Explain Soil as Three phase system | Phase Diagram & Formulas | What is Water content & its formulas

 

Soil As Three Phase System

    The soil mass in general is a three phase system composed of solid, liquid and gaseous matter. The soli phase consists of mineral, organic matter or both.

    The mineral portion consists of particles of different sizes and shapes. The organic fraction is the plant and animal residue which may be present in various stages of decomposition.

• The solids enclose the open spaces termed voids.
• The liquid phase is actually a water in soil and fills partly or wholly the voids in it.
• The gaseous phase, usually air, occupies the voids not filled by water.
• The relative volume wise and weight wise proportions of the three phases in a soil mass are important factors influencing its physical properties.
• It is therefore necessary to study them. Though the three phases present can not be separated as shown in the following fig. they are shown as occupying separate spaces, for your better understanding.

Phase Diagram/ Three phase diagram

The diagrammatic representation of the different phases present in a soil mass is called the phase diagram.

 Fig. (a) shows a three phase system which is present in a partially saturated soil. When it is fully saturated i.e. all the voids are filled with water and thus gaseous phase is absent and the soil becomes a two-phase system (Fig.(d)).

Also, if the soil becomes totally dry and consists of only solid and gaseous phases. In this case also, it is a two phase system. This is shown in Fig. (c).

From saturated condition i.e. (d) it shows two phase system the voids are fully filled only with water and hence we can conclude…..

Vv = Vw.

Total weight W = Ws + Ww

&

Total Volume V = Vs + Va + Vw                   ...(Va is very small so neglected)

 

For Dry condition W =  Ws

                              V = Vs + Vw

 

 

Water content

          Water content is defined as the ratio of the weight of water to the weight of solids in a given soil-mass.

 Water content =  Weight of Water/ Weight of solids

 

Percentage of water content = (Weight of water/ weight of solids) x 100

                                             = (Ww/ Ws) x 100         ...[0<= w<= infinity]

 

Water content is expressed as a percentage, though in formulae giving relationships between quantities, it is expressed as a decimal fraction.

In laboratory the water content is determined by oven drying method.