Theoretical study on equivalent stiffness of F-type socket joints in rectangular pipe jacking tunnels

The equivalent stiffness is an important parameter for calculating the longitudinal deformation of tunnels. To explore the influences of the equivalent stiffness on the rectangular pipe jacking tunnel, taking the rectangular pipe jacking tunnel of Hailiang Square in Hohhot as the design reference, the analytical solution for the equivalent stiffness of the joint of the rectangular pipe jacking tunnel is established by using the equivalent principle of longitudinal deformation and the section shear coefficient of the Timoshenko beam. The laboratory experiments are used to explore the influence factors for the equivalent stiffness. The results show that: (1) Under the action of shear, the shear stiffness of the joint is mainly divided into elastic stage, yield stage and failure stage. (2) The theoretical results of the equivalent stiffness are nearly the same as the model experimental data, which verifies the rationality of the analytical solution. (3) Reducing the width and increasing the height of the pipe section can effectively increase the equivalent stiffness of the joint. The section size has small effects on the equivalent shear stiffness, and the bending deformation should be taken as the key research in the design of the pipe section. The steel sleeve ring is proportional to the equivalent stiffness and inversely proportional to the lifting rate. It is recommended that the thickness of the steel sleeve ring be 13~17 mm.