Sandy Soil Characterisation and Site Response Analysis at La Plaja Catania Beach (Italy)

The city of Catania, located on the eastern zone of Sicily, is prone to high seismic risk. The seismic microzonation is now being studied for this area. In situ investigations of sandy soil were carried out in order to determine the soil profile and the geotechnical characteristics for the site under consideration, with special attention for the variation of shear modulus and damping with depth. Geological borings, SPT (Standard Penetration Tests), CPT (Cone Penetration Tests) and dynamic in situ tests have been performed. Among them Down Hole (DH) tests and Seismic Dilatometer Marchetti Tests (SDMT) have been carried out, with the aim to evaluate the soil profile of shear waves velocity (Vs);. Moreover the following investigations in the laboratory were carried out on undisturbed samples: Resonant Column tests; Oedometer tests; Direct shear tests. The available data enabled one to compare the shear waves velocity profile obtained by empirical correlations, Down Hole tests and Seismic Dilatometer Marchetti Tests. A comparison between the in situ small shear strain and laboratory shear strain, evaluated by different tests, have been also performed. The Seismic Dilatometer Marchetti Tests were performed up to a depth of 23 meters. The results show a very detailed and stable shear waves profile. The shear waves profiles obtained by SDMT compare well with other in situ and particularly with laboratory tests. Synthetic seismograms have been drawn for each site long a set of six receivers placed at different depths, starting from the surface up to almost 170 m. After evaluating the synthetic accelerograms at the bedrock, the ground response analysis at the surface, in terms of time history and response spectra, has been obtained by a non-linear model. In particular the study has regarded the evaluation of site effects in correspondence of the sites, to which corresponds a different value of the Seismic Geotechnical Hazard.