Differential settlement of metro tunnels and its zonal control in soft deposits

Based on the measured settlement (a period of 4 years after operation) of West Extension Line of Nanjing Metro Line 1, the differential settlement characteristics of this line are analyzed. After 4 years’ operation, the cumulative settlement reaches the maximum value of 122 mm, and 4 settlement troughs are formed along the line and each settlement trough has the trend to be wider. By comparing the cumulative settlement to the geological conditions and the adjacent construction activities along the line, the reasons for the differential settlement of the line are investigated. The results show that the non-uniform distribution of the soft soil layer under the metro tunnel and the adjacent construction activities are the main causes for the differential settlement. For the problem of differential settlement of the metro tunnels in soft soil area, the zonal control of the metro line should be adopted by considering the engineering geological conditions and the development intensity of the surrounding projects.