Plasticity Index is defined as which of the following?

Plasticity Index is defined as which of the following?

• A. PL-LL
• B. LL-PL
• C. LL+PL
• D. PL/LL

Answer: (B)

Plasticity Index measures the width of the plastic state of a soil. It is defined as the difference between the liquid limit and the plastic limit: PI = LL − PL. The liquid limit is the moisture content at which soil transitions from plastic to liquid, while the plastic limit is the moisture content at which it changes from plastic to semisolid. Subtracting PL from LL gives the moisture-range over which the soil remains plastic, which is exactly what the Plasticity Index quantifies. The other forms don’t reflect this moisture-range concept: PL − LL would be negative, LL + PL is just a sum without representing range, and PL/LL is a ratio that doesn’t measure plasticity width.

Plasticity Index measures the width of the plastic state of a soil. It is defined as the difference between the liquid limit and the plastic limit: PI = LL − PL. The liquid limit is the moisture content at which soil transitions from plastic to liquid, while the plastic limit is the moisture content at which it changes from plastic to semisolid. Subtracting PL from LL gives the moisture-range over which the soil remains plastic, which is exactly what the Plasticity Index quantifies. The other forms don’t reflect this moisture-range concept: PL − LL would be negative, LL + PL is just a sum without representing range, and PL/LL is a ratio that doesn’t measure plasticity width.