Geoscience Reference
In-Depth Information
V T = V a + V w + V s
(12.1)
where
V T = Total volume.
V a = Air volume.
V w = Water volume.
V s = Solids volume.
The volume of the voids is the sum of V a and V w . However, because the weighing of air in the soil
voids would be done within the Earth's atmosphere as with other weighings, the weight of the solids
is determined on a different basis. We consider the weight of air in the soil to be zero and the total
weight is expressed as the sum of the weights of the soil solids and the water:
W T = W s + W w
(12.2)
where
W T = Total weight.
W s = Solids weight.
W w = Water weight.
The relationship between weight and volume can be expressed as
W m = V m G m - w
(12.3)
where
W m = Weight of the material (solid, liquid, or gas).
V m = Volume of the material.
G m = Specific gravity of the material (dimensionless).
w = Unit weight of water.
With the relationships described above, a few useful problems can be solved. When an environ-
mental engineer determines that, within a given soil, the proportions of the three major components
need to be mechanically adjusted, this can be accomplished by reorienting the mineral grains by
compaction or tilling. The environmental engineer may want to blend soil types to alter the propor-
tions, such as increasing or decreasing the percentage of void space.
How do we go about doing this? Relationships between volumes of soil and voids are described
by the void ratio ( e ) and porosity (η). To accomplish this, we must first determine the void ratio (the
ratio of the void volume to the volume of solids):
V
V
v
s
e
=
(12.4)
We must also determine the ratio of the volume of void spaces to the total volume. This can be
accomplished by determining the porosity (η) of the soil, which is the ratio of void volume to total
volume. Porosity is usually expressed as a percentage:
η = V v / V T × 100%
(12.5)
where
V v = Void space volume.
V T = Total volume.
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