Geotechnical characterization of a polluted marine basin

The work presents the results of an intense experimental research into the chemo-mechanical coupling phenomena involving the sediments from the Mar Piccolo basin (Taranto, South of Italy), severely contaminated by both heavy metals (e.g. Hg, Pb, Cd, Cu and Zn) and organic pollutants (PCBs, PAHs, and dioxins). Among the different matrices involved in the environmental studies, i.e. sediments, water and biota, this research focuses on the submarine sediments and reports the results of both the chemical and the geotechnical investigations carried out during the off-shore campaign, prompted by the Special Commissioner for urgent measures of reclamation, environmental improvement and redevelopment of Taranto. Geotechnical tests were carried out on more than 50 samples, taken from up to 30 m below the seafloor. The standard equipment and procedures were properly adapted to take into account the influence of salt and organic compounds in the pore fluid. The geotechnical testing programme included tests aiming to characterise physical properties, composition and state of the sediments, oedometer tests to determine the 1D compression and consolidation properties of the soil and CIU triaxial tests for the measurements of both isotropic compressibility and strength. Furthermore, an apparatus was developed for both the squeezing of the sediment and the pore flid extraction of pore fluid during compression. Off-shore piezocone tests were also carried out and the results were used to interpret the stratigraphy and derive engineering properties of soils. The integration of the geotechnical and chemical data allowed to investigate the effects of the chemo-mechanical interaction processes on the geotechnical behaviour of the sediments, in the light of the most relevant literature. The Mar Piccolo represents a “natural laboratory” and an emblematic case in the worldwide panorama of polluted sites. Hence, the study offered the possibility to produce and analyse an uncommon coupled database of both geotechnical and chemical results concerning natural geomaterials altered by the presence of different sources of contamination.