In case of a perfectly saturated soil, the voids are completely filled with _____. 

I. air

II. water

Degree of saturation:

It is defined as the ratio of the volume of water to the volume of voids in the soil mass.

For fully saturated soil:

The fully saturated soil contains only sand and water, VW = VV, hence S = 100%

It is a two-phase soil mass.

Additional Information  For dry soils:

The dry soil contains only soil and air and no water, therefore VW = 0, hence S = 0%

It is a two-phase soil mass.

For partially saturated soil:

The partially saturated contains soil, air, and water, hence 0 % < S > 100%

It is a three-phase soil mass.