Geotechnical properties of Soft Clayey Sediments from the Submerged Tiber River Delta, Italy.

The geotechnical properties of the fine-grained sediments of the Tiber River prodelta slope are described. Laboratory investigations depict the overall physical and mechanical behavior of the sediments and give information regarding their in-situ conditions due to gravitational campaction. In spite of relative homogeneity in terms of the basic geotechnical properties, noticeable differences between materials sampled at different water depths and at different depths below the seafloor can be detected. This variation is observed when in-situ material properties are taken into account and can be explained if the different depositional and burial conditions of the sediments are considered. In particular, differences in compressibility and undrained behavior have been found between sediments sampled immediately underneath the seafloor and the underlying materials as well as between the entire present-day prodelta clays and the "aged" sediments of the delta front, which were originally deposited in a prodelta slope environment. These considerations cart be generalized to other small marine deltas, which are not characterized by the exceptional depositional rates typical of the extensively studied large deltas but frequently occur worldwide and host offshore engineering activities.