## 4 Results
### Slope Stability Analysis in Evolving Saturation Scenarios  
The slope stability under static conditions was analyzed considering the different saturation scenarios in varying time windows, i.e., from 14 August 2018 to 17 August 2018, and at different depths, i.e., from 20 up to 60 cm b.g.l., as well as evaluating the overall stability of the entire thickness of alteration covers, ranging over the area between 20 cm and 1.6 m (Figure 7). The slope stability analysis was performed applying the general formulation proposed by [PERSON] [4] and the [PERSON] and [PERSON] [38] relation for assessing suction stress, which considers the stabilizing contribution of the negative pore  
Figure 6: Maps show the variation of the water content at different depths over time within the shallow altered soil covers. pressure in unsaturated conditions. This contribution appears to be relevant considering that the soil covers rarely and locally reach full saturation conditions in the considered study area. Three loading conditions were considered in the slope stability analysis within the shallow portion of the cover (20-40-60 cm b.g.l. ), which respectively account for: (i) the full saturation conditions with breakage of the capillary fringes; (ii) saturation values as a function of time and space in accordance with the 1D infiltration profiles obtained by Hydrus numerical modelling; and (iii) depth higher than 60 cm, where a minimal or negligible increase in saturation can be assumed and in which only the frictional contribution function of the effective stresses must be considered. The static SF values obtained by the slope stability analysis at 20-40-60 cm b.g.l. reflect the different saturation profiles and pressure heads in the soil cover (Figure 7), whose stability is directly dependent on the counterbalancing of suction stabilization and soil weight destabilization. For constant depth and lithotechnical properties, values of the static SF increase as the suction stress increases (more negative), as it results in an effect of \"apparent cohesion\" in shallow cover stability [52,53]. Minimum SFs were maintained where the suction stress values were lower. By increasing the time, the static SF decreases weakly with increasing rainfall from T1 (14 August 2018) to T2 (15 August 2018). After T2, the water content remains unchanged, especially at 20 cm depth, and there are no more  
Figure 7: Maps showing the static SF at different depths over time within the shallow altered soil covers. The zoom boxes highlight the slight variation of SF factor in the surficial part of the covers with increasing both time and depth. clear variations in the value of the static SF. By increasing the depth, the reduction of the static SF become more visible (60 cm depth in Figure 7). The slope stability analysis under static conditions was also carried out considering the whole thickness of cover as generalized for the total extension of the study area, assuming the potential mobilization of the entire alteration cover. In this analysis, the suction term was considered unchanged, and the weight volume unit was considered both in saturated, natural, and dry conditions imposing the respective \(\gamma\) of the analyzed soil. From the results of this analysis (Figure 8), it emerges that the rainfall played an aggravating role in stability conditions, worsening the SF as a function of depth, time, and cumulative rainfall. Minimum SFs were reached at the bottom of the soil cover, where an SF close to 1 was computed. The slope stability analysis under static conditions highlighted the contribution of the rainfall from two different points of view: at the shallowest levels (i.e., 10 cm b.g.l.) the soil cover thickness is not sufficient to establish slope instability conditions since the destabilizing actions, determined by the lithostatic weight, are too low despite the degree of saturation imposed being close to 100% and the capillary fringes are broken. This fact leads to general stability conditions over the entire area.