The problematic expansive soils undergo alternate swelling and shrinkage on imbibation of water in monsoon and on evaporation thereof in summer. As a result, civil engineering structures constructed on swelling soils are severely damaged. Stabilization of expansive soils has been successfully done with various chemicals. Calcium chloride is a hygroscopic material and absorbs water. It does not allow shrinkage cracks to develop in summer. Plasticity and strength characterisitcs of expansive soil treated with different percentages of calcium chloride have been studied and presented. This paper also compares the strength behaviour of expansive soils treated with calcium chloride and lime.
Black cotton soils cover about 20% of land in India. They undergo volume changes due to changes in moisture content. In monsoon they imbibe water and swell, and in summer on evaporation of water, they shrink. This alternate swelling and shrinkage causes distress in many civil engineering structures like lightly loaded buildings, retaining walls, canal linings and pavements. This dual problem has been combated by researchers through innovative techniques. Different foundation techniques are adopted in practice to overcome the problems posed by expansive soils to various structures. While some special foundation techniques do not alter the nature of the soil, some change the nature of the soil. They are briefly discussed below. While under-reamed piles and granular pile-anchors do not change the nature of the soil, they counteract the problem effectively. Under-reamed piles are bored cast in-situ piles with enlarged bases and connected at their top by plinth beams. Enormous uplift resistance is mobilized along the surface of the pile and reduces heave. In the case of multi under-reamed pile, frictional resistance is mobilized over a larger perimeter and reduces heave. They have been widely used in India.