Figure 15-24.-Mixing a sample weighing 25 to 100 pounds.
Figure 15-25.-Quartering a small sample.
corners of the canvas and pulling over the samples
as if preparing to fold the canvas diagonally, as
shown in figure 15-24. Then flatten and quarter
Samples Weighing Less Than
For samples of this size, place the sample on
the canvas or a clean sheet of paper. Mix it
thoroughly with a trowel, form it into a conical
shape, and then flatten it with the trowel. Using
the trowel, divide the sample into quarters, and
discard two diagonally opposite quarters, as
shown in figure 15-25. Remix the remaining
material, and repeat the process until the sample
is the size needed for the test.
In soil testing, the Navy follows procedures
laid down by the American Society for Testing
Materials (ASTM). Generally speaking, a com-
plete soil test proceeds according to the following
1. Determine the moisture content of repre-
sentative samples. (This is preceded, of course,
by the extraction of representative samples.)
2. Perform a mechanical analysis of the
sample to determine the sizes of soil particles (or
grains) and the distribution of sizes; this means
the percentage of each size contained in the whole
3. Determine the specific gravity of represen-
tative samples. The specific gravity of a substance
is expressed in terms of the ratio of the weight
of a given volume of the substance to the weight
of an equal volume of water. A cubic foot of
water weighs 62.43 lb.
For soil, determine the absolute specific grav-
ity; by this we mean determine the ratio of the
weight of a dense volume (volume exclusive of air
spaces) to the weight of an equal volume of water.
A cubic foot of dry sand, for example, weighs
about 100 lb. With air exhausted, however, a
cubic foot of sand weighs about 165.44 lb.
Therefore, the specific gravity of sand equals
165.44 divided by 62.43, or about 2.65.
4. If the soil is clay or a similar fine-grained
soil, determine the Atterberg limits. Over a cer-
tain range of moisture content, a fine-grained soil
remains plastic. A reduction below the bottom of
the range causes the soil to become semisolid; an
increase above the range causes it to become fluid.
The upper moisture content is called the liquid
limit; the lower is called the plastic limit.
5. Compaction testing is used to determine the
moisture-density relationships; or, in other words,
to determine what moisture content results in
maximum compaction for a given compactive