Volcanic Soil Characterisation and Site Response Analysis in the City of Catania

According to the frequency and the importance of the seismic effects suffered in past times, the city of Catania, located on the eastern zone of Sicily, must be considered one of the most high risk seismic areas in Italy. This paper describes and compares the results of in situ and laboratory investigations that were carried out in order to determine the soil dynamic characteristics in the test site of "Via Monterosso" in the city of Catania. The site mainly consists of an alternance of lava in blocks, scoriaceous lava, grey-black pyroclastic sand and red volcanic rocks. The following in situ investigations were carried out in order to determine the soil profile and the geotechnical characteristics for the volcanic soil and rock site under consideration, with special attention for the variation of shear modulus and damping with depth: Down Hole (D-H) tests and geotechnical borings. Moreover, the following laboratory investigations were carried out on undisturbed samples retrieved with a 86 mm diameter Shelby sampler: Resonant Column and Torsional shear tests; Oedometer tests; Direct shear tests. The laboratory results for G and D were compared with those obtained for similar soil types. It was also possible to compare in situ and laboratory small shear modulus and to determine the G-? curve for soil non-linearity evaluation. Moreover, two expressions were proposed respectively to allow the complete shear modulus degradation with strain level and the inverse variation of damping ratio with normalized shear modulus. Finally, synthetic seismograms have been drawn for the 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 histories and response spectra, has been obtained by a 1-D non-linear model.