Temporal variation laws of longitudinal stress of pipe jacking with large-section steel structure

The longitudinal force on the section of pipe jacking tunnel affects the structural stability and construction safety as well as the waterproof performance and joint stiffness of the circumferential weld. By calculating and solving the mathematical equations for the longitudinal force, the frictional resistance, the force on the face and the back-stopping force, the relationship between the longitudinal force of tunnel section and the jacking mileage is established. The theoretical solution is compared with the field test results, and they are in good agreement. The analysis results show that: (1) The variation law of longitudinal force of pipe section with time is a gradually convergent curve, and decreases rapidly after the tunnel is coalescent. The theoretical values match well with the measured ones. (2) The longitudinal stress on the section at the stop and after the tunnel coalescence is small, which is not conducive to the annular seam waterproofing, and the longitudinal stiffness of the tunnel is small, which is easy to produce differential settlement. (3) The elastic coefficient of the back-stopping device, jacking mileage, size and buried depth of tunnel are the important influencing factors for the longitudinal stress on the section of pipe jacking, and they are positively correlated to different degrees.