Abstract:

During the longterm operation of Shanghai Metro, the problem of differential settlementinduced metro operation safety should be solved. Hence, the deformation of the tunnel on Shanghai Metro Line No. 4 is evaluated from the aspects of curvature radius, relative deformation and absolute settlement of tunnel deformation curves; the characteristics of longterm deformation are preliminarily discussed; and the relationship between metro tunnel deformation and lower soil is analyzed. Some conclusions are drawn as follows: (1) The deformation of the metro tunnel varies from settlement to uplift with time; 3 years after tunnel operation is the time point for abovementioned variation. (2) The maximum deformations of the tunnel concentrate surrounding the metro station, where the curvature radius of deformation curve is less than 500 m and the relative bending is greater than 1/250, especially the connection between station and tunnel. (3) The variation of curvature radius of deformation curve of Shanghai Metro Line No. 4 mainly occurred during the first year since its operation; and the relative deformation and absolute settlement in safety range decreases with time. (4) The uplift of the metro tunnel is caused by expansion of lower soil, and may be caused by water buoyancy as well.

Key words: metro tunnel, longterm settlement, uplift, ground deformation, curvature radius, relative deformation, absolute settlement