Civil Engineering Reference
In-Depth Information
the hole thus formed is obtained by pouring into it sand of known density from a special graduated con-
tainer; given the weight of sand in the container before and after the test, the weight of sand in the hole
and hence the volume of the hole can be determined.
The apparatus shown in Fig.
14.7
is suitable for fine to medium grained soils and is known as the small
pouring cylinder method.
For coarse grained soils a larger pouring cylinder is used. This cylinder has an internal diameter of
215 mm and a height of 170 mm to the valve or shutter. The excavated hole in this case should be about
200 mm in diameter and some 250 mm deep. This larger pouring cylinder can also be used for fine to
medium grained soils.
Example 14.3:
Sand replacement test
During construction of a highway, a sand replacement test was performed to determine
the in-situ density of the subgrade. The following results were obtained:
Total mass of sand used in test
=
8500 g
Mass of sand retained in cylinder at end of test
=
2500 g
Mass of soil removed from hole
=
5036 g
Previously the following had been established in the laboratory:
Mass of sand held in cone beneath cylinder
=
1760 g
Density of sand
=
1.6 Mg/m
3
.
Determine the bulk density of the subgrade soil.
Solution:
Mass of sand in hole M
,
=
8500 2500 1760
−
−
=
4240
g
sand
M
4240 10
1 6
×
−
6
sand
sand
−
3
3
⇒
Volume of hole V
,
=
=
=
2 65 10
.
×
m
.
ρ
.
−
6
M
V
5036 10
2 65 10
×
×
soil
⇒ =
ρ
b
=
=
1 90
.
Mg m
/
3
.
.
−
3
Nuclear density gauge
This instrument consists of an aluminium probe which is pushed into the soil, connected to a detection
and measuring unit placed on the soil surface. Neutrons emitted from a source in the probe lose their
energy by collision with soil and water particles. A detector fitted to the instrument then picks up the
number of slow neutrons deflected back to the instrument. Since this number depends upon the amount
of water present in the soil, measurements of the water content, the bulk density and the dry density of
the soil can be obtained directly. The apparatus gives a rapid and dependable reading and thus the test
has become much more widely used than the sand replacement method test. However, as the apparatus
uses a nuclear source, strict legislation exists as to its use which can render it unapproved for use on some
projects.
14.4.2 Moisture content determination
Quick moisture content determinations are essential if compaction work is to proceed smoothly, and the
Highways Agency
Manual of contract documents for highway works, MCHW 2
(2009b) permits the use
