The plasticity index is the size of the range of water contents where the soil exhibits plastic properties. The PI is the difference between the liquid limit and the plastic limit (PI = LL-PL).

What is the plasticity index theory?

The difference between liquid and plastic limits is called the plasticity index, and it represents the range of water content over which the soil is plastic. The plasticity index, in combination with water content at liquid limit (wL), indicates how sensitive the soil is to the changes in moisture content.

What is the formula of flow index?

Flow index I_f = (W₂-W₁)/(logN₁/N₂) = slope of the flow curve.