Site investigations and geotechnical problems in the Southern part of the historic centre of L'Aquila

This paper describes the results of extensive site investigations (boreholes, Down-Hole tests, surface wave. tests, electrical tomography, seismic noise measurements) carried out in L'Aquila (Italy) in the area of Via. XX Settembre, dramatically damaged by the April 6, 2009 earthquake. Peculiar subsoil conditions locally detected at shallow depths in this area include underground caves, fine-grained soils interposed within, or placed above, coarse-grained breccias (typical of L'Aquila downtown) and man-made fills. Low and variable Vs values in the upper portion of the subsoil may have locally originated major amplification of the ground motion during the main shock. The visual inspection of as-built foundations of collapsed or demolished buildings, also described in the paper, has highlighted the poor construction technique in use at the time of construction (≈ 1950 to 1965). The peculiar unfavourable local subsoil conditions, in combination with the inadequacy of the existing foundation systems, require serious consideration and cautious choices from designers involved in projects for rehabilitation\/reconstruction of damaged buildings in this area.