## 5 Conclusions  
In this study, using simulation and numerical modeling, a stability analysis was conducted for a hypothetical slope, representative in terms of its geometry, dimensions, and material characteristics of the waste dumps in the Motru coalfield in the Oltenia region of Romania. As a result of the simulations, (1) quantitative and qualitative results were obtained for the factor of safety (FoS) values for four different slope angles, in two plasticity cases. Naturally, the FoS decreases as the slope angle increases, and for the same slope angle, the FoS value for the non-associative plasticity case is always lower than that for the associative plasticity case. This indicates that the influence of considering non-associative plasticity is insignificant for the material parameter values considered. (2) The simulation results also provide an intuitive graphical representation of the equivalent plastic strain values of the studied mass for different slope angles just before the occurrence of failure (sliding), illustrating the localization of plastic strain nuclei and the failure surface for all various slope angles. This highlights the development of multiple failure surfaces within the sloped mass, a phenomenon that is more evident at smaller slope angles. (3) The 3D extension of the plane section provides a spatial representation of key characteristics like displacements, deformations, and stresses, which helps to highlight the behavior of the mass outside the sliding zone. The ability to visualize the magnitude of displacements, not just relative deformations, across the entire analyzed mass allows for a better estimation of the rock mass behavior depending on the slope angle and it also enables the correlation of qualitative aspects related to displacements and deformations with quantitative ones, such as the FoS, offering more comprehensive information for stability assessment. Moreover, the possibility of visualizing not only the magnitude of displacements but also the displacement trend--direction and orientation--at different points within the analyzed area is useful for predicting the future behavior of the slope. (4) Considering the values obtained for the FoS, it is more appropriate to use the non-associative flow rule, a conclusion also backed by [57], where [PERSON] et al. suggest that this flow rule should be adopted for slope stability analysis. (5) In most cases, factors like dilatation angle, soil moduli, or domain change cause differences of just a few percent and are not critical for engineering use of the SSRM. Regarding the limitations of the SSRM generally, and when used in this research, there is a possible sensitivity to non-linear solution algorithms and flow rules in certain very special cases like soft or thin band problems, which is supported by the existing literature. Also, the method cannot detect other failure surfaces, which, even if less critical than the SSRM solution, still must be taken into consideration in engineering practice. Finally, increasing the complexity of the geometry, mesh elements, or additional variables can lead to very long computing times as compared to the LEM. As a future research direction, we want to approach the simulation of a similar model using the FDEM technique using the Geomechanica IRAZU software and compare the results. Also, again using the COMSOL software, we want to enhance the presented model by taking into consideration the influence of water infiltration. There is a possibility to extend the research outside of the Motru coal basin, namely to the Jilt, Rovinari, or other coal basins within the Oltenia Region, where there are dumps with different material characteristics. The model can also be adapted for the evaluation of the working face of open pit mines. It can be concluded that the SSRM and LEM both have their respective advantages and limitations, and neither method is clearly superior for routine analysis and design.