Shallow landslides triggered by rainfalls: modeling of some case histories in the Reggiano Apennine (Emilia Romagna Region, Northern Italy)

On April 10-11, 2005, the Emilia Romagna Apennine was affected by an intense rainfall event that triggered dozens of soil slips in the Province of Reggio Emilia. These shallow landslides occurred mainly on slopes of cultivated lands, often blocking roads, causing damages to crops and economic loss. Based on the analysis of an inventory of aerial photographs, it was possible to locate 45 sites where soil slips have occurred. In this paper, the area of study is described from a geological and climatic point of view. The authors analyze both the predisposing factors, related to the morphology of the territory, and the phenomena triggering factors, related to the rain trend. Once the geometrical features and characteristics of the soil slopes were available, a physically based triggering model, recently developed by the authors, was locally applied at each site. The model, which is based on the limit equilibrium method and on the hypothesis of infinite slope, is briefly described. It assumes a partial saturation condition of the soil and provides the safety factor of each slope as a function of time-variable rainfall intensity. The choice of the input parameters of the model is explained in detail. It is underlined, in particular, how the only parameter that has been determined through a procedure of back analysis, i.e., the discharge capability, is comparable to the typical permeability values obtained through field measurements by other authors, for similar kinds of soils and conditions. In this article, the results of the application of our model to the study areas, within a three-year time frame, are presented. Furthermore, on the basis of the analysis carried out, some observations on the operating mode of the model are carried out and its ability to predict a phenomenon triggering is evaluated.