Study On Environmental Effects And Structural Performance Of Shield Tunnel

Soil disturbance is inevitably during the construction of the shield tunnel, which brings about the additional soil displacement and stress and may affect the safety and normal use of the surface structures, foundations and adjacent pipelines, etc. On the other hand, some engineering cases adjacent to the existing tunnel, for example the deep excavation, the loading and unloading process and the construction of tunnel adjacent to the existing tunnel, etc, bring about the additional displacement. Excessive longitudinal displacement may induce longitudinal crack of tunnel segment joint. So it is important to predict the soil deformation and additional stress induced by tunnel construction, and the prediction of longitudinal displacement of tunnel also bears the important significance. This dissertation firstly recites and analyzes the researching status, and points out their advantages and disadvantages in detail. Then based on the above analyses, some main original works are made as follows:(1) The soil displacement and additional stress induced by ground loss during the tunnel construction are studied, in which the image method are introduced. The three-dimensional soil displacement calculation formulas are deduced by assuming non-uniform elliptical soil displacement pattern, which is gained by analyzing the influence of four different ground movement models on soil displacement. Based on the displacement calculation formulas, the additional stress calculation formulas due to ground loss are deduced from elastic theory. Then combing the analytical example, the distributions of addition stress are discussed.(2) Based on the research of the parameters getting, the calculation formulas of primary parameters applicable to various stratums are put forward. The non-uniform elliptical soil displacement pattern, which is more appropriate for the actual cases, is adopted. With the calculation formulas of parameters and the elliptical displacement pattern, the revised stochastic medium theory, applicable to the calculation of surface and subsurface soil displacement is brought forward.(3) With the application of Mindlin solution, the soil three-dimensional displacement and additional stress induced by bulkhead addictive thrust and skin friction between shield and soil are analyzed. Assuming soil is not drained, the soil displacement calculation formulas induced by the deflecting sheer of shield are put forward, which are based on the movement of cross section of the shield. Regards the slurry injecting as the reverse process of ground loss, the calculation formulas of displacement and stress inducedy by slurry injecting are deduced. It is shown in an engineering case, the results by the method above are comparable with the actual data and the results of finite element analysis.(4) Assuming the shield tunnel as a continuous homogeneous beam with the same rigidity and structural characteristics, the calculation formulas of equivalent longitudinal stiffness of tunnel are deduced. Concerning the influence of the limited influence area of longitudinal crack and the transverse effective rigidity ratio, the improve equivalent longitudinal continuous calculation model of tunnel is constructed.(5) Assuming the shield tunnel as an infinite beam, the analytical formulas of longitudinal displacement of tunnel are deduced, in which the continuum elastic solution method is introduced and calculation formulas of the equivalent bending stiffness are applied. And the shearing effects of foundation and the interaction between tunnel and soil are also concerned in the deducing process.(6) Based on the Mindlin solution, the calculation formulas of superimposed load induced by loading or unloading on tunnel are deduced. Then the distributing and influence factors of load imposed on tunnel are studied. Combing the continuum elastic solution method and the displacement calculation formulas induced by loading or unloading, the longitudinal displacement of tunnel is worked out. With an engineering case, it is proved that the results from the method in this dissertaion are comparable with the method of Winkler foundation model and the finite element analysis.(7) Through the numerical intergration method, the calculation foumulas of the soil displacement and stress, caused by pile penetration are deduced from the the image method. Furthermore, a continuum elastic solution method is presented for estimating the longitudinal displacement and bending moment of a shield tunnel around the jacked pile. The method is based on the calculation formulas of displacement above. A three-dimensional numerical analysis is conducted to investigate the effects of jacked pile on an adjacent shield runnel by MIDAS/GTS. The results between the calculation formulas and three-dimensional numerical analysis are validated.(8) The superimposed load distributing and influence factors imposed on existing tunnel induced by construction of parallel tunnels and perpendicularly crossing tunnels are studied, in which the calculation formulas of image method induced by ground loss are introduced. The longitudinal displacement characteristics of tunnel are studied by introducing the continuum elastic solution method. Through the analyzing of an analytical example, the distributing and influence factors of longitudinal displacement of tunnel are analyzed.