# Define Specific Gravity, Bulk Specific Gravity, Air Content and Percentage Air Voids-Soil

## Specific Gravity(G)

Specific gravity is defined as the ratio of the weight of a given volume of soil solids at a given temperature to the weight of an equal volume of distilled water at that temperature, both weights being taken in air.

In other words, it is the ratio of the unit weight of soil solids ( $\gamma_{s}$ ) to the unit weighs of water ( $\gamma_{w}$ ).
Thus, $G = \frac{\gamma_{s}}{\gamma_{w}}$

The Indian Standard specifies 270° C as the standard temperature for reporting the specific gravity

## Mass or Apparent or Bulk Specific Gravity

It is the ratio of the bulk unit weight of soil mass (𝛾) to the unit weight of water ( $\gamma_{w}$ ).
Thus, $G_{m} = \frac{\gamma}{\gamma_{w}}$

## Air Content

The air content is defined as the ratio of the volume of air voids (Va) to the volume of voids (Vv).
Thus, $a_{c} = \frac{V_{a}}{V_{v}}$

## Percentage of Air Voids

The percentage of air voids are defined as the ratio of the volume of air voids (Va) to the total volume (V) of the soil mass. It is expressed as percentage.
Thus, $n_{a} = \frac{V_{a}}{V } \times 100$