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Void ratio
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Void ratio, in materials science, is related to porosity and defined as the ratio:
 <math>e = \frac{V_V}{V_S} = \frac{V_V}{V_T  V_V} = \frac{\phi}{1  \phi}</math>
and
 <math>\phi = \frac{V_V}{V_T} = \frac{V_V}{V_S + V_V} = \frac{e}{1 + e}</math>
where <math>e</math> is void ratio, <math>\phi</math> is porosity, V_{V} is the volume of voidspace (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 (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.^{[1]}^{[2]}
Note that in geotechnical engineering, the symbol <math>\phi</math> usually represents the angle of shearing resistance, a shear strength (soil) parameter.
Because of this, the equation is usually written:
 <math>e = \frac{V_V}{V_S} = \frac{V_V}{V_T  V_V} = \frac{n}{1  n}</math>
and
 <math>n = \frac{V_V}{V_T} = \frac{V_V}{V_S + V_V} = \frac{e}{1 + e}</math>
where <math>e</math> is void ratio, <math>n</math> is porosity, V_{V} is the volume of voidspace (air and water), V_{S} is the volume of solids, and V_{T} is the total or bulk volume.^{[3]}
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
References
 ^ Lambe, T. William & Robert V. Whitman. Soil Mechanics. Wiley, 1991; p. 29. ISBN 9780471511922
 ^ Santamarina, J. Carlos, Katherine A. Klein, & Moheb A. Fam. Soils and Waves: Particulate Materials Behavior, Characterization and Process Monitoring. Wiley, 2001; pp. 3536 & 5153. ISBN 9780471490586
 ^ Craig, R. F. Craig's Soil Mechanics. London: Spon, 2004, p.18. ISBN 0203494105.
