Effects of Unsaturated Soil State on the Local Seismic Response of Soil Deposits

The work is part of a wider research program in progress since many years at the Dipartimento di Ingegneria Idraulica, Geotecnica e Ambientale (DIGA) of the Università degli Studi di Napoli Federico II, focusing on the analysis of the effects of the partially saturated state on the seismic response of soil deposits. This study is particularly relevant for the relatively high seismic area of the city of Naples (Italy), where unsaturated soils are often encountered. The paper summarises a parametric study based on the experimental results obtained during a comprehensive laboratory program carried out using a RCTS device working in suction controlled conditions. A set of 1D linear analyses were carried out and interpreted in terms of transfer function, in order to highlight the role played by the unsaturated condition on the amplification function. Finally a rationale synthesis of the results is attempted in order to quantify the effect of the unsaturated state on subsoils characterized by different PI values. Results clearly show relevant effects of unsaturated state of soil deposits on the local seismic response in terms of both amplification ratio and natural frequency. The unsaturated state could be meaningful in the local response especially that of deposits of limited thickness.