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 are 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.
Based on detailed historical data, the application history of reinforced soil in hydraulic engineering in China is studied. Archaeological research shows that ‘grass wrapped sludge’ technique was invented in ancient China about 5,000 years ago and the technique was widely used in dam construction for flood control, river regulation and breach blocking. Geosynthetic reinforcement and protection techniques were introduced to China only in the 1960s to 1970s, while the application of reinforced soil in hydraulic engineering has a much longer history. Geosynthetics reinforcement is inheritance and development of ancient wisdom for modern civilisation.
Comparison of dewatering effect between electro-osmosis and filter pressing based on AMORAS, which is a dredged sludge disposal project in Antwerp, was presented in this paper. Water content of sludge can be reduced to less than 40% by electro-osmosis, which is better than the required value of 54~67% (mass of water / mass of dry soil, according to water content definition in geotechnical engineering and it is different from the definition in dredging and sludge disposal engineering, which is mass of water / total mass of original soil). Electro-osmosis dewatering is quicker and it can reduce the volume for sludge storage. EKG (ElectroKinetic Geosynthetics) solved the problems of electrode corrosion and reduce the energy consumption to an acceptable level. The best record at the moment is 0.58 kW.h/m3 and the key progress lies in the develop of smart DC power source. The other challenge is large power requirement for DC source and it has been solved by roll poling program embedded in the smart power source. Application of EKG and electro-osmosis is growing from the lab to large scale engineering application in the field. http://electrokinetic.cn/?p=1082
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EKG (electro-kinetic geosynthetics) electrode can be used instead of metal electrode for electro-osmotic treatment of soil. In order to study the resistance characteristics of EKG electrode, the testing technique of resistivity of EKG electrode and the measuring technique of contact resistance between electrode and soil were put forward, and the resistivity of EKG electrode with different length and contact resistance between electrode and soil were measured under different current. The experimental results show that the volt-ampere relationship of EKG electrode is basically linear. The volt-ampere relationship of contact resistance between electrode and soil is nonlinear. The contact resistance varies with the current, and is approximately a power function with the current. The experimental results are relatively stable using the new technique to measure the EKG resistivity. Compared with the traditional method by potential probe, the soil resistance measured by the new method is larger, and the contact resistance is smaller. The testing technique can provide reference for the test of EKG resistivity and contact resistance, which can help to make a more accurate estimate of the initial current and energy consumption of the electro-osmosis and provide guidance for the engineering application of electro-osmosis.
Electro-Kinetic Geosynthetics (EKG) presents a new category of geosynthetics. It inspires enthusiasm to apply electro-osmosis (EO) in large scale engineering applications, such as soft ground improvement , sludge dewatering, soil remediation, etc. This paper presents a kind of specially designed EKG and DC power source to carry out electro-osmotic consolidation for soft ground in vertical direction instead of horizontal direction. It is aiming at providing a better consolidation effect without degradation along depth for deep soft ground improvement. In-situ experiment shows that bearing capacity of the hydraulically filled sludge could be increased to 80-90 kPa after upward gradient electro-osmosis treatment and consolidation effect along depth is more homogenous than that of horizontal electro-osmosis using normal E-board. Development of EKG materials and automated DC power source are two key breakthroughs that pushing forward both researches and applications EO technique, which has over 200 years of history already.
Single mineral montmorillonite was taken as electro-osmosis object to explore the microcosmic mechanism of electro-osmosis. Four sets of parallel tests were designed using self-made metal electrodes and EKG (electro-kinetic geosynthetics) electrodes. The results of electro-osmosis were analyzed; the changes of the physicochemical aspects such as ion migration, electrical parameters and swelling properties were discussed. The experimental results show that Al³⁺ migration ability is much greater than Cu²⁺ and Fe²⁺, the latter two are difficult to move under the action of electric field force, the metal ions produced by the electrode reaction have little effect on the electro-osmotic drainage; the electro-osmosis weakened the ethylene glycol expansibility of montmorillonite, and in addition to the copper electrode, electro-osmosis under the aluminum, iron, EKG electrode has stronger inhibition on the expansion of soil near the cathode; the electro-osmotic effect reduced the absolute value of zeta potential of montmorillonite; the infiltration of Al³⁺ in the aluminum electrode seriously reduced the emission of Ca²⁺, and the infiltration of Fe³⁺ and Fe²⁺ in the iron electrode constrained the migration of Na⁺ in the soil near the anode. The iron electrode and the EKG electrode have acidification effect on the soil, while the copper and aluminum electrodes are not so.
In order to investigate the permeability of montmorillonite clay with different salt content under an electric field, a laboratory device was designed to capture the drainage, current intensity, voltage, and water content during electro-osmotic drainage tests at four different salinities in montmorillonite. The results show that the permeability increased significantly during electro-osmotic drainage in the electric field. Under 40 V voltage the drainage rate in electro-osmosis was as large as 1 000 times that in normal drainage tests. The electric permeability coefficient increased first and then decreased with an increase in the salt content because of the effect of montmorillonite molecular structure and electrolyte concentration. When the salt content was near 0.5%, the drainage reached a maximum. With the salt content increasing, the effective potential of the soil decreased but the current and the potential drop between cathode and anode increased, reflecting that the energy consumption at the interface increased with the increase of salinity. In addition, a short-circuit connection between the cathode and anode electrodes resulted in a charge redistribution in the process of electro-osmosis. After the electro-osmosis, the potential distribution was found not uniform:the potential of the middle region was the lowest, and the direction of current was different in the soil. © 2016, Editorial Department of Journal of Southwest Jiaotong University. All right reserved.
In the present study, zinc molybdate (β-ZnMoO4) and graphitic carbon nitride (g-C3N4)-modified β-ZnMoO4 (β-ZnMoO4/g-C3N4) were prepared to decontaminate aqueous solutions from the antibiotic sulfamethazine (SMZ). Our results revealed that the hydrothermal synthesis method greatly influenced the photocatalytic activity of the resultant catalysts. The pristine β-ZnMoO4 samples obtained under more intensive synthesis conditions (24 h at 280 °C) showed higher photocatalytic activity than that prepared for 12 h at 180 °C (denoted β-ZnMoO4-180). In the case of in situ hydrothermal synthesis of β-ZnMoO4/g-C3N4, a surface-modified sample was only obtained under the reaction conditions of 180 °C for 12 h. Compared with the sheet-like β-ZnMoO4-180 sample, the β-ZnMoO4-180/g-C3N4 composite showed enhanced photocatalytic activity for the degradation of SMZ. By contrast, the hydrothermal reaction at 280 °C caused the gradual decomposition of g-C3N4. It is believed that the structural incorporation of g-C3N4 into β-ZnMoO4 at 280 °C might disrupt the crystal growth, thereby deteriorating the performance of the composite catalysts formed at this temperature. For the composite catalysts prepared by the ultrasonic method, a remarkable increase in the degradation rate of SMZ was only observed at a high g-C3N4 content of 8 mol%. The photocatalytic degradation of SMZ by β-ZnMoO4-180/g-C3N4 composite catalysts followed pseudo-first-order kinetics. Further study of the photocatalytic mechanism revealed that holes and superoxide radicals were the dominant oxidative species in the photodegradation process. The enhanced photocatalytic performance of the composites was attributed to the higher separation efficiency of the photogenerated electron-hole pairs at heterogeneous junctions. The degradation intermediates of SMZ were detected by liquid chromatography-mass spectrometry, from which plausible reaction pathways for the photodegradation of SMZ were proposed. Our results indicated that the synthesis method for g-C3N4 composites should be carefully selected to achieve superior photocatalytic performance. © 2017 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences
Originally published as: Pugh, R.C. (2000) “A full-scale field trial of electrokinetically enhanced cohesive reinforced soil using electrokinetic geosynthetics.” Winning postgraduate student paper awarded by the IGS UK Chapter.
For citation: Yan-feng Zhuang. Challenges of electro-osmotic consolidation in large scale application. Geosynthetics 2015. 15th-18th Feb. 2015, IFAI, Portland, Oregon, USA: 447-449. New product of Electro-Kinetic Geosynthetics (EKG) has drawn a lot of attention to electro-osmotic consolidation. Although recent in-situ experiments exhibit promising results, there are still some problems to be tackled before EKG can go to large scale application. Major challenges for large scale application lie in the following aspects. The first, high electric power required for electro-osmotic consolidation of hydraulic-filled sludge; this requires special design of power source. The second, achievement of bearing capacity of at least 80kPa for sludge after electro-osmotic consolidation so that the secondary treatment can be omitted. The third, new electro-osmosis theory to provide design method for in-situ application of electro-osmotic consolidation.
Based on the phenomena of electric charge accumulation observed in the model experiments, an electro-osmosis theory named electric charge accumulation theory is brought out in this paper. By substituting the principle of current continuity with charge conservation, the differential equation of charge accumulation model is built. The analytic solution of the differential equation shows that: the spatial distribution of electric potential follows a superposition of linear and trigonometric function, and finally levels off to a linear distribution, which is hypothesized by Esrig; the decreasing of potential gradient follows a certain style of exponential function, and levels off to a constant; the decreasing styles of electric current and soil conductivity are approximatively accordant with those in energy level gradient theory. Finally, the electric charge accumulation theory is validated by some tested data.
There will be transition zones of electric current near the electrodes, if the electric conductive area of electrodes is smaller than that of soil. Electroosmosis tests show that the electric current in the transition zones follows a complicated two-dimensional path, while the electric current outside these zones is approximately one dimension. The thickness of transition zones is potty compared to the whole thickness of soil between anodes and cathodes. Conception of interface resistance on zero thickness interfaces, which is a simplified expression for finite thickness transition zones, is presented in this paper to simplify the two-dimensional problem within the transition zones into one dimension. Studies show that the interface electric resistance is inversely proportional to the ratio of electric conductive areas between electrodes and soil. A brief formula is deduced to predict the in situ interface electrical resistance, which presents a more accurate estimation of electric current and energy consumption to the design of electroosmotic consolidation engineering.
From aspect of energy consumption, an electro-osmotic consolidation theory named energy level gradient theory is brought out in this paper, and detailed electrical analyses on electro-osmotic process are completed in the light of experiments. The analyses interpret the distribution and variation pattern of electric current, electric potential, difference of potential and electrical resistivity of soil in the electro-osmotic process. Based on energy level gradient theory, formulae of electro-osmotic drainage, pore water pressure, consolidation settlement and electrical energy consumption are also presented in this paper. Comparing them with those formulae in the Esrig theory, the author also give some analyses and discussion to show the similarities and differences between these two electro-osmotic consolidation theories.
Electro-Kinetic Geosynthetics (EKG) inspires enthusiasms for research on electro-osmosis. Mechanically dewatering of hydraulically filled sludge is difficult due to low hydraulic permeability of sludge, while electro-osmosis provides a promising solution. Two types of EKG, E-board and E-tube, are developed for sludge dewatering. EKG solved the problem of electrode corrosion and new challenges is high electric power requirement. Energy level gradient theory is presented as a fundamental theory to propose design method for sludge dewatering. Key parameters of flow coefficient and time factor are discussed, including their test method, value range and scale effect. Roll polling electro-osmosis scheme is the solution for high power requirement. Estimation of power and design of roll polling electro-osmosis scheme is core of electro-osmotic dewatering design. Novel DC power source is custom built to realize the roll polling scheme. The DC power source of 80V/1000A has roll polling program embedded and it is in charge of 12 independent sections, which can deal with ~2000 square meters of hydraulically filled area.