Site characterization and seismic response analysis in the area of Collemaggio, L'Aquila (Italy)

The paper describes the geotechnical investigations and analyses carried out for the restoration of the ancient Basilica di Collemaggio, L'Aquila (Italy), severely damaged by the 2009 earthquake. The subsoil model was defined based on a comprehensive investigation including boreholes, measurements of shear wave velocity VS by seismic dilatometer (SDMT) in backfilled boreholes (non-penetrable soils) to 93 m depth and laboratory cyclic tests (double specimen direct simple shear, DSDSS). An "enhanced" seismic source was designed to improve the interpretation of VS at large depths. Site response analyses were carried out with 2D FLAC finite difference code. Literature data and DSDSS test results were used for non linear cyclic characterization of soils. The input motions were seven real accelerograms compatible with reference response spectra on outcropping rock from the Italian code. The results, expressed in terms of free-field acceleration response spectra, showed amplification up to 2.5 s with maximum values > 2 in the period range 0.1-0.4 s.