Civil Engineering Reference
In-Depth Information
V
v
V
V
s
(a) Actual form
(b) Idealised form
Fig. 1.10
Cross-section through a granular soil.
Fig. 1.11
Water and air contents in a soil.
1.8.1 Void ratio and porosity
From a study of Fig.
1.10
the following may be defined:
Void ratio
Volume of voids
Volume of solids
V
V
v
e
=
=
s
Porosity
Volume of voids
Total volume
n
=
V
V
V
e
v
v
n
=
=
=
V
+
V
1
+
e
v
s
1.8.2 Degree of saturation (S
r
)
The voids of a soil may be filled with air or water or both. If only air is present the soil is dry, whereas if
only water is present the soil is saturated. When both air and water are present the soil is said to be
partially saturated. These three conditions are represented in Figs
1.11a
, b and c.
The degree of saturation is simply:
Volume of water
Volume of voids
V
V
w
S
=
=
(
usually expressed a
s a percentage)
r
v
1.8.3 Particle density (
ρ
s
) and speciic gravity (G
s
)
The specific gravity of a material is the ratio of the weight or mass of a volume of the material to the
weight or mass of an equal volume of water. In soil mechanics the most important specific gravity is that
of the actual soil grains and is given the symbol G
s
.
