Identification of Tunnel Settlement Caused by Land Subsidence in Soft Deposit of Shanghai

This paper provides a straightforward way to evaluate tunnel settlement caused by land subsidence in the soft deposits of Shanghai. By analyzing field measurements of tunnel settlement and land subsidence, it was found that the tunnel settlement was caused by ground subsidence under the tunnel, and was unrelated to the compression of the upper soil layers. Because significant compaction of the upper layers can occur due to urban construction, the measured land subsidence, which is the ground surface subsidence, cannot represent the sublayer subsidence. To solve this problem, this paper takes metro stations as the monitoring point at the depth of the tunnel, and uses a cubic spline function to fit the line of the station points. The derived fitting curve is then used to represent the ground subsidence under the tunnels. The rationality of taking the stations as monitoring points is verified based on a load transfer analysis. The proposed method is applied to investigate the settlement of metro tunnels in Shanghai. It was found that land subsidence–induced settlement accounts for 62.5% of the maximum cumulative settlement in some sections of Metro Lines No. 1 and No. 2 up until 2010.