Phase Diagram of soil

In the soil particle around the solid  you got
void in the soil. In that void sometimes air filled and sometimes water, also both of
water and air fill sometimes.
When only water filled in the void then there will two phase that is solid and water.
When only air filled then in that case also only two phase that is solid and air.
When both air and water filled then there will be three phase diagram ie solid, water, air.

Firstly, said that in the void water and air fill. From that concept if we have asked to find the volume of void then we can find it by considering the volume of water and volume of air, simply sum of volume of water Vw and Va.
        Volume of void (Vv) = Vw+Va        ----1
     Total volume (V) = Vw + Va + Vs      ----2
Where Vs stands for volume of solid in the soil.
Eqn 2 also can be written as
                    V = Vv + Vs ------3

As similiar way weight can be also find by using equation given below.

           Weight of void (Wv) = Ww + Wa ----1
      Weight of air nearly equal to zero ( Wa=0)
      Therefore, W= Ww ----2

Now total weight (W) = Ww + Ws  ----3