Dynamic Geotechnical Characterization for the Microzonation of the Seismical Area of Catania

The city of Catania is located on the eastern coast of Sicily, which is one of the most seismically active areas of Italy. The eastern coast of Sicily has been struck by various disastrous earthquakes with a MKS intensity from IX to XI in the last 900 years. Many historical buildings were damaged by the South Eastern Sicily earthquake of 13/12/1990 with a Richter magnitude M = 5.4 and are now under restoration. The Catania soils consist of Pleistocene clay, silty sand, volcanic sand and volcanic rocks. In this paper the geotechnical charcteristics of sandy soils were investigated. The following in situ investigations were carried out in order to determine the soil profile and the geotechnical properties of seismical area of Catania, with special attention to the variation of shear modulus and damping with depth: Boreholes, SPT, Down Hole (DH) tests, and Seismic tomography. Moreover the following investigations in the laboratory were carried out on undisturbed samples: Resonant Column and Torsional Shear tests, Oedometer tests, Direct Shear tests. The available data enabled one to obtain correlations between the small strain shear modulus (DH and laboratory tests) for the specific site. It was also possible to compare in situ and laboratory small strain shear modulus. The influence of strain rate and number of loading cycles on the G-g and D-g curves, as well as on the shear strength and pore pressure build up, was evaluated by means of laboratory tests. Finally two expression to allows the complete shear modulus degradation with strain level and the inverse variation of damping ratio with normalised shear modulus respectively were proposed. This enables to the evaluations of site effects and earthquake design loads for the restoration and strengthening of the historical buildings.