The construction of the foundation pit has a negative impact on the existing shield tunnel below, and if not properly controlled, it could lead to construction risks and affect operational safety. In this paper, the construction of a viaduct pit over an existing metro tunnel is used as an example, then the soil and tunnel deformation under various construction conditions are analyzed by numerical method and the effect of strengthening measure is quantified. The results show that the shield tunnel produced a large vertical deformation and a small horizontal displacement during the construction, while grouting can reduce the ground uplift by about 30% and the deformation of the existing tunnel by 50%.

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