Black Cotton Soils and Their Swelling Pressure

In India black cotton soils are found in the regions of Western Madhya Pradesh, Deccan plateau, Andhra Pradesh, some portion of Gujarat, Uttar Pradesh, Maharashtra and Karnataka covering more than 20% landmass of her. Here the soils that swell are named, as defined above, black cotton soil. Generally montmorillonite, the giant mineral portion of black cotton soils, becomes weathered to form less active particles of clay group like kaolinite and illite. But this process needs heavy weathering from rainfall. This active montmorillonite, when becomes saturated with water from a unsaturated state, it gets swelled and if reverse condition are occurred it gets shrunk. 

Geotechnical engineers are concerned with the magnitude of swelling pressure under desire environmental changes.

Swelling pressure:

Swelling pressure of soil is the maximum stress (Force/Area) that is required to keep the volume, supposed to be subject to swell, unchanged. This is a index that indicates how much trouble will exert an expansive soil. Usually a swelling pressure <20 kpa is not considered to be result much problem to foundation.ffff

The potential of a soil to swell is a function of loading condition and the water content expected to under foundation. The swell pressure and swell potential of black cotton soil can be examined by the ASTM (ASTM D 4546-90)Standard test procedure. This is the test method of cohesive soils for one dimensional or swells potential. If the soil sample are disturbed during sampling, the soil are compacted to achieved field water content and density as well with standard compaction mould like proctor.