Electrokinetic stabilization of soil is a ground improvement technique. Method of electrokinetic stabilization, their applications, advantages and factors affecting it are discussed in this article.
Instability of the substructure is found to cause detrimental damage to the whole building. It is seen that the most common cause of the movement of the foundation is due to the volume change of active clays.
This movement of soil may be a response to the environment or vegetation changes. Most notable changes are seen in long dry spells with clay shrinkage and clay swelling. These are after effects of external factors like removal of large trees or hedges.
The procedure of providing an electrical current through a soil mass (that is under consideration) in order to migrate charged particles in the soil to change the properties, leading to an overall stabilization of the soil is called as electrokinetic stabilization.
This method of soil stabilization is mainly employed for weak clayey soils. As we know, weak clayey soil requires treatment for high strength. They also possess a low hydraulic conductivity, which prevents the use of chemical grout by conventional hydraulic means.
Suitability of Electrokinetic Stabilization in Problematic SoilsThe electrokinetic stabilization of soil should be implemented in those soils which gains certain mineralogical properties and which are chemically active. Fine-grained soils are applicable for this treatment as they consist of a larger fraction of clayey particles and hence are less permeable. Less permeable soils mean those that cannot be easily drained. These soils under consideration, in any construction site, can me named as expansive soils or dispersive soils, high compressible soil etc. in different identities based on nature and behavior.
Electrokinetic Treatment - DefinitionElectrokinetic treatment is electrochemical processing of the soil which uses electric current or a potential difference on the soil that must be treated with the help of certain charged electrodes. Electrokinetic treatment of soil helps in the removal of heavy metal particles, organic as well as inorganic compounds that make the soil less permeable and defective for construction purpose. As explained the treatment is done on soil particles that already carry charges. Mainly they are negatively charged. As per the procedure, when it is subjected to a potential difference the particles within the soil (can be positive or negative) move to the oppositely charged electrodes.
Electrochemical Reactions in Electrokinetic TreatmentThe whole process of electrokinetic treatment involves promotion of charged particles throughout the system of soil. These can be categorized under 4 mechanisms:
- Electro migration
Fig.1. Figure Showing The 4 mechanisms in an electrokinetic treatmentSoil under consideration consists of many contaminants. The majority of the contaminants are the heavy metals which are positively charged. There are also other impure materials in the soil that must be removed, which also possess a positive charge. Now when the potential difference is applied to the whole system by means of a direct current, there is a possibility that some of the positively charged particles get adsorbed on the clay (negatively charged). Which results in a diffuse double layer (DDL). Movement of charged particles to attract opposite charges is because of electro-osmosis. Formation of DDL layer is called electrophoresis. Electrolysis is the process of diffusion of ions into the solution under the action of the applied electric field. The effect of these four stages would result in a variation of hydrological, engineering as well as physiochemical properties of the soil.
Factors Affecting Electrokinetic Stabilization of SoilFollowing factors affect the effectiveness of electrokinetic treatment
1. Type of soil and MineralThis treatment as understood from the procedure is more suitable for clayey soils.e.g. illitic and bentonite clays
2. The Water ContentThe presence of water content should facilitate easy conduction to promote the movement of ions. The soils with a pH value greater than 9 are found to be more active towards this method.
3. The Source of CurrentHigher the electric current more the charge on the soil compared to lower supply. Good constant supply of power would provide the system with a constant rate of performance in terms of continuous EK treatment.
4. Electrode NatureMost preferred electrodes are graphite and pressed carbon coated electrodes. Usage of metals is found to be more effective compared to carbon or platinum. Metals like iron or copper can also be used.
5. Time of processingThe treatment depends upon the voltage levels, the migration time of particles, the spacing of electrodes as well as the whole system configuration.
6. CostThe economy of the method depends upon the extent to which the soil is contaminated. The whole system and arrangement of the electrokinetic system depend upon the soil properties like its pore water, texture.etc. Other factors like a process designed, preparations, resources costs etc.
Applications of Electrokinetic Stabilization of SoilElectrokinetic stabilization of soil can be employed for the following methods of ground improvement:
- Increase stability of unstable embankments and excavations
- Slope stabilization
- Strengthening of backfill
- Treatment of salt affected soils
- Dispersive soil treatment
- Injection of grouts
- Dewatering of dredged soil
- Decontamination of soil and groundwater
Advantages of Electrokinetic Stabilization of SoilElectrokinetic stabilization of soil gain certain advantages when compared to other conventional methods of soil treatment such as:
- It is found to be less expensive in terms of cost effectiveness
- The installation of whole EK treatment system can be rapid
- The site conditions can be both in-situ and ex- situ
- Simplicity in operation from start to end
- No noise pollution as the whole treatment is silent
- Other site activities are not affected
- Treatment time period is short
Disadvantages of Electrokinetic Stabilization of SoilThe treatment also owns certain limitations which are mentioned as follows:
- Heat generation in excessive amount during the treatment
- Cracking of the electrodes due to heat generation
- Electrochemical reaction results in chlorine gas which is found to be harmful
- High variation of pH value resulting to degradation of anode or cathode electrodes
- Improper usage of Chemical agent to affect the whole system
Techniques to Increase Efficiency of Electrokinetic Stabilization of Soil
- Use of chemical stabilizer as enhancement agents promotes faster rate of ion formation and contaminant removal
- Desorption and precipitation of the contaminant have to be prevented
- Usage of inexpensive electrodes like graphite, carbon fibers or activated carbon instead of using highly expensive electrodes like titanium
- Usage of hollow electrodes facilitating movement of solution through it increasing EK process
- Minimize Toxic effects on the soil.