## 4 Results and Discussions
### Identification of Slope Hazards and Field Validations  
According to the procedures of slope hazard identification as described in Section 3.2, the slope and the aspect for the study area are analyzed and introduced as shown in Figure 6. From Figure 6a, the potential hazards are concentrated in the areas with relative high slope value, especially from Huangtian Town to Zhukou Town. Considering the aspect as presented in Figure 6b, the main reason is that the surface deformation obtained by the InSAR method is a displacement component along the line of sight, rather than the real value. The radar wave incident direction of the Sentinel-1A satellite ascending data used in this study is about NE80\({}^{\circ}\). For slopes with dip direction (about NW350\({}^{\circ}\) or SE170\({}^{\circ}\)) orthogonal to this direction, it is difficult to judge the actual possible surface deformation by the LOS deformation velocity. Therefore, in this study, the abovementioned situation was excluded for slope hazard investigation. Based on the above analysis, finally six potential slope hazards (named P1-P6) were identified as illustrated in Figure 7. As seen from the figure, the areas of P3 and P4 are in nearly the same positions where historical hazards occurred. To summarize, the single hazard area is not large and is highly coincident with the highway cutting slope regions rather than natural slopes. Figure 5: (**a**) Average ground deformation velocity of the study area; (**b**) potential hazards detected based on InSAR results. To better analyze the potential hazards, annual average deformation velocity and time-series deformation of typical PS points are plotted in Figures 8 and 9, respectively. In Figure 8, the studied PS points are marked and numbered (e.g., ps-4-1 representing the first PS point selected for slope potential hazard P4) consequently. Considering the comparison between different slope, the initial deformation for each PS point is recalculated to zero. The potential hazard P1 showed obvious deformation on the InSAR results map. The deformation area is mainly located in the south part of the slope, as shown in Figure 8. The deformation evolution of point ps-1-1 indicates that the slope has a continuous downward moving trend during the study period. The abnormal deformation area of potential hazards P2 and P5 is relatively small (Figure 8), and the time-series deformation of P2 shows more obvious reduction trend than P5. P3 is located on the cutting slope of the bridge-to-subgrade transition zone, covered with dense natural vegetation. It can be seen from Figure 8 that the obvious deformation abnormal area is consistent with the slope range. Two chosen PS points are located at the center (ps-3-1) and crest (ps-3-2) of the slope, respectively. In Figure 9, the deformation evolution of two positions is both slightly decreasing before 31 December 2020; after the date, the crest remains stable while the center of the slope becomes to move downward apparently. Figure 6: (a) Slope map of the study area; (b) aspect map of the study area. Figure 8: Average deformation velocity map for the identified potential hazards. Figure 7: Potential hazards identification based on the combined procedure. For P4, two obvious abnormal deformation areas can be seen from Figure 8. One area is located on the existing cutting slope (PS points ps-4-1 and ps-4-2), and the other is a bare slope (PS points ps-4-3 and ps-4-4). The overall deformation of this area is not large, but obvious decreasing can be seen of ps-4-1 and ps-4-3 during 7 October to 30 December 2020. Consequently, the LOS deformations for four PS points stay still and begin to increase after 28 February 2021. This is a strange phenomenon and may be explained by the decomposition of ground deformation as following. As the highway from Chatian to Zhukou is approximately parallel to the azimuth direction of Sentinel-1A satellite, the cutting slope can be classified into two types, i.e., westward slope and eastward slope.