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.