## 5 Analysis Results
### Surface Settlement and Influence Range around the excavation  
During foundation excavation for the reconstruction of subway stations, the stratum is inevitably disturbed, and surrounding surface settlement occurs due to the unloading action of the soil. According to practical engineering experience, there are two types of surface settlement: triangular and groove. Triangular surface settlement mainly occurs when cantilever excavation or deformation of the building enclosures is large. Groove surface settlement mainly occurs when the retaining structure has a large depth in the soil, is buried in a rigid stratum, or when there is a support at the top of the envelope. In the present case, the surface settlement around the main foundation excavation corresponds to groove settlement. Under the condition of train load operation, excavation has a significant influence on the soil settlement and structures. Figure 10 shows the distribution of vertical displacement at the bottom of the foundation excavation. Settlement measurement points A1, B1, C1 and D1 were selected for a systematic comparative analysis of settlement deformation. The surface settlement curve of each point under different working conditions is shown in Figure 11.  
Figure 8: Layout of measuring points of different piles.  
Figure 10: Distribution of vertical displacement at the bottom of the excavation (unit: m).  
Figure 9: Layout of soil settlement measuring points around the excavation.  
By comparing working conditions 5 and 6 at points A1, B1, C1, and D1, it is clear that the train dynamic load has a great impact on the soil settlement around the foundation excavation. The settlement of the short side of the foundation excavation increased by approximately 20% based on the comparison of points A1 and B1. By comparing points C1 and D1, the increment of the long side of the foundation excavation was greater than that of the short side, and the increment of the settlement at point C1 was approximately 41%. The settlement at point D1 increased by approximately 49% when applying the train load. Although points C1 and D1 were on the same side, different settlements were produced. This is because point D1 is near the station of Line 3. In the normal operation of the station, the flow of people generated additional loads to the structure and soil. Therefore, the settlement at point D1 is greater than that at point C1.  
In situ construction monitoring was performed. Taking the most unfavorable working condition 6 as an example, the selected monitoring points were close to points A1, B1, C1, and D1. Figure 12 shows the comparison of the measured data and finite element calculation results when the excavation reached the depth of 26.45 m at the bottom of the excavation. In Figure 12, the monitoring data at the four points are in good agreement with the simulation results. The deformation trend is roughly the same, while there is a certain value difference between the monitoring and simulation results at points C1 and D1 so that the calculation results are slightly smaller than the monitoring data because the soil  
Figure 11: Surface settlement curves at various points under different working conditions. (**a**) Point A1; (**b**) Point B1; (**c**) Point C1; (**d**) Point D1.  
condition was simplified for convenient calculation, and the simulation working condition did not fully reflect the actual engineering construction. The results at points A1 and B1 are similar, and the maximum settlement located near points A1 and B1 in the short side direction of the foundation excavation were approximately 0.53 times the excavation depth.