231
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Electro-osmotic consolidation: Laboratory tests and numerical simulation
Électro-osmotique de consolidation :
les tests de laboratoire et simulation numérique
Hu L., Wu H., Wen Q.
State Key Laboratory of Hydro-Science and Engineering, Department of Hydraulic Engineering,
Tsinghua University, Beijing, 100084 CHINA
ABSTRACT: Electro-osmotic consolidation is an attractive soil improvement technique for soft clay. A review of research and
practical applications of electro-osmosis was performed. The achievements and major bottleneck of the current technique were briefly
discussed, and the potential areas for scientific research and engineering application were proposed. A laboratory testing facility was
developed for the electro-osmotic consolidation, and the electrical voltage, soil mass displacement, water discharge and electrical
current can be monitored during testing process by use of online transducers. Moreover, the microscopic phenomenon is investigated
by use of Environmental Scanning Electron Microscopy (ESEM). A theoretical model for electro-osmotic consolidation is briefly
introduced, which couples Biot’s consolidation equation with the electro-osmotic flow and control equation for an electrical field, and
incorporates the nonlinear variation of the mechanical, hydraulic and electrical properties. The FEM software was developed based on
the theoretical model to describe the electro-osmotic consolidation process, and the model tests are simulated. The numerical results
showed good agreement with the testing data in terms of ground settlement, indicating the rationality of the analytical model. It is also
shown that the variations of electrical conductivity have a significant effect on the consolidation process. The developed software can
predict the displacement behavior of soil mass and provide useful data for system design of electro-osmosis treatment.
RÉSUMÉ : La consolidation électro-osmotique est une technique attrayante d’amélioration de l’argile. Une révision des demandes de
recherche et de pratique de l’électro-osmose a été effectuée. Les réussites et le goulot d’étranglement majeur de la technique actuelle
ont été brièvement discutés, et les domaines potentiels de la recherche scientifique et l’application d’ingénierie ont été proposés. Un
centre d’essais en laboratoire a été développé pour la consolidation électro-osmotique, et la tension électrique, le déplacement massif
de sol, l’évacuation de l’eau et le courant électrique peuvent être contrôlés pendant le processus d’essai en utilisant des capteurs en
ligne. En outre, le mécanisme microscopique de la migration de l’eau interstitielle et des ions est étudié par l’utilisation de
microscopie électronique à balayage environnemental (ESEM). Un modèle théorique pour la consolidation électro-osmotique est
brièvement présenté, qui couple l’équation de consolidation de Biot avec le flux électro-osmotique et l’équation de commande d'un
champ électrique, et intègre la variation non linéaire des propriétés mécaniques, hydrauliques et électriques. Le logiciel FEM a été
développé sur la base du modèle théorique pour décrire le processus de consolidation électro-osmotique, les essais sur modèle sont
simulés. Les résultats numériques montrent un bon accord avec les données de test en termes de tassement du sol, indiquant la
rationalité du modèle analytique. Il est également montré que les variations de la conductivité électrique ont un effet significatif sur le
processus de consolidation. Le logiciel développé permet de prédire le comportement de déplacement de masse de sol et de fournir
des données utiles pour la conception de systèmes d’électro-osmose.
KEYWORDS: electro-osmosis; axisymmetric test; scanning electron microscopy; theoretical model; numerical simulation
1 INTRODUCTION
Electro-osmotic consolidation provides an attractive soil
improvement technique, during which flow of pore water occurs
from the anode toward the cathode under the electric field in
soils. The electro-osmotic consolidation technique has been
used in various geotechnical engineering applications, including
stabilization of slopes, excavations, and embankments,
controlling groundwater flow, increasing pile capacity and the
strength of clays, and dewatering tailings and sludge,
meanwhile, numerous laboratory studies have been published,
mostly based on soil column tests (Casagrande, 1948;
Casagrande, 1983; Shang and Dunlap, 1998; Mitchell and Soga,
2005; Jones et al., 2008). Recently, the combination of electro-
osmosis and vacuum preloading was investigated by means of
axial-symmetric model tests (Li et al., 2009; Wu and Hu, 2012).
The theory for electro-osmosis was also developed to
predicte the soil behavior during consolidation. One-
dimensional
analytical
solutions
for
electro-osmotic
consolidation were proposed by previous researchers (Esrig,
1968; Wan and Mitchell, 1976). The analytical solutions for 2D
problems were also developed (Shang, 1998; Su and Wang,
2003; Xu et al. 2011). Lewis and Humpheson (1973) formulated
a finite element model to analyze the groundwater flow in two-
dimensional electric fields. Rittirong and Shang (2008)
proposed a 2D finite difference model to obtain excess pore-
water pressure during electro-osmosis, analyzing the subsurface
settlement and undrained shear strength.
Up to now, most of the analytical solutions are based on the
assumption of uniform electric field, which is not applicable for
most field applications due to the complexity of electrode
configuration, complicated boundary conditions and anisotropic
soil properties. Furthermore, the previous model focused on
predicting pore water pressure, while the ground settlement was
not considered. A comprehensive numeircal model is demanded
to predict the soil behavior and provide data for system design
of electro-osmosis treatment.
In this paper, a laboratory testing facility for axial-symmetric
model was developed for the electro-osmotic consolidation, and
the electrical voltage, soil mass displacement, water discharge
and electrical current were monitored during testing process by
use of online transducers, and the coupled effect of mechanical,
hydraulic and electrical field was discussed. A theoretical model
was birefly introduced (Hu et al., 2012), and FEM software was
developed based on the theoretical model to describe the
electro-osmotic consolidation process. The software was
verified by comparison of numeical results and test data. The
ESEM tests were conducted to observe the change of soil
particles.
