Phase diagram for different saturation

A phase diagram shows soil as separate blocks of solids, water and air, with volumes on the left and weights on the right. Here $V_s, V_w, V_a$ are volumes of solids, water and air, $V_v = V_w + V_a$ is the void volume, and $W_s, W_w$ are the weights (air weight is taken as zero).

Partially saturated

  Volume              Weight
 +--------+  ---   +----------+
 |  Air   | Va     |    0     |
 |--------|  | Vv  |----------|
 | Water  | Vw     |   Ww     |
 |--------|  ---   |----------| W
 | Solids | Vs     |   Ws     |
 +--------+        +----------+
   V=Vs+Vw+Va         W=Ws+Ww

Fully saturated ($S = 100\%$, $V_a = 0$)

 +--------+  ---   +----------+
 | Water  | Vw=Vv  |   Ww     |
 |--------|  ---   |----------|
 | Solids | Vs     |   Ws     |
 +--------+        +----------+

Dry ($S = 0$, $V_w = 0$, $W_w = 0$)

 +--------+  ---   +----------+
 |  Air   | Va=Vv  |    0     |
 |--------|  ---   |----------|
 | Solids | Vs     | Ws = W   |
 +--------+        +----------+