Site monitoring of mechanical characteristics of pipes during steel curved pipe jacking under large buried depth

In order to study the mechanical characteristics of pipes during steel curved pipe jacking under large buried depth, the axial strain and hoop strain of curved pipe jacking are monitored and analyzed through site tests, based on the curved pipe jacking roof of Gongbei tunnel. The results show that the strain of pipe slightly increases with the increase of jacking distance, and maintains a certain range. The stress curve of pipe fluctuates in the process of jacking, but gradually restores stability after jacking stoppage. The axial stress of pipe is mainly affected by the jacking force, and the hoop stress mainly depends on the ring load out of pipe. Pressure stress concentration is located inside the pipe jacking curve. Under large buried depth, the axial stresses of pipe top and bottom are controlled by the circumference deformation because of Poisson effect. With the increasing distance between the pipe and the jacking machine head, the mechanical characteristics of pipe change from axial compression at both sides to one-side compression. The compression occurs inside the pipe bending with more obvious stress concentration.