Bending Performance of the Steel Longitudinal Joint for Quasi-Rectangular Pipe-Jacking Tunnels

Pipe jacking is a special tunneling method for installing underground pipelines or tunnels with the minimum surface disruption. Longitudinal pipe-to-pipe joints are important for tunnels with the pipe-jacking technique. The longitudinal joint generally adopts the socket type, that is, a bell-and-spigot joint, designed for use with gaskets work well for jacking. The joints should have sufficient bearing surfaces to transmit the required axial thrust and have the ability to resist lateral forces from ground movements during tunnel construction and operation. This paper focuses on the mechanical performance of the longitudinal joint of the superlarge cross section quasi-rectangular pipe-jacking tunnel under the action of local bending moments caused by lateral forces. A full-scale ultimate bending test of the local joint specimen was carried out to study its bearing mechanism, ultimate bearing capacity, and failure mode. Numerical simulations were then employed to analyze the performance of the joint specimen and were verified by the experimental results. The damage evolution process and bearing mechanism changes of the joint specimen were analyzed by numerical simulations. The results show that the bell part contributes much more to the bending of the joint than the spigot part. The bolt contributes little to the bearing capacity and stiffness of the joint but plays a role in positioning the pipe to pipe in the installation. The bending failure of the joint is characterized by weld fractures between the longitudinal rib and its flange next to the V-groove weld at the bottom of the bell part. The V-groove weld connecting the bottom of the spigot part and the bell part primarily affects the bending capacity of the joint.