air but can again become effective when you heat a wet
sample. Organic soils are undesirable as foundation or
base course material. They are usually removed from
the construction site and wasted.
BITE OR GRIT TEST
The bite or grit test is a quick and useful method that
is used to identify sand silt, or clay. In this test, a small
pinch of solid material is ground lightly between the
teeth. The soils are identified as follows:
. SANDY SOILS. The sharp, hard particles of
sand grate harshly between your teeth and are highly
objectionable. This is true even of the fine sand.
l SILTY SOILS. The silt grains are so much
smaller than sand grains that they do not feel nearly so
harsh between your teeth. They are not particularly
gritty although their presence is still easily detected.
l CLAYEY SOILS. The clay grains are not at all
gritty, but feel smooth and powdery like flour between
the teeth. Dry lumps of clayey soils stick when lightly
touched with your tongue.
The slaking test is used to assist in determining the
quality of certain soil shales and other soft rocklike
materials. To perform this test, place the soil in the sun
or in an oven to dry. Then allow it to soak in water for
at least 24 hours. After this, examine the strength of the
soil. Certain types of shale disintegrate completely and
lose all strength.
The acid test is used to determine the presence of
calcium carbonate. It is performed by placing a few
drops of hydrochloric acid on a piece of soil. A fizzing
reaction (effervescence) to this test indicates the
presence of calcium carbonate. The degree of reaction
gives an indication of the concentration. Calcium
carbonate normally is desirable in a soil because of the
cementing action it adds to the stability. (Some very dry
noncalcareous soils appear to effervesce after they
absorb the acid. This effect can be eliminated in all dry
soils by moistening the soil before applying the acid.)
This cementing action normally develops only after a
long curing period and cannot be counted upon for
strength in most military construction. The primary use
for this test is to give abetter value of fine-grained soils
that you have tested in place.
The shine test is another means of measuring the
plasticity characteristics of clays. A slightly moist or dry
piece of highly plastic clay has a definite shine when
rubbed with a fingernail, a pocketknife blade, or any
smooth metal surface. On the other hand, a piece of lean
clay does not display any shine, but remains dull.
The feel test is a general-purpose test that requires
experience and practice before reliable results can be
obtained. Two characteristics you can determine by the
feel test are consistency and texture.
The natural moisture content of a soil is of value as
an indicator of the drainage characteristics, nearness to
the water table, or other factors that may affect this
property. A piece of undisturbed soil is tested by
squeezing it between the thumb and forefinger to
determine its consistency. The consistency is described
by such terms as hard, stiff, brittle, friable, sticky,
plastic, or soft. Remold the soil by working it in your
hands. Observe changes, if any. You can use the feel test
to estimate the natural water content relative to the liquid
or plastic limit of the soil. Clays that turn almost liquid
on remolding are probably near or above the liquid limit.
If the clay remains stiff and crumbles upon being
remolded, the natural water content is below the plastic
The term texture, as applied to the fine-grained
portion of a soil, refers to the degree of fineness and
uniformity. The texture is described by such expressions
as floury, smooth, gritty, or sharp, depending upon the
sensation produced by rubbing the soil between the
fingers. Sensitivity to this sensation may be increased
by rubbing some of the material on a tender skin area
such as the wrist. Fine sand feels gritty. Typical dry silts
will dust readily and feel relatively soft and silky to the
touch. Clay soils are powdered only with difficulty but
become smooth and gritless like flour.
Q1. The purpose of a geological survey is to take
which of the following actions?
1. Locate rock formations in the field and
determine their physical characteristics
2. Determine rock age and distribution
3. Determine types of rock and their mineral
4. All of the above