Research On Caculation Method And Control Standard Of Stratum Subsidence Of Newly-built Subway Tunnel Passing Underneath Existing Tunnel Line In Soil Area

To build a new subway tunnel passing underneath the existing tunnel section is likely to cause the latter displace and settle. Especially, the superimposed effect caused by two parallel tunnels in different time of excavation will has a severely harmful effect in tunnel structure. It will be a efficient technology strategy to reliably predict the extent of influence of two-line tunnel under-through construction on the existing tunnel line and to find the rule of ground stratum subsidence, then to prevent the existing tunnel from warping by controlling the settlement standard in the process of underneath pass. Meanwhile, this technology strategy is the main technological problem in nowadays newly-built subway tunnel underneath pass program. With the No.5 subway line in Xi’an close passing underneath No.2 line as the target of research, the deformation characteristics of stratum subsidence and the structure of the existing subway tunnel are analyzed in this thesis. Moreover, the research on methods of prediction of subway tunnel distortion and on early warning system of existing subway tunnel structure. The results are shown as follows:(1)The mainly influential factors in the process that the newly-built subway tunnel pass underneath the existing subway tunnel section include: structural stiffness of the existing tunnel structure, depth of the existing tunnel and the characteristics of the soil mass of surrounding rock. Considered these factors, the parameter of settlement trough width is revised. And computational formula of stratum subsidence in the process that single-line subway tunnel closely pass underneath the existing subway line is deduced.(2)Based on influential intensity and spread range between the newly-built double-line subway tunnel and the existing subway tunnel, the sections of mutual effect can be divided into three categories: strong influential section, weak influential section and no influential one. Among those categories, the overall curve of surface settle line of strong influential section can have two types including v-type settlement and w-type settlement. Moreover, experiential theoretical formula of double-line subway tunnel passing underneath existing line in strong influential section and that in weak influential section are deduced.(3)The controlling elements of deformation of the existing tunnel structure mainly refer to tunnel structural bending moment, radius of curvature, allowable stress, tunnel deformation and shearing stress etc.. The theoretical analysis combines with analogies of experience to confirm control baseline of tunnel structure settlement in the process that the newly-built tunnel pass underneath existing tunnel line in loess area. In order to evaluate the safety and stability, early warning system of existing subway tunnel and evaluation system of deformational safety level.