## 5 Conclusions  
1. Structurally complex soil conditions in the area of the upland slopes (especially considering glacitectonic disturbances) require optional stability analyses, which take into account both the spatial variability of the soil structure and the variability of soil strength parameters. 2. For a more precise recognition of the spatial variability of the position of the soil layers, it is recommended to use quasi-3D electrical resistivity imaging (ERI; the so-called 2.5D electrical resistivity imaging). This method is necessary to obtain a 'continuous' image of the course of the disturbed roof of key structural surface (clays), which can determine the conditions of the equilibrium state of slopes, deep excavations, etc. 3. Identification of the Neogene clay elevation with the ERI method made performing a multivariant stability analysis possible. The results of the analysis allowed the determination of nomograms defining changes in SF depending on c' and \(\phi^{\prime}\). 4. The variability of soil properties caused by exogenous factors, in particular in the weak zones (e.g., on the clay roof), resulted in an alternation of strength parameters of the soil, which may change over time. For this reason, the use of parametric sensitivity analyses of computational models is recommended. Figure 7: The three-dimensional dependencies of SF on the value of the internal friction angle and cohesion for different calculation methods. The analysed models indicated that the Neogene clay elevations were the main factor influencing the stability of the massif in the slope area. Changes in soils' strength parameters were the secondary factor in modifying the structural factors of stability. For example, according to applied models, changes in the strength parameters in the range of \(\phi^{\prime}\pm 5^{\circ}\); \(c^{\prime}\pm 5\) kPa resulted in changes of SF \(\pm\) 0.2. The value of internal friction angle was a more important factor influencing slope stability, as this parameter considerably depends on the stress state and indirectly on the geometry of the layers building the slope. 6. Stability predictions quite significantly depend on the applied calculation techniques, both analytical methods based on the conditions of moment equilibrium (e.g., Bishop) or forces (e.g., Janbu) and modelling using the finite element method (FEM). In calculations of the stability conditions performed in this paper, the influence of the weak layer was taken into account. Both Janbu and FEM 2D methods produced similar results. The values of the SF index calculated by the Bishop and FEM 3D methods were higher than those obtained with the other methods. The overestimation of the stability value in the case of the Bishop method was related to the use of a circular-cylindrical slip surface, which did not coincide with the probable slip surface related to the course of the weak layer (e.g., the weathered roof of Neogene clays, which is a screen for seeping groundwater). In addition, the highest values of SF results in the FEM 3D method require further research. 7. The conducted analyses showed the necessity of mapping the structural conditioning of stability and the necessity of deliberate selection of modelling method that takes into account the variability of both geometric factors and strength characteristics. It was proven by the usefulness of the use of geophysical prospection, which enriches the point characteristics obtained from traditional ground exploration by drilling. Thus, local disturbances and their influence on changes in slope stability can be taken into account. Conceptualisation and design: K.K. and L.K. ; literature review: L.K. and S.K. ; methodology and validation: K.K., L.K. and S.K. ; formal analysis: K.K., L.K. and S.K. ; investigation and data collection: K.K., L.K. and S.K. ; data analysis and interpretation: K.K., L.K., P.D. and S.K. ; writing--original draft preparation: K.K., P.D., L.K. and S.K. ; writing--review and editing: P.D., K.K. and L.K. ; supervision: P.D.