Phase diagram; void ratio, saturation

Phase diagram

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

Here $V_v = V_w + V_a$ is the volume of voids; $W_w$ and $W_s$ are weights of water and solids.

Void ratio ($e$)

The ratio of the volume of voids to the volume of solids:

$$e = \frac{V_v}{V_s}$$

It is a ratio (no unit) and can be more than 1 (for example in soft clays).

Degree of saturation ($S$)

The ratio of the volume of water to the volume of voids, in percent:

$$S = \frac{V_w}{V_v} \times 100$$

$S = 0$ for dry soil and $S = 100\%$ for fully saturated soil.