Influence of soil non-linear behaviour on seismic response of soft soil deposits.

The paper describes the results of 1D seismic response analyses carried out using a non-linear model implemented in the finite difference computer code FLAC-2D. Soil deposits belonging to soil class C (180 < Vs,30 < 360 m/s), according to Eurocode 8 and to the Italian seismic regulation, were considered and ideal profiles of the shear wave velocity were assumed varying the bedrock depth from 30 to 90 m. A set of horizontal acceleration time histories, recorded during seismic events which occurred in Italy with magnitude in the range 5.5-6.5, were used as input motions. The analysis results were discussed in terms of soil amplification factor and stress reduction coefficient and in terms of response spectra and peak acceleration values at ground surface. The study shows that computed ground motion are significantly affected by the bedrock depth while a less evident influence of the equivalent shear wave velocity Vs,30 was observed. The obtained results are in a good agreement with literature while significant differences with the provisions of Eurocode 8 of the Italian seismic regulation were observed.