The liquid limit and plastic limit of a soil sample are 65% and 29% respectively. The percentage of the soil fraction with grain size finer than 0.002 mm is 24. The activity of a soil sample is
- A0.50
- B1.00
- C1.50Correct
- D2.00
Solution
Concept
Activity (Skempton)
Formula
Activity A = PI / (% of clay-size particles < 2 μm)
Step-by-step solution
1. PI = LL − PL = 65 − 29 = 36. 2. Clay fraction (finer than 0.002 mm) = 24%. 3. A = 36 / 24 = 1.5.
Explanation
Activity is the ratio of plasticity index to the percentage of clay fraction. Values above 1.25 are called active clays.
Shortcut
Activity = PI ÷ clay %.
Common mistake
Using LL (65) instead of PI.
Correct answer: C) 1.50