Research On Subway Tunnel Deformation Due To Large-scale Unloading And Its Control

Rapid construction and operation of subway tunnels has aroused more and more excavations implemented adjacent to them, which have consequently induced additional load (include loading and unloading) to the tunnels and ground below, which cause significant deformation to the metro tunnels and threatened their operation greatly. At present the effect of large-scale excavations above metro tunnels is one of the most concerned problems by geotechnical engineers, And how to control the displacement and how to protect the existing tunnels become the important engineering issue.Based on the People's Square excavation project, this paper carried out research on the influence rule of key parameters of large-scale unloading to the maximum rebound and the longitudinal deformation model of the tunnel. And the control approach of the deformation is also analyed. Main work and results about the dissertation were listed as follows.Firstly, a brief discussion about the classification of large-scale unloading under excavation above the tunnel is given, and boundary of the rebounding area is defined. At last, the conception of the key zone which should be controled and the the large-scale unloading area was pointed out.Secondly, according to analytical method, the study analyzed the effect of key parameters of large-scale unloading on the maximum rebound and the longitudinal deformation model of the tunnel, and obtained the longitudinal deformation model of tunnel due to large-scale unloading. Then, the conclusion is verified by the field measurement research.Then, considering the rheology of soft soil, using the commercial FDM software—FLAC 3D, the effect of unloading time on deformation of the tunnel during the large-scale excavation is investigated. By comparison, the paper also analysed the regulation of the tunnel's rebound deformation under different unloading sequences.