**Hi,**

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**Three Phase Diagram:**

A soil mass consist of the solid particles and the voids in between them. These voids are filled with air or/and water. So there is a three phase system, but when the voids are only filled with air, or only filled with water then soil becomes a two phase system. Three phase system can be represented with a diagram as shown below. When the voids are only filled with water, it is said to be saturated.

Total volume of the soil mass, V = (Va+Vw) +Vs

Where, V = Total Volume

Va= Volume of air mass

Vw = Volume of water mass

Vs = Volume of solids

But, Va+Vw = Vv

So,

V = Vv+ Vs

Where Vv= Total volume of voids.

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**Void Ratio(e):**

Void ratio is the ratio of the volume of the voids to the volume of the solid in the soil.

It is denoted by 'e'.

e= Vv/Vs = n/(1-n)

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**Porosity (n): **

Porosity is defined as the ratio of the volume of the total voids to the total volume of the soil mass.

It is denoted by 'n'

So n = Vv/V = e/(1+e)

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**Degree of Saturation(Sr):**

Degree of saturation is defined as the ratio of the volume of the water to the total volume of the voids present in the soil mass.

Sr = Vw/Vv, For fully saturated soil mass Vw=Vv, So Sr=1

For fully dry soil mass, Vw= 0, So Sr=0

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**Water content(w):**

It is the ratio of the weight of the water to the weight of the solids in the given soil mass. Weight of solids can be found by weighing the soil mass after drying it completely.

w = Ww/Ws

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**Air Content(na): **

It is the ratio of the volume of air(Va) to the total volume of the voids(V).

na= Va/V*100

Thanks!

Reference: