Question

A project engineer receives a laboratory report of a sample of soil having a moist unit weight of soil is 20.5 KN/m³, water content available is 25 % and the specific gravity of the solid of the soil is 3.35. Find the dry unit weight of the soil.

1. 16.8 kN/m3
2. 18.4 kN/m3
3. 18.8 kN/m3
4. 16.4 kN/m3

Answer 1

Correct Answer - Option 4 : 16.4 kN/m3

Concept:

The formula for finding dry unit weight of soil is given by:

\({γ _d} = \frac{γ }{{1 + w}}\)

where, 

γ_d = Dry unit weight of soil

γ = Moist Unit weight of soil

w = Water content

Calculations:

Given Data:

\(γ\) = 20.5 kN/m³

w = 25 % = 0.25

So, 

\({γ _d} = \frac{20.5 }{{1 + 0.25}}=16.4\;kN/m^3\)

Confusion Point:

There is no use of specific gravity in finding out dry unit weight of soil