Figure 13-2.—Data sheet for soil compaction test.
material, you remove the collar and weigh the mold and
compacted material. Then take moisture content
samples from the top and bottom of the specimen and
determine the moisture content for each. If the two
moisture contents differ, use the average between
them.
A modification of the above procedure uses a 5
1/2-pound tamper and the material is placed in three
equal layers, rather than five; otherwise, the test is the
same. The procedures can be found in ASTM D 698.
Data and Calculations
Figure 13-2 shows the test results and calculations
for a compaction test. As you can see, this test used a
10-pound tamper and Proctor mold. Five runs were
made. After compaction, the weight of the compacted
soil and mold was recorded for each run. From this, the
weight of the mold was subtracted to get the weight of
the soil for each run. Then the wet unit weight was
computed using the formula shown.
Lines A, B, C, D, and E contain the data for the
moisture-content test for each run. Note that for each
run, there were two tests: one from the top of the mold
and the other of soil from the bottom. The averages
were set down beside average moisture content.
Finally, the dry unit weight (density) in pounds per
cubic foot (pcf) for each run was calculated by the
formula shown. As you can see, for the same
compactive effort, the density varied with the average
moisture content.
The ultimate objective of the compaction test is to
determine the OMC; that is, the moisture content that
yields maximum density for a given compactive effort.
13-3
