What is plasticity index

This soil can hold very less amount of water and with little increase of water it reaches to its liquid limit and starts flowing. We know water molecules are hold by clay particles so low PI value or small water content range displays that soil contains less number of clay particles.

Hence they capture less amount of water to make the soil plastic. While high PI value indicates soil can hold large amount of water in it and still manages to stay at plastic state. It can hold more water into it because it contains large amount of clays hence highly plastic soil. Coarse grained soils cannot achieve the plastic state of consistency because soil needs clay minerals to become plastic which coarse soils does not contain.

Their liquid limit and plastic limit are said to coincide because at higher water content soil starts flowing without even reaching at plastic limit.

Also in some cases plastic limit of soil is found greater than the liquid limit or in another cases both PL and LL cannot be determined. In all these conditions soil is considered to have plasticity index zero and soil is reported as Non-Plastic NP.

Plasticity Index Of Soil. These limits are: Liquid Limit Plastic Limit Shrinkage Limit In liquid state water content of the soil is such that it behaves like liquid and offers no resistance to flow. In plastic state soil can be moulded in any shape due to a property called plasticity.

Soil may be classified based on the plasticity index values. Video version :. Share this post :. Published on : View Comments. Reference Books : 1. Test Your Vocabulary. Can you spell these 10 commonly misspelled words?

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