What is the purpose of Relative Density?

It is to determine the denseness of a granural soil.

How do you calculate relative density of soil?

Based from the formula mentioned above, $Dr = (e_{max}-e)/(e_{max}-e_{min}) x100%$

Higher relative density increases soil strength by improving particle interlocking and reducing void space.

Relative Density is used to describe the state of compactness of granural soils compared to their loosest and densest possible states.

It can be expressed using this formula:

$D_r= \frac{e_{max}-e}{e_{max}-e_{min}}$

where:
e = void ratio of the soil (in-situ)
$e_{min}$ = void ratio (densest)
$e_{max}$ = void ratio (loosest}

We can also express Relative Density in terms of dry unit weight:

Where:
$\gamma_{dmin}$ = dry-unit weight (loosest)
$\gamma_d$ = dry-unit weight (in-situ)
$\gamma_{dmax}$ = dry unit weight (densest)

These values are used to assess the properties of the granural soils.