Electro-osmotic Consolidation Research Articles

Semi-analytical solution for one-dimensional coupling consolidation of original soil and electro-osmotic layer using horizontal electrodes

The application of horizontal electro-kinetic geosynthetics for electro-osmotic consolidation is becoming increasingly widespread. Such horizontal electrodes are typically arranged at intervals, allowing pore water in original soil to pass through the intervals and penetrate into the electro-osmotic layer. In this study, a one-dimensional semi-analytical solution for a double-layered electro-osmotic system incorporating the original soil was presented and verified. The effects of the soil properties on the consolidation process were investigated. Results revealed that original soil can achieve a significant consolidation effect, even better than electro-osmotic dredged soil. A smaller permeability coefficient of original soil significantly prolongs the consolidation time, while a thicker original soil can improve the average consolidation effect of the two layers. The proposed model provides new electrode arrangement ideas and theoretical support for horizontal electro-kinetic geosynthetics for electro-osmotic reinforcement.

Electroosmosis of gold tailings under multiple electrokinetic geosynthetics electrodes

In dry-stack tailing ponds with high fine-grained content, a high long-term saturation line can lead to dam failure. Electroosmotic consolidation is an effective method for reducing dam saturation lines. However, traditional electrodes have low corrosion resistance and poor contact, which limits the development of electroosmotic drainage technology for tailings. In this study, an electroosmotic drainage device, an electrokinetic geosynthetic (EKG) electrode, was designed. The influence law of the electrode material, potential gradient, and number of electrodes on the water drainage, current, and resistance was analyzed. The results show that the EKG electrode has excellent corrosion resistance, with its weight loss after electroosmosis, water drainage, and equivalent allowable current being 1.67%, 122%, and ∼2.3 times that of a copper electrode, respectively. Furthermore, it was found that the optimal potential gradient was 1.2 V/cm, and the water drainage cannot be improved by an exceedingly high potential gradient. The current pathway in the test box was in parallel, and the water drainage increased to 410% and the contact resistance decreased by 83% when the number of electrodes was four. These results and novel methodology provide new ideas for EKG electrode design and represent an effective method for saturation line control in gold tailing ponds.

Numerical assessment of equivalent hydraulic conductivity and electro-osmotic conductivity for electro-osmotic consolidation under two-dimensional plane-strain analysis

Numerical assessment of equivalent hydraulic conductivity and electro-osmotic conductivity for electro-osmotic consolidation under two-dimensional plane-strain analysis

Effects of electrode materials and potential gradient on electro-osmotic consolidation for marine clayey soils

This study conducted experimental investigations into the effects of electrode material and potential gradient on the effectiveness of electro-osmotic consolidation (EO) in strengthening soft soils. Seven laboratory tests were conducted on high-water-content marine clayey soils through EO. In these experimental tests, four different types of electrodes made of steel, copper, aluminum, and composite carbon fiber (CCF) were employed in four tests each to evaluate the consolidation effectiveness. Additionally, four tests, one was the comparitive study for different eletrode materials, were carried out to determine the optimal gradient for the EO using CCF electrode. Several critical properties of the tested soils were examined and evaluated in this study, including the effective voltage utilization, potential distribution, water discharge, discharge rate, energy consumption, and soil bearing capacity. The test results indicated that the CCF electrode had superior performance in water discharge, discharge rate, and average soil water content compared to metal electrodes. Furthermore, CCF led to uniform enhancement of soil strength, with treated soil bearing capacities 6.3 to 12 times higher than initial values, and 1.9 to 2.5 times higher than those attained with metal electrodes. Additionally, an effective potential gradient of 1 V/cm was identified for the EO with the CCF electrode, providing a higher discharge rate and a larger soil strength in a uniform distribution. Moreover, the use of CCF electrode significantly reduced corrosion compared to metal electrodes during the consolidation process, further contributing to improved consolidation efficiency. This study offers valuable insights and recommendations for the utilization of CCF in marine clayey soils, effectively addressing the challenges posed by electrode corrosion and high energy consumption in EO applications.

Experimental and Numerical Investigation of One-Dimensional Electroosmotic Consolidation Based on Segment Inheritance Strategy

The attenuation of effective potential is a significant factor leading to the low postdrainage efficiency in the electroosmotic consolidation and drainage methods. In this study, the influence of the attenuation of effective potential on the electroosmotic consolidation process and the problem of solving the governing equations were investigated. A 102.5-hr one-dimensional electroosmotic consolidation test was performed to monitor the changes in the properties of the soil interior and the soil–electrode interface, and the variation curve of the effective potential in the test model was measured. The time-dependent nature of the potential distribution due to the attenuation of effective potential contradicts the assumption of introducing intermediate variables. To address this key issue, the variation curve of the effective potential was linearly segmented, ensuring the validity of introducing intermediate variables within each local state segment. Based on the continuity between state segments, the initial conditions of the governing equations in different state segments were updated, thereby extending the differential iteration within local state segments to the entire electroosmotic time domain. A finite-difference program for this method was developed using the Python language. Calculations and analyses based on the measured potential data were performed, revealing that a decrease in potential leads to a reduction in the effectiveness of electroosmotic drainage and consolidation in terms of the instantaneous distribution of pore pressure and the overall average degree of consolidation. This method can reflect the influence of the attenuation of effective potential on the pore water pressure during the electroosmotic consolidation process. The research findings of this paper can provide theoretical and numerical support for the improvement and engineering application of the electroosmotic consolidation and drainage method.

Analytical models for electroosmotic consolidation of layered soil systems considering the boundary effects of horizontal electrodes

AbstractThe pore water can usually flow through the horizontal electrodes, resulting in the top sand layer and the bottom unelectroosmotic layer inevitably affecting the consolidation process of the electroosmotic layer. However, the traditional assumption of the fully drained or undrained electrode boundaries is unable to reflect these boundary effects. In this study, one‐dimensional analytical models for electroosmotic consolidation of the layered soil systems considering the boundary effects of horizontal electrodes are proposed. The solutions for the models are derived using the separate variable method and Laplace transform method. The rationality of the one‐dimensional model is also illustrated by comparing it with the results produced by the two‐dimensional model and the accuracies of the solutions are verified through a series of analytical and numerical validation examples. Parametric studies are conducted to investigate the effects of the sand layer and the unelectroosmotic layer on the consolidation process. Results show that both the sand layer and the unelectroosmotic layer may significantly delay the consolidation progress. The time factor corresponding to 90% average degree of consolidation (Tv_90%U*) can increase by over 1.5 times in comparison with the model without a sand layer when the permeability coefficient ratio of the subsoil to the upper layer reaches 10. The delayed effect is particularly pronounced when the thickness of the unelectroosmotic layer with higher compressibility is relatively larger, potentially resulting in a tenfold or even greater increase in Tv_90%U*.

Electrochemical perspective on the applicability of electroosmosis for clay consolidation

There are three main electrochemical factors affecting the electroosmotic flow in clay soil: the voltage loss at the clay/electrode interface, the type of current carriers in the soil, and the ion composition change in the clay due to voltage application. Appropriate evaluation of these factors is important to cost effectively implement electroosmosis for in situ soil consolidation projects. In this study, three different experimental systems were developed and used to investigate electrochemical reactions occurring in reconstituted and natural marine clay during electroosmotic consolidation. The results of polarization tests show that the voltage loss at the clay/electrode interface is different depending on the combination of the clay material and electrode material. The results of electroosmotic element test also show that electroosmotic dehydration does not increase if large current–voltage value is applied and that an optimal current–voltage value for causing electroosmosis depends on the cohesive soil composition. If the clay contains a lot of oxidizable ions, such as sodium, these ions affect electrophoresis and chemical reactions that occur in the soil. Therefore, the optimal configuration to apply electric current also differs depending on the clay. The results of laboratory-scale electroosmotic dehydration tests, arranged in a realistic in situ layout, are performed to study the relationship between soil dehydration, consolidation, and surface crack generation.Graphical abstract

Semi-analytical solution for two-dimensional electro-osmotic consolidation of double-layered soil

This study proposed a semi-analytical solution for 2D electro-osmotic consolidation of double-layered soil. The method of Laplace transform is employed to derive the solution in the frequency domain. Then the numerical approach of inverse Laplace transform is used to obtain the explicit solution in the time domain. A finite element simulation is conducted to validate the proposed solution's accuracy. The verification example shows excellent agreement between the two methods. Based on the parametric study, it is found that the value of soil parameters in the second layer has significant influences on the behaviour of electro-osmotic consolidation. The larger the electro-osmosis coefficient in the second layer, the smaller the excess pore pressure at a given time. Additionally, a higher coefficient of volume compressibility in the second layer results in higher excess pore pressure. Compared with the 1D case, the distribution of excess pore pressure at the steady state is non-linear with depth in the 2D electro-osmotic consolidation, rather than a linear distribution. Furthermore, the dissipation rate and steady-state excess pore pressure could be underestimated if the electro-osmotic consolidation is modelled as a 1D case.

One-dimensional large strain electro-osmotic consolidation model based on multi-field coupling

Current electro-osmotic consolidation theories and numerical models usually ignore the variation of chemical fields and are applicable to soft clay soils with a single chemical composition. In this paper, a numerical model, called EC4, is presented for one-dimensional large strain electro-osmotic consolidation with coupled electrical-hydro-chemical fields. The algorithm accounts for non-linear variation of soil parameters, ion transport and a variety of chemical reactions, including ionization-neutralisation reactions, ion adsorption–desorption reactions and electrolytic water reactions at electrodes. The laboratory electro-osmotic consolidation tests on kaolin samples with different NaCl concentrations were conducted. The laboratory results were used to verify the accuracy of EC4. Then EC4 was implemented to example problems to investigate the effect of important chemical characteristics on the electro-osmotic consolidation. The effects of electrical voltage and initial pH on settlement, degree of consolidation, excess pore pressure and energy consumption of multi-field coupled electro-osmotic consolidation were further analyzed.

A novel evaluation method of consolidation efficiency of electro-osmotic system

Energy consumption has emerged as a hot topic and cutting-edge research theme in the application of electro-osmotic consolidation of low-permeability soils. However, the resistance of circuits in an electro-osmotic consolidation system is complex, whereby electric energy can be converted into various forms of energy. Based on the law of energy conversion, this study proposes a new method for the quantitative evaluation of energy conversion in an electro-osmotic consolidation system. The most important energy created during electro-osmotic consolidation is the molecular migration kinetic energy, which can drive the drainage of water and cations and the consolidation of soil, which is referred to as the effective energy consumption (EEC). The second form of energy is interfacial thermal energy (ITE), which is associated with increasing interfacial resistance. The third form of energy is the soil thermal energy (STE), which is associated with the rising temperature of the system due to the passage of electric current. In the experiments conducted here, the EEC proportion was overestimated by 57–80% in the electro-osmosis process without considering the ITE and STE. The efficiency of electro-osmotic drainage can be considerably enhanced if appropriate measures can be taken to reduce the proportion of ITE and STE.

One-dimensional large strain electroosmotic consolidation of ultra-soft geomaterials

Electrokinetic (EK) consolidation has been proven to effectively consolidate ultra-soft geomaterials, such as coal washeries, mine tailings, oil sands tailings and so on. The conventional consolidation model based on the small strain theory encountered difficulties with these geomaterials due to continuous changes in material properties during consolidation. This research developed a one-dimensional large strain EK (LSEK-1D) consolidation model for ultra-soft geomaterials. The model is validated using experimental laboratory results regarding settlements and times on mature fine oil sand tailings (MFT), a major environmental challenge for the oil industry in Northern Alberta, Canada. Moreover, the effects of initial sample heights and applied current densities on consolidation times are evaluated. The experimental data on consolidation times of MFT is consistent with the LSEK-1D model. The LSEK-1D model was used to find the scale effect of drainage path on the EK consolidation behaviour of MFT. The model can also be used for other ultra-soft geomaterials and to facilitate the geotechnical engineering design for EK application.

Improvement of different biopolymers on electroosmotic consolidation of soil

Improvement of different biopolymers on electroosmotic consolidation of soil

An analytical solution of electroosmotic consolidation concerning effective voltage attenuation

An analytical solution of electroosmotic consolidation concerning effective voltage attenuation

Numerical simulation of electro-osmotic consolidation considering tempo-spatial variation of soil pH and soil parameters

Electro-osmotic consolidation is an effective method to remove water from soft soils with high water content and low permeability. The previous analytical solutions and numerical simulations ignored the change of soil pH during the treatment. In the present study, a multi-field numerical model considering soil pH variation and non-linear soil parameters was developed. The laboratory tests and numerical simulation indicated that electro-osmosis conductivity was affected by soil pH significantly. According to experiment results in this study, the decrease of soil pH near anode induced an 78% reduction in electro-osmosis conductivity, while the increase of soil pH near the cathode induced a 66% increase of electro-osmosis conductivity. The fully coupled model showed a better agreement with the experiment results in the development of the excess pore water pressure. The simulation on the electro-osmotic consolidation combined with vacuum preloading test showed that the model was capable to analyze the problem with complex operating conditions.

Experimental investigation on a combination of soil electrokinetic consolidation and remediation of drained water using composite nanofiber-based electrodes

A novel electrokinetic geosynthetic (EKG) can be efficient in achieving multiple objectives. In this study, a new EKG as an electrode and a drainage channel in the electro-osmotic consolidation was fabricated by electrospun nanofibers containing graphene nanoparticles (GNs) attached to a carbon fiber substrate. To investigate the effectiveness of the fabricated electrodes in electro-osmotic consolidation and remediation of water drained from the system, an experimental apparatus was constructed while considering loading capability in expanded ranges and applying the electric field, and was filled with copper (Cu)-contaminated kaolinite. Experiments were divided into control (CT) and EKG groups, and three categories, C-EK, ES1-EK, and ES2-EK (using carbon fiber, electrospun nanofibers containing 1 wt% GNs, and electrospun nanofibers consisting of 2 wt% GNs, respectively). All the experiments were conducted with the same conditions, loading, drainage condition, and duration. However, EKG experiments were performed by employing the electric field under the vertical pressure in the range of 7–113 kPa, while the CT was conducted without the electric field. According to experimental results, 18 wt% polymethyl methacrylate in the dimethylformamide solvent containing 1 and 2 wt% GNs was selected for making a nanofibrous layer on the carbon fiber. The average diameters of the fibers were 404 ± 36 and 690 ± 62 nm and yielded at 1 and 2 wt% GNs, respectively. The results revealed that using the EKG accelerated kaolinite consolidation. The average degree of consolidation was 68 and 85% in the CT and EKG experiments, respectively. Furthermore, the fabricated electrodes were highly effective as a drainage channel for remediating water drained from the system. Moreover, the highest Cu removal efficiency was obtained in ES2-EK (97%) and ES1-EK (92%), respectively. Conversely, the lowest Cu removal efficiency was observed in the C-EK group (85%).

Influence of the intermittent vibration ratio on the electro-osmotic consolidation of dredged sludge

During electroosmosis experiments, the electrical interface resistance between electrodes increases with soil cracking, which hinders the further improvement of electroosmosis efficiency. To improve the effectiveness of later stage electroosmosis, the consolidation effect of dredged sludge was studied using electroosmosis combined with excitation loading. In this study, a series of experimental tests were used to analyze the influence of the intermittent vibration ratio on the consolidation effect of sludge. The electric current, effective potential, drainage, surface settlement, water content and undrained shear strength were monitored during sludge improvement. After testing, it was concluded that compared with the pure electro-osmotic method, the consolidation effect of the electro-osmotic method combined with the excitation loading method had significant performance improvements on the soil. In addition, the optimal intermittent vibration ratio was obtained, which could provide a design basis for engineering practice.

Effects of Applied Voltage and Concentration of Chemical Solution on the Electro-osmotic Consolidation of Kaolin

Effects of Applied Voltage and Concentration of Chemical Solution on the Electro-osmotic Consolidation of Kaolin

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.