Concept:
The relation between air content (aC) and degree of saturation (S) is given by
aC + S = 1
Also,
\(n\; = porosity\; = \frac{{{V_V}}}{V}\)
\({a_C} = air\;content = \frac{{{V_a}}}{{{V_V}}}\)
Where,
VV = volume of voids
Va = volume of air
V = total volume of soil
Calculation:
Given,
n = 0.7
S = 40 % = 0.4
V = 100 m3
We have
\(
n\; = \frac{{{V_V}}}{V}\)
\(0.7 = \frac{{{V_V}}}{{100}}\)
∴ VV = 0.7 × 100 = 70 m3
aC + S = 1
\(\frac{{{V_a}}}{{{V_V}}}\; + \;S\; = \;1\)
\(\therefore \;\frac{{{V_a}}}{{70}} = 1 - 0.4\;\)
Va = 42 m3