# Soil and Rockfill Dams Safety Assessment for Henan Province: Monitoring, Analysis and Prediction
## 5 Discussion  
### Deformation Monitoring Analysis of Xiaolangdi Soil and Rockfill Dam  
The Xiaolangdi Water Control Project is located at the exit of the Yellow River gorge in the middle reaches of the river, within the Xiaolangdi area of Mengjin County, Henan Province  
Figure 8: (**a**) Soil and rockfill dam with core wall and height; (**b**) three soil and rockfill dam types and deformation. Province. The dam adopts a clay-inclined core wall rockfill dam with a maximum height of 160 m and a length of 1667 m. There is an 8 m-wide raceway at the top of the dam, with an upstream slope of 1:1.75 and a downstream slope of 1:2.6. The Xiaolangdi Dam is currently the largest soil and rockfill dam in Henan Province, with a filling capacity of 51.85 million m\({}^{3}\) and a storage capacity of 12.65 billion m\({}^{3}\)[50]. Figure 9 provides a clear overview of the study area. This experiment utilized the PS-InSAR technique to process 55 Sentinel-1A images, generating an average deformation map of the Xiaolangdi Reservoir Dam from March 2017 to September 2021 in the line-of-sight direction. Based on the degree of deformation observed during different time periods, the deformation of the dam body was statistically analyzed, as shown in Figure 10. Negative values indicate movement away from the satellite direction and represent the deformation of the dam body. In contrast, positive values indicate movement towards the satellite direction and represent the rise of the dam body. It can be observed from the figure that the PS points are mainly concentrated on the  
Figure 9: Overview map of the study area. dam body of the reservoir. The deformation of the Xiaolangdi Reservoir Dam decreases gradually from the top to the bottom, with the central part exhibiting greater deformation than the two sides. The maximum cumulative deformation recorded reaches \(-\)86.09 mm. Beginning in March 2017, it took about nine months for significant deformation to appear at the top of the dam in December 2017. Subsequently, noticeable stepped shape deformation was observed in March 2019, and this pattern continued in the following time periods. These findings indicate that the Xiaolangdi Reservoir Dam has undergone significant deformation over approximately two years. Based on the deformation monitoring results of the Xiaolangdi Reservoir Dam, a detailed analysis was conducted on the critical parts of the dam body and the deformation  
Figure 10: Cumulative deformation in LOS direction of Xiaolangdi Reservoir Dam at each stage. of its longitudinal-transverse section. As shown in Figure 11, the critical areas of the dam body were designated, along with longitudinal section B-B1 and transverse section A-A1, and critical monitoring points were set at positions 1-19. The displacement obtained by satellites is only deformation perpendicular to the slope surface. The upstream and downstream slope dams are not in the same direction as the deformation of the dam crest, resulting in deformation deviation. The above method, as Section 3.1 in this study, was used to convert the vertical deformation of different slope dam surfaces to vertical to the level surface. For the Xiaolangdi soil and rockfill dam, the upstream slope dam has less deformation information due to the influence of the storage level, slope, and incidence angle. So, the deformation of the downstream slope dam perpendicular to the level surface is mainly considered, and the deformation of the dam crest and the downstream slope dam is converted to the same direction to improve the reliability of the analysis results. The transformed deformation rate diagram is shown in Figure 12. Points 1 to 3 with deformation rates ranging from \(-21\) mm/a to \(-12\) mm/a; points 4 to 6 with deformation rates ranging from \(-12\) mm/a to \(-7\) mm/a; and points 7 to 9 with deformation rates ranging from \(-7\) mm/a to \(-2\) mm/a. Figure 11: Transverse and longitudinal sections and the distribution of key points.