| The original formation balance condition are broken by the excavation of large area excavation when the large foundation pit engineering is constructed using the pile anchor technique beside the existing subway shield tunnel.The soil around the foundation pit is made under the action of unbalanced force towards the foundation pit deformation and displacement. And this unbalance effect lead to stress redistribution of the surrounding rock existing around shield tunnel. But the existing of shield tunnel is designed according to the original condition of surrounding rock, moreover the subway shield tunnel is sensitive to the rock mass deformation, it is easy to appear uneven settlement due to deformation of soil. The normal use of shield tunnel and structural safety will be threatened when the unloading influence of foundation pit excavation reaches a certain degree, such as the rail line of the requirements of train operation is’t satisfied, the shield joint bolt appear tensile fracture, the waterproofing measures of segment joint are failure, and longitudinal rupture of shield lining segments appear. So at what range the effect of excavation on nearby existing shield tunnel is strong, and construction countermeasures must be taken to ensure the normal use of shield tunnel and the successful construction of the foundation pit. Within what scope the effect of the excavation on nearby existing shield tunnel is weak even without the influence, and only need using the general auxiliary construction measures even don’t need to take countermeasures. This is a problem before the general scholars and geotechnical engineers that need to be solvedThis paper takes the project of large foundation pit near the existing the existing subway shield tunnel in Shenyang central plaza south field as the background. Longitudinal deformation curvature is determined as partition criterion on the basis of the analysis of longitudinal equivalent stiffness model. Then using large-scale finite element software Abaqus, by changing the distance between the shield and the retaining structure of foundation pit, three dimensional numerical simulation of12kinds of working conditions of the four types are established when the existing shield tunnel is located in the side of foundation pit, ground-45°direction of foundation pit, passive soil excavation area and the bottom of the foundation pit. And the surface subsidence deformation of foundation pit excavation, the deformation of existing shield tunnel and horizontal deformation of the diaphragm wall are analyzed. Main conclusions and the results are as follows:(1)Based on the research of the longitudinal equivalent stiffness model, the mechanical and mathematical relationships of the longitudinal deformation of shield tunnel radius of curvature and crack of shield tunnel segment joint and internal force of bolt is known, then the longitudinal deformation curvature radius are determined as influence judgment criterion.(2)The corresponding longitudinal deformation curvature radius of shield tunnel are respectively made as division threshold of the strong-weak affected zone and weak-without influence zone that the rail line of shield tunnel in the critical state and segment joint bolt are just in the elastic limit state. Then the construction engineering influence zoning map is established which is about the construction of foundation pit near the existing shield tunnel based on the technology of pile anchor, and some corresponding construction measures are proposed.There are some reference value design to similar engineering design and construction. |
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