Performance of an operational shield tunnel due to construction of a large cross-sectional straight-walled arch tunnel above-crossing

Abstract

Innovative strategies for managing deformation have been proposed based on insights from the Hohhot Urban Rail Transit's Line 2, where a large cross-sectional and straight-walled arch tunnel traverses the flank obliquely above and directly over an operational shield tunnel. These strategies involve implementing sandbag loading on both left and right drifts and progressively demolishing the CD (center diaphragm) method. Simulations have been conducted to comprehensively understand the deformation induced by constructing the large cross-sectional and straight-walled arch tunnel above the operational shield tunnel. These simulations have been complemented by on-site monitoring to authenticate the reliability of the simulated outcomes. The study findings underscore that the most effective deformation control entails applying a 2.0 m high sandbag load on the section directly above the operational left shield tunnel (spanning from trusses 49 th to 87th). This approach involves, for every alternate truss, the demolition of two consecutive trusses of CDs via an alternate bay construction method once the secondary lining is completed. The comparison between simulated and measured uplift reveals a notable alignment, with maximum uplift of the ballast bed and arch crown registering at 2.75 mm and 3.92 mm, respectively. The overall clearance convergence ranges from −2.69 mm to 1.50 mm, all within the prescribed control standards.

Keywords

• Large cross-sectional and straight-walled arch tunnel
• Center diaphragm
• Above-crossing
• Shield tunnel
• Uplift deformation
• Sandbag loading