Void ratio
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 as follows: and where formula_3 is void ratio, formula_4 is porosity, "V" is the volume of void-space (such as fluids), "V" is the volume of solids, and "V" 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 one of the state variables  of soils and represented by the symbol e. Note that in geotechnical engineering, the symbol formula_4 usually represents the angle of shearing resistance, a shear strength (soil) parameter. Because of this, the equation is usually rewritten using formula_6 for porosity: and where formula_3 is void ratio, formula_6 is porosity, "V" is the volume of void-space (air and water), "V" is the volume of solids, and "V" is the total or bulk volume.