Performance of Existing Subway Tunnels Undercrossed by Four Closely Spaced Shield Tunnels

Abstract

With the extending of existing networks of metro systems, existing subway tunnels are more and more commonly undercrossed by new underground tunnels. Excessive deformation and even damage may occur in existing subway tunnels due to the influence of new tunnel construction. This paper studies a case of two existing subway tunnels undercrossed by four closely spaced tunnels in Shenzhen. The displacement of the existing tunnels, the soil pressure, and the bending moment of the new tunnels are monitored. Considering the multiple soil disturbance, a three-dimensional numerical model is established for the analysis of tunnel settlement induced by multiundercrossing. The calculation results match well with the measured tunnel settlement data and the accuracy of proposed numerical approach is verified. Compared with the vertical displacement of the existing tunnels, the horizontal displacement is less affected by new tunnel construction underneath. The vertical displacement profile of the existing tunnels displays V, U, and W shapes, and the position of maximum displacement always shifts toward the new shield tunnel. Affected by the expansion of the disturbed area in the soil, the construction of two or more tunnels close to each other will lead to the increase of the bending moment of the new tunnels themselves.