Question

The laboratory tests on a sample yielded the following results:
Plasticity index : 32%
Liquidity index : 0.15
Activity number : 1.58
Which of the following inferences can be drawn?
1. The soil is very stiff.
2. The soil is medium soft.
3. The soil is highly plastic.
4. The soil is medium plastic.
5. The soil is active.
Select the correct answer using the codes given below:

• A. 1, 3 and 5
• B. 1, 3, and 4
• C. 2, 3 and 5
• D. 1, 2 and 4

Answer 1

The correct option is A 1, 3 and 5

(a)
Since the liquidity index of soil is negative so soil is in semi-solid state or very stiff.

Consistency Liquidiy Consistency index (Cl) index (LI) 1.00 - 0. 75 0.00- 0.25 Stiff 0.75 - 0.50 0.25-0.50 Medium soft 0.50 - 0.25 0.50 - 0.75 Soft 0.25 - 0.00 0.75 - 1.00 Very soft

$CI=\frac{w_L-w}{PI}$

$andLI=\frac{w-w_p}{PI}$

where
w is natural water content
$w_L$ is liquid limit
$w_P$ is plastic limit
PI is plasticity index
Cl + LI = 1.00
If CI > 1 or LI < 0, then soil is very stiff.
If CI < 0 or LI > 1 soil behaves as liquid.

Activity number Classification
0.75 Inactive
0.75-1.25 Normal
> 1.25 Active

So soil is active

Liquid limit Plasticity
0 - 3 0 % Low
35- 50% Medium
>50% High

Plasticity Index Plasticity
0 Non plastic
1 - 5 Slight
5 - 10 Low
10-20 Medium
20-40 High
> 40 Very high

So soil is high plastic