Dynamic response of a large landslide during a strong earthquake

摘要

This paper reports the stability analysis results of a slope, located in the northeastern Alps of the Friuli Venezia Giulia (Italy), subjected to an earthquake of equal magnitude to that which shook the area in 1976. The soil mass involved in the landslide was greater than 1 million m3 and caused heavy structural damage, especially in the village of Salars. The failure surface mostly develops inside the shale formation present below the detrital cover. The geotechnical properties have been measured by laboratory tests and geophysical investigations, accompanied by the monitoring of deep movements, water table variations and weather conditions. Soil investigations and displacement monitoring point out a generalised situation close to instability confirmed by the results of the pre-seismic stability analysis. Both simplified and advanced methods have been used to analyse the slope stability conditions. Dynamic slope behaviour has been analysed by means of a finite element analysis and the results have allowed the displacements, accumulated during the paroxysmic phase, to be estimated using Newmark's method; the calculated displacements have also been compared to those obtained by statistical correlations proposed by other authors. Moreover the increments of pore water pressures have been evaluated using correlations with shear stress increments along the sliding surface; these new values of pore water pressure have subsequently been used to estimate the post-seismic slope stability conditions and only a slight reduction of the safety factor was observed. This is due to high confinement pressures existing along the failure surface. The theoretical displacement accumulated in dynamic conditions has resulted in nearly twice that measured annually and may therefore cause further damage to, or the collapse of, buildings already damaged by the natural evolution of the landslide movement.