PSI - Issue 62

Salvatore Misiano et al. / Procedia Structural Integrity 62 (2024) 576–584 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

580

5

= ∑ = − = ∙ ∙ δ − ∙ ∙ δ ∙ = ∙ δ ∙ (1− δ )

(10)

= 2 3 ∙ ′

(11) Where 1 is evaluated in eq.1, and m is the basal friction between the soil mass that is sliding and the portion of the slope that is acting like a temporary and erodible basement, also called top-soil. 2.3. Incorporated Mass During the evolution of the landslide path, the possible incorporation of mass caused by the erosion of the top layer, over which the moving mass is sliding, must be considered. In order to evaluate a possible amount of mass that could be incorporated into the moving body, it is necessary to assess two dynamic , called respectively b , that is the ratio between the stabilizing and destabilizing forces assessed along the surface that separate the bottom stable soil (bottom-soil) and the potential erodible layer, and t , namely the ratio between the stabilizing and destabilizing forces along the sliding surface, where there is a separation between the potential erodible soil (top soil) and the mass in motion (Fig. 4)

Fig. 4. Bottom and top-soil factors of safety.

Once defined, the height of the top-soil which might be eroded, at the step i , is evaluated as follows: ∆ℎ = 1− − ∙ = ∙ℎ −1 ∙ ∙ + [1− ∙(1+ ∙ )]∙ ( ) (14) Where and are the Skempton parameters (Skempton 1954), referred to the interstitial pore water pressure; c t and c b are respectively the cohesion of the top and bottom soil. The Eq. 12, 13 are obtained manipulating formulas of the effective stresses of Iverson 1992. Using these formulas, the physical phenomenon is simplified and reduced to a one-dimensional where the area is assumed to be constant, and the height of the moving mass could be only increased. Thus, at the last step, the final volume is assessed as V fin =A it ∙ ℎ . 3. Results 3.1. Study Area The object of the study is an area of Enna municipality, in Sicily (southern Italy), where during the night between 2 nd and 3 rd of February 2014, a soil slip was triggered by a long period of intense rainfall, turning into a debris flow which impacted the “Madonna del Monte” overpass , located in the Italian highway A6. (12) (13) = ∙(ℎ −1 + )∙ ∙ + [(ℎ −1 + )− ∙ℎ −1 ∙(1+ ∙ )+ ∙ ]∙ ( ) (ℎ −1 + )∙