Lesson 2/Learning Event 4
Learning Event 4
CONDUCT A FIELD TEST FOR #40 SIEVE MATERIAL
Tests for identification of the fine-grained portion of any soil are performed on the portion of the
material which passes a #40 sieve. This is the same soil fraction used in the laboratory for Atterberg
limits tests, such as plasticity.
Some or all of the following tests produce observations that pertain to the Unified Soil Classification
System. Such tests as are appropriate to the given soil sample should be made. Some tests appear to
yield duplicate results. The purpose of these tests is to get the best possible identification in the field.
Thus, if a simple visual examination will define the soil type, only one or two of the other tests have to
be made to verify or check the identification. On the other hand, when the results from a test are
inconclusive, some of the similar tests should be tried to establish the best identification.
ODOR TEST
Organic soils of the OL and OH groups usually have a distinctive, musty, slightly offensive odor which,
with experience, can be used as an aid in their identification. This odor is especially apparent from fresh
samples. It is gradually reduced by exposure to air, but can again be made more pronounced by heating
a wet sample.
DRY STRENGTH TEST
The dry strength, or breaking test, as well as the roll test and the ribbon test, is used to measure the
cohesive and plastic characteristics of the soil. The test normally is made on a small pat of soil about
1/2 inch thick and about 1 1/2 inches in diameter. The pat is prepared by molding a portion of the soil in
the wet plastic state into the size and shape desired and then allowing the pat to dry completely.
Samples may be tested for dry strength in their natural condition as they are found in the field, but much
reliance should not be given to such tests because of the variations that exist in the drying conditions
under field conditions. Such a test may be used as an approximation, however, and verified later by a
carefully prepared sample.
After the prepared sample is thoroughly dry, attempt to break it using the thumb and forefingers of both
hands, as shown in Figure 18. If it can be broken, try to powder it by rubbing it with the thumb and
fingers of one hand.
Typical Reactions
These are the typical reactions that are obtained in this test for various types of soils:
Very Highly Plastic Soils (CH) have very high strength. Samples cannot be broken or powdered
by use of finger pressure.
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