Objective In order to investigate tunnel structural deformation, it is necessary to analyze the impact of box culvert foundation pit excavation on existing metro tunnels.

Method Taking the project of the Longji River Channel box culvert excavation above the Peijiaying Station-Wangsheren Station section on Jinan Metro Line 3 as an example, FLAC 3D software is used to simulate and analyze the impact of box culvert foundation pit excavation on the structural deformation of the lower existing metro tunnel under conditions with/without grouting reinforcement. During on-site construction, a series of monitoring points are set up inside the existing metro tunnel to monitor and analyze the structural deformation of the tunnel throughout the entire process.

Result & Conclusion  In the process of the foundation pit excavation, the maximum heave at the pit bottom under the non-grouting/grouting reinforcement conditions is 9.421 mm and 8.466 mm, respectively. When the excavation depth reaches the maximum value of 7.55 m, the difference in tunnel heave deformation between the two conditions is 0.950 mm. The vertical stress in the soil above the tunnel exhibits a U-shape distribution, while the vertical displacement shows an inverted U-shape distribution. Grouting reinforcement can effectively control the deformation of the stratum and the existing tunnel structure, and the deformation control effect becomes increasingly significant as the excavation depth increases.