Void ratio, in materials science, is a quantity related to porosity and defined as the ratio:
e
=
V
V
V
S
=
V
V
V
T
−
V
V
=
ϕ
1
−
ϕ
and
ϕ
=
V
V
V
T
=
V
V
V
S
+
V
V
=
e
1
+
e
where
e
is void ratio,
ϕ
is porosity, VV is the volume of void-space (such as fluids), VS is the volume of solids, and VT is the total or bulk volume. This figure is relevant in composites, in mining (particular with regard to the properties of tailings), and in soil science. In geotechnical engineering, it is considered as one of the state variables of soils and represented by the symbol e.
Note that in geotechnical engineering, the symbol
ϕ
usually represents the angle of shearing resistance, a shear strength (soil) parameter. Because of this, the equation is usually rewritten using
n
for porosity:
e
=
V
V
V
S
=
V
V
V
T
−
V
V
=
n
1
−
n
and
n
=
V
V
V
T
=
V
V
V
S
+
V
V
=
e
1
+
e
where
e
is void ratio,
n
is porosity, VV is the volume of void-space (air and water), VS is the volume of solids, and VT is the total or bulk volume.
