Lesson 2/Learning Event 4
Highly Plastic Soils (CH) have very high strength. Samples can be broken with great effort, but
cannot be powdered.
Medium Plastic Soils (CL) have medium strength. Sample can be broken and powdered with
Slightly Plastic Soils (ML, MH, or CL) have low strength. Samples can be broken quite easily
and powdered readily.
Non-plastic Soils (ML or MH) have very little or no strength. Samples crumble and powder on
being picked up in the hands.
FIGURE 18. DRY STRENGTH TEST
The test described above is one of the best for distinguishing plastic clays and non-plastic silts or fine
sands. However, a word of caution is appropriate. Dry pats of highly plastic clays quite often display
shrinkage cracks. To break the sample along such a crack will give an indication of only a very small
part of the true strength of the soil. It is important to distinguish between a break along such a crack,
and a clean, fresh break that indicates the true dry strength of the soil.
The feel test is a general purpose test, and one that requires considerable experience and practice before
reliable results can be obtained. Some of the following characteristics can be readily estimated by
proper use of this test.
The natural moisture content of a soil is an indicator of the drainage characteristics, nearness to water
table, or other factors which may affect this property. A sample of undisturbed soil is tested by
squeezing it between the thumb and forefinger to determine its consistency. This consistency is