Study of the effects of soil suction on the unsaturated soil behaviour and its importance on seismic response

The paper summarises part of a wider research program in progress since many years at the Dipartimento di Ingegneria Geotecnica (DIG) of the Università degli Studi di Napoli Federico II, focusing on the analysis of the effects of subsoil conditions on the local seismic response. The study accounts for the effects of the par-tially saturated state on the seismic response of soil deposits and is particularly relevant for the relatively high seismic area of the city of Naples (Italy), where unsaturated soils are often encountered. The paper summarises the results of 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 high-light 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 characterised by different PI values.