Small Shear Strain Modulus Degradation by the Seismic Dilatometer Marchetti Tests (SDMTs)

In this paper some Italian sites, prone to high seismic risk, were studied to know the dynamic soil profile. For site characterization of soil deep investigations have been also undertaken. Borings and dynamic in situ tests have been performed. Among these Cross-hole (CH), Down-hole (DH) and Seismic Dilatometer Marchetti Tests (SDMT) have been carried out, with the aim to evaluate the soil profile of shear waves velocity (VS). Moreover the following laboratory tests were carried out on undisturbed and/or reconstituted samples: Oedometer tests, Direct shear tests, Triaxial tests, Resonant Column and Torsional shear tests. The availability of a large number of different tests for the same site both on site and in the laboratory allows us to correctly define the dynamic characteristics of the soils under study. In particular the purpose of this study is to verify the possibility of obtaining by SDMT the construction of stiffness strain decay curves for different soil type. At various test sites was evaluated the small strain stiffness (Go from VS) and then introduced a working strain stiffness (GDMT) based by the values of the constrained modulus MDMT. The working strain moduli GDMT are compared with reference stiffness decay curves obtained by dynamic laboratory tests. The shear strains ?DMT associated with working strain moduli GDMT enable us to define the trend of in situ stiffness decay curves for different soil tested.