## 5 Conclusions  
Taking the deep and large foundation pit of a composite supporting system in Beijing adjacent to the existing subway station as the project background, this study evaluates the deformation law of the existing subway station and track caused by deep and large foundation pit excavation by combining numerical simulation and field measurement. The specific conclusions are as follows:  
(1) Based on the analysis of the field measured data, the retaining pile rises continuously with the excavation of the foundation pit, and the horizontal deformation of the retaining pile is inclined to the inner convex drum of the foundation pit. With the advancement of the construction process of the foundation pit, the position of the maximum horizontal displacement of the pile gradually moves downward; the entrance and exit structure of the station is greatly affected by the foundation pit excavation. After the foundation pit excavation is completed, the maximum horizontal and vertical displacement deformation values of the entrance and exit are 3.6 and 1.7 mm, respectively. When the excavation depth of the foundation pit is 14.5-25.5 m, the vertical displacement of the station and track begins to significantly change, and the maximum vertical displacement is 1.43 and 1.24 mm, respectively. The horizontal displacement of the station and track increases with the excavation of the foundation pit. (2) Through the comparative analysis of the simulated value and the measured data, it is concluded that the trend of the deformation calculation results of the retaining pile and the main structure of the station is basically consistent with the measured results. The measured horizontal displacement of the retaining pile is close to the simulated value, and the measured vertical deformation of the main structure of the station is approximately 0.5 times the simulated value. The measured and simulated deformation trends of the track structure are consistent in all stages of foundation pit excavation. The deep and large foundation pit model of the composite support system can reflect the influence of construction on the deformation of adjacent existing stations and track structures and verify the applicability of the model to supporting projects. (3) Through the model calculation and analysis under the working conditions of different support parameters, it can be seen that the support parameters that can be adopted for construction are a pile diameter of 1.0 m, embedded depth of 8 m, four internal supports and 1.0 m \(\times\) 1.0 m inner support section. The deformation of the existing station and track is less affected by the pile diameter of the retaining pile and the cross-section size of the internal support and more affected by the embedded depth of the retaining pile and the number of internal support tracks. When the embedded depth of the retaining pile is greater than 8 m, which is the optimal embedded depth of this project, and when there are more than four internal support tracks, the reduction in the maximum deformation of the station and track is no longer clear. (4) The general trend is that the greater the embedded depth, the smaller the influence is on the subway. However, it is found that when the embedded depth increases to 8 m and above, the influence of the further increase in the depth on the deformation tends to be less obvious. Therefore, the inflection point of 8 m can be a certain reference value for engineering foundation pit design. **Author Contributions:** Conceptualization, H.P. and L.Z. ; data curation, H.P. and H.L. ; formal analysis, Z.L. ; funding acquisition, H.P. ; methodology, L.Z. ; resources, H.P. ; writing--original draft, Q.T. ; writing--review and editing, G.W. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the Scientific Research and Development Project of China National Railway Group Co., Ltd. (N2020G009). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable.