Overall, this combined experimental and numerical study clarifies the mechanical behaviour and failure mechanisms of inverted-T composite wet joints, providing theoretical guidance for the design of such joints in large-span prefabricated arch tunnels.