Shear deformation characteristics and failure mechanisms of tunnel segment inter-ring joints: Numerical and experimental study

Abstract

The dislocation of inter-ring joints in tunnel segments poses a significant risk to tunnel structural safety. Therefore, gaining insights into the shear deformation and failure behavior of these inter-ring joints is paramount. In this study, we developed a robust three-dimensional numerical simulation model grounded in the concrete damaged plasticity (CDP) constitutive model. Complementing this, full-scale experiments were conducted on circumferential joints, subjecting them to both positive and negative shear loads. To enhance our understanding, we employed distributed optical fiber sensing (DOFS) and acoustic emission (AE) detection technologies. Our investigation delved into the deformation process, mechanical behavior of bolts, and failure characteristics of inter-ring joints featuring double bolt-tenon and mortise structures. Various parameters were explored, including longitudinal force, bolt preload, and the height-to-thickness ratio of the tenon and mortise (h/t). Notably, our results unveiled distinct stages in the shear deformation process of the joints. In the final failure stage, the tenon exhibited crushing failure, while the mortise underwent shear failure. As the h/t ratio increased, the mortise's failure mode transitioned from overall failure at the root to localized failure at the contact area. Analyzing the mechanical behavior of bolts, we observed more favorable outcomes in positive shear than in negative shear. Bolt preload emerged as a modest factor for enhancing the load-carrying capacity of the joint in positive shear, with minimal impact in negative shear. Furthermore, an increase in longitudinal force was found to positively enhance the joint's load-carrying capacity in both shear conditions. Our findings contribute valuable insights for optimizing the design and safety considerations of tunnel structures.