Proceedings of The Fourteenth (2004) International Offshore and Polar Engineering Conference
Toulon, France, May 23−28, 2004
Copyright © 2004 by The International Society of Offshore and Polar Engineers
ISBN 1-880653-62-1 (Set); ISSN 1098-6189 (Set)
Soil Improvement Using Electroosmotic Method with the Injection of Saline Solution
1
Shao-Chi Chien1 Chang-Yu Ou2 Yi- Kuan Wang2
National Science and Technology Center for Disaster Reduction
Taipei, TAIWAN, China
2
Department of Construction Engineering University of Science and Technology
Taipei, TAIWAN, China
This behavior mechanism of field for electroosmosis is very different
from laboratory experiment. Further, concerning researches focused on
electroosmosis in the past, elctroosmotic method with the injection of
saline solution have less been discussed.
This paper presents the development of the ground improvement
method for electroosmosis with the injection of saline solution. A
special electroosmotic apparatus was designed. This apparatus was
specially designed to perforate tubular electrode so as to inject saline
solution from anode, to drain from cathode and to simulate field stress
by applied axial load. A series of experiments on the electroosmotic
method with the injection of saline solution for Taipei silt clays were
performed to assess the effectiveness of the electroosmosis with the
injection of saline solution and to study the mechanism of the process.
This research was also based on the electric double layer theory and the
test results discussed effect of electroosmosis with the injection of
saline solution. The polarity reversal of electrodes was applied to
discuss the influence.
ABSTRACT
To enhance effect of electroosmostic improvement and to shorten the
time of treatment, this research made use of interaction between
chemical solution and soil particles under the influence of electric field,
such as cation exchange, water adsorption, and particle cementation.
The elctroosmostic method with the injection of saline solution was
developed in this study. The results of this research showed that using
the electroosmostic treatment with the injection of calcium chloride
(CaCl2) treatment for a period of 9 days, the undrained shear strength of
soil increased averagely by 350% compared to the initial strength and
120% compared to electroosmostic treatment without the injection of
saline solution. However, after the electroosmostic treatment with the
injection of calcium chloride (CaCl2) treatment for a period of 1 day,
the undrained shear strength of soil near anode is 1.36 times compared
to electroosmostic treatment without the injection of saline solution
treated for a duration of 9 days. The elctroosmostic method with the
injection of saline solution can certainly enhance electroosmostic effect
of improvement and shorten the time of treatment.
ELECTROOSMOTIC EXPERIMENTAL CELL
Table 1 summarizes the features of former experiment designs of the
electroosmotic cell. Most electroosmotic cells consist of plate
electrodes resulted in current and electroosmtic flow, parallel to the
direction of the consolidated pressure. Such the conditions in the
laboratory are far from encountered in field application.
In the development of the electroosmotic cell for this study, the
following factors were taken into account ： (1)adopting tubular
perforation electrode as anode and cathode conformed with the field
condition of electroosmosis; (2) injecting saline solution from anode
and water drained from cathode; (3)simulating the initial field stress
condition; and (4)measuring the distribution of pore-water pressure,
potential difference within the sample, settlement of sample,
temperature of sample, and pore-water pH value during the treatment.
The electroosmotic cell with the injection of saline solution was made
of 280 mm diameter 330 mm length high plexiglas tube bounded by a
top and bottom plexiglas plate (Fig. 1). Plexiglas was used because of
its electrical and hydraulic impermeability. The top plate was bored
with holes for connecting perforated tubular electrode, pressure equip
ment, LVDT, and drained path. On the bottom plate was laid out
monitor instruments and drained paths (Fig. 1). Lead wires were used
from both electrodes to the power supply device. Drainage could be
controlled at both ends of the cell. The tubular stainless steel pipe was
KEY WORDS: Electroosmotic; Injection.
INTRODUCTION
When an electric potential is applied across a wet soil mass, cations of
double layer in a soil would be attracted to the cathode and anions to
the anode. As these cations migrate to the cathode, they drag water with
them. Because there are more cations than anions in a soil containing
negatively charged clay particles, there is a net flow of water towards
the cathode. This flow is called electroosmosis. Since the flow of water
towards the cathode causes soil consolidation, soil undrained strength
would be increased.
The field application of the electroosmosis in silts, silt clays, and soft
sensitive clay successfully was demonstrated (Casagrande, 1961;
Bjerrum, 1967; Fetzer, 1967 and Lo, 1991b) and then some
investigators continually proceeded with laboratory treatment to
explore ground improvement by electroosmosis, as shown in Table 1.
Despite some discussion concerning electroosmosis experiment in the
past, the experiments mostly adopted modified oedometer cell or
triaxial cell which joined metal plate in the top and bottom of sample
for electroosmosis. Field electroosmotic treatments all use tubular
electrodes which would be vertically inserted into ground to treat soil.
689