## 1 Introduction  
The support function of a composite support system can effectively reduce the deformation of the existing subway station structure caused by foundation pit construction. Domestic and foreign scholars have performed many studies on the safety and stability of foundation pit construction and its impact on the safety of adjacent existing subway structures based on theoretical analysis, numerical analysis and field monitoring analysis. (1) Theoretical analysis method  
[PERSON] et al. [1] established an analytical model to study the influence of tunnel deformation caused by circular foundation pit excavation and compared it with the existing centrifugal test data and the analytical solution of square excavation. It is determined that the results of the three are within a small error range, and the reliability of the solution is verified. Based on the Mindlin solution, [PERSON] [2] calculated the surrounding surface settlement and the change in additional stress in the adjacent subway section during the excavation of the foundation pit and verified the influence of foundation pit dewatering and foundation pit sidewall stress release on the additional stress in the adjacent subway section. [PERSON] et al. [3] studied an existing subway station near a deep foundation pit based on plate and shell theory, numerical simulation and field measurement methods; based on the relevant theoretical analysis, it was concluded that the excavation depth has the greatest impact on the lateral structural deformation of the station, followed by the excavation length, additional load and stiffness of the existing station, while the soil gravity has the least impact. Based on the [PERSON] foundation model, [PERSON] et al. [4] optimized the two-stage simplified analysis method of longitudinal deformation of adjacent subway sections caused by construction for adjacent double foundation pit construction projects and analyzed the influence of simultaneous excavation of double foundation pits in soft soil on the vertical displacement of tunnels. (2) Numerical analysis method  
[PERSON] et al. [5] analyzed the influence of dynamic stress redistribution on deformation using a two-dimensional mathematical model. [PERSON] et al. [6] investigated and analyzed more than 20 domestic engineering examples of subway tunnel deformation caused by excavation and unloading of foundation pits, comprehensively analyzed the deformation law of subway tunnels adjacent to foundation pits with the excavation process using the finite element method and proposed an empirical formula for the maximum uplift and subsidence value of double-track tunnels in soft soil areas. [PERSON] et al. [7] applied the numerical simulation method to study the variation law of the structural deformation and the geometric shape and position of the existing track under the conditions of different excavation depths of the foundation pit and distances from the existing shield tunnel. [PERSON] et al. [8], based on the foundation pit of a subway station in Xi'an adjacent to the existing subway station and section project, according to the factor of relative distance between the new foundation pit and the existing station, using the finite element method based on the parameter factors of different relative distances, analyzed the surface settlement, the deformation law of the retaining structure of the foundation pit itself and the adjacent station with the excavation process. (3) Measurement analysis method  
[PERSON] and [PERSON] [9] analyzed the geodetic monitoring records of some recently constructed tunnels and their deformation factors. A previous study [10] has shown that tunnel ground deformation monitoring is a common means to select and control the excavation and support methods predicted in the design and ensure the safety of tunnel excavation (including the safety of personnel in the tunnel and the safety of the ground structure) and construction quality.