Study on the Impact of Adjacent Horizontal Unloading on the Security Zone and Tunnel Structure of an Operating Subway

The construction of deep foundation pits that are adjacent to an operating subway tunnel can cause significant disturbance to the surrounding soil and tunnel structure. Assessing the stability of the soil in the security area of the tunnel is key to controlling the displacement of the tunnel structure. Assuming that the soil behind the wall is in the elastic stage of small deformation, the unloading stress distribution law of the soil on the excavation surface of the side wall is inversely calculated using the horizontal displacement curve of the retaining structure. Based on the analytical solutions for the horizontal displacement and surface settlement of the soil behind the wall proposed in this paper, the spatial distribution characteristics of the deformation transfer of the soil in the security area are obtained. Considering the interaction between the soil in the security area and the tunnel structure, by simplifying the soil in the security area to a Pasternak foundation model, the tunnel displacement that is caused by deformation transfer can be obtained. The correctness of the theoretical model is verified by comparing it with the measured data for the soil displacement behind the wall and the tunnel structure in project cases of foundation pit excavation.