The plasticity index is equal to
- ALiquid limit minus shrinkage limit
- BPlastic limit minus shrinkage limit
- CLiquid limit minus plastic limitCorrect
- DNone of the above
Solution
Concept
Definition of soil plasticity index
Formula
PI = LL - PL
Step-by-step solution
1. The plasticity index measures the range of moisture content in which soil remains in a plastic state. 2. It is defined mathematically as the numerical difference between the liquid limit and the plastic limit. 3. Therefore, Plasticity Index = Liquid Limit - Plastic Limit. Answer: C
Explanation
The plasticity index measures the range of moisture content in which a soil remains in a plastic state. It is defined mathematically as the liquid limit minus the plastic limit of the soil. A higher numerical difference indicates greater clay content and higher plasticity in the soil mass.
Why the other options are wrong
A) Subtracting the shrinkage limit from the liquid limit does not yield the plasticity index. B) The plastic limit minus the shrinkage limit represents the shrinkage index. D) Option C is correct.
Shortcut
PI = LL - PL (Plasticity Index = Liquid Limit minus Plastic Limit).
Common mistake
Incorrectly subtracting the shrinkage limit instead of the plastic limit from the liquid limit.
Correct answer: C) Liquid limit minus plastic limit