Field investigations on interaction between jacking pipes and closure of pipe roofs in soft ground

The pipe roofs play a key role in protecting the passing objects in underground crossing projects. In order to construct a strictly closed pipe roof, high jacking precision of each pipe is required. However, the jacking interaction of various adjacent pipes is extremely complicated, which brings uncertainty to the attitude change of each pipe jacking and the final closure error of the pipe roof. This study relies on a certain project crossing a middle ring line by the large-scale ‘pipe roof-box culvert' method and uses the real-time monitoring approach to record the attitude and deformation of each steel pipe during the jacking process of the pipe roof. Based on the measured data, the interaction of various pipes in the process of jacking as well as the attitude and deformation of the closed pipe roof is analyzed. The results show that: (1) The interaction between the pipes is reflected by the constraint and guiding effects of the previous pipe jacking (anterior pipe) on the attitude of the rear jacking pipe (posterior pipe), and the relative deviation is generally controlled within 4 cm. (2) Affected by the longitudinal stiffness of the steel pipe, the attitude correction of 70% pipes lags behind the machine head which results in relatively large accumulative deviation at the previous stage, but with the decrease of the longitudinal stiffness, the attitude of the pipe changes sharply at the receiving terminal under hard correcting. (3) The attitude of closed pipe roof is well maintained at the originating terminal and the reinforced zone. An obvious change occurs in the middle section, and some pipes even have a large distance among them. Finally, at the receiving terminal, the deviation of most pipes is relatively reduced. © 2020, Editorial Office of Chinese Journal of Geotechnical Engineering. All right reserved.