Question

If the soil sample is having porosity 50% and degrees of saturation at 90% then its percentage air voids is :

• A. 5%
• B. 50%
• C. 45%
• D. 4.5%

Answer 1

The correct option is A 5%

$Given:Porosity;n=\frac{V_v}{V}=50\%=0.5$

Degree of saturation; $S=\frac{V_w}{V_v}=90\%=0.9$

To find, $n_a=percentageairvoid$

$S+a_c=1$

$a_c=$ Air content

$a_c=1-S=1-0.9$

= 0.1 = 10%

$n_a=n\times a_c$

$=0.5\times 0.1=0.005=5$%

$n_a=5$%

Note :

(i) Percentage air void $\left(n_a\right)$: It is the ratio of the volume of air $\left(V_a\right)$ to the total volume of soil mass (V).

$n_a=\frac{V_a}{V}=\frac{Volumeofair}{Volumeofsoil}$

(ii) Air content $\left(a_c\right)=$air content is defined as the ratio of the volume of air $\left(V_a\right)$ to the volume of voids in soil mass $\left(V_v\right)$.

$a_c=\frac{V_a}{V_v}=\frac{Volumeofair}{Volumeofvoidsinsoilmass}$