Wall and Ground Movements due to Deep Excavation of Tianjin Subway Station

Abstract

This paper analyzes wall deflection and ground surface settlement due to deep excavation. 21 case histories of Tianjin subway line 6 are collected and analyzed. And the results are compared with previous field studies worldwide. The mean value of maximum wall deflection δhm is 0.11%H, in which H is the excavation depth. The upper limit of δhm is 0.44%H when H is less than 8m and 35mm when H is more than 8m. When excavation finished, δhm ranges from 0.02%H to 0.24%H with an average value of 0.12%H. The depth of maximum wall deflections Hδhm is within 0.75H±8m and the average Hδhm is 0.69H when excavation finished. It’s greatly affected by the embedded depth ratio. Hδhm can be predicted by exponential function more accurately. The distribution of δvm generally extends to a distance of 2H from the diaphragm wall. The bound of stiff clay line proposed by Clough and O’Rourke (1990) and bilinear curve proposed by Erin H. Y. Leung (2007) can be used as the upper bound for ground surface settlement for excavation of Tianjin subway line 6. The ratio between δvm and δhm generally ranges from 0.34 to 2.66, with an average value of 1.13. It’s consistent with the average value of 1.21 collected from literature in similar soil conditions. This paper is a reference for design and construction of Tianjin’s deep excavation of subway station.