Gargano, Sara (2020) Experimental and numerical study of the behaviour of unconsolidated soils and of the effectiveness of electrokinetic treatment. [Tesi di dottorato]

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Dredging activities of harbours and rivers are becoming very important in many countries all over the world and, as a consequence, the disposal of dredged sediments is a critical concern from an environmental point of view. In order to facilitate the disposal or the reuse of large volume of dredged soils, usually under-consolidated and with a high water content, an electrokinetic treatment can be adopted with the goal to dewater and strengthen the sediments. The application of an electric field to an unconsolidated clayey soil has the beneficial effect of removing the water that cannot be removed using mechanical dewatering alone. The primary objective of this study is to investigate the effects of the electrokinetic (EK) treatment on dredged sediments and its potential application in the field, considering a numerical modelling and the factors that affect its efficiency. Several tests have been carried out in special devices with large dimensions that have allowed the retrieving of specimens, at the end of EK tests, to be tested in triaxial cells or traditional oedometric cells. In particular, the EK tests have been carried out with different combinations of mechanical and electric loads and at different electric voltages and pore fluid salinities, in order to study the influence of different factors on the effectiveness of the treatment. Some specimens have been also subjected to XRD and SEM analyses to analyse the influence of the EK treatment on the chemical composition and on the structure of the soil. As regards the influence of other factors on the efficiency of electrokinetic consolidation (when it comes to the dewatering aspect), previous published researches together with the current one have been deeply analysed and the parameter ranges for assessing the acceptability of the electro-osmotic treatment have been indicated. Furthermore, a one-dimensional finite difference numerical code (LASSEC1) has been developed to solve in a coupled way the mechanical and electro-osmotic consolidation process of soft clayey soils, considering large and small strains conditions. The numerical results have been compared with experimental data. In addition, parametric analyses have been conducted with LASSEC1, that can be used for practical applications, like, for instance, the design of reclaimed areas. Then, other analyses under different conditions have been undertaken to establish the treatment time and the electric energy cost. Considering all these factors, the EK treatment efficiency can be optimized. Finally, other issues, not covered in this thesis, have been collected and can be a starting point for possible developments of this research.

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