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Quiet often soil engineers encounter situations where the sites selected for construction is not suitable, because of too low bearing capacity or differential settlements which exceeds the tolerable limits. Higher void in cohesive soils decreases the inter particle attraction, where as in non cohesive soils results in low relative density, low angle of internal friction and high permeability. This in turn means that lower shear strength, low bearing capacity, and easy movement of water.
By lowering the void ratio in a soil deposit, the soil particles get closer which leads to increase in shearing strength i.e. the bearing capacity of the soil and minimize the probable settlement as well as the differential settlement.
Soils for foundation can be altered to conform to desired characteristics. Based on soil and the ground water conditions on the construction site, soil improvement techniques are designed by taking care of feasibility and economy. Soil stabilization is one such technique which increase strength, increase or decrease permeability, reduces compressibility, improve stability, or decrease heave due to frost or swelling.
Mechanical Stabilization is a method by which soil properties are improved by changing its gradation. Hence it is also called as granular stabilization. Sometimes to achieve the desired grading, two or more types of natural soil are mixed with binders. The binders provide internal friction, cohesion and imperviousness to a soil. The binder added should provide sufficient plasticity and not swelling. The resistance to temperature and moisture changes is also improved long with bearing capacity. It is also widely used in bases, sub-bases and surfacing of roads. The mechanically stability of the mixed soil depends upon the factors such as strength of aggregate, mineral composition, gradation, plasticity, compaction.
Thermal Stabilization is an expensive method, rarely used in practice but provides remarkable improvement in the properties of soils. In the method of heating, the soil is subjected to a temperature of about 400’C to 600’C which results in some irreversible changes like clay clods are converted into aggregates. Conversely in the method of cooling, the temperature of the soil is reduced to the freezing point. This method is applied in tunnel construction through fine sand or loose silt. It is useful in solidifying the soil beneath foundation.
Chemical Stabilization stabilizes soils deposits with the help chemicals. Though this technique is more expensive, it is preferred because of controlled setting time and curing. Calcium chloride and sodium chloride added by 0.5% and 1% to the weight of the soil.