| Subway is the traffic lifeline of city, so the adjacent foundation pit design should take its influence on subway tunnel into consideration. There is a lot of research results about the environmental effect of excavation.But relatively few theories have been done on deformation of foundation pit support, deformation law of the surrounding soil and the structure deformation of metro tunnel nearby, thus causing lots problems still remain to be solved.It's analyzed and mentioned that there are defects and deficiencies of analytic method on calculating tunnel deformation caused by adjacent foundation pit excavation. Then the software FLAC3 D was used to conduct a foundation pit excavation course simulation in the vicinity of Wuhan Metro Line No. 4.It was studied that deformation laws of the retaining structure, the bottom soil and tunnel structure under the condition of interact between foundation pit excavation and tunnel affected. Respectively discussed how the pit top load, property of soil, retaining structure layout, tunnel and excavation of horizontal and vertical distance influence the deformation of the adjacent tunnel. Summarized and put forward the control standard and reasonable reinforcement measures and suggestions for tunnel deformation. The main results are as follows:(1)Two kinds of analytic method,additional stress method and additional displacement method, were discussed. The thesis focuses on the solution methods of additional stress, additional displacement and elastic foundation beam deformation.It was pointed out that shortcomings and deficiencies of these two analytic methods do exist: additional stress method, is computational complex, unable to consider the influence of construction process and its force assumption of lateral unloading model of foundation pit excavation with a support is not reasonable; additional displacement method is a semi theoretical and semi empirical formula method, greatly influenced by subjective factors of human hypothesis, and early monitoring data is essential to verify its reliability.(2)FLAC3D was used to simulate the process of foundation pit excavation near a Wuhan Metro Line No. 4. The maximum displacement of enclosure structure appears at the bottom of foundation pit.Tunnel has great effect on retaining wall deformation ——for wall near the tunnel,there is a larger displacement at the top, and a smaller displacement at the bottom of the foundation pit;maximum deformation of the subway tunnel appears at place close to the midpoint of the foundation pit long side, while the tunnel deformation is far smaller away from the pit.In comparison with the results of three-dimensional model, the maximum vertical displacement calculation value of plane model tunnel is less than 10% while the maximum horizontal displacement calculation value is lager than 10%. a large pit top loading will increase level tunnel deformation; if appropriate changes happens in surrounding soil material of the subway tunnel, vertical deformation of the tunnel changes little while the level deformation changes a lot.(3)The tunnel deformation control standards were summarized and put forward: vertical deformation of the allowable value should be less than 10 mm, level of allowable deformation value should be less than 5mm, early warning value is the allowable value of 80%. Foundation pit subsection excavation and constructing the pit floor timely, can significantly reduce the subway tunnel deformation;control effect of fast loading on the pit floor and passive zone of pit soil reinforcement is obvious. Tradition measures such as increasing the foundation pit support or improve tunnel section stiffness,are proved to have a poor the deformation control effect. |
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