Soil Stabilisation
Soil stabilization is the process of improving the engineering properties of soil to make it more stable. It is necessary when the soil available for construction is unsuitable for its intended purpose. In its broadest sense, stabilization includes techniques such as compaction, preconsolidation, drainage, and other processes. Generally, soil stabilization involves improving soil properties by blending and mixing it with other materials. A cementing agent or chemical is added to natural soil to achieve stabilization. The improvements typically include increased dry unit weight, enhanced bearing capacity, reduced volume change, and better performance of in-situ subsoils, sands, and various waste materials, all aimed at strengthening road surfaces and other geotechnical applications.
Soil stabilization helps reduce the permeability and compressibility of the soil in earth structures while increasing its shear strength. It is essential for enhancing the bearing capacity of foundation soils. The main objective of soil stabilization is to improve natural soils for constructing highways and airfields. This process utilizes a wide variety of additives, including lime, cement, and fly ash. Additional byproducts used in stabilization include lime-kiln dust (LKD) and cement-kiln dust (CKD). Various methods and materials can be used to stabilize soil, with the following types being common:
1. Lime Soil Stabilization:
Lime stabilization is achieved by adding lime to soil, which is particularly effective for stabilizing clayey soils. When lime interacts with the soil, there is an exchange of cations in the adsorbed water layer, leading to a reduction in the soil's plasticity. The resulting material becomes more friable than the original clay, making it more suitable for use as a subgrade. Lime stabilization improves both the density and bearing capacity of the soil.
2. Cement Soil Stabilization:
Cement soil stabilization involves mixing pulverized soil with Portland cement and water, then compacting the mixture to create a strong material. The cement contains active ingredients that facilitate the disintegration of soil particles while also helping to bond the soil. Other materials that may be added to the mixture include lime, calcium chloride, sodium carbonate, sodium sulfate, and fly ash. The amount of cement used varies depending on the type of soil being stabilized.
3. Bitumen Soil Stabilization:
Bitumen stabilization utilizes a non-aqueous system of hydrocarbons that are soluble in carbon disulfide, typically performed with asphalt as a binder. Inorganic soils that can be mixed with asphalt are suitable for bituminous stabilization. In cohesionless soils, asphalt binds the soil particles together, acting as a bonding or cementing agent.
4. Chemical Soil Stabilization:
In chemical soil stabilization, various chemicals are added to the soil, which react with the soil to change its structure. These chemicals seal the spaces between soil particles, preventing water from penetrating. Common chemicals used for soil stabilization include sodium chloride, calcium chloride, and sodium silicate.
5. Electrical Soil Stabilization:
Electrical soil stabilization is performed on clayey soils through a process known as electro-osmosis. In this method, a direct current is passed through the clayey soil, causing pore water to migrate toward the negative electrode (cathode). This occurs due to the attraction of positive ions (cations) in the water toward the cathode. The strength of the soil is significantly increased due to the removal of water. Electro-osmosis is an expansive method primarily used for the drainage of cohesive soils.
6. Thermal Soil Stabilization:
Thermal soil stabilization involves either heating or cooling the soil. Heating the soil reduces its water content, which in turn increases its strength. When soil is heated to high temperatures, irreversible changes occur that render the soil non-plastic and non-expansive. Conversely, when cooling the soil for stabilization, there may be a slight loss of strength in clayey soil due to increased interparticle repulsion. However, cooling the soil to the freezing point causes the pore water to freeze, thus stabilizing the soil.
Applications of Soil Stabilization:
- Road Construction: Improves the load-bearing capacity of subgrades and base courses.
- Foundation Support: Enhances the strength and stability of foundations, particularly in areas with weak soil.
- Erosion Control: Vegetative and polymer stabilizations are used to prevent soil erosion, especially in slopes or coastal areas.
- Landfills and Waste Disposal: Stabilization is used to create a stable surface for landfills, ensuring proper containment and avoiding contamination.
