Chao Zhang

Joints are the weakest part of rectangular pipe jacking tunnels, and the structural form of the joint is closely related to its bending resistance. In this work, the F-type socket joint of a rectangular pipe jacking tunnel is selected as the object of study. The bending mechanical properties of the joints connected by steel screws and those connected by bent bolts are compared via a three-point bending test. The results show that the two longitudinal connection joints have similar bending stiffnesses. Compared with the bent bolt connection joint, the steel screw connection joint has better toughness, and the load at which the joint enters the plastic stage and the bearing capacity are increased by 0.47 times and 1.02 times, respectively. The failure modes of the joints connected by steel screw connections and those connected by bent bolts are crushing of the concrete of the top plate and cracking of the concrete above the screw holes, respectively. When a bent bolt connection is used, the reinforcement at the screw hole should be locally strengthened, or ultrahigh-performance concrete (UHPC) should be used at the screw hole to improve the load-bearing capacity of the joint.

The joint bending test was carried out to study the bending mechanical property and deformation characteristics of the F-type socket joint in rectangular pipe jacking tunnels under the conditions of foundation settlement, construction disturbance and different upper loads. The supporting function of soils under different geological conditions on the rectangular pipe jacking was simulated by arranging different numbers of equivalent foundation springs at the bottom of the pipe. The test results show that the greater the foundation stiffness is, the greater the joint bending moment will be at the same loading displacement, which leads to greater joint opening deformation. When the pipe joint itself produces large deformation, the change rate of joint opening slows down, and the slope of the bending stiffness curve of the joint increases. The bending bearing capacity of the joint is closely related to the foundation stiffness. The greater the foundation stiffness is, the higher the bending bearing capacity.