# From Climate Conditions to the Numerical Slope Stability Analysis of Surface Coal Mines
## 7 Conclusions  
A new framework has been presented in evaluating coal and lignite mine slope stability due to precipitation. The main advantage of this framework is the comprehensive analysis of climate conditions and rainfall and the numerical slope stability analysis, including all steps in the procedure. Initially, climatic records were documented and analyzed to evaluate the baseline conditions; the focus was mainly on precipitation. Subsequently, the range of rainfall intensity was specified for stability analysis. Rainfall analysis included mean and maximum mean monthly precipitation for the past 30 years and maximum daily rains for the past ten years. This approach was direct and practical; an advanced statistical analysis might have increased accuracy but would have required more detailed data and would have been less practical. The case of Greek lignite mining areas was employed to illustrate the methodology. It was concluded that in the areas under investigation, rainfall intensity varies from very low (1 mm/h) to documented intensities up to 9 mm/h, lasting up to a day (24 h); very few extreme phenomena in terms of rainfall are documented. Furthermore, climatic projections of future trends were used to anticipate possible deviations from the baseline rainfall conditions. Nowadays, several methodologies are proposed for climatic projections; some open-access tools have been used and described to evaluate these projections in this work. The tools proposed in this work are readily applicable for most areas, open and free to use, and relatively easily implemented. Rainfall projections show that the reference range of past events is not expected to change significantly in the areas under investigation, independent of future emission scenarios. On the other hand, the mean temperature is expected to increase depending on future emissions. Finally, the effect of rainfall infiltration on the stability of a typical open-pit lignite mining slope was numerically investigated. The finite element method (FEM) was employed for the groundwater and rainfall analysis and was combined with the shear strength reduction method for stability evaluation. A fully coupled flow-deformation analysis was conducted, allowing for the simultaneous evaluation of the unsaturated transient seepage flow and soil mechanical response. The impact of the critical factors--the SWCC soil parameter, g\({}_{\text{a}}\), the initial groundwater head, H\({}_{\text{w}}\), the saturated permeability, k\({}_{\text{s}}\), and the rainfall intensity, q--were investigated through parametric finite element analyses. Rain infiltration primarily produces dissipation of suction stresses in the unsaturated zone, which induces a decrease in unsaturated soil shear strength, with the subsequent deterioration of pit slope stability. However, it is demonstrated that the impact magnitude of the examined parameters varies significantly. According to the numerical results, the effect of the SWCC material parameter, g\({}_{\text{a}}\), in SF's decrease rate during rainfall is more important among the other parameters. As g\({}_{\text{a}}\) decreases, the reduction rate of the pit slope's safety factor during rainfall dramatically increases. The initial groundwater head, H\({}_{\text{w}}\), and the rainfall intensity, q, showed a modest effect in reducing the pit slope's SF. As H\({}_{\text{w}}\) decreases (higher initial groundwater table location) or as the rainfall intensity, q, increases, SF's reduction rate during rainfall moderately increases. Finally, as the parameter k\({}_{\text{s}}\) increases, the SF reduction rate during rainfall increases slightly. Further work could include a more in-depth sensitivity analysis of the parameters affecting slope stability and various geometries. The particular geometry, stratigraphy, geotechnical, and groundwater conditions should be evaluated for any specific case study. Conceptualization, I.E.Z. and N.C.K. ; methodology, I.E.Z. and A.I.T. ; software, A.V.D. and R.K.; validation, I.E.Z. and A.I.T. ; formal analysis, A.I.T.