What is the moisture content range referred to as the plasticity index (PI)?

The plasticity index (PI) is a measure of the plasticity of a soil, which helps in understanding its behavior under varying moisture conditions. It is specifically defined as the difference between the liquid limit (LL) and the plastic limit (PL) of a soil. This difference, or range, represents the moisture content over which the soil remains plastic, which is a critical factor in geotechnical and civil engineering applications.

By calculating the plasticity index using the formula ( PI = LL - PL ), engineers and soil scientists can classify soils based on their plastic behavior. Higher plasticity index values indicate soils with greater plasticity, which can affect their stability, compaction, and behavior under load. Therefore, the correct representation of the moisture content range that defines the plasticity index is indeed LL minus PL. This fundamental understanding is crucial when evaluating soil properties for construction and related engineering projects.