# Soil and Rockfill Dams Safety Assessment for Henan Province: Monitoring, Analysis and Prediction
## 5 Discussion
### Deformation Monitoring Analysis of Xiaolangdi Soil and Rockfill Dam
Figure 13a revealed that the upper part of the Xiaolangdi Reservoir Dam had experienced a deformation of approximately 80 mm over the past five years, showing a downward trend and a more linear deformation curve. This indicates that the deformation in the upper part of the dam is periodic. The middle section of the dam exhibited a deformation of approximately 40 mm, which is relatively slow in comparison with the upper part and reveals slight oscillations, as illustrated in Figure 13b. On the other hand, Figure 13c highlights that the lower part of the dam has sunk by around 20 mm, and the deformation consistently exhibits a high magnitude of oscillation. Overall, the deformation of the Xiaolangdi Reservoir Dam gradually diminishes from top to bottom. This can be attributed to two reasons: Firstly, the dam's significant weight contributes to noticeable deformation in the upper part. It follows that being a large-scale soil and rockfill dam, the long-term accumulation of soil and rock materials causes soil compaction, leading to distinct diminishing deformation from the top to the bottom. As the lower part of the dam is beneath the reservoir water level, the magnitude of the deformation is influenced by the water pressure generated due to fluctuations in the reservoir's water level. This explains why the deformation magnitude of points 4 to 6 is relatively minor in comparison with points 7 to 9. Figure 12: The deformation rate of the Xiaolangdi Reservoir Dam vertical to the level surface. The rest of the monitoring points, consisting of points 10 through 19, are distributed as follows: points 10 and 11 at the base of the dam, points 12 and 13 at the left abutment, points 14 to 16 at the right abutment, and points 17 to 19 at the spillway. Points 10 and 11 at the dam's base exhibit a similar uplift trend, but point 11 has a greater magnitude than point 10, as depicted in Figure 14a. Points 12 and 13 at the left abutment have experienced a 10 mm uplift on average over the past five years. The outer point 12 experienced higher deformation than the inner point 13, as shown in Figure 14b. Points 14 to 16 at the right abutment display a comparable deformation pattern, with points 15 and 16 oscillating around zero while monitoring point 14, located on the outer side of the right abutment, undergoes a relatively significant uplift with a similar trend in deformation, as shown in Figure 14c. Finally, points 17 to 19 at the spillway have experienced an average uplift of around 15 mm in the past five years. They continuously oscillate due to water pressure during flood discharge, as shown in Figure 14d. The Xiaolangdi Dam displays unique deformation characteristics at each monitoring point compared to other areas. The right side of the dam is relatively stable compared with the left, where more noticeable deformation occurs on the outer side of the abutment. Meanwhile, the dam base remains relatively stable with lower levels of deformation. In contrast, the spillway shows obvious deformation due to long-term water flow impact and displays a further regular pattern. Figure 13: (**a**) Deformation at points 1, 2, and 3 in the upper part of Xiaolangdi Dam; (**b**) deformation at points 4, 5, and 6 in the middle of Xiaolangdi Dam; (**c**) deformation at points 7, 8, and 9 in the lower part of Xiaolangdi Dam. We further analyze the section of the Xiaolangdi Dam, specifically cross-section A-A1 in Figure 15a and longitudinal-section B-B1 in Figure 15b. It appears that the middle section of the dam has experienced larger deformation in the past five years compared with the sides. The maximum deformation reached 86 mm, while the right side of the dam was relatively stable compared with the left. Moreover, Figure 15b shows that the deformation of the Xiaolangdi Dam decreases progressively from the top to the bottom of the dam in the vertical direction.