What aspect of soil does the plasticity index measure?

The plasticity index measures the plasticity characteristics of soil, providing insight into how soil behaves under different moisture conditions. This index is determined by subtracting the plastic limit from the liquid limit of the soil. The plastic limit is the water content at which soil transitions from a plastic state to a semi-solid state, while the liquid limit is the point where soil becomes entirely fluid.

Therefore, the plasticity index gives a quantifiable measure of the range of moisture contents where the soil can act as a plastic material, influencing its capability to deform without breaking. This characteristic is crucial for understanding the soil's suitability for construction projects, as it helps predict how soil will respond to compaction and loading. High plasticity soils may be more prone to expand and contract with moisture changes, affecting stability and performance in building foundations, while lower plasticity soils may provide more stable support. Thus, understanding the plasticity characteristics through the plasticity index is vital for successful construction and engineering practices.