Construction Mechanical Mechanism of Shallow Subway Tunnel Group with Large-Span Variable Cross Section

The number of tunnel crossings or line switchings in the vicinity of subway transfer stations is increasing with the construction of subway tunnels. The construction interaction of the subway tunnel group with variable cross section and the time and space effects of strata deformation has become a major problem that limits the development of subway tunnel spaces. Thus, this study analyzed the deformation law of the upper strata and surrounding rocks in a subway tunnel group with large-span variable cross section caused by different construction processes using ABAQUS numerical simulation analysis. The research focused on the construction interaction mechanism and stratum deformation law of such a subway tunnel group and considered Shenzhen Metro Line 7 as the study subject. The stratum deformation law caused by twin tunnels excavation was referred. Results showed that (1) the construction process significantly influenced the construction safety of tunnel groups with large-span variable cross section; (2) constructing small cross-sectional tunnels first increases the lateral deformation and settlement of the vault in large cross-sectional tunnels, which are far from small cross-sectional tunnels, but reduces the settlement of the vault in the small cross-sectional tunnels and the lateral deformation of the surrounding rock between the large and small cross-sectional tunnels, which benefits tunnel groups with large-span variable cross section; and (3) as shown by the comparison of the final numerical simulation data that in which the large cross-sectional tunnel was constructed after the completion of the small cross-sectional tunnel construction had the lowest project risk. © 2018, Springer International Publishing AG, part of Springer Nature.