Field performance of steel pipes during curve jacking in Gongbei tunnel

Pipe-soil contact pressure is a critical parameter in the whole pipe jacking construction process. Most of the existing pipe jacking standards do not distinguish rigid and flexible pipes, in terms of pipe-soil pressure calcu-lation methodologies, nor do they take into account the impact of different construction conditions. In order to study the mechanical characteristics during curved steel pipe jacking with large buried depth, the contact pressure and pipe stress of curved pipe jacking were monitored and analyzed, based on Gongbei curved pipe jacking roof tunnel project. The results show that contact pressure and pipe stress are significantly asymmetric during the jacking process. In general, the values of contact pressure at crown and bottom are relatively close, and the crown pressure is slightly larger than that at the bottom. The horizontal contact pressure inside of pipe jacking curve is less than the outside. The pipe axial stress is mainly affected by jacking force, and hoop stress mainly depends on ring load out of pipe. The compression occurs inside of pipe jacking curve with more obvious stress concentration. With the increase of jacking distance, the pipe axial stress transforms from full sectional compression to local compression.