Effect of Electro-kinetic Consolidation on Fine Grained Dredged Sediments

Abstract The management of the huge amount of dredged sediments is an important issue to be solved worldwide, and dewatering is by far the most critical step when fine grained sediments are involved. Different technologies have been proposed in time to speed up the process. Even though electro-kinetic treatment is in principle one of them, it has not been implemented yet at an industrial scale, and only few trial applications are known. For such a reason, a multidisciplinary research activity is ongoing at the University of Napoli Federico II in the framework of the EU commitment ROSE with the aim to analyse the effectiveness and feasibility of such a technology from the lab to the site scale. In this paper, some evidences stemming from lab tests are presented. The results indicate that the application of low voltages improves the mechanical behaviour of the tested soil. In this case, however, the improvement is due more to a change in microstructure than to a decrease in void ratio

Effect of the pore fluid salinities on the behaviour of an electrokinetic treated soft clayey soil

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. This paper presents the results of some electrokinetic tests performed on reconstituted clayey specimens at different pore fluid salinities (0.2 < sc < 30 g/l) treated with electrokinetic (EK) technique. The results indicate that the presence of small quantities of salts in the pore fluid enhances the electro-osmotic consolidation. On the contrary, for high salt concentrations of the pore fluid the electro-osmotic dewatering is significantly reduced. The mechanical behaviour of treated specimens has been investigated at the micro (SEM) and macro scale (triaxial and oedometer tests). The experimental results highlighted the relevant and expected contribution of the pore fluid characteristic on the effectiveness of the treatment as ground improvement technique

A simple expression of the shear strength of anisotropic fibre-reinforced soils

This paper refers on the shear strength of soils reinforced with short randomly distributed fibres, which is a new and effective ground improvement technique. The shear strength of these soils is usually anisotropic because of compaction. In the paper, some of the main characteristics of these soils, and some considerations on anisotropy in strength are reported. Than, the expression recently introduced by Lirer et al. (2011) to simply model the failure envelope of the reinforced soil is discussed. This expression is based on simple micromechanical considerations and on a number of experimental results, and takes into account the main characteristics of the soil and of the fibres as well as the effect of fibre to grains relative dimensions. However, it only allows to calculate the maximum value of the shear strength of the composite material, being related to the results obtained in triaxial compression tests with fibres mostly oriented in the horizontal direction. In the paper, a possible evolution of the formulation of this shear strength envelope is proposed, to take into account anisotropy. A simple trigonometric reduction function is introduced, which complies with the expected behaviour of reinforced soils under different loading conditions. The proposed approach has the advantage of being a rather general expression that can be used by knowing just some simple and basic information on the host soil and on the fibres

Small strain shear modulus of undisturbed gravelly soils durino undrained cyclic triaxial tests.

The determination of the small strain shear modulus G0 of gravels is a very important issue, both under monotonic or cyclic loading conditions. In the paper, the results of a series of triaxial tests carried out in a large apparatus on frozen (undisturbed) specimens of gravel are presented, along with the description of a new experimental device developed to measure the velocity of the shear waves Vs. During undrained cyclic tests, Vs values were measured before and after liquefaction, to analyse the effect of this peculiar stress history on the small strain stiffness G0 of coarse grained soils. The small strain shear stiffness decreases as pore pressure in the specimen builds up. However, even in tests in which liquefaction was attained during the cyclic loading phase, G0 showed to depend only on the current value of the effective stress: its values become smaller than the initial one (before cyclic loading was applied) but not nil, depending on the transient value of the pore pressure and therefore of the effective stress. Furthermore, the experimental results showed that, since there was no sudden drop of G0 upon liquefaction triggering, the gravel did not have a structure which significantly affected its mechanical behaviour