materials by hand. Generally, No. 4 and No. 200 sieves
are used for separating gravel, sand, and fines.
. PIONEER TOOLS. Use a pick and shovel or a
set of entrenching tools for collecting samples. A hand
auger is useful if samples are desired from depths of
more than a few feet below the surface.
. STIRRER. The spoon issued as part of the mess
equipment serves in mixing materials with water to the
desired consistency. It also can aid in collecting samples.
. KNIFE. Use a combat knife or pocketknife for
collecting samples and trimming them to the desired
size.
. MIXING BOWL. Use a small bowl with a
rubber-faced pestle to pulverize the fine-grained portion
of the soil. Both may be improvised. You could use a
canteen cup and wood pestle.
. PAPER. Several sheets of heavy paper are
needed for rolling samples.
. PAN AND HEATING ELEMENT. Use a pan and
heating element to dry samples.
c SCALES. Use balances or scales to weigh
samples.
The Unified Soil Classification System, as shown
in appendix V, considers three soil properties: (1)
percentage of gravel, sand, or fines, (2) shape of the
grain size distribution curve, and (3) plasticity. Other
observed properties should also be included in the soil
description, whether made in the field or in the
laboratory.
The following descriptions represent some of the
typical characteristics used in describing soil:
. Dark brown to white or any suitable color shade
description
l Coarse-grained, maximum particle size 2 3/4
inches, estimated 60-percent gravel, 36-percent sand,
and 4-percent fines (passing through No. 200 sieve)
l Poorly graded (gap-graded, insufficient fine
gravel)
. Gravel particles subrounded to rounded, or
predominately gravel
. Nonplastic
. Mostly sand with a small amount of nonplastic
fines (silt)
c Slightly calcareous, no dry strength, dense in the
undisturbed state
VISUAL EXAMINATION
Visual examination should establish the color, grain
size, grain shapes (of the coarse-grained portion), some
idea of the gradation, and some properties of the
undisturbed soil.
Color is often helpful in distinguishing between soil
types, and with experience, one may find it useful in
identifying the particular soil type. Color may also
indicate the presence of certain chemicals. Color often
varies with moisture content of a soil. For this reason,
the moisture content at the time of color identification
should be included. Some of the more familiar color
properties are listed below.
. Generally, colors become darker as the moisture
content increases and lighter as the soil dries.
. Some fine-grained soils (OL, OH) with dark
drab shades of brown or gray, including almost black,
contain organic colloidal matter.
. In contrast, clean, bright looking shades of gray,
olive green, brown, red, yellow, and white are associated
with inorganic soils.
l Gray-blue or gray- and yellow-mottled colors
frequently result from poor drainage.
l Red, yellow, and yellowish brown result from the
presence of iron oxides.
. White to pink may indicate considerable silica,
calcium carbonate, or aluminum compounds.
The maximum particle size of each sample
considered should always be estimated if not measured.
This establishes the upper limit of the gradation curve.
Gravels range down to the size of peas. Sands start just
below this size and decrease until the individual grains
can barely be seen by the naked eye. The eye can
normally see individual grains about 0.05mm in size or
about the size of the No. 200 screen. Thus silt and clay
particles (which are smaller than this dimension) are not
detected as individual grains.
While the sample for grain sizes is being examined,
the shapes of the visible particles can be determined.
Sharp edges and flat surfaces indicate an angular shape;
smooth, curved surfaces are associated with a rounded
shape. Particles may not be completely angular or
completely rounded. These particles are called
16-16
