Civil Engineering Reference
In-Depth Information
From the above definition it is seen that, for a soil sample with volume of solids V
s
and weight of
solids W
s
,
W
V
s
G
=
s
γ
s w
where
γ
w
=
weight of water and, if the sample has a mass of solids M
s
,
M
V
s
G
=
s
ρ
s w
where
ρ
w
=
density of water (
=
1.0 Mg/m
3
at 20°C) i.e.
M
V
W
V
s
s
G
=
=
s
ρ
γ
s w
s w
The density of the particles
ρ
s
is defined as:
M
V
s
ρ
s
=
s
therefore,
=
ρ
ρ
s
G
s
w
BS 1377: Part 2 specifies methods of test for determining the particle density. For fine, medium or coarse
soils the Standard specifies the use of a one litre gas jar fitted with a rubber bung and a mechanical
shaking apparatus which can rotate the gas jar, end over end, at 50 rpm (Fig.
1.12)
.
The test consists briefly of placing oven dried soil (approximately 200 g for a fine soil and 400 g for a
medium or coarse soil) into the gas jar along with about 500 ml of distilled water at room temperature.
The jar is sealed with the bung and shaken, first by hand and then in the machine, for 20 to 30 minutes.
The bung is then removed, the jar topped up carefully to full capacity with further distilled water and the
glass plate slid on top to seal the jar without trapping any air inside. From various weighings that are
made the specific gravity of the soil can be calculated. (See Example
1.6.
)
If
ρ
s
is measured in units of Mg/m
3
and the water temperature is assumed to be 20°C, it follows that
ρ
s
and G
s
are numerically equal. G
s
is dimensionless.
Fig. 1.12
Determination of particle density.
