| The development of urban rail traffic and great exploitation of urban underground space will inevitably lead to many constructions over the existing subway tunnels. However, the unloading function during soil excavation would change the stress state of the surrounding soil, which will bring vertical deformation and additional internal force to the existing subway tunnel. Thus, the safety and normal operation of the existing tunnel will be affected.The vertical deformation of existing tunnel induced by the unloading function of different kinds of constructions over it is first analyzed via theoretical analysis and numerical analysis. Then, combined with the control standard of tunnel deformation based on reliability, the reasonable control measures on tunnel deformation are analyzed. In addition, the effectiveness of the theoretical analysis results above are examined taking an example of the underground traffic engineering at Jinrongjie, and the results provide an effective theoretical basis for the practical engineering. The main contents are shown as follows:1. Based on the past study of the excavation unloading effect on the existing subway tunnel and considering the time effect of soil stress and strain which is the Theological property of soil, the additional stress of tunnel induced by excavation unloading in the soil which is considered as a viscoelastic material is derived out firstly by use of mindlin formula, according to the correspondence principle between elasticity and viscoelasticity. Then, by the choice of typical open-cut and undermining engineering over the existing subway line, with the result of the solution, the tunnel vertical deformation law induced by different excavation unloading constructions is analyzed by employing the principle of viscoelastic foundation beam model and the time effect of the excavation unloading on the deformation is also analyzed. The tunnel vertical deformation formulas induced by open-cut triangular and undermining excavation unloading above are deduced for the first time. And formulas for vertical relative deformation of a underlying existing single-section tunnel due to excavation unloading are also deduced for the first time considering the affect of tunnel deformation joints.2. By means of FLAC3D numerical analysis software, Using the viscoelastic plastic constitutive relation, numerical simulation analysis on the tunnel vertical deformation induced by excavation unloading above is conducted with consideration of the soil rheology, based on the typical open-cut and undermining engineering over the existing subway line. In addition, a comparison between numerical simulation results and theoretical analysis results is done.3. To ensure the safety of tunnel during soil excavation over it, structural performance failure functions of both reinforced concrete tunnel and shield tunnel under serviceability state are established. Furthermore, combining the target reliability index β, the control value of the tunnel deformation is studied. And it is the first time to propose the control value of the tunnel vertical deformation based on reliability analysis.4. Taking the typical open-cut engineering over the existing subway line as study object, the influence of time-space effect of excavation unloading on tunnel vertical deformation is analyzed, which can provide a theoretical basis for time-space effect rules in practical excavation. And a reasonable grouting range to control the tunnel deformation is presented.5. Analysis on the vertical deformation of underlying existing Subway Line2tunnel induced by excavation unloading is conducted by theoretical analysis and3D numerical simulation, taking as an example the underground traffic engineering at Jinrongjie, Beijing. Based on the analysis results, the deformation control standard and reasonable grouting range are proposed. At last, a contrast analysis on the analytical results and in-situ monitoring data is carried out.
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