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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. [ABSTRACT FROM AUTHOR]

Highlights • The effects of soil pH and ionic species on the electro-osmotic consolidation of kaolin are studied. • The addition of sodium ions increased both electro-osmotic flow rate and total volume of the discharged water. • The precipitation of copper at cathode reduced both electrical conductivity and dewatering efficiency. • The initial soil pH showed a remarkable effect on water content distribution. Abstract The application of an electric field on soil mass induces both electro-osmotic flow and electro-migration, which has been used for the dewatering of soft soils and remediation of contaminated soils. The physical and chemical properties of soft soils are influenced by the soil pH as well as ionic species and their concentrations, which subsequently influence the dewatering and remediation efficiency. In the present study, one-dimensional column experiments were conducted to investigate the influence of soil pH and ionic species on the electro-osmotic consolidation process of kaolin. The initial drainage rate, total volume of the discharged water and the voltage loss near the anode increased with the increase in the initial soil pH. After electro-osmosis, the water content was lower near the anode and higher near the cathode for sample with higher initial soil pH. The addition of copper ions reduced the dewatering efficiency while the addition of sodium ions increased the drainage rate and total volume of discharged water. Moreover, the precipitation of copper ions increased the voltage loss near the cathode. [ABSTRACT FROM AUTHOR]

Abstract Laboratory tests were conducted on kaolinite to investigate the effectiveness of electro-osmotic consolidation combined with vacuum preloading using electrokinetic geosynthetics (EKG). The results showed that the combined method could remove more water and induce larger surface ground settlements compared with the traditional vacuum preloading or electro-osmotic consolidation. Vacuum preloading was quite effective during the first 4 h, though the electro-osmotic consolidation took a main role in dewatering process after 9 h. The combined method could also hinder the development of cracks, induce higher negative pore water pressure and hence increase the efficiency of electro-osmotic consolidation. The results showed that deep electro-osmotic consolidation technique combined with vacuum preloading could result in significant water removal efficiency along with shorter electrode length. Furthermore, both electro-osmotic consolidation and the combined method could consolidate the soil efficiently with low energy consumption. [ABSTRACT FROM AUTHOR]

Electro-osmotic consolidation is an effective method for soft ground improvement. A main limitation of previous numerical models on this technique is the ignorance of the non-linear variation of soil parameters. In the present study, a multi-field numerical model is developed with the consideration of the non-linear variation of soil parameters during electro-osmotic consolidation process. The numerical simulations on an axisymmetric model indicated that the non-linear variation of soil parameters showed remarkable impact on the development of the excess pore water pressure and degree of consolidation. A field experiment with complex geometry, boundary conditions, electrode configuration and voltage application was further simulated with the developed numerical model. The comparison between field and numerical data indicated that the numerical model coupling of the non-linear variation of soil parameters gave more reasonable results. The developed numerical model is capable to analyze engineering cases with complex operating conditions. [ABSTRACT FROM AUTHOR]

Electro-osmosis can be a potential improvement technique for expansive soils. One-dimensional column experiments were conducted to comprehend the impact of electro-osmosis on the consolidation behavior and the geotechnical properties of a sodium bentonite with different electrode materials, including two reactive electrodes (copper and iron) and two inert electrodes (graphite and stainless steel). The change in drainage rate, electric current and voltage loss close to the anode were similar for the four electrodes, with a rapid change stage in the first 2 h followed by a slow change stage in the next 6 to 8 h and finally a stable stage. The rapid voltage loss in the first stage was caused by soil cracking near the anode due to severe volume shrinkage and gas generation. Soil properties, including plasticity, swelling potential, zeta potential, and cation exchange capacity decreased emarkably in the vicinity of the anode. During electro-osmosis, the reactive electrodes caused more significant change in soil properties than the inert ones. Electro-osmosis technique can reduce the swelling potential of the bentonite, however, the zone of influence is restrained. [ABSTRACT FROM AUTHOR]

Electro-osmotic stabilization has long been studied as a soft soil improvement technique, while the influence of an applied electrical field on the soil microfabric and minerals is always ignored. In this study, three laboratory experiments were conducted on sodium bentonite using copper, iron and graphite electrodes to investigate the microfabric and chemical composition change before and after electro-osmotic stabilization. The soil samples near the anode were identified using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). The microfabric of the sodium bentonite changed from flocculated fabric to aggregated fabric after electro-osmotic stabilization. Regular calcium sulfate tubes were generated near the copper and iron anodes. EDX tests showed that the content of sodium near the anode decreased, while the copper, iron and calcium presented substantial increase, indicating that the sodium ions were substituted by copper, iron, and calcium ions in copper, iron and graphite experiments respectively. The change of microfabric and the ion exchange reactions between sodium, copper, iron and calcium ions are the main reasons for the significant decrease of the plasticity index and free swelling ratio. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In present study, the non-linear variations of soil compressibility, hydraulic and electro-osmosis conductivities were analyzed through laboratory experiments, and incorporated in a one-dimensional model. The analytical solutions for excess pore water pressure and degree of consolidation were derived, and numerical simulations were performed to verify its effectiveness. The results indicated that both the non-linear variations of hydraulic and electro-osmosis conductivities showed remarkable impacts on the excess pore water pressure and degree of consolidation, especially for soils with relative high compressibility. A further comparison with previous analytical solutions indicated that more accurate predictions could be obtained with the proposed analytical solutions. [ABSTRACT FROM AUTHOR]