Study of the mechanical behaviour and damage characteristics of three new types of joints for fabricated rectangular tunnels using a numerical approach

Joints are the weakest parts of prefabricated tunnels, and it is important to consider the material nonlinearities, mechanical properties and complex behaviours of joints in structural design. Based on existing joints, this paper proposes the design of three new types of joints for fabricated rectangular tunnels, including self-weight mortise and tenon joints, bolt mortise and tenon joints and steel plate mortise and tenon joints. To explore the mechanical behaviour and damage characteristics of these new joints, three-dimensional finite element numerical models are established with a plastic damage model to reflect the nonlinear mechanical characteristics of each component of the joint. The results of the numerical analysis are compared with experimental data, verifying the validity of the process. Then, the compressive and bending capacity, steel reinforcement bar stress and concrete damage characteristics of rectangular tunnel joints under different combinations of axial loads and displacement loads are defined. It is indicated that the mortise and tenon joint type significantly affects the damage evolution process of the concrete at these joints. Among the three joint types, the bolt mortise and tenon joint has the largest damage area of concrete and, consequently, the most damage elements due to its reasonable joint structure. Hence, from the perspective of the mechanical performance of the structure, the bolt mortise and tenon joint provides the largest flexural bearing capacity and structural safety, followed by the steel plate mortise and tenon joint. The self-weight mortise and tenon joint has the smallest flexural bearing capacity, but it is the simplest joint proposed and is easier to construct than the other two joints.