GNGTS 2021 - Atti del 39° Convegno Nazionale

417 GNGTS 2021 S essione 3.2 3.2 Geotechnical in situ tests Specific geognostic investigations consisted in carrying out two continuous dynamic penetrometric tests using a “light” dynamic penetrometer model SUNDA with a 30 kg impact mass were carried out. The penetrometric tests were performed on the central sector of the building facade and at the southeast corner of the building. The dynamic penetrometric test consists in driving vertically into the ground a conical metal tip placed at the end of a steel rod, which can be extended with the addition of subsequent rods; the insertion takes place by beat, dropping a hammer weighing 30 kg from a height of 0.2 m and counting the blows necessary for the penetration of each section of 0.10 m (N’). 3.3 Geotechnical laboratory tests In order to determine the geotechnical proprieties of soil, three undisturbed samples were taken by punches steel type Shelby ( = 85 mm) in pits (P) made on the south side of the building at different depth (P1 at SW building side = 1.50 m, P2 in the central sector building side = 1.60 m, P3 at SE building side = 1.70 m). On both samples we proceeded to the execution of geotechnical analysis for soil identification by grain sizeanalysis (sievedistributionaccording toASTMD421-07andhydrometric test according to ASTM D422-07), Atterberg Limits (Liquid Limit, Plastic limit, and Plasticity Index according to ASTM D4318-10), classification according to “Casagrande’s Plasticity Chart” and HRB/CNR UNI 10006 classification and, finally, determination of the compressibility and deformability features of soils by oedometer tests. Three oedometric tests according to A.G.I. (1994) references in order to measure the deformation response of samples at different loads were performed. 4. Results 4.1 Seismic survey The tomographic model of compression waves velocity defined by section A1-A2 (see Fig. 2) highlights the following seismostratigraphic sequence: • A low speed surface seismic layer (200 ÷ 300 m/s, blue color) defined by a thickness of about 2-3 meters and consisting of reworked deposits in conditions of very low density. • A second seismostrate, characterized by a weakly increasing velocity gradient with depth Fig. 2 - Thomografic model of subsoil up to 12 m (above) and detail of P-waves velocity model in the first meters of subsoil (down)