Effect of Undercrossing Shield Tunnels Excavation on Existing Rectangular Pipe-Jacking Tunnels

Shield tunneling underneath existing rectangular pipe jacking can often lead to uneven settling. To solve the problem of excessive deformation of the existing underground pedestrian passages, excavated via the rectangular pipe-jacking method due to the adjacent shield tunnels construction beneath, a safety control plan has been proposed based on the shield tunnels constructed beneath a well-type underground pedestrian passage in Hohhot Subway. This plan involves the use of both numerical simulations and on-site monitoring to investigate the deformation patterns of the rectangular pipe jacking. The results suggest that the combined approach of interlayer soil grouting and steel support reinforcement is not only appropriate but also feasible for on-site implementation. It can be concluded that interlayer soil grouting for reinforcement was applied successfully to improve the strength of surrounding soils. Steel support reinforcement is advantageous for controlling the relative deformation between pipe segments. The maximum settlement induced by the shield tunneling for Passage A and Passage B was measured at 17.67 mm and 10.08 mm, respectively, with the final settlement distribution of the rectangular pipe jacking taking on a “W” shape. This study could provide a reference for the design and construction of shield tunnels that undercross existing rectangular pipe-jacking tunnels.