## 5 Results and Discussions
### Numerical Stability Analysis for Increased Lake Water Level
PLAXIS 2D offers detailed insights into the behaviour of the dams by providing crucial data on deformation, displacement, stresses, and strains under varying water levels, specifically for scenarios where the water level rises by 5 m and 10 m. The stability analysis incorporated the geotechnical properties of the moraine sediment dams into the finite element model. The Mohr-Coulomb model, an elastic-perfectly plastic constitutive model frequently used in geotechnical engineering, was chosen to represent the stress-strain behaviour of the soil. This model is valued for its practical application in design and analysis due to its simplicity and effectiveness in capturing general soil behaviour. The Mohr-Coulomb model requires five key parameters: [PERSON]'s modulus (E\({}^{\prime}\)), friction angle (\(\phi\)\({}^{\prime}\)), [PERSON]'s ratio (\(\
u\)\({}^{\prime}\)), cohesion (\(c\)\({}^{\prime}\)), and the dilatancy angle (\(\psi\)\({}^{\prime}\)). The dilatancy angle is often approximated as \(\phi\)\({}^{\prime}\)--30\({}^{\circ}\) when the friction angle exceeds 30\({}^{\circ}\), as described by [PERSON] (1986) [40]. The use of this model enables a comprehensive evaluation of the dams' stability under different loading conditions, providing valuable information for predicting potential failure scenarios and their impacts. In the finite element (FE) analysis, the impact of rising lake water levels on the stability of the moraine sediment dams was thoroughly investigated. The simulation encompassed three critical water level scenarios: the submerged base level of the dams and water levels rising by 5 m and 10 m above the submerged base level. It is important to note that the base level of the dams is generally not submerged due to the continuous discharge from the outlet of dam AB, as shown in Figure 1. The FE analysis shows the total displacement of 1.25 m, 18.72 m, and 24.67 m for dams AB, CD, and EF under all three critical scenarios. These displacement values reveal that dam AB exhibits significantly lower displacement compared to dams CD and EF across all water level scenarios. This suggests that dam AB has considerably higher stability and resistance to deformation under varying water levels. The relatively minor displacement of dam AB, even with a water level increase of 10 m, highlights its robustness and effectiveness in maintaining structural integrity despite rising water pressures. In contrast, the much larger displacements observed in dams CD and EF under similar conditions suggest that these dams are more susceptible to deformation and instability. Figure 6 illustrates that the total displacements for all three dams were quite similar across the different water level scenarios. This uniformity indicates that while the absolute displacements differ significantly between the dams, the relative impact of water level rise is consistent in terms of how it affects the overall stability of each dam. The similarity in displacement patterns across the scenarios emphasises that dam AB remains the most stable structure, while CD and EF show greater sensitivity to water level changes. The analysis of critical stability parameters like displacement, volumetric strains, shear strains, and deviatoric stress revealed consistent results across all three scenarios of water level rise. As shown in Table 2, the effects of water level increases, whether by 5 m or 10 m, were similar for the dams. This indicates that the dams' stability responses remain relatively stable under varying water levels up to a 10-metre rise. It is noteworthy that permafrost conditions are prevalent both on and within the dam structures and their surrounding sites. Perrafrost plays a crucial role in enhancing the strength and stability of these dams by preventing seepage and reducing the risk of structural failure. The presence of permafrost contributes to the overall stability of the dam structures by providing additional support through its high shear strength and low permeability.