Abstract:

As the newly-built Metro Line 11 in Shanghai went through Line 4, a method of data monitoring was used to analyze the deformation of the existing tunnel overlapped by Line 11 under construction with lower- and upper-shields. Cubic spline interpolation was used to simulate the deformation curve. A deformation curve of the full-length profile of the cross section was obtained. Based on an improved longitudinal equivalent continuous model of the tunnel, the relationship between the tunnel’s longitudinal deformation curve and the amount of stretching of the circular seam was calculated. Combined with the specifications, control indicators of deformation for the existing tunnel caused by Line 11 were proposed. The results showed that the maximum deformation in excavation engineering should be controlled first when the lower-shield was constructed, and then the upper-shield. At the same time, deformation of the inside and outside circle should be concentrated in its centerline around 2.5 times the outer diameter of the shield tunnel. In constructing the lower part, subsidence in the outer circle was larger because the outer circle was more influenced and the pre-disturbance was mainly concentrated in the outer center region. The results provided a theoretical basis for constructing overlapped metro lines, especially for protecting an existing tunnel when the lower-shield was constructed first.

Key words: curve deformation,  field monitoring ,  shield construction ,  spline interpolation , multi-line overlapping