SOIL DENSITY TESTING
Nuclear Testing for Soil Density.
This test method is the most accurate and easiest
to perform. It is conducted with an instrument
designed to measure density and moisture of soil.
The measuring probe uses a radioactive source
in combination with Geiger tubes to measure
either density or moisture.
An external detector probe is inserted into the soil
to the desired depth. Basically, gamma rays
being emitted from the detector probe are
absorbed by the soil and water atoms. The
denser the soil and the more water present, the
more rays are absorbed. Therefore, fewer rays
manage to reach the instrument detector to be
counted. Thus, the denser the soil, the lower the
count rate will be.
VISUAL TESTS
In order to obtain satisfactory compaction results,
it is beneficial to recognize the soil type and
moisture content. Since it is not always possible
to have accurate test data available before
starting the job, it is important to have a quick
field test. A simple method most often employed
in the industry is to pack a soil sample by hand
into the shape and size of a golf ball. Place the
ball between the index finger and thumb. If the
material shatters into fairly uniform fragments, the
soil is close to the optimum moisture.
If the material weeps in your hand or does not
break but flattens out, the soil is over optimum
moisture. When the soil cannot be formed into a
ball or is difficult to shape, it is probably under
optimum moisture content, and moisture must be
added.
To help classify the soil, roll a sample by hand into a thin roll about 1/8 inch in diameter.
If there is no problem rolling the material into this shape, the soil is usually clay and
extra care must be exercised when attempting to compact. Ideally, the material cannot
be rolled into the 1/8 inch diameter, indicating less clay content which is more desirable
for compacting.
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