EFFECT OF ELECTRO OSMOTIC TECHINQUE IN CONSOLIDATION OF SOIL

INTRODUCTION
Electro osmotic consolidation means the consolidation of soft clays by the

application of electric current.
It was studied and applied for the first time by Casagrande.
It is inherent that fine grained clay particles with large interfacial surface will

consolidate and generate significant settlement when loaded.
The settlement creates problem in the foundation engineering.
Electro osmosis was originally developed as a means of dewatering fine grained soils

for the consolidation and strengthening of soft saturated clayey soils.
Electro osmotic dewatering essentially involves applying a small electric potential

across the sediment layer.
It is the process where in positively charged ions move from anode to cathode.
ie. Water moves from anode to cathode where it can be collected

and pumped
out of soil
Electro osmotic flow depends on soil nature, water content, pH and on ionic type

concentration in the pore water.


ELECTRO OSMOTIC CONSOLIDATION
Due to the applied electric potential the electrolysis of water occurs at the

electrodes
2H2O -> O2 (g) + 4H+ +4e- oxidation (anode)
4H2O + 4e- -> 2H2 (g) + 4OH- reduction (cathode)
The clay particles have a “ve charge. These “ve charge produce an electro static

surface property known as the double layer which creates a net abundance of cations

in pore space.
Electro osmotic transfer of water through a clay is a result of diffuse double layer

cations in the clay pores being attracted to a negatively charged electrode or

cathode.
When electrodes are placed across a saturated clay mass and direct current is applied

,water in the clay pore space is transported towards cathode by electro osmosis.
In addition frictional drag is created by the motion of ions as they move through the

clay pores helping to transport additional water.
The flow generated by the electric gradient is called electro osmotic flow.



EVALUATION OF ELECTRO OSMOTIC CONSOLIDATION

Determination of parameters
Electrical operation systems for field application
Materials
Spacing between electrodes
Cost of electrodes and installation cost


CASE STUDY 1 ELECTRO OSMOTIC DEWATERING OF DREDGED

SEDIMENTS :- BENCH SACLE INVESTIGATION AT INDIANA HARBOUR (USA)

The Indiana Harbour has not been dredged for over 20 years due to lack of an

acceptable disposal site
It resulting in the accumulation of large amount of highly contaminated sediments
The main problem with the disposal of sediment to the CDP was slow consolidation of

sediment due to its very high water content.
This study investigated the feasibility of using an electro osmotic dewatering

technology to accelerate dewatering and consolidation of the sediment there by

allowing more rapid disposal of sediment in to the CDP.

MATERIAL (SOIL SAMPLE)

Samples were obtained by dredging from the Indiana Harbour.The

sediments were tested for water content, optimum moisture content and pH


CASE STUDY 2EFFECT OF USING ELECTRO CONDUCTIVE PVD IN THE CONSOLIDATION OF RECONSTITUTED ARIAKE CLAY

The deposits of Ariake clay consolidate generate significant settlement when loaded

which causes problems in foundation engineering.
The low permeability of clay results in longer duration to achieve primary

consolidation.
To shorten the consolidation time vertical drains are installed to shorten the

drainage path.
The induced consolidation of reconstituted Ariake clay was conducted using electro

conductive PVD as electrodes and the results were compared with an ordinary PVD

MATERIAL (SOIL SAMPLE)

The soil sample used was leached marine Ariake clay collected at Saga

Plain in Saga Japan. The sample excavated at about 2m depth was generally a very soft

gray silty clay (about 66% clay, 26% silt, 8% fine sand) with natural water content

of about 110% “ 120%


ADVANTAGES

The consolidation period can be reduced by electro osmotic consolidation technique.
The process is very efficient in low permeability clays in which the electro osmotic

permeability is greater than the hydraulic permeability.
Electro osmotic permeability was 200 to 1000 times greater than the hydraulic

permeability.
This method is suitable for local application on small volumes or for impermeable

barrier construction.
After treatment water content decreases and shear strength increases and it was more

than what was expected just from dewatering.


DISADVANTAGES
The pH of soil will increase to as high as 11 or 12 at the cathode and decrease to

almost 2 at the cathode.
Metal anodes will corrode.
The applied voltage and electric current generates heating.
The heating effect increases power consumption.


CONCLUSION

Dewatering of sediment can be enhanced by the electro osmosis induced by the

application of an electric potential
Incorporating electro kinetic item in the properties of PVD is very useful in

dewatering highly compressible and low permeability clay
Faster rate of settlement was achieved using electro conductive drains
Significant rate of increase in strength of EO-treated soils was achieved as a

consequence of decrease in water content formation of menisci in the soil voids and

bonding of soil particles by insoluble chemical precipitates as a result of the

complex chemical reactions generated and ion re-exchange which altered the plasticity

of clay.
Application of electric potential will result in energy consumption.