A diagram of the soil mass which shows the different components of soil .i.e. (solid, water and air) is called phase diagram.
The diagram which contains only 2 phases i.e.(solid and water or solid and air) is called 2 phase diagram.
The diagram which shows 3 phases i.e.( air,water and solid) is called three phase diagram.
Saturated soil and Dry soil represents 2 phase diagram. Similarly, Partially saturated soil represents 3 phase diagram. Examples are shown below;
fig: Phase diagram of soil