Measurement Study on Characteristics of Tunnel Deformation Differences in Reinforced Area of Large-diameter Shield Originating End

Abstract

Objective To ensure the smooth launch of shield tunneling, local ground reinforcement is usually carried out around the originating shaft, resulting in differences in tunnel deformation on both sides of the reinforced area, which can affect tunnel structural safety. However, the characteristics and law of deformation differences are still unclear yet. Hence, it is necessary to conduct a field measurement study on the characteristics of tunnel deformation differences in the reinforced area at large-diameter shield tunnel originating end. Method Taking the large-diameter shield tunnel project on Shanghai City Railway Airport Link Line as example, based on field measurement data, the differential characteristics of shield excavation construction ground vertical deformation, tunnel vertical deformation, and tunnel lateral convergence in the reinforced area of the originating shaft are analyzed. The influence law of local ground reinforcement on deformation differences during large-diameter shield tunnel excavation in soft soil stratum is investigated. Result & Conclusion Local ground reinforcement leads to significant differences in shield tunnel deformation response. The development of ground vertical deformation transitions from 4 stages (disturbance settlement, unloading uplift, consolidation settlement, and relative stability) in the non-reinforced area to 3 stages (disturbance settlement, unloading uplift, and relative stability) in the reinforced area. For tunnel vertical deformation, fluctuating uplift dominates on the non-reinforced side, while settlement dominates in the reinforced area, causing a differential settlement of 0.022% Ls (Ls as the distance between 2 monitoring points along tunnel axis) in the critical area reaching, exceeding the warning value for differential settlement of segmental structures. Regarding tunnel lateral convergence, the reinforced area tunnel structure exhibits a vertical egg-shaped deformation, while a horizontal egg-shaped deformation in the non-reinforced area. During construction, particular attention should be paid to preventing shear damage to circumferential joint bolts and concrete damage to bolts holes caused by segmental structure settlement and convergence differences in the critical area.

Keywords

• shield tunnel
• originating end reinforced area
• tunnel deformation difference
• field monitoring