# Failure Assessment of Embankment Dam Elements: Case Study of the Pirot Reservoir System
## 6 Conclusions  
The paper presents an analysis of the functionality of the dam elements of the multi-purpose water system, using the finite element method, for the example of the Zavoj dam. Numerical analyses of the filtration and stability of the facility were conducted, and key structural elements whose potential damage could cause a collapse or loss of water system performance were identified. The key elements whose functionality were analyzed are the grout curtain, the overflow section with the shuice gates, and the spillway, i.e., the slope above the spillway. In recent years, earthquakes have been a frequent occurrence in Serbia and the surrounding area. For this reason, seismic load has been used as a load scenario in the conducted stability analyses presented in this paper. The impact of the grout curtain damage and loss of water resistance function on the change of flow under the dam body was analyzed, as was the possibility of damaging the overflow section and shuice gates, as well as the loss of partial stability of the slope above the spillway, whose potential damage would reduce the capacity of the spillway. Based on the results of numerical simulations, it was concluded that damage to the grout curtain in different zones would not significantly increase leakage under the dam body. In the worst-case scenario, the amount of leachate below the dam would increase several times in relation to the nominal conditions. This increase in flow is almost negligible in relation to the average annual flow of the river Viscoica, but damage to the grout curtain could cause local erosion, which can be progressive and, in the long term, can compromise the global stability of the structure. Additionally, water losses represent a loss of energy, and thus significant financial loss. By analyzing the strength of the concrete overflow section and the shuice gates, it is clear that this element of the structure is very robust, and during an earthquake of the highest intensity there is no real possibility of damage. This conclusion is supported by the large amount of remaining load-bearing capacity of this part of the structure. During an earthquake of the highest intensity, the displacement of the entire part of the overflow may occur, whereas the relative displacement in the shuice gates region is small and this displacement will not compromise their function. Numerical analyses of stability have shown that the spillway, i.e., the slope above the spillway, is the weakest element of this structure due to seismic loading. For the purposes of partial stability analysis, a new measure called remaining load-bearing capacity was introduced. It has been shown that due to the effect of seismic loading, either in the direction of the waterflow or in the direction of the dam axis, a partial loss of stability of this slope can occur. At the same time, a part of the terrain could bury and fill the spillway along the entire length or one of its parts and thus significantly reduce the performance of the spillway to release outflows during the flood events. This hypothetical scenario can occur in the case of the simultaneous action of an earthquake and a reservoir high water level, which would cause catastrophic consequences for the dam itself and thus for the population and property downstream of the dam. Based on the conducted analyses using the finite element method, a functional dependence between the earthquake intensity and the spillway capacity was formed, i.e., a surrogate model. Considering the simplicity of the surrogate model, it can be incorporated within the system of dynamic approach intended to simulate the functionality of the water system elements under the stress such as multiple hazard events: earthquakes and floods. **Author Contributions:** Numerical analysis and results presentation, D.R. ; conceptualization, supervision, methodology and writing, D.R., M.S., D.I. and M.Z. ; funding acquisition and project organization, M.S. and N.M. All authors have read and agreed to the published version of the manuscript.