Overconsolidation and Stiffness of Venice Lagoon Sands and Silts from SDMT and CPTU

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 ratio Mdmt/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. The SDMT and 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.