Mona Malekzadeh

An Overview of Electrokinetic Consolidation of Soils

Electrokinetic stabilization is one of the techniques that improve the geotechnical properties of the soils. It was pioneered by Casagrande in late 1940s and has not seen much development since then, especially in large-scale field applications. Some bench scale studies have been carried out during the past two decades and there have been some small scale field studies and limited field applications, mostly on soft soils. Due to lack of understanding of the physiochemical and electrochemical changes in the soil during electrokinetic stabilization, uncertain energy costs, loss of efficiency with time and the corrosion of electrodes, this method is usually considered as a last resort for large-scale practical applications. The objective of this paper is to highlight the critical parameters affecting electrokinetic consolidation, and to discuss their effects on the efficiency of the process. A better understanding of these critical parameters and their effects will enable geotechnical engineers to design the electrokinetic consolidation operation more effectively and make it an economically viable process for many situations.

Electrokinetic stabilization of soft clay

Electrokinetic is the movement of ions, charged solid particles and water between two electrodes under the influence of an electrical field. Electrokinetic can be applied to the fields such as stabilization of soft soils and slopes, decontamination of pollutants, and sealing and leak-detection system of geomembrane, etc. The aim of this study was to evaluate the use of electrokinetic as an effective method to strengthen the soft clay soil with high compressibility. An in situ soil treatment technique using the principles of electrokinetic was tested using laboratory experimental models. The effectiveness of this approach in stabilizing and improving the physical properties of soft clay was tested and examined. In the study, soil specimens were compacted in glass tanks to reproduce in-situ density and in-situ water content. Mild steel electrodes were inserted into the soil and a direct current was passed through the soil under a constant potential gradient of 35–60 Volts for a period of 14 days. Distilled water and saturated lime solutions were introduced to the soil from anode to cathodes over the testing period. The physical and index properties of the soft clay were tested before and after the electrokinetics stabilization and the results were discussed. Test results indicated that introducing lime into the soil by electrokinetic method reduced the plasticity index of the soil and resulted in a lower compressibility of the soft clay. Treatment of soil by electrokinetic method enabled the measurement of the compressive strength of the soil which resulted in an increase in soils strength.

Use of Posidonia Oceanica Ash in Stabilization of Expansive Soils

Posidonia oceanica (PO) is the most plentiful seaweed of the Mediterranean Sea, which grows all along the coastal areas, forming widespread meadows. The leaf rejuvenation process of Posidonia oceanica typically occurs in fall when an increase in wave action causes the dead seaweeds to be transported and usually piled up along the coastal areas. This paper investigates the effect of PO ash stabilization on behaviour of an expansive clay. The ash was obtained by combustion of crushed PO pieces in a muffle furnace at 550°C. Atterberg limits, linear shrinkage, particle size distribution, one-dimensional swell, and unconfined compression tests have been carried out on natural soil as well as soil mixtures with 5% and 10% PO ash. There has been no significant improvement in the soil properties with 5% ash inclusion, whereas 10% ash has noticeably reduced the swell amount and increased the compressive strength. It is therefore concluded that there is a potential for the use of PO ash in geotechnical engineering applications.

Experimental study on intermittent electroconsolidation of singly and doubly drained dredged sediments

Electroconsolidation or electroosmosis of the soil is the movement of water from anode to the cathode when the electric current is applied to the soil through electrodes. The flow of water to the cathode is due to the electroosmosis (movement of water), electrophoresis (movement of soil particles), and electromigration of ions. In reclamation areas when the sediments of high moisture content are poured into the paddocks, they undergo a sedimentation process until the moisture content of the sediments reduces and the dredged sediments settle. Construction on these areas is not possible until the soil gains enough strength through consolidation, which takes a long time due to its low permeability. In this study, the potential application of electrokinetic stabilization to accelerate the settlement and dewatering of dredged sediments is investigated, along with the effect of irregular intermittent electric potential, type of drainage (singly and doubly), and efficiency of the method based on power consumption and soil resistivity.

One-dimensional electrokinetic stabilization of dredged mud

ABSTRACT Reuse of dredged marine sediments for land reclamation is a sustainable method for disposing the large quantities of dredged spoil, accumulating every year worldwide. However, due to their high water content and low permeability, dewatering and self-sedimentation of the material takes a long time to be completed. Therefore, different methods, such as prefabricated vertical drains and vacuum preloading, are used to improve the consolidation properties of the dredged mud at the port of Brisbane. Among these stabilization methods, vacuum preloading is determined as the most effective method to increase the consolidation of the dredged mud. However, clogging during vacuum consolidation is undesirable. Therefore, electrokinetic stabilization draws attention since it is an environmentally friendly and time efficient method to dewater and consolidate dredged mud significantly. The effectiveness of the electrokinetic stabilization depends on the properties of the soil and the electrode configurations. One-dimensional and two-dimensional electrode configurations are the most popular configurations. In this study, the effect of one-dimensional electrode configuration, which is installation of electrodes in arrays of anodes and cathodes on consolidation parameters of dredged mud, is investigated. Based on this study, the dredged mud sediments can be stabilized using one-dimensional electrokinetic stabilization which resulted in improving compression index and coefficient of volume compressibility and reduction of soil plasticity index.

Assessing the Use of Aluminium Electrodes on the Electrokinetic Dewatering and Stabilization of Dredged Mud Slurries

Every year a large amount of dredged sediments are disposed or used for land reclamations. To reduce the time lag for construction purposes, electrokinetic stabilization is suggested as an environmentally friendly and cost effective method to dewater and stabilize the dredged mud deposited in the paddocks. However, the physiochemical changes due to the electrochemical reactions in the dredged sediments are drawbacks of this technique that need to be investigated. The type of electrode to be used in the stabilization affects the physiochemical changes, and therefore using the correct type of electrodes is important. Different electrodes are used to stabilize different types of soils. Literature suggests that aluminum is a good option as it improves the soil and causes electrochemical strengthening by inducing Al3+ ions into the soil. In this study, the effect of aluminum mesh electrodes on the electrokinetic stabilization of the dredged mud is investigated. After the completion of the electrokinetic stabilization, samples are taken from different depths and water content, pH, electrical conductivity and atterberg limits are determined. From cathode to anode, the liquid limit decreases and plastic limit increases significantly. Near the anode, pH is reduced by 90% and the electrical conductivity increased. Higher salt content is also observed near the anode at the bottom of the column. The lowest water content and highest strength are obtained near the anode. Almost 54 % of the water is removed from the system due to electroosmosis. Despite the electrochemical changes in the soil, its settlement was about 17% which was not very significant; however, variation of electric current shows that the aluminum mesh is corroded before the settlement of the soil is completed. Therefore aluminum mesh electrodes are not suggested to be used for electrokinetic stabilization of dredged mud sediments.