Micro to macro behaviour of contaminated marine sediments: experimental evidence of bio-chemo-mechanical processes

The research deals with a multiscale investigation carried out on contaminated marine sediments from a natural deposit to assess the effects of bio-chemo-mechanical coupled processes which may act in complex natural environments and affect the geotechnical properties of the clays. The research has been triggered by the emblematic case of the contaminated Mar Piccolo (MP) basin in Taranto (Southern Italy), where the high degree of pollution recorded in the clayey sediments at the sea bottom, has been found to worsen water quality and promote bioaccumulation of pollutants in several species. Several samples of sediments from the top layer exhibited peculiar geotechnical properties, in terms of plasticity and activity indexes, compressibility and hydraulic permeability. While the prime suspect for such unconventional behaviour was the chemo-mechanical coupling between soil skeleton and contaminants, an original laboratory analysis carried out on some selected sediments samples showed that the biogeochemical degradation of organic matter and the presence of microfossils and diatoms significantly affect the micro to macro behaviour of polluted marine sediments.