The addition of coarse particles like sand or silt to a soil, particularly clay causes
- ADecrease in liquid limit as well as plasticity indexCorrect
- BDecrease in liquid limit and increase in plasticity index
- CIncrease in liquid limit as well as plasticity index
- DDecrease in liquid limit and no change in plasticity index
Solution
Concept
Effect of sand or silt on clay plasticity
Step-by-step solution
1. Coarse particles do not hold water or show plasticity. 2. Adding them reduces the clay fraction, so both LL and PI decrease.
Explanation
Plasticity comes from the clay fraction. Mixing sand or silt dilutes the clay, so the liquid limit and the plasticity index both fall.
Shortcut
More clay → LL and PI up. More sand/silt → LL and PI down.
Common mistake
Thinking that PI is unaffected.
Correct answer: A) Decrease in liquid limit as well as plasticity index