Research On The Mechanical Influence Of Deep Excavation To Adjacent Existing Tunnel

Relying on the Harbin Railway Bureau station work sites, this thesis analyzes and summarizes deformation characteristics and mechanisms the of the adjacent existing tunnel, at the same time, establishing a mechanical model of the interaction among the excavation, tunnel and soil; Applying finite element software Plaxis, considering reciprocity of foundation excavation, soil, adjacent subway tunnels, this thesis establishes relevant analysis model, the mechanical influence of deep excavation to adjacent tunnel in the deep foundation excavation process is simulated. The simulated factors include the spacing between the excavation and tunnel,the tunnel depth, excavation depth, soil conditions, bracing structure of the foundation pit. Finally, this thesis obtains distortion and mechanics discipline of adjacent subway tunnel by above factors. Meanwhile, this paper uses the theory of systems engineering and the multi-level fuzzy comprehensive evaluation method in which evaluating the bracing structure of relying on deep pit.The conclusion is that the bracing structure scheme is reasonable in the relying on deep pit. Finally, the existing problems are discussed briefly and the corresponding recommendations are given. Main conclusions are as follows:(1) Mainly for two types of deformation characteristics induced by excavation tunnel: First, in the pit side of the tunnel deformation oblique bottom of the pit, the convergence of the tunnel section shows a cross-duck-shaped, tunnel deformation is given priority to with horizontal deformation. Secondly, located at bottom of the pit tunnel along the longitudinal direction of deformation shows a normal distribution curve, tunnel deformation is given priority to with vertical deformation.(2) By relying on the Harbin Railway Bureau station work sites, the results of computing simulation and monitoring results are consistent, its error rang is of about20%,it verifies the feasibility of the plaxis two-dimentional finite element method.(3) Spacing between the excavation and tunnel has a significant effect on the deformation of tunnel structured and less influence on the internal forces, the relationship between them is nonlinear. The critical spacing is of12m;Buried depth on the tunnel displacement and internal force affect significantly, the relationship between them is nonlinear. When the tunnel floor height is higher than the height at the bottom of the excavation, tunnel horizontal deformation first decreases and then increases as the tunnel buried depth increases, the vertical deformation decreases gradually as tunnel buried depth increases. When the tunnel floor height is lower than the height at the bottom of the excavation, tunnel horizontal deformation is gradually decreases with tunnel buried depth increases, the vertical deformation has a tendency to increase,more than a certain value, the impact is no longer significant. The increase of excavation depth effect on tunnel structure horizontal displacement and vertical displacement is obvious, when above a certain value, the impact is no longer significant, it has less influence on the internal forces; The change of soil conditions has significant effects on displacement of tunnel structure, no significant influence on the internal force(4) Deep foundation pit with row pile and retaining structure’s support for tunnel deformation impact is minimal, with row pile and anchor the impact it has a greater influence, but in a reference deformation within20mm, the biggest effect with pile, it exceeds the reference value of the deformation of20mm. Different supporting structure has little effect on the internal forces of the tunnel lining(5) Using the multi-level fuzzy comprehensive evaluation method in which evaluating the bracing structure of relying on deep pit, and a calculation analysis and evaluation was carried out. According to the maximum membership principle, the result is better than that of pile anchor supporting structure The conclusion is that the bracing structure scheme is reasonable in the relying on deep pit.