Experimental and numerical study on the mechanical properties of F type socket joints for rectangular pipe jacking with steel screw connection

To solve the problems of insufficient stiffness and poor integrity of traditional F-type socket joints, steel screw connections are set along the longitudinal direction between rectangular pipe jacking joints. However, the mechanical properties of F-type socket joints with steel screw connections have not been fully investigated, and the influence of the coefficient of subgrade reaction has not been considered. In this work, through model tests and numerical simulations of F-type socket joints with steel screws under different coefficients of subgrade reaction, the influence of steel screws on the deformation and damage characteristics of F-type socket joints is discussed, and the bending mechanical response of F-type socket joints under different coefficients of subgrade reaction is analyzed. Compared with traditional F-type socket joints, the use of steel screw connections can reduce the risk of steel ring warping and cross-sectional deformation of the joints and improve the stiffness and load-carrying capacity of the joints. However, the use of steel screw connections exacerbates damage to the chamfered parts of the jack joints. With an increase in the coefficient of subgrade reaction, the benefit of the steel screw on the joint stiffness gradually decreases. For every 0.5-fold increase in the coefficient of subgrade reaction, the effect of the steel screw on the joint bending load-carrying capacity of the joint is reduced by approximately 23%. The failure mode of joints containing steel screws is mainly the crushing of concrete in the compression zone, and the penetration cracks extend from the joint to the bottom of the pipe section. The higher the jacking force is, the higher the load-carrying capacity of the joint and the better the bending resistance.