SOIL STABILISATION AND TYPES

Soil Stabilisation

Soil stabilisation is the process of improving the engineering properties of the soil and thus making it more stable.It is required when the soil available for construction is not suitable for intended purpose.In its broadest senses, stabilisation includes compaction, preconsolidation, drainage and many other processes.Generally, soil stabilization is a method of improving soil properties by blending and mixing other materials.A cementing materials or a chemical is added to a natural soil for the purpose of stabilisation.Improvements include increases the dry unit weight, bearing capabilities, volume change, the performance of in situ subsoils, sands and other waste materials in order to strengthen road surface and other geotechnical applications.

Soil stabilisation is used to reduce the permeability and compressibility of the soil mass in earth structures and to increase its shear strength.Soil stabilization is required to increase the bearing capacity of foundation soils.The main purpose of soil stabilisation is to improve the natural soils for the construction of highways and airfields.This process is accomplished using a wide variety of additives, including lime, cement and flyash.Other material byproducts used in stabilization include lime-kiln dust (LKD) and cement-kiln dust (CKD).There are various method and materials that can used to stabilising the soil.Following are the types of Soil Stabilisation:

1. Lime Soil Stabilisation
2. Cement Soil Stabilisation
3. Bitumen Soil Stabilisation
4. Chemical Soil Stabilisation
5. Electrical Soil Stabilisation
6. Thermal Soil Stabilisation

1. Lime Soil Stabilisation

Lime stabilisation is done by adding lime to the soil.It is very useful for stabilisation of clayey soils.When lime reacts with soil, there is exchange of cations in the adsorbed water layer and a decrease in plasticity of the soil occurs.The resulting material is more friable than the original clay and is therefore, more suitable as subgrade.Lime stabilisation improve the density and bearing capacity of the soil.

2. Cement Soil Stabilisation

Cement soil stabilisation is done by mixing pulverised soil and portland cement with water and compacting the mix to attain a strong material.The cement contains active ingredients that help in disintegration of soil particles.Besides that, the cement helps in concealing the soil.Other materials added into the mixture include lime, calcium chloride, sodium carbonate, sodium sulphate and fly ash.The amount of cement that's added into the mixture varies depending on the type of soil that's being stabilised.

3. Bitumen Soil Stabilisation

Bitumens are non-aqueous system of hydrocarbons that are soluble in carbon di-sulphide.Bitumen stabilisation is generally done with asphalt as binder.In any inorganic soil which can be mixed with asphalt is suitable for bituminous stabilisation.In cohesionless soils, asphalt binds the soil particles together and thus serves as a bonding or cementing agent.

4. Chemical Soil Stabilisation

In chemical soil stabilisation, soils are stabilised by adding different chemicals.These chemicals react with the soil which in return cause its structure to be changed.The chemical seal the space between particles, leaving no room for water to penetrate through.Among the most common chemicals that are used for soil stabilization include sodium chloride, calcium chloride and sodium silicate.

5. Electrical Soil Stabilisation

Electrical soil stabilisation of clayey soils is done by a process known as electro-osmosis.In this method a direct current is passed through a clayey soil, pore water migrates to the negative electrode (cathode).It occurs because of the attraction of positive ions (cations) that are present in water towards cathode.The strength of the soil is considerably increased due to removal of water. Electro-osmosis is an expansive method and is mainly used for drainage of cohesive soils.

6. Thermal Soil Stabilisation

Thermal soil stabilisation is done by heating the soil or by cooling the soil.When the soil heated, water content of soil decreases and strength of soil is increased.When soil is heated at high temperature some irreversible changes occurs which make the soil non-plastic and non-expansive.

When soil is cooling for stabilising the soil, a small loss of strength occurs in clayey soil due to an increase in interparticle repulsion.However, if the temperature is reduced to the freezing point, the pore water freezes and soil is stabilised.