Comparison of moduli determined by DMT and backfigured from local strain measurements under a 40 m diameter circular test load in the Venice area

A full-scale instrumented test embankment (40 m diameter, 6.7 m height, applied load 104 kPa) was constructed at the site of Treporti, typical of the highly stratified, predominantly silty deposits of the Venice lagoon. DMT results at Treporti and comparisons of DMT-predicted vs measured settlements, indicating good agreement, have been presented by Marchetti et al. (2004). This paper concentrates mainly on the comparison of moduli obtained by DMT and from back-analysis of the test embankment performance. The moduli comparisons were carried out not only when the load was fully applied, but also at various stages during loading. In this way it was possible to reconstruct the in situ curves of decay of soil stiffness with strain level. Such curves were backfigured from vertical strains measured at 1 m depth intervals under the increasing loads throughout the embankment construction. The comparison of these curves with datapoints corresponding to DMT constrained moduli (Mdmt) indicates that Mdmt can be possibly associated to a strain range εv ≈ 0.1 to 1 %, 0.5 % on average. This finding may help for the development of methods for deriving in situ decay curves of soil stiffness with strain level from seismic dilatometer (SDMT).