Effects of deep soil mixing on existing shield tunnels in soft soil ground

Abstract

To mitigate the impact of adjacent construction on existing shield tunnels, deep soil mixing (DSM) has been widely used to reinforce the soft soil ground around shield tunnels. However, the construction of DSM may cause the movement of existing shield tunnels under soft soil and sensitive ground conditions, and reasonable installation parameters will reduce the impact of DSM construction on the existing shield tunnels. Based on the field tests of DSM installation parameters and a program of field measurements of existing shield tunnels during the DSM construction in Suzhou, the reasonable installation parameters of DSM were selected, and the movement of soil behind the soil mixing walls (SMWs) during multirow DSM installation was investigated. The movement of the shield tunnels caused by DSM construction were discussed in detail. The field test results showed that the DSM columns installed at a higher speed and a lower water-cement ratio enlarged the movement of the surrounding soil. The DSM should be installed at a lower speed and a higher water-cement ratio to reduce the movement of the shield tunnels. The field measurement results showed that the displacement of the tunnel lining was primarily caused by the construction of DSM zones beside the shield tunnels, which led to vertical compression and horizontal expansion of the tunnel lining. The construction of DSM immediately above the shield tunnels caused uplift to the tunnels. In addition, the deformed shapes of the two shield tunnels were asymmetric, and the displacement of the spring lining was larger than that of the crown. By taking the reasonable installation parameters of DSM and under the protection of the SMWs, the deformation of the shield tunnels caused by the construction of DSM was effectively controlled, and the maximum displacement was within the control value of the shield tunnels in this study.