## 4 Results and Discussion  
### Comparison of Damage to Subway Box Structures and Finite Element Analysis  
In this study, the visual inspection mesh diagram and numerical analysis results were comparatively analyzed, and are shown in Figures 9-14. Compressive stress occurred in the upper part of the Cell 1 wall in the 20-40 m section, and transverse cracks occurred owing to the compressive stress in the upper and central parts of the wall. The analysis results of the stress in the wall at the maximum heaving section showed that the tensile stress that occurred on the lower side of the upper slab was transferred to the upper side of the wall, as shown in Figure 9. Therefore, the magnitude of the analyzed stress at the center of the wall reached the ultimate strength of the concrete. The analysis results of the wall stress in the transition section showed that shear stress that exceeded the allowable shear stress occurred in the wall at the 40-60 m section because of the extreme difference in the displacement and stress of the structure, which occurred in the maximum heaving and settlement sections, as illustrated in Figure 10a. Figure 9: Comparison between the visual inspection mesh diagram and analysis results (Cell 1 wall) for the heaving section. Figure 11: Comparison between the visual inspection mesh diagram and analysis results (Cell 1 wall) for the settlement section. Figure 10: Comparison between the visual inspection mesh diagram and analysis results (Cell 1 wall) for the transition section: (**a**) 40–60 m; (**b**) 80–100 m.  
Figure 12: Comparison between the visual inspection mesh diagram and analysis results (Cell 2 wall) for having section. Figure 13: Comparison between the visual inspection mesh diagram and analysis results (Cell 2 wall) for the transition section: (**a**) 40–60 m; (**b**) 80–100 m.  
However, the level of shear stress was small and the onsite crack level was also relatively small in the 80-100 m section where the settlement was converged in the maximum settlement section, as illustrated in Figure 10b, which was a transition section whose deviation of displacement was evaluated to be relatively small. Therefore, the damage level at the transition section directly affected the deviation in the displacement at the adjacent section, verifying that the transition section where settlement and heaving occurred simultaneously, was more vulnerable. Transverse cracks in the lower part of the wall and lateral cracks in the construction joints occurred in the 60-80 m section of Cell 1 because of the compressive stress of the slab below the settlement end point, as shown in Figure 11.  
The stress analysis results in the wall at the maximum settlement section showed that the tensile stress that occurred on the upper side of the lower slab was transferred to the lower side of the wall, thus affecting the section up to the center of the wall, as illustrated in Figure 11. Therefore, the level of the analyzed stress reached the ultimate strength of concrete. Additionally, the range of the stress levels in the analysis result was relatively consistent with the location and scale of crack occurrence. Comparing the visual inspection mesh diagram and FEA of the Cell 2 wall, it can be inferred that transverse cracks occurred in the 20-40 m section because of the compressive stress of the heaving wall, as shown in Figure 12.  
In the 40-60 m section, when compressive stress was applied to the wall at the boundary point, a transverse crack at the top of the wall and a diagonal crack in the slab at the bottom of the end point occurred, as shown in Figure 13a. In the 80-100 m section, as shown in Figure 13b, oblique cracks occurred owing to the compressive stress on the wall at the boundary point. Transverse and oblique cracks occurred in the lower part owing to the compression of the end wall.