GNGTS 2015 - Atti del 34° Convegno Nazionale

We applied the staggered grid method (Vesnaver and Böhm, 2000) for all lines, using a base regular grid with low lateral resolution (28 m) obtaining a final high lateral resolution grid (7 m). As inversion algorithm we used the SIRT method (Simultaneous Iterative Reconstruction Technique) and the minimum time approach for the ray tracing (Böhm et al. , 1999).We estimated the reliability of inversion by computing the time residuals (difference between picked and computed travel times); we obtained 1.4 ms rms residual (equivalent to 2.6 % on picked travel times). An example of 2D velocity model is shown in Fig. 2b. Geological/geotechnical borehole data. In addition to geophysical acquisition, a geological-geotechnical survey and geotechnical laboratory analyses were carried out in order to define the geolithologic, lithostratigraphic and geotechnical features of the area. �� ����������� In particular, eleven sea drillings reaching the first metres of the Flysch bedrock were performed. Of these, four were carried out onshore along the edge of the pier by positioning the drilling rig at the TMT head. The other seven were performed offshore with a barge. In addition to geolithologic and lithostratigraphic identification and classification, various tests were performed on core samples with the use of a pocket penetrometer and pocket vane in order to identify the Uniaxial Compressive Strength (UCS) and Undrained Shear Strength (Su) values and assess the cohesive soils. During the drilling, seventeen undisturbed samples were also extracted, with a Shelby- type tube sampler, along with twelve semi-disturbed samples, which subsequently underwent geotechnical laboratory analyses, as well as twenty Standard Penetration Tests (SPT). The SPT data revealed values between 1 and 32, with rejection on the lithological contact with the Flysch. From the SPT data, Phi values for sandy lithologies were assessed with various methods and revealed an average range of 20°-30° for levels which were less dense, and 30°- 40° for Fig. 3 – Bathymetric map. 68 GNGTS 2015 S essione 3.2