| "The aim of the paper is to prevent the modelling of the ground effects of seismic waves on a large devris lying on a steep montain slope, with particuler attention paid to the triggering of slope movements. The study site is located below a huge rock fall named ""Monte Salta Landslide"" along the northern slope of the Vajoint valley, at the border between the Veveto and the Friuli Venezia Giulia Regions in north eastern Italy. The Mt Salta landslide is induced by the presence of the Mt Borga regional thrust, which uplifts limestone Jurassic in age on top of a Formation Cretaceous in age. Above the thrust zone, folded, higly fractured bedding planes dip steeply towards the slope free face, producing a highly unstable setting. Several historical landslide events were reported in the area; the first one dates back to the XVII century. The landslide deposit completely mantled the slope with a thick cover of rock blocks. The study area is classified as high seismic hazard and moreover has different vulnerable elements that can be affected by the remobilization of blocks like a village, the national road and a big quarry that was opened on the landslide deposit with the intent to exploit part of the debris material for construction purposes. The study was carried out in collaboration with the Department of Civil Defence of Friuli Venezia Giulia Region. Numerical analysis to simulate the slope behavior was performed, using distinct element method and applying UDEC code. The 2D models were built on 3 cross-sections and elasto-plastic behaviour was assumed for both rock matrix and discontinuities. The earthquake effect was modelled in pseudo-dynamic way, i.e. by magnifying the acceleration and applying also its horizontal component. The seismic force of the study area was calculated on previous studies in 0.28g. The results proved that the increase of the vertical component alone has a small influence on the system behavior. Hence, the acceleration vector was deviated at 5°and then at 10°from vertical. A small increment of the displacement was observed in the first case, whereas in the second case very large movement occurred. Therefore, it can be concluded that, besides the magnitude of the earthquake, even small seismic waves in horizontal direction could trigger significant movements and therefore hazardous conditions. The scenario carried out by the model should be helpful for planning more functional countermeasure works or civil defence evacuation plan. " |
