Research On The Shield Tunnel Exerts Negative Influences On Nearby Existing Tunnels

This research is based on shield tunneling construction of the line one of Changsha Metro shield tunnel, by comprehensive use of numerical stimulation,field test and numerical analysis method to analyze the special and common problems of shield tunnel approaching construction. The gist and primary new findings of this dissertation includes:1) To improve the deficiencies in the existing methods in the simulation of shield tunneling aspects, the working mechanism of shield tunneling is comprehensively understood. The more roundly and reasonably three dimensional numerical calculation model is established (including the influence factors of rock stress release, roof thrust of excavation face, grouting of the shield tail and the solidification of grouting body).2) By using3-D numerical simulation for3different conditions (including the cross, parallel, overlapping tunnels), to obtain the variation of surface subsidence caused by new tunnel construction, the existing tunnel deformation and internal force of the structure and the assessment of existing structural safety caused by the construction of new tunnel. Some conclusions about the shield tunnel cases and the universality study were gained, in overlapping area of the existing tunnel, the construction of shield tunnel will bring additional internal force and deformation of the existing structures, the adverse effects on the structure are presented; Outside the region, the construction of new tunnel have a relatively limited impact on existing structures.3) Parallel tunnel static calculation models in16different conditions are established. In this dissertation, according to the definitions of adjacent influence degree and influence subzone, the coefficient of the geometric adjacent degree α0ij, the one influence by depth α4ij and the synthesis coefficient Kij are studied by using statistical mechanics, with the base of the land displacement criterion and strength criterion Therefore the influence subzones based on ration of depth (H/D) with geometric adjacent degree A are put forward.4) By using3-D numerical method to simulate the construction process of shield tunnel approaching Neighboring Underground street and existing tunnel, The influence of ground surface deformation, additional bending moment and axial force are revealed. At the same time, according to the original data obtained by the monitoring of surface settlement, pile foundation displacement and bending moment and axial force changes, comparing and demonstrating with the numerical results, and puts forward the active reasonably protection measures and inhibiting formation of deformation. The results of this research provide some value for similar projects in the future.