SOIL DENSITY TESTING
LABORATORY TESTS
A lab procedure called the Proctor Test measures a soil sample to determine the
moisture content and whether or not compaction is being achieved. There are several
ways of testing for soil density, which were originally developed by R. R. Proctor in
1933. The Proctor method of compaction control established the relationship between
the soil related to a condition called optimum moisture content.
Moisture Content. Each soil type has an optimum moisture content at which maximum
density can be achieved with the smallest amount of compactive forces. The optimum
moisture for a given soil is established in the laboratory. The correct amount of water is
necessary in order for the soil particles to slide by each other in the compaction
process. The water, in effect, acts as a lubricant. If there is too much water in the soil,
the water will take up space between the particles and not allow them to bond together.
The graph below illustrates the effect of moisture on soil density.
As the moisture content is increased to the optimum percentage, the density will
increase. If too much moisture is added, the soil’s density will decrease.
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