According to the research findings, it can, therefore, be said that plasticity is associated with fine-grained soils and not with coarse-grained soils. Coarse-grained soils can be classified on the basis of the size of their constituent particles, whereas for fine-grained soils, particles are too small to be sized. That is why fine-grained soils are classified on the basis of their plasticity. Also, the content of water in soil alters its properties and is thus, a matter of major concern when the foundations are being designed. While the size of particles becomes smaller, it effectively serves to increase the surface area of contact between the soil particles and water.
The increased contact area enhances the water absorbing capability of fine-grained soils. Hence, fine-grained soils, typically Clay has a lot of capability of absorbing water. As a result of that, the clay minerals and the entrapped water particles interact in such a way, that the engineering properties of the soil become a function of the moisture content it contains. It is evidently clear from the discussion that shear strength of Clay is influenced by the moisture content of Clay and also on the rate of water absorption or expulsion.
This is evident from the fact that the shear strength of Clay which contains 50 % water will be far less than that achieved at a moisture content of 10 %. Besides, the plasticity index is also used together with the liquid limit to realize the category in which a particular soil sample belongs. This is achieved with the help of charts commonly known as the Plasticity charts or the A-line charts.
It is shown in the figure that categorizes soils as organic or inorganic, coarse and fine-grained soils on the basis of their plasticity indices and liquid limits. As the plasticity index of a soil rises, its volume change characteristics become enhanced. “ Fat or plastic clays plot above the line” .
Scienceray.com. “Effect on Shear Strength Due to Various Water Content in Clay Soil”.
2010. Web. 21 June, 2010.
www.mite.com.au. “"A" line charts and what they mean”. 2007. Web. 21 June, 2010.
www.fairfaxcounty.gov. “Clarification of the definition of expansive soil”. Land Development News.
2009. Web. 21 June, 2010.
www.foundation-repair-guide.com,. “Getting Control of Expansive Soil”. 2007. Web. 21 June, 2010.