Location
Arlington, Virginia
Date
14 Aug 2008, 2:15pm - 4:00pm
Abstract
In this paper, the theory about electro-osmotic treatment of soil is summarized. The correlation between conventional soil char-acteristics and the most important electro-osmotic parameters, soil resistivity and electro-osmotic permeability coefficient, is indicated. Two case records exemplify the correlation between theory and reality. One of the case records concerns improvement of the preconsolidation pressure of a clay layer situated underneath a lake, which had to be filled with sand to create a building site, 800 m2 in size, for a magazine to be built. The electrodes consisted of iron rails with a weight of 25 kg/m. No dewatering at the cathodes took place. The applied potential varied from about 70 to 90 V. Unfortunately, a mistake in coupling was made. Thus, what was intended as anodes became cathodes and vice versa. All the same, the goal of electro-osmotic treatment, namely to increase the preconsolidation pressure to the intended level, was ful-filled. The settlement caused by electro-osmosis was documented in relation to energy consumption and electric current con-sumed but was considerably smaller than expected. The other case record concerns investigation of the influence of electrode diameter on the effect of electro-osmosis. Three test fields with electrodes consisting of, respectively, reinforcement bars 25 mm in diameter, iron tubes 38 mm in diameter and iron tubes 64 mm in diameter were arranged as part of examination works in civil engineering education at Chalmers Univ. of Technology. No dewatering at the cathodes took place. In the beginning of the study all test fields were coupled in parallel with an applied potential of 7 to 9 V. Later on, only one test field was coupled up in turn. In these cases the potential applied was 25 to 40 V. A careful study of the soil characteristics and the electro-osmotic parameters was carried out before the installation of the electrodes. During the electro-osmotic treatment, a study was made of the potential gradient between anodes and cathodes, the settlement in relation to energy consumption and electric current consumed, and the effect of electro-osmosis on pore water pressure, undrained shear strength and sensitivity. The anode consumption was particularly large in the test area with electrodes 25 mm in diameter. During the electro-osmotic treatment, gas was developed, most probably because of a large content of shells in the upper part of the clay layer. Therefore, swelling took place in the upper part, which counteracted the settlement caused by the electro-osmotic treatment. It is recommended to provide the cathodes with a pumping device in order to eliminate the effect of hydraulic backflow from cathodes to anodes.
Department(s)
Civil, Architectural and Environmental Engineering
Meeting Name
6th Conference of the International Conference on Case Histories in Geotechnical Engineering
Publisher
Missouri University of Science and Technology
Document Version
Final Version
Rights
© 2008 Missouri University of Science and Technology, All rights reserved.
Creative Commons Licensing
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.
Document Type
Article - Conference proceedings
File Type
text
Language
English
Recommended Citation
Hansbo, Sven, "Soil Improvement by Means of Electro-Osmosis" (2008). International Conference on Case Histories in Geotechnical Engineering. 41.
https://scholarsmine.mst.edu/icchge/6icchge/session07/41
Soil Improvement by Means of Electro-Osmosis
Arlington, Virginia
In this paper, the theory about electro-osmotic treatment of soil is summarized. The correlation between conventional soil char-acteristics and the most important electro-osmotic parameters, soil resistivity and electro-osmotic permeability coefficient, is indicated. Two case records exemplify the correlation between theory and reality. One of the case records concerns improvement of the preconsolidation pressure of a clay layer situated underneath a lake, which had to be filled with sand to create a building site, 800 m2 in size, for a magazine to be built. The electrodes consisted of iron rails with a weight of 25 kg/m. No dewatering at the cathodes took place. The applied potential varied from about 70 to 90 V. Unfortunately, a mistake in coupling was made. Thus, what was intended as anodes became cathodes and vice versa. All the same, the goal of electro-osmotic treatment, namely to increase the preconsolidation pressure to the intended level, was ful-filled. The settlement caused by electro-osmosis was documented in relation to energy consumption and electric current con-sumed but was considerably smaller than expected. The other case record concerns investigation of the influence of electrode diameter on the effect of electro-osmosis. Three test fields with electrodes consisting of, respectively, reinforcement bars 25 mm in diameter, iron tubes 38 mm in diameter and iron tubes 64 mm in diameter were arranged as part of examination works in civil engineering education at Chalmers Univ. of Technology. No dewatering at the cathodes took place. In the beginning of the study all test fields were coupled in parallel with an applied potential of 7 to 9 V. Later on, only one test field was coupled up in turn. In these cases the potential applied was 25 to 40 V. A careful study of the soil characteristics and the electro-osmotic parameters was carried out before the installation of the electrodes. During the electro-osmotic treatment, a study was made of the potential gradient between anodes and cathodes, the settlement in relation to energy consumption and electric current consumed, and the effect of electro-osmosis on pore water pressure, undrained shear strength and sensitivity. The anode consumption was particularly large in the test area with electrodes 25 mm in diameter. During the electro-osmotic treatment, gas was developed, most probably because of a large content of shells in the upper part of the clay layer. Therefore, swelling took place in the upper part, which counteracted the settlement caused by the electro-osmotic treatment. It is recommended to provide the cathodes with a pumping device in order to eliminate the effect of hydraulic backflow from cathodes to anodes.
