The void ratio of a mixture is the ratio of the volume of voids to volume of solids.
It is a
dimensionless quantity in
materials science, and is closely related to
porosity
Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measur ...
as follows:
:
and
:
where
is void ratio,
is
porosity
Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measur ...
, ''V
V'' is the volume of void-space (such as fluids), ''V
S'' is the volume of solids, and ''V''
''T'' is the total or bulk volume. This figure is relevant in
composites, in
mining
Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic ...
(particular with regard to the properties of
tailings
In mining, tailings are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different to overburden, which is the waste rock or other material that overli ...
), and in
soil science
Soil science is the study of soil as a natural resource on the surface of the Earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to th ...
. In
geotechnical engineering, it is considered one of the state variables of soils and represented by the symbol ''e''.
Note that in
geotechnical engineering, the symbol
usually represents the angle of shearing resistance, a
shear strength (soil)
Shear strength is a term used in soil mechanics to describe the magnitude of the shear stress that a soil can sustain. The shear resistance of soil is a result of friction and interlocking of particles, and possibly cementation or bonding of par ...
parameter. Because of this, the equation is usually rewritten using
for porosity:
:
and
:
where
is void ratio,
is porosity, ''V
V'' is the volume of void-space (air and water), ''V
S'' is the volume of solids, and ''V
T'' is the total or bulk volume.
[Craig, R. F. ''Craig's Soil Mechanics.'' London: Spon, 2004, p.18. .]
Engineering applications
* Volume change tendency control. If void ratio is high (loose soils) voids in a soil skeleton tend to minimize under loading - adjacent particles contract. The opposite situation, i.e. when void ratio is relatively small (dense soils), indicates that the volume of the soil is vulnerable to increase under loading - particles dilate.
* Fluid conductivity control (ability of water movement through the soil). Loose soils show high conductivity, while dense soils are not so permeable.
* Particles movement. In a loose soil particles can move quite easily, whereas in a dense one finer particles cannot pass through the voids, which leads to clogging.
See also
*
Void (composites)
A void is a pore that remains unfilled with polymer and fibers in a composite material. Voids are typically the result of poor manufacturing of the material and are generally deemed undesirable. Voids can affect the mechanical properties and lif ...
External links
Relation between void ratio and porosity
References
{{Geotechnical engineering, state=collapsed
Materials science
Soil mechanics
Earth sciences
Soil science
Mining terminology