Experimental evidences of bio-chemo-mechanical processes in contaminated sediments

Abstract

The research shows the results of a micro to macro testing programme 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 collected in the basin from the top layer exhibited peculiar geotechnical properties, in terms of plasticity and activity indexes, compressibility and hydraulic permeability. The results of the geotechnical testing were interpreted taking into account the XRD mineralogical results and the chemical composition of the soil matrix. Furthermore, thermogravimetry tests results were examined to explore the nature of the sediment skeleton and of its organic matter content, based on the main thermal reactions occurring within different temperature ranges. Lastly, scanning electron microscopy and mercury intrusion porosimetry were performed to assess the sediment pore size distribution as well as their content in microfossils and diatoms. The original multiscale analysis carried out on some selected sediment samples showed that the biogeochemical degradation of organic matter and the presence of microfossils and diatoms significantly affect the micro to macro behaviour of marine sediments.