Totani, Gianfranco

This paper presents a review of results obtained by a large number of seismic dilatometer tests (SDMT) carried out in the area of L’Aquila (Central Italy), after the April 6th, 2009 earthquake. Due to the characteristics of the soils (mostly coarse-grained, nonpenetrable materials), SDMT measurements were generally performed in backfilled boreholes, using the technique briefly described; in these conditions only the shear wave velocity VS, without the other DMT parameters, was measured. The test results illustrated in the paper include: (a) SDMT typical results obtained by the normal penetration procedure (in a limited number of sites, mostly silts); (b) VS-only profiles obtained by the backfilled borehole procedure; (c) comparisons of VS profiles obtained by SDMT and by other techniques (Down-Hole, Cross-Hole, surface waves tests); (d) comparisons of VS measured by SDMT and those estimated from mechanical DMT data. The VS profiles provided by SDMT, combined with the information obtained from geological data and from other investigations, including boreholes down to a maximum depth of 300 m in the city centre, have been used for the soil characterization in numerical seismic response analyses. An example is illustrated in the paper.

The paper reports about the in-situ and laboratory tests executed in the aftermath of the April 6, 2009 L’Aquila earthquake, aimed at contributing to the definition of geotechnical models for site response analyses in the Aterno valley. The investigation started immediately after the earthquake and was entrusted by the Civil Protection Department to different public institutions and private companies; the experimental activities here reported were coordinated by the Italian Geotechnical Society. In the paper, after briefly depicting the geological setting of the L’Aquila basin and the Aterno river valley, an overview of their subsoil conditions is given, based on the geotechnical tests executed before the 2009 earthquake. Thereafter, the specific investigations planned for the characterization of reconstruction sites and seismic microzonation are widely described. The in situ tests consisted of seismic dilatometer and multi-receiver surface wave tests; the resulting shear wave velocity profiles were compared each other, and against independent Down-Hole tests and ambient noise measurements. The laboratory investigation included cyclic/dynamic simple/torsional shear tests on undisturbed samples. The results, summarized in terms of variation of stiffness and damping with shear strain, highlighted some peculiar properties of the soils in the Aterno valley, which could be related to their index properties.

This study is part of an extensive research program carried out at the Treporti test site (Venice, Italy), where a cylindrical trial embankment was constructed and monitored from the beginning of its construction until complete removal, 4 years later. This paper concentrates mainly on the evaluation of overconsolidation and stiffness of the Venice lagoon sands and silts. The possibility of estimating the overconsolidation ratio (OCR) in sand by the combined use of seismic dilatometer (SDMT) tests and piezocone (CPTU) tests is investigated. A tentative correlation for estimating the OCR in sand from the ratioMDMT=qt is constructed. Field compression curves have been back-figured from 1-m field oedometer curves reconstructed from local vertical strains measured by a sliding deformeter under the embankment center. TheSDMTand CPTU soundings performed before embankment application and postremoval have permitted analyzing how the OCR caused by the embankment was reflected by the before/after SDMT and CPTU results. The paper also illustrates the possible use of the SDMT to assess the in situ decay of stiffness with the strain level, by comparison with the stiffness decay curves of the elements on the centerline back-figured from the observed embankment behavior under increasing loading.