Environmental Engineering Reference
In-Depth Information
Volume-Weight Relationships
Definitions
of the various volume-weight relationships for soils are given in
Table 3.8.
Commonly used relationships
are void ratio
e
, soil unit weight (also termed density or mass
density and reported as total or wet density
γ
t
, dry density
γ
d
, and buoyant density
γ
b
),
moisture (or water) content
w
, saturation degree
S
, and specific gravity
G
s
of solids.
Determinations of basic soil properties are summarized in
Table 3.9.
A nomograph for
the determination of basic soil properties is given in
Figure 3.2.
Sand Cone Density Device (
Figure 3.3a)
A hole 6 in. deep and 6 in. in diameter is dug and the removed material is stored in a
sealed container. The hole volume is measured with calibrated sand and the density is cal-
culated from the weight of the material removed from the hole (ASTM D1556-00).
Rubber Balloon Device
A hole is dug and the material is stored as described above. The hole volume is measured
by a rubber balloon inflated by water contained in a metered tube (ASTM D2167-94).
Nuclear Moisture-Density Meter (ASTM D2922)
A surface device, the nuclear moisture-density meter, measures wet density from either the
direct transmission or backscatter of gamma rays; and, moisture content from the transmis-
sion or backscatter of neutron rays (
Figure 3.3b)
.
The manner of measurement is similar to
that of the borehole nuclear probes (see
Section 2.3.6).
In the direct transmission mode a rod
containing a Celsium source is lowered into the ground to a desired depth. In the backscat-
ter mode, the rod is withdrawn and gamma protons are scattered from the surface contact.
A rapid but at times approximate method, measurement with the meter yields satisfactory
results with modern equipment and is most useful in large projects where soil types used as
fills do not vary greatly. Frequent calibration is important to maintain accuracy.
Borehole Tests
Borehole tests measure natural density and moisture content. Tests using nuclear devices
are described in Section 2.3.6.
Moisture content (w)
The moisture meter is used in the field (ASTM D4444-92). Calcium carbide mixed with a
soil portion in a closed container generates gas, causing pressure that is read on a gage to
indicate moisture content. Results are approximate for some clay soils.
For cohesive soils, moisture content is most reliably determined by drying in the labo-
ratory oven for at least 24 h at 104°C.
Moisture-Density Relationships (Soil Compaction)
Optimum moisture content
and
maximum dry density relationships
are commonly used to
specify a standard degree of compacting to be achieved during the construction of a load-
bearing fill, embankment, earth dam, or pavement. Specification is in terms of a percent of
maximum dry density, and a range in permissible moisture content is often specified as
well (
Figure 3.4)
.
Description
The density of a soil can be increased by compacting with mechanical equipment. If the
moisture content is increased in increments, the density will also increase in increments
