Stability of slopes is a topical and substantial issue, affecting areas where there are natural slopes as well as man-made slopes in urban areas, e.g. railway and road embankments, deep excavations or dams [1, 2, 3]. In these all cases, there are a large number of factors influencing the final safety factor value. Furthermore, numerical evaluation of the slope equilibrium state requires accurate representation in a computational model of soil and water conditions, which are determined by the geological structure. This is particularly important in areas which have been tectonically active or subject to intensive geodynamic processes in their geological history [e.g. 4, 5, 6, 7]. This is due to the potential occurrence of peculiar geological features, such as soil layers with reduced strength parameters [e.g. 8], layering associated with strength anisotropy [e.g. 9] and the presence of fault or discontinuity zones in the soil or rock mass [e.g. 10, 11]. For this reason, numerical models often do not adequately replicate real geological conditions. As a consequence, the modelled equilibrium state may not accurately correspond to reality and the computational geometry of the mass movement slip surface may be incorrect.
Moreover, in numerical modelling there are various consequences deriving from the calculation method selected for slope stability analysis, as discussed in  and . Appropriate definition of the slope numerical model is also important (including: right type, sufficient number and proper size of finite elements). These aspects of modelling were discussed by the authors in an earlier publication .
This paper presents universal multistep significance analyses of the impact of individual specific soil and water conditions of a theoretical slope on its stability, expressed in terms of safety factor (SF). An evaluation of this type should be conducted in each case where there is a complex geological structure, on the basis of a properly planned parametric analysis, taking into account different cases of selected geological features.