The standard count is taken from Para 1-11.
1-24. DETERMINE DRY WEIGHT
Subtract the moisture in PCF from wet weight for each
density depth to obtain a dry weight. The dry weight (DA
Form 5448-R) is then used for the determination of
Percent Compaction and Moisture (See Fig 1-10).
1-25. COMPUTE PERCENT COMPACTION
The tester has now provided the actual, in place density
and moisture obtained during compaction of the soil
Whether this is good enough for the project is not known
until we compare this in place density with the soil
maximum density produced from a laboratory sample of
the soil being tested (found in a Corps of Engineers
handbook or determined by actual laboratory tests). This
is the "Proctor" value or soil maximum density. To obtain
a Percent Compaction (DA Form 5448-R) we divide the
dry density by the Proctor value which is assumed to
equal 130 PCF. (See Fig. 1-11).
% SOIL MAXIMUM DENSITY
1-26. COMPUTE PERCENT MOISTURE
Percent moisture is expressed as a percent of the dry
weight in soil testing. Therefore we must divide the
moisture in PCF by the dry weight in PCF to obtain
percent moisture dry, DA Form 5448-R (See Fig 1-12).
H20 IN PCF
= % MOISTURE DRY
1-27. COMPLETION OF TEST
Upon completion of the testing and before tester is
placed in carrying case, remove battery pack and store it
separately. It is not necessary to turn the tester off or
perform other operations. Also insure that the tester
handle is in safe position prior to placing the tester into
1-28. CALIBRATION CHARTS
CPN calibration curves or charts are determined from
tests taken on CPN calibration standards.
CPN uses a variety of standards for gauge calibration
standards. Unfortunately, there is no "National Bureau of
Standards" in the nuclear soil gauging industry. Each
manufacturer does his best to provide an accurate set of
standards and he checks these standards against other
standards wherever possible. The major manufacturers
generally agree quite closely on their standards although
some disagreement may exist here and there with
standards of users who have made them themselves.
If the chart produces results suspected of being in error
(conflicts with field results of other testers or of other
compaction measurements) do the following:
Check operation of tester. (See Para 1-7).
Check accuracy of other testers.
Retest a prior site that was correct
1-29. MOISTURE MEASUREMENT ERRORS
The moisture channel is actually a "hydrogen analyzer".
It responds to moderated neutrons, the moderation
largely a function of neutron collisions with hydrogen and
only incidentally a function of collision with the large
nuclei of other atoms.
Thus, any source of hydrogen will result in moderated
neutrons and the tester will attempt to respond
This can be used to our advantage in deliberately
measuring asphalt content where the only hydrogen
that we would expect to "see" would be from the
hydrocarbons in the AC and not from moisture.
However, the hydrogen analyzer aspect of the tester can
also be to our detriment if the soil we are trying to
measure has hydrogen from other than free water
around the mineral particles.