GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 3.2 420 This soil according to the Casagrande’s Plasticity Chart corresponds to “mediumcompressibility silt” and according to the USCS classification is classifiable as to ML/CL. In accordance with the HRB Classification - A.A.S.H.T.O. - CNR-UNI-10006 standards the soil corresponds to A-4 with a group index equal to 8, that is to say a loamy soil that is not very compressible with slight shrinkage/swelling properties. Sample C3 Liquid Limit: 36.75% Plastic Limit: 21.24% Plasticity Index: 15.51% According to the Casagrande’s Plasticity Chart this soil corresponds to “clay of medium plasticity” and according to USCS classification it is classifiable as CL. In accordance with the HRB Classification - A.A.S.H.T.O. - CNR-UNI-10006 standards the soil corresponds to A-6 with a group index of 10, that is to say a clayey soil that is not very compressible with high shrinkage/swelling properties. The oedometric tests, thrusts up to 8 kg/cm 2 . Taking into consideration the load range of 0.5- 1 kg/cm 2 , which is believed to be the stress rate transmitted to the foundations by the elevated structure, the settlements are as follows (D in Fig. 3).: sample C1: ɛ = 4.475% sample C2: ɛ = 2.820% sample C3: ɛ = 2.960% this means that on a thickness of only 2 meters of soil placed below the foundations (the laying surface of which is not known) there can be subsidence of the order of about 9 - 5.5 - 6 cm, respectively. The maximum settlement occurs in correspondence with pit1, exactly where the greatest presence of fractures is observed. A difference of 3.5 cm with respect to pits 2 and 3 cm with respect to pit 3 may well be considered the primary cause of the lesions produced in the structure. This aspect suggests not only the anthropogenic nature of the soils (reworked soils with different degrees of compaction/densification), but also the likely cause of the lesions, attributable to differential settlements. It is observed that always in correspondence to the load range of our interest (0.5 - 1 kg/ cm 2 ) the oedometric modulus (stress-strain ratio in conditions of prevented lateral expansion) assumes the following values: sample C1 (0.30-0.70 m): 71.428 kg/cm 2 sample C2 (1.50-1.80 m): 64.935 kg/cm 2 sample C3 (1.70 - 2.10 m): 57.471 kg/cm 2 these results confirm the presence of at least 3 layers of backfill with different densification levels within the first two meters starting from the ground level. The examination of the consolidation coefficient Cv is of the order of 10 -3 cm 2 /s for the samples C1 and C2, while it is of the order of 10 -2 cm 2 /s for the sample C3, whose value is indicative of rather rapid settlements, with a course of a few days. The permeability coefficient is of the order of 10 -8 cm/s for samples C1 and C2, while it is of the order of 10 -7 cm/s for sample C3. 5. Discussion and Conclusions The seismic survey carried out on highlighted an extremely regular stratigraphic situation, without anomalies or heterogeneity of the subsoil (such as cavities or localized voids). It is evident the presence of a very little thickened surface layer, distributed on the whole south side for a thickness of about 2 m, referable to fill/reworked soils deriving from the re-