What does a Plasticity Index value indicate?

A Plasticity Index (PI) value is an important parameter in geotechnical engineering that indicates the range of moisture content within which a soil remains in a plastic state. It is calculated as the difference between the liquid limit and the plastic limit of a soil sample. The liquid limit is the moisture content at which the soil changes from a plastic to a liquid state, while the plastic limit is the moisture content at which the soil transitions from a plastic to a semi-solid state. Therefore, the Plasticity Index provides insight into the soil's behavior when subjected to changes in moisture content.

A high Plasticity Index indicates a wide range of moisture content over which the soil can remain plastic, suggesting that the soil is more versatile and capable of withstanding significant changes in water content without losing its structural integrity. Conversely, a low PI indicates that the soil has a limited moisture range in which it can behave plastically, making it less adaptable to changes in environmental conditions.

The other options focus on different properties of soil that are not directly associated with the Plasticity Index. For instance, the amount of air in the soil is related to porosity, while density and permeability pertain to the physical and hydraulic behavior of soils, respectively. Each of those properties serves its