Modified Calculation Model for Segment Floating in Slurry Shield Tunnel

Abstract

Concrete remains the most commonly used material for lining segments in shield tunnels. Extensive segment floating can easily result in segment dislocation, crack damage, and water leakage. Based on the river-crossing slurry shield tunnel project between Anfeng Station and Dongxin Station of Nanchang, Metro Line 4 (Jiangxi, China), this study addressed the problem of segment floating, which is frequently encountered during the construction of slurry shield tunnels, by theoretically calculating segment floating. In the calculation, the segment floating was divided into two stages: before and after the initial setting of the slurry. First, the stress components of the segment before the initial setting of the slurry were analyzed. The improved Terzaghi loose earth pressure formula, which accounts for the degree of soil arching effect, was adopted to calculate the force of the overlying soil. Then, the mechanical model before the initial setting of the slurry was established and the corresponding theoretical solution was derived. On this basis, the influence coefficient of segment floating before the initial setting of the slurry was proposed. Then, the stress of the segment after the initial setting of the slurry was analyzed, the compression of the overlying soil layer was calculated using the elastic mechanics formula for foundation settlement, and the calculation expression for segment floating after the initial setting of the slurry was obtained. Finally, according to the calculation results for the segment floating theory and segment stress mechanism, targeted antifloating measures were proposed for the follow-up excavation work. The results showed that (1) the buoyancy of the segment calculated in stages is in good agreement with the value measured on-site, that is, when considering the degree of the soil arching effect, the calculated value is closer to the measured average value, thus verifying the feasibility of the calculation model; (2) there are two stages of segment floating, and the amount of segment floating before the initial setting of the slurry is dominant; and (3) the antifloating measures adopted in the subsequent excavation process can ensure the performance quality and safety of segments.