Mechanical performance of novel joints in prefabricated UHPC panels for shield tunnel reinforcement: An experimental and numerical investigation

Abstract

To overcome the limitations of insufficient performance enhancement, poor construction quality control and low efficiency associated with existing reinforcement methods for shield tunnels, a prefabricated UHPC panel (PUP) reinforcement method is proposed, along with a novel joint for panel connection, referred to as the assembled bolt-plate joint (ABPJ). A series of flexural tests are conducted to systematically reveal the effects of load type and key design parameters on the mechanical behaviour of the ABPJ, and corresponding optimization strategies are proposed. A refined finite element (FE) model for the interlayer composite damage behaviour of bonded reinforced segmental structure was developed based on coupled CZM (Cohesive Zone Model)-XFEM (eXtended Finite Element Method) method, clarifying the influence of the ABPJ on the load-bearing performance and damage mechanisms of the reinforced structure. The results show that the technical framework of the prefabricated UHPC panel reinforcement method encompasses three key aspects: standardized design, industrialized production, and prefabricated construction. The flexural failure of the ABPJ is governed by the formation of plastic hinges, which may develop either at the groove wall or at the joint interface. The former is caused by the combined effects of flexural tension and the weakening of the cross-section due to grooving, while the latter results from insufficient stiffness of the connecting plate. To ensure adequate bidirectional flexural stiffness, the ABPJ connecting plate thickness should not be less than 20 mm. Under axial compression combined with positive bending, the development of gaps at the ABPJ compromises the structural integrity, leading to interlayer composite failure characterized by adhesive layer cracking and interfacial debonding, and a reduction in load-bearing capacity of approximately 25 % for the reinforced structure. Under axial compression combined with negative bending, the high level of axial force helps maintain compression at the joint interface, making the presence of the ABPJ have a negligible effect on the reinforcement effectiveness.