# Soil and Rockfill Dams Safety Assessment for Henan Province: Monitoring, Analysis and Prediction
## 4 Results
Among the soil and rockfill dams studied, the Baisha Reservoir Dam is a homogeneous earth dam with severe consolidation effects and the highest annual deformation rate, followed by the inclined wall soil and rockfill dam, Yanshan Reservoir Dam. Clay heart wall sand shell dams are a relatively stable type of dam. The clay core sand shell dam employs low-permeability viscous soil as the seepage control material in the middle of the dam. Due to its good stability, this type of dam is widely used in the construction of large-scale soil and rockfill dams. In fact, the proportion of clay core sand shell dams in the large-scale soil and rockfill dams studied in this study reached 64.7%. A buffer zone with a radius of 5 m is established around severe deformation zones of 17 soil and rockfill dams to improve experimental accuracy and prevent accidental errors. The average deformation of all points in the buffer zone is selected for mapping. Figure 8a,b represents the relationship between the height of soil and rockfill dams with core wall and the deformation, and the relationship between soil and rockfill dams with different materials and deformation. In Figure 8a, the blue mark represents the height of the soil and rockfill dam, and the red ellipsoid represents the deformation of the soil and rockfill dam. It can be found that the height and deformation trend of soil and rockfill dam with the core wall are basically the same. The Boshan Reservoir Dam is only abnormal because it was built in 1954, 70 years ago. In such a long period of time, the soil mass is compacted under the influence of gravity, and the porosity between particles of bulk earth rock becomes smaller, so the deformation is not serious. The Xiaolangdi Reservoir Dam, with the highest height of 160 m, and the narrow-mouthed reservoir dam, with the second highest height of 77 m, both have experienced significant deformation. The former, as the highest soil and rockfill dam in Henan Province, should be a key area of concern, and Section 5 of this study will focus on its analysis. In Figure 8b, both the homogeneous dam and inclined wall dam have abnormal deformation. The Baisha Dam, a homogeneous dam, has reached \(-173\) mm, and the Yanshan Dam, an inclined wall dam, has reached \(-142\) mm, but the Xiaolangdi Dam, a core wall dam, has only \(-86\) mm. This is because the homogeneous dam is horizontally compacted in layers, and the permeability of the soil is non-uniform, forming a high saturation line in the dam body. Therefore, it can cause the soil to soften or mud, thereby causing significant deformation. The abnormal deformation of the inclined wall dam may be caused by the small contact stress between the inclined wall and the foundation, poor bonding with the foundation, and poor permeability of the material itself. Compared with the above two types of dams, the core wall has excellent low permeability and low deformation characteristics. Therefore, the deformation of the core wall dam is the smallest and positively correlated with its own dam height. Therefore, more excellent core wall dams in terms of structure and materials should be given special attention. We evaluated the safety status of 17 soil and rockfill dams in the study area according to the cumulative deformation of large soil and rockfill dams in Henan Province from March 2017 to September 2021 and requirements in the local \" Design code for rolled soil and rockfill dams \" (SL274-2020) [49]. In order to prevent excessive deformation, the dam crest needs to reserve deformation superelevation, in which the superelevation value of the soil impervious dam body is 2% of the design height of the dam body. For a 100 m high soil and rockfill dam, the allowable value of deformation after construction is 2000 mm. Dams with cumulative deformation greater than 100 mm in the study area include the Baisha Reservoir Dam and the Yanshan Reservoir Dam.