Analysis of Shear Mechanical Properties of Distributed Mortise-Tenon Joints in Super-Large Diameter Shield Tunnels

The distributed mortise-tenon joint is a novel type of joint used in large-diameter shield tunneling to resist longitudinal shear dislocation deformation between adjacent rings. Using the Wuhu Chengnan Extra‑Large Diameter River‑Crossing Tunnel as a prototype， this study established a numerical model for the joint and segment shear behavior， incorporating the effects of local plastic damage. The research investigated the shear‑resistance evolution of distributed mortise‑tenon joints and their influence on longitudinal load transfer in the tunnel. A comparison was made with continuous mortise‑tenon segments. Finally， the reliability of the numerical results was verified against a theoretical calculation model. The results showed that： 1） Under applied displacement， the shear force variation in distributed mortise-tenon joints exhibited three distinct stages （I-III）. In Stage I， the joint contributed negligibly to shear resistance. In Stage II， the shear resistance increased sharply， reaching 64.4% of the total by the end of this stage. In Stage III， the shear force began to stabilize. 2） During shearing， the mortise-tenon joints above the waist experienced relatively rapid growth in shear resistance and contributed significantly， accounting for 76% of the total at the end of the engagement stage. 3） The longitudinal stress relaxation coefficient λ of the distributed mortise-tenon segment reached 17.1% at the ultimate shear limit， whereas that of the continuous ring-type mortise-tenon segment reached 29.6%. The relatively smaller relaxation area of the former is beneficial for controlling the longitudinal stability and preventing leakage of the overall tunnel structure.