Deformation Control of Subway Stations under the Influence of the Construction of Deep and Large Foundation Pits with Composite Support Systems

The excavation depth of a deep and large foundation pit of a composite support system is 25.5 m, the minimum clear distance from the main structure of the station is 10.6 m and the closest distance to the entrance and exit structure is only 3.6 m. Relying on this project, numerical simulation, field monitoring and other methods are used to study the deformation law of the self-supporting system, the ground settlement and the subway station under construction. Then, the influence of different support parameters on the deformation of the subway station and track is analyzed, and the internal relationship between the deformation value of the station and track and the support parameters is further discussed. The main work and achievements are as follows: (1) Through field measurement and analysis, the deformation history of the station and track in the excavation is studied. The obtained results show that the interbracing + pile–anchor composite support structure has better control over the deformation of adjacent stations and tracks. Comparing the simulated value of station and track deformation with the measured data, it is concluded that the simulated and measured deformation trends remain consistent, and the maximum deformation value corresponds to the middle position of the foundation pit. This confirms the rationality and reliability of the composite support system model. (2) The analysis of the influence of different support parameters on the maximum deformation value of the subway station and track shows that the deformation of the station and track is less affected by the pile diameter of the retaining pile and the size of the interbracing section. It is greatly affected by the embedding depth of the retaining pile and the number of support channels. It is suggested that the optimal parameters should be a pile diameter of 1.0 m, embedding depth of 8 m, four interbracings and an interbracing section of 1.0 m × 1.0 m.