The range in water content in which soil is in a plastic state is referred to as what?

The correct answer is the Plasticity Index. This term specifically defines the range of water content over which a soil exhibits plastic behavior, which means it can be molded or shaped without cracking or breaking. The Plasticity Index is calculated by taking the difference between the liquid limit and the plastic limit of the soil. The liquid limit is the maximum moisture content at which the soil remains in a liquid state, while the plastic limit is the minimum moisture content at which the soil transitions from a plastic to a solid state. Thus, the Plasticity Index provides essential information about the engineering properties of soil, especially its workability and stability in construction projects.

Moisture Index, while related to moisture content, does not specifically define the plastic range but instead gives an overall indication of how moisture affects soil behavior more broadly. Dilatancy Range is a term that relates to changes in volume under stress and is not specific to the plasticity of soil. The Liquid Range refers to the moisture content where the soil is in a liquid state, rather than its ability to deform plastically, which is why the Plasticity Index is the most accurate term for the range in question.