In the construction fields, the main characteristic required for the soil is their capacity to resist the super imposed loads safely by a control in stresses and deformations. Each site situations are varying and it require different concepts to meet design characteristics, which is mainly depends on the type of soil strata existing. Among the different types of soils, the construction activities on expansive soils requires adequate care since it was a fine-grained soil that shows large volume change when exposed to varying water content. Changes in season and climatic conditions cause clay to swell and shrink which is due to the influence of water. These soils are mostly reactive due to the presence of mineral, montmorillonite. Construction of civil engineering structures on expansive soil is highly risky due to its susceptibility towards water, which can results problems in super structures. The damages in structures due to volume changing behavior of expansive soil are increased worldwide.
Evolving civilization plays a key parameter in improving the weak grounds and making them useful. Proposed and existing structures completely relay upon the type and strength of foundations, which are an inevitable constraints. The structure remains healthy as the foundation strength is improved and becomes appropriate. Therefore, the study and analysis of soil with its index and engineering properties are essential to conclude the foundation details and other parameters. Natural soil has both a complex and variable material and it has to be considered as the basic engineering material to meet all types of construction activities. The major problems such as the low bearing capacity and high compressibility, becomes a challenging issues by the Civil Engineers. To suggest a suitable geotechnical design of structure, it requires a detailed soil feasibility studies to fix the characteristics of the subsoil.
II. OBJECTIVE AND SCOPE OF STUDY:
The objectives of the present study are formulated as below:
To study the consequence of Microbial Induced Calcite Precipitation (MICP) on strength characteristic of soils.
To find out optimum bacterial cell concentration and cementation reagent (MICP) for the strength improvement.
To study the improvement of California Bearing Ratio (CBR) and Free Swell Index of MICP treated soil.
To study the influence of curing period on treatment of soil with MICP.
Microstructural analysis by using Scanning Electron Microscope (SEM) for the arrangement of particles and cementitious formation after treatment.
A. Ground Improvement
Ground improvement techniques include soil stabilization with chemical, grouting, mechanical means and using reinforcement, out of which soil stabilization is the most commonly, used practice. Grouting consists of injecting cement or other admixtures in situ in the soil, so that the pores are filled with the admixture hence, thereby filling the voids in the soil particles.
B. Soil Stabilization
Soil stabilization is a technique of improving the load bearing abilities and performance of sub soils present at site in order to strengthen the structures built on it. The key objective of soil stabilization is to increase the strength of problematic soils. The other objective of soil stabilization is to improve materials found onsite to create a strong sub base and base courses in highway applications. Soil stabilization is the alteration of properties of soil to enhance their physical and chemical characteristics. It can improve the shear strength of a soil and control the shrink-swell properties of a soil, thus improving the load bearing capacity of a sub- grade to support pavements and foundations.
Soil Stabilization can be utilized on roadways, parking areas, site development projects, airports and many other site conditions where sub-soils are not suitable for construction. Stabilization can be used to treat a wide range of sub-grade materials, varying from expansive clays to granular materials and can be accomplished using a wide variety of additives.
Mechanical Stabilization: Mechanical stabilization consists of using machines to alter the physical properties of weak soil to improve their load carrying capacities. This is mainly used for coarse-grained soils such as sand. There are four types of mechanism used for mechanical stabilization- Vibration, Impact, kneading and pressure. They mainly concentrate on compression and drainage of the soil.
Lime Stabilization: In the earlier days, soil stabilization was mainly done using lime. It was mainly used due to the presence of pozzolanic compounds in it. Pozzolanic materials are those, which undergo hydraulic reactions upon contact with water to produce cementitious bonds between the soil particles hence, densifying the soil to take more loads.
Cement Stabilization: Another common method in practice is the stabilization of soil using cement, which hardens the soil structure making it more durable over time and improving its strength.
Stabilization Using Alkaline Solutions: Recent studies have shown that using alkaline solutions in the soil also aids in the stabilization process where the fluid occupies the pores in the soil structures and reacts to form crystalline compounds that increase the soils strength.
Stabilization Using Electro Kinetic Method: Geo polymers are increasingly being used in the soil stabilization area along with electro kinetic process that involves in applying a low direct current between electrodes with opposite potentials in a very low permeable soil.
Chemical Stabilization: Chemical stabilization uses chemicals like calcium chloride, sodium chloride, and asphalt emulsions, chemicals containing phosphorus, alumina and silica. Any chemical that has a coagulating effect. These chemical admixtures are either grouted or mixed with the soil that alter the properties of soil. There are various chemical stabilizers available in the industry that include liquid ionic stabilizer that mainly comprises of d-limonene, which is a by-product of citrus processing and sulfuric acid.
Stabilization Using Industrial Waste: Use of lime and cement to the discovery of many products such as Ground Granulated Blast furnace Slag (GGBS) which is a byproduct of the iron industry, containing about 40% lime. The strength improvement depends on the amount of GGBS used and the effect of curing period. The strength generally increases with the increase in GGBS content.
Stabilization Using Agricultural Waste: While the entire above admixture mentioned belong to the industrial wastes, nowadays agro based industries also are looking for disposing their wastes in new methods. This has led to utilizing wastes like wood ash, rice husk ash, groundnut shell ash, and bagasse from sugarcane, eggshell powder in soil due to their high calcium content. It has also given rise of using natural fibers from banana trees and bamboo for providing reinforcement properties to the soil.
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