On the mechanism of soft clay being improved entirely in the ECT treatment
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ORIGINAL PAPER
On the mechanism of soft clay being improved entirely in the ECT treatment Chang-Yu Ou 1 & Chien-Yu Lin 1 & Shao-Chi Chien 2 Received: 30 December 2018 / Accepted: 23 March 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The objective of this study was to demonstrate that the clay strength can be improved significantly over the entire sample during electroosmosis simultaneously with the injection of 0.75 M CaCl2 solution for 72 h, then 1.5 M KOH solution for 48 h, then Na2SiO3 solution for 72 h, and then injection of deionized water for 168 h. Such an improvement was significant in terms of the improvement strength and improvement area as compared with the previous studies in the literature that the clay strength was improved only near the anode or cathode while the areas between the electrodes remain weak. The mechanism of the improvement was also studied by examining the physical and chemical properties of the treated clay at each phase of treatment. The cone resistance, water content, pH value, and the Ca2+ concentration were measured at each phase. Results also indicated that the quality of the Na2SiO3 solution might degrade in the anode compartment during treatment because of electrolysis of water. However, it was found that such a degradation was not very serious, which would not influence the test results significantly. For simplification, it may not be necessary to replace the possible degraded Na2SiO3 solution with the fresh one. Keywords Electrokinetic chemical treatment . Full improvement . Chemical solutions . Deionized water . Properties of the treated soft clay
Introduction Electroosmosis has been used to improve soft clay for many years. The main mechanism of electroosmosis for improving soft clay is dewatering or consolidation, thereby increasing the undrained strength of soft clay. Since such an increase is limited, to enhance the effect of electroosmosis, chemical solutions were injected into soft clay during electroosmosis via several physicochemical behaviors with electrical and hydraulic flows coupling across the clay such as electroosmosis flow, electrophoresis, and electromigration (e.g., Ozkan et al. 1999; Asavadorndeja and Glaw 2005; Chien et al. 2009; Moayedi et al. 2012; Mosavat et al. 2013; Moayedi et al. 2014; Peng et al. 2015). This method is called as electroosmotic or electrokinetic chemical treatment (ECT). CaCl2 and Na2SiO3
* Chang-Yu Ou [email protected] 1
National Taiwan University of Science and Technology, Taipei, Taiwan
2
Hsuan Chuang University, Hsinchu, Taiwan
solutions are two main chemical solutions used to be injected into soft clay in the ECT process. CaCl2 solution was expected to induce pozzolanic reaction near the cathode to form cementing agents, C-S-H/C-A-H. With the cementing agents, the clay strength can be improved significantly (Etim et al. 2019). Na2SiO3 solution would gel in acidic environment near the anode due to electrolysis of water. Cementation therefore occurs, leading to the increase of soil strength
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