Explain three phase system of soil

Soil mass is a complex physical system consisting of three distinct phases such as soil grains, liquid (water) and air (gas) at normal condition. In other words a soil mass consists of solid soil particles, containing void space between them. The space between the soil particles is known as void and these voids may be filled either with air or water or both.

The soil will behave as a two phase system when its void space is filled with either water or air alone. When all void space is filled with either water, the soil mass is fully saturated and exist in two phases as solid and water. When all the void space is filled with air the soil mass becomes dry soil and exists

in two phases as solid and air. But as when the soil mass is partially filled up by water as well as air and hence it behaves three phase system.

The diagrammatic representation of the different phases in a soil mass is called the phase diagram. The three constituents of a soil mass do not occupy sep....

Soil mass is a complex physical system consisting of three distinct phases such as soil grains, liquid (water) and air (gas) at normal condition. In other words a soil mass consists of solid soil particles, containing void space between them. The space between the soil particles is known as void and these voids may be filled either with air or water or both.

The soil will behave as a two phase system when its void space is filled with either water or air alone. When all void space is filled with either water, the soil mass is fully saturated and exist in two phases as solid and water. When all the void space is filled with air the soil mass becomes dry soil and exists

in two phases as solid and air. But as when the soil mass is partially filled up by water as well as air and hence it behaves three phase system.

The diagrammatic representation of the different phases in a soil mass is called the phase diagram. The three constituents of a soil mass do not occupy separate but are blended together forming a complex material as shown in figure.

The total volume V of the soil mass is equal to the sum of volume of solid particle

`V_s`  volume of water `V_w` and volume of air `V_a`. i.e. - `V =V_s+V_w+V_a`.

Also, Volume of voids (`V_v`) equal to the sum of volume of air and volume water,

i.e., `V_v = V_a + V_w`

and, ` V = V_v + V_s`

Similarly,

Total weight (W) = Weight of soil grains (`W_s`) + Weight of water (`W_w`) + Weight of air (`W_a`)

i.e., `W = W_s+ W_w + W_a`

Also,

Weight of void` (W_v) = W_a + W_w`

However, the weight of air being negligible i.e., `W_a~= 0` hence,

`W_v = W_w`

Thus, total weight of soil mass is;

`W = W_{w} + W_{s}`