Electro-osmotic Consolidation Research Articles

Laboratory experiments on cyclic and progressive electrokinetic remediation and electroosmotic consolidation for Zn-contaminated soft clay

Laboratory experiments on cyclic and progressive electrokinetic remediation and electroosmotic consolidation for Zn-contaminated soft clay

A closed-form solution for axisymmetric electro-osmotic consolidation considering smear effects

A closed-form solution for axisymmetric electro-osmotic consolidation considering smear effects

Molecular dynamics study on the zeta potential and shear plane of montmorillonite in NaCl solutions

Zeta potential and the position of the shear plane are key physical properties characterizing the behavior of clay minerals in the colloidal system, and have been applied in many fields such as electroosmotic consolidation and electro-kinetic decontamination. In the past decades, numerous studies have been conducted on measuring and calculating the zeta potential. Nevertheless, few researchers have been reported to achieve a systematic understanding and predicting the zeta potential and the shear plane's position, especially for clay particles. This paper provided a molecular dynamics (MD)-based method to determine the zeta potential and shear layer thickness simultaneously to fill the gap. In the paper, the structure of the electrical double layer (EDL) was investigated for montmorillonite mesopore containing NaCl electrolyte in the concentration of 0.20–1.30 mol/L. The density profiles of ion species were well predicted by the Stern model, combining the Stern potential's determination. The calculated zeta potential based on the electroosmotic velocity profile in nonequilibrium molecular dynamics (NEMD) simulation was improved by introducing the slip length and was found to be closely comparable to the experimental values. Furthermore, the results confirmed that the shear plane cannot be observed from the electroosmotic velocity profile and self-diffusion coefficient of species in the MD simulation. The position of the zeta potential was determined by the Stern model and triple-layer model (TLM), showing a certain distance from the Stern plane. The zeta position was found that has a linear relationship with the Debye length and linearly depends on the ionic strength in the log scale, in agreement with previous investigations. The findings provided a systematic insight into the electrical double layer structure, zeta potential and shear plane for montmorillonite.

Experimental investigation on electro-osmotic treatment combined with vacuum preloading for marine clay

An electro-osmotic consolidation (EO) combined with vacuum preloading (VP) was investigated on marine clay using laboratory tests. To improve consolidation efficiency and reduce the settlement difference, a new prefabricated device was designed to combine EO and VP for the tests. The results indicated that the vacuum preloading with intermittent electro-osmotic consolidation (VP–I-ECM) provided more water discharge with higher discharge rate and produced larger soil settlement compared to traditional vacuum preloading and electro-osmotic consolidation. For the combined method, the VP effectively removed water from the soil for the first 12 h, and its efficiency decreased with the time. After 12 h, the intermittent EO was used to further consolidate the soil and maintain a high level of drainage rate. Test results also showed that the combined method of VP-I-ECM significantly improved the shear strength and bearing capacity of the marine clay to satisfy the construction requirements with a significant reduction in the anode erosion and the energy consumption. This research study provides useful information for the design guide and practical application of the combined technique for improving marine clay.

Improving settlement and reinforcement uniformity of marine clay in electro-osmotic consolidation using microbially induced carbonate precipitation

Improving settlement and reinforcement uniformity of marine clay in electro-osmotic consolidation using microbially induced carbonate precipitation

Analytical Investigation of Electroosmotic Consolidation in Unsaturated Soils Considering the Coupling Effect and a Nonuniform Initial Water Content

Electroosmosis often dewaters soil into unsaturated conditions. Due to the shrinkage deformation and decrease of effective voltage that occur during the electroosmotic consolidation as the soil changes from the saturated to unsaturated state, an analytical solution with the consideration of the coupled deformation and time-decreasing effective voltage was developed for one-dimensional (1D) electroosmotic consolidation in unsaturated soils. The effect of nonuniform distribution of the initial water content was also considered. To validate the effectiveness of the proposed analytical solution, a laboratory test was conducted. Thereafter, the proposed solution was used in a parametric study to investigate the effects of the coupled deformation, distribution pattern of the initial water content, and decrease rate of the effective voltage. The results indicated that the coupling effect increases with a decrease in the desaturation coefficient, and the coupling effect is significant for soft soils with high retention capability and compressibility. The nonuniform distribution of initial water content also had a great influence on the consolidation rate. When the initial water content increased from the anode to the cathode, the consolidation rate was fast in that direction but slow in the other direction. Finally, with the consideration of time-decreasing effective voltage, the calculated maximum matric suction and drainage decreased and the completion time of electroosmotic consolidation was shortened. In summary, the analytical solution developed in this study could capture the actual problems for electroosmosis consolidation in field applications to some extent.

A hydro-mechanical coupled solution for electro-osmotic consolidation in unsaturated soils considering the decrease in effective voltage with time

For electro-osmotic consolidation in unsaturated soils, coupled deformation, inconsistent changes in hydraulic conductivity and electro-osmotic permeability with matric suction, and a decrease in effective voltage with time occur simultaneously. To consider all of these processes, an analytical solution was proposed. The time-stepping method was adopted in the calculation of the solution to depict the nonlinear change in shrinkage deformation with matric suction. The accuracy of the proposed analytical solution was validated by comparison with results from laboratory tests and from a previously presented solution without considering coupled deformation. Then, a parametric study was conducted. The results indicate that the dissipation of the pore water pressure is slow when considering coupled deformation, but a large volume of water is discharged in the end, especially for soils with a large volumetric shrinkage index Cm. A larger final negative pore water pressure and discharged water can be predicted by considering the inconsistent changes in hydraulic conductivity and electro-osmotic permeability. Finally, with the consideration of the decrease in effective voltage over time, both the maximum negative pore water pressure and final drainage decrease, which is consistent with field observations.

Effect of anode condition on electro-osmotic consolidation combined with vacuum preloading

Electro-osmotic consolidation combined with vacuum preloading is a potential technology to dewater the soft soils and slurry. The anode condition has a significant effect on dewatering efficiency during operation, which is not adequately addressed. In this study, laboratory tests were conducted to study the effect of different boundary conditions of anode on the soil-improvement result using the combination of electro-osmotic consolidation and vacuum preloading, then to obtain the best combination mode. During the physical modeling tests, the soil mass was treated by vacuum preloading first and then further processed by the combined method. Three model tests were conducted to study the effect of different vacuum conditions on electrode, while CaCl2 solutions were injected at the anode in another two tests to study the effect of the electro-osmotic chemical treatment. The discharge of water and electrical current were measured during the tests, and the soil strength were measured after the implementation of the tests. The results indicated that the combined method was more effective to remove pore water from the soil mass compared with the traditional vacuum preloading. Although the vacuum preloading and electro-osmosis drove the water flow in the opposite direction near the anode, the vacuum pressure applied on the anode prevented the soil cracks, which increased electrical current obviously and removed 15% more pore water. The injection of CaCl2 solution at the anode showed slight effect on dewatering process, however, the bearing capacity was increased significantly.

Behaviour of electroosmotic consolidation by electrode configuration and fracture grouting

Electroosmotic consolidation effect of electrode configuration and fracture grouting with sodium hydroxide were investigated. In this study, a series of laboratory tests were performed by using a homemade electroosmotic cell. Results indicate that electroosmotic consolidation that uses fracture grouting with sodium hydroxide effectively improved the mechanical properties of dredged clay sediment, and the optimised ratio of the number of cathodes to anodes was 1:2. In terms of drainage, current, water content, and vane shear strength, electroosmotic consolidation did not improve by increasing the number of cathodes. When the sodium hydroxide solution was injected into the soil, it neutralises the acidity near the anode, suppresses the development of electrode corrosion, reduces the voltage loss between electrodes, facilitates water drainage, and increases soil consolidation. The technique can provide design guidance for the treatment of dredged clay sediment.

Study on Electroosmosis Consolidation of Punctiform Electrode Unit

In the electroosmosis method, when the distance between the opposite electrode and the same electrode is equal, the two‐dimensional effect of electroosmotic consolidation is significant, and the use of one‐dimensional model will overestimate the potential gradient, making the calculated pore pressure value too large. Aiming at this problem, according to the electrode arrangement rule and the minimum composition, a punctiform electrode unit model is proposed, and electroosmotic experiments are carried out on the symmetric and asymmetric unit models. The two‐dimensional electroosmotic consolidation governing equation of the punctiform electrode unit is established. The electric potential field of the electrode unit and the finite element form of the electroosmotic consolidation equation are given by the Galerkin method. The PyEcFem finite‐element numerical library is developed using Python programming to calculate. The research results show the following: (1) The two‐dimensional effect of the potential field distribution of the punctiform electrode unit is significant. The reduction of spacing of the same nature electrode in the symmetrical unit can make the potential distribution close to a uniform electric field. The asymmetry prevents the electric potential field distribution from being reduced to a one‐dimensional model. (2) The number of anodes will affect the electroosmosis effect of the soil. The more the anodes, the better the electroosmosis reinforcement effect of the soil, and the distribution of negative excess pore water pressure will be more uniform. (3) In the early stage of electroosmosis, the more the drainage boundaries, the faster the generation of negative pore pressure, but in the middle and late stages of electroosmosis, the potential value becomes the decisive factor, and the amplitude of negative pore water pressure in asymmetric units is higher than that in symmetric units. The potential distribution will not affect the degree of consolidation but will affect the extreme pore water pressure.

Large scale soft ground consolidation using electrokinetic geosynthetics

Field test of electro-osmotic consolidation with area of 800 square meters was carried out using electrokinetic geosynthetics (EKG). By introducing this field test, new concepts and solutions of difficulties in large scale application of electro-osmosis is introduced. Strategies of building smart DC power source to meet the large current intensity requirement of electro-osmosis are introduced. Roll polling program is a key program for the control system of smart DC power source. It reduces the requirement of current intensity to 1/3; it also decreases the energy consumption to less than 1 kW·h/m3. Design method for electro-osmotic consolidation is demonstrated while designing a field test. It is based on the energy level gradient theory. Design includes power estimation, wires and cables configuration, treatment time estimation and settlement estimation. The field test show that large scale application of electro-osmotic consolidation is feasible with acceptable power requirement and energy consumption. Electro-osmosis can accelerate consolidation and achieve better consolidation effect.

Introduction to anion-exchange membranes and their use in electro-osmotic consolidation

Electro-osmotic consolidation has long been of interest to the geotechnical community due to its potential to improve on current methods of clay soil consolidation. However, electro-osmotic consolidation is not widely used because of the change in soil pH and increase in soil resistance with long-term application of electrical current. This paper studies the efficiency of a novel method of using anion-exchange membranes to minimise the change in soil pH, and hence to prevent change in soil resistance. Settlements were measured for electro-osmotic tests subjected to different voltages with and without a membrane. The results showed that the membrane was always more effective in removing water, particularly at voltages below the limiting current. This demonstrates that using an ion-exchange membrane during electro-osmosis will remove significantly more water than conventional electro-osmosis for the same applied voltage. This occurs because the anion-exchange membrane blocks the migration of hydrogen ions formed near the anode into the soil, which would in turn increase soil electrical resistance. The increase in efficiency could finally push electro-osmotic treatment into the market as a viable solution for soil consolidation projects.

Coupling of electrochemical\u2013temperature\u2013mechanical processes in marine clay during electro-osmotic consolidation

Electro-osmotic consolidation has been applied in several geotechnical engineering applications that contain a series of complex processes, including electrochemical processes, temperature changes, and mechanical evolution. To explore the combination of electrochemical–temperature–mechanical processes in marine clay, electro-osmotic consolidation experiments were conducted using a self-made electro-osmotic consolidation system under various durations and voltages. The following findings was obtained: (1) the change in the pH value increased during electro-osmotic consolidation and as the voltage rise; (2) the temperature increased with a rise in voltage in the initial stage of the experiments, which was induced by Joule heating; (3) the temperature rise promoted the electro-osmotic consolidation process, which included a rise in the coefficient of consolidation and a reduction in water content; (4) horizontal shrinkage occurred when the horizontal stress increment was greater than the critical stress condition. In addition, the volume difference reached a constant value, and was proportional to the voltage rise. After the discussion, a coupling analysis was conducted, which can help to better understand the mechanism of electro-osmotic consolidation and can provide reference for engineering applications.

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.

Feasibility of Ion Exchange Membranes to Control pH during Electro-Osmotic Consolidation

Abstract Electro-osmosis is an established method of consolidating soft fine-grained soils. Its efficiency is controlled by the electrical resistance of the soil-electrode system. Because of an increase in soil electrical resistance during treatment, its cost efficiency is reduced, limiting the widespread use of this technique, especially in developed nations. One of the main causes of electrical resistance is hydrolysis of water molecules around the electrodes. The acidification of the anode, in particular, reduces the negative surface charge of clay particles and, thus, the zeta potential. According to the Helmholtz-Smoluchowski model, the zeta potential is directly proportional to the electro-osmotic permeability. This article studies the use of ion exchange membranes to assess their ability to prevent flow of hydrogen ions into the soil. The test with an anion exchange membrane showed minimal change of the pH in the soil around the anode compared to a control, which is better for electro-osmotic consolidation.

Experimental on electro-osmotic consolidation of bentonite reinforced by nano-Fe3O4

In order to study the effect of nano-Fe3O4 on the electro-osmotic consolidation of bentonite, four groups of electro-osmotic consolidation tests (T1, T2, T3 and T4) of bentonite with different content of nano-Fe3O4 (0‰, 1‰, 2‰ and 3‰) were carried out with self-design electro-osmotic test device, and the change laws of current, potential, drainage, water content, pH value and shear strength during the test were analyzed. The results showed that the current and effective potential decreased with the increasing of time. After 48 hours, the current of T1-T4 decreased by 99.48%, 97.60%, 96.81% and 95.77%, respectively. The effective potential of T2 decreased the slowest, and the potential loss was significantly lower than the other groups. During the test, the drainage rate increased with the increasing of time. T2 has the largest drainage volume and the fastest drainage rate, and its water content is the lowest. The pH value increased with the increasing of the distance from the anode, while the shear strength decreased with the increasing of the distance from the anode. The results showed that nano-Fe3O4 could significantly increased the consolidation and drainage effect of bentonite.

Semi-analytical solutions to one-dimensional electro-osmotic consolidation in unsaturated soils

Semi-analytical solutions to one-dimensional electro-osmotic consolidation in unsaturated soils

Analytical solution for one-dimensional electro-osmotic consolidation of double–layered system

Abstract Electro-osmotic consolidation can be used as a valid and innovative technique for ground improvement. Considering the limitation of previous studies that layered soil heterogeneity was not taken into account, this paper presented an analytical model for one-dimensional(1D) electro-osmotic consolidation of double-layered soil, and a computer program of fully explicit solutions for excess pore pressure and degree of consolidation was developed. In order to validate its accuracy, a series of verification examples were conducted using analytical approach and the finite difference method. Comparison results demonstrated excellent accuracy of the proposed solutions. Furthermore, parametric studies were conducted to investigate the influence of relative permeability and compressibility relationship on the consolidation behavior. It can be found that the differences of hydraulic conductivities and electro-osmosis conductivities in the two layers will lead to a sharp change of the excess pore pressure profiles at the interface of two layers. A larger value of coefficient of volume compressibility in the second layer will slow down the dissipation process of excess pore pressure. A thicker layer with higher compressibility will result in a slower the rate of dissipation of the excess pore pressure, and a thicker layer with higher permeability causes a smaller value of the excess pore pressure, while in the layer of lower permeability, the opposite occurs.

Study on electro-osmotic consolidation of bentonite reinforced by nano-montmorillonite

In order to study the effect of nano-montmorillonite on the electro-osmotic consolidation of bentonite, four groups of electro-osmotic consolidation tests were carried out with different content of nano-montmorillonite (0‰, 1‰, 2‰ and 3‰), and the change rules of current, potential, drainage, water content, pH value and shear strength were analyzed. The results showed that the current, potential and drainage rate decreased with the increase of time. After 48 hours, the current of T2 decreased by 91.23%, which has the lowest decrease rate. Meanwhile, T2 has the largest total discharge and lowest water content. With the distance increasing from anode, the pH value increased, while the shear strength decreased. The research results indicated that nano-montmorillonite has a significant effect on the consolidation of bentonite.

Study on the Electro‐Osmosis Characteristics of Soft Clay from Taizhou with Various Saline Solutions

Chemical electro‐osmosis with an injected saline solution can be described as an efficient method for adjusting the soil microstructure and improving soil conductivity, and the effect of electro‐osmotic consolidation on soft foundations can also be improved by this novel technology in regard to foundation treatment. To better study the electro‐osmotic characteristics of soft clay from Taizhou with different grouting solutions, a series of chemical electro‐osmotic experiments concerning the injection of CaCl2, MgCl2, NaCl, KCl, and deionized water were conducted in the laboratory based on custom test devices. The actual treatment effects of these experiments were compared by monitoring the drainage, current, voltage, elemental mass fractions in the soil, and soil structure. The chemical electro‐osmotic method was further studied from a theoretical perspective based on the inherent link between the macro‐ and microlevel indexes. The results of the model test indicated that the crystal structure of the soil changed from an initial flocculated structure to a granular or laminated structure with the injection of CaCl2 and MgCl2 saline. Na+ was hereby replaced by multicharged ions, which served as the key factor that affected both the drainage efficiency and conductivity of the electro‐osmotic process. Moreover, a novel one‐dimensional electro‐osmotic consolidation equation was introduced that considered variations in the electro‐osmotic permeability coefficient, which better illustrated how the excess pore water pressure was deduced when compared with Esrig’s consolidation equation. Furthermore, the results of this experiment may be adopted as a reference or as evidence for the subsequent promotion and application of the electro‐osmosis method.