EVALUATION OF SEISMIC SITE EFFECTS IN A REAL SLOPE THROUGH 2D FE NUMERICAL ANALYSES

The seismic site effects are the result of wave amplification processes related to the topographic irregularities, the sequence of soil layers, the morphology of the stratigraphic contacts, the dynamic properties of the soils and the input motion features. These local effects may be responsible for damages to structures and infrastructures located in different portions of the urban area, as well as they may be the trigger for landslide instability processes. In the present paper, the numerical simulations of the site effects occurring in a real natural slope have been performed through 2D finite element (FE) linear visco-elastic analyses, aiming at investigating and quantifying the influence of both the topography and the buried stratigraphy on the seismic amplification at the ground surface. The considered case study is the western slope of Chieuti, in the south of Italy, location of a deep landslide instability mechanism mainly related to static actions. After an earthquake occurred in August 2018, a worsening of the landslide-related damages affecting buildings and roads has been observed, thus requiring further investigations on the effects of the dynamic loading. Therefore, a detailed seismic geotechnical model has been developed for this case study, based on a suite of in-situ investigations, including MASW and down-hole tests. The site response analyses have been conducted with reference to three longitudinal sections and one transversal section, crossing the crest of the hillslope. The numerical results are illustrated in terms of topographic and stratigraphic amplification factors, quantifying the effect of the slope topography and the buried stratigraphy, respectively. The results show that, for this specific case study, the stratigraphic effects are predominant with respect to the topographic ones, due to the strong subsoil heterogeneity characterizing the upper portion of the slope. However, topographic effects are relevant at the crest of the hillslope, inducing further amplification of the motion.