## 4 Case Study
### Structural Diagnosis of the Arch Dam under Abnormal Uplift Pressure
Under the measured uplift pressure, the equivalent stress in the riverbed shows the obvious abrupt change. The research has also shown that the compressive stress, at the foundation of the riverbed, decreases with the measured uplift pressure increases, which is not conducive to the long-term safety and stability of the arch dam. At present, under the action of measured uplift pressure, the equivalent tensile and compressive stress values of the concrete arch  
Figure 14: Comparison of equivalent stress of dam foundation under design and measured uplift pressure. dam still meet the standard requirements, which indicates that the structural strength of the concrete arch dam is relatively high. (2) Deformation analysis of arch dam  
The displacement of the concrete arch dam is analyzed under the same working condition of the stress analysis. The displacement changes of the dam and the foundation in the riverbed are shown in Table 4, of which distribution is shown in Figure 15. Upward is positive for vertical displacement, the downstream is positive for displacement along the river, and the left to the right bank is positive for transverse displacement. Table 4 and Figure 15 presents that: 1 Compared with the design uplift pressure, the vertical settlement of the dam body is reduced from 1.13 cm to 1.12 cm under the measured uplift pressure, appearing at 1/3 height of the dam crest. 2 The downstream displacement of the dam body increased from 3.32 cm to 3.33 cm, appearing in the middle of the dam crest. 3 The maximum transverse settlement of the dam body decreased from 1.10 cm to 1.09 cm, appearing at a quarter arch. Transverse displacement from both banks to the riverbed decreased. 4 Under the design and measured uplift pressure, the displacement distribution regularity is highly similar. From Table 4 and Figure 16, we can see that: 1 compared with the design uplift pressure, the vertical displacement of the dam body changes from 1.27 \(\times\) 10\({}^{-4}\) m downward to 8.96 \(\times\) 10\({}^{-5}\) m upward under the measured uplift pressure, appearing in the upstream surface; 2 the downstream displacement along the river decreased from 3.38 \(\times\) 10\({}^{-3}\) m to 3.37 \(\times\) 10\({}^{-3}\) m, appearing in the middle of the foundation surface. 3 The maximum transverse settlement of the dam body is from 7.33 \(\times\) 10\({}^{-4}\) m decreased to 7.08 \(\times\) 10\({}^{-4}\) m, appearing in the right bank and downstream side of the foundation. 4 With the increase of uplift pressure, the foundation surface in the riverbed showed an upward tendency in vertical displacement, upstream along the river, moving to the middle in transverse displacement. 5 Under the design and measured uplift pressure, the displacement distribution of the dam is similar. The displacement distribution under the measured uplift pressure conforms to the general law, and the change of uplift pressure has little effect on the safety and stability of the dam body. The FEM results show that the dam deformation is still relatively safe under the abnormal uplift pressure. According to the analysis of the structural behavior of the arch dam under the abnormal uplift pressure, the stress and deformation of this concrete arch dam are still within the allowable safety range of the concrete material. Meanwhile, the structural behavior of this  
Figure 16: Contour map of foundation displacement under the measured uplift pressure (Unit: m). dam meets expectations in a short time. However, the monitoring of the uplift pressure should be strengthened, and attention should be paid to the development of abnormal uplift pressure value and its scope. The operation should avoid the high water level as much as possible and deal with the leakage of the dam foundation as soon as possible to ensure the safety of the concrete arch dam.