GNGTS 2014 - Atti del 33° Convegno Nazionale

104 GNGTS 2014 S essione 3.1 the transients, (i.e. anthropogenic disturbances). For the analysis, only the stationary portion of the signal has been taken into account. The final functions HVSR of each measurement are represented by frequency (x-axis the 0 to 64Hz) - amplitude H/V spectral ratios (y-axis) graphs. For each station the outcome of the statistical tests (guidelines SESAME, 2005) showed that all measurements have met the 3 criteria experiencing the reliability of the H / V curve and the goodness of implementation of the measure. For 2 of the 3 recordings also the main peaks of resonance were significant and clear for all the six criteria analyzed; only the recording N3 does not meet the first of the 6 parameters assessing the clarity of the peak. In order to obtain stratigraphic information from the H / V spectra, which could be compared with those obtained previously by mechanical drillings, the average velocity of shear waves in the investigated sector had to be estimated. It was ​obtained by down-hole prospecting, performed in correspondence of the drillings. In this way, the inversion of equation 1 allowed obtaining information on the depth of the impedance contrast causing the peak observed in the spectra of our recordings. Geostructural surveys have been performed at two measurement stations (SL-1 and SL-2) located in the SE portion of the cliff (Fig. 3), according to ISRM (2007) recommendations. Scan lines were placed at the most fractured portions of the slope and inside a karst cave. For each discontinuity dip-immersion, spacing, persistence, opening, in-filling, roughness, uniaxial compressive strength (UCS) and hydraulic conditions have been measured. Moreover, several unstable blocks, with volumes ranging between 2 and 460 m 3 , have been surveyed along the southeastern portion of the slope. All the surveyed factors were used for the Bieniawski (1976) classification, to assign a quality class to the rock mass, as well as to calculate its main geomechanical parameters. Bieniaswki’s Rock Mass Rating (RMR) system Fig. 2 – Map of the geognostic and geophysical surveys location and the relative stratigraphic sections and H/V spectral ratios.