## 3 Stratum-Foundation Pit-Station-Track Interaction Model
### Comparative Analysis of Monitoring Results and Numerical Simulation
#### 3.3.3 Comparison of the Deformation Results of the Track Structure  
Through the analysis of the measured data of station and track deformation, it can be seen that the foundation pit has little impact on the existing subway line in the first two excavation stages (i.e., when the excavation depth is 0-9.5 m), and significant impact occurs in the fourth and fifth excavation stages. In this section, the vertical deformation data of YGD-1-YGD-16 corresponding to the right track of the model in the third excavation stage, the fourth excavation stage and the fifth excavation stage are selected for comparative analysis.  
From the comparison between the measured and simulated values of the settlement of the existing track structure in Figure 24a, it can be seen that the measured and simulated values of the vertical displacement of the existing track structure caused by the completion of the third excavation stage of the foundation pit are similar in trend, and there is a certain error in the value, with an error value between 0.04 and 0.61 mm. The measured maximum deformation value occurs at measuring point YGD-7, and the simulated maximum deformation value occurs at YGD-9. The measured maximum value of the vertical displacement of the overall track structure is 0.45 mm; the simulated maximum value is 1.01 mm, and the maximum error difference is 55%. As the model is an ideal state with some assumptions, there will be a difference (about 0.5 mm) to an extent compared with the measured data. This condition is in the normal range of similar projects in other studies, and the trend and the order of magnitude between the measured data and simulated data are consistent, so it is not such a big problem in the calculation.  
Figure 24b shows that the measured and simulated vertical displacements of the existing track structure caused by the completion of the fourth excavation stage of the foundation pit have similar trends, and the error value of the measurement value is between 0.28 and 0.99 mm. The measured maximum deformation value occurs at measuring point YGD-8, which deviates southward compared with the third stage, and the simulated maximum deformation value occurs at YGD-9. The measured maximum value of the vertical displacement of the overall track structure is 0.84 mm; the simulated maximum value is 1.73 mm, and the maximum error difference is 51%.  
Figure 24c shows that the measured and simulated vertical displacements of the existing track structure caused by the completion of the fifth excavation stage of the foundation pit have similar trends, and the error value of the measurement value is between 0.27 and 1.22 mm. The measured maximum deformation value occurs at measuring point YGD-8, and the simulated maximum deformation value occurs at YGD-9. The measured  
Figure 23: Comparison of simulation and actual measurement of vertical displacement at each monitoring point of the station.  
maximum vertical displacement of the overall track structure is 1.24 mm, and the simulated maximum is 2.42 mm. The maximum error difference is 49%.  
In conclusion, through the comparative analysis of the simulated value and the measured data, it is concluded that the deformation calculation trend of the retaining pile and  
Figure 24: Comparison of the simulation and actual measurement of vertical displacement of each measuring point of the track.  
the main structure of the station is basically consistent with the measured result trend. 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.