Void ratio

Void ratio, in materials science, is a quantity related to porosity and defined as the ratio:

and

where ${\displaystyle e}$ is void ratio, ${\displaystyle \phi }$ is porosity, 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 (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 ${\displaystyle \phi }$ usually represents the angle of shearing resistance, a shear strength (soil) parameter. Because of this, the equation is usually rewritten using ${\displaystyle n}$ for porosity:

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