TM 5-6635-386-12&P
The standard count is taken from Para 1-11.
1-28. CALIBRATION CHARTS
FIELD COUNTS
= RATIO
CPN calibration curves or charts are determined from
STANDARD COUNT
tests taken on CPN calibration standards.
1-24. DETERMINE DRY WEIGHT
CPN uses a variety of standards for gauge calibration
including natural standards and artificial (metal)
Subtract the moisture in PCF from wet weight for each
standards. Unfortunately, there is no "National Bureau of
density depth to obtain a dry weight. The dry weight (DA
Standards" in the nuclear soil gauging industry. Each
Form 5448-R) is then used for the determination of
manufacturer does his best to provide an accurate set of
Percent Compaction and Moisture (See Fig 1-10).
standards and he checks these standards against other
standards wherever possible. The major manufacturers
1-25. COMPUTE PERCENT COMPACTION
generally agree quite closely on their standards although
some disagreement may exist here and there with
The tester has now provided the actual, in place density
standards of users who have made them themselves.
and moisture obtained during compaction of the soil
Whether this is good enough for the project is not known
If the chart produces results suspected of being in error
until we compare this in place density with the soil
(conflicts with field results of other testers or of other
maximum density produced from a laboratory sample of
compaction measurements) do the following:
the soil being tested (found in a Corps of Engineers
handbook or determined by actual laboratory tests). This
Check operation of tester. (See Para 1-7).
is the "Proctor" value or soil maximum density. To obtain
a Percent Compaction (DA Form 5448-R) we divide the
Check accuracy of other testers.
dry density by the Proctor value which is assumed to
equal 130 PCF. (See Fig. 1-11).
Retest a prior site that was correct
DRY WEIGHT
% SOIL MAXIMUM DENSITY
1-29. MOISTURE MEASUREMENT ERRORS
=
OPTIMUM
COMPACTION
The moisture channel is actually a "hydrogen analyzer".
It responds to moderated neutrons, the moderation
1-26. COMPUTE PERCENT MOISTURE
largely a function of neutron collisions with hydrogen and
only incidentally a function of collision with the large
Percent moisture is expressed as a percent of the dry
nuclei of other atoms.
weight in soil testing. Therefore we must divide the
moisture in PCF by the dry weight in PCF to obtain
Thus, any source of hydrogen will result in moderated
percent moisture dry, DA Form 5448-R (See Fig 1-12).
neutrons and the tester will attempt to respond
accordingly.
H20 IN PCF
= % MOISTURE DRY
This can be used to our advantage in deliberately
DRYWIEGHT
measuring asphalt content where the only hydrogen
that we would expect to "see" would be from the
1-27. COMPLETION OF TEST
hydrocarbons in the AC and not from moisture.
Upon completion of the testing and before tester is
However, the hydrogen analyzer aspect of the tester can
placed in carrying case, remove battery pack and store it
also be to our detriment if the soil we are trying to
separately. It is not necessary to turn the tester off or
measure has hydrogen from other than free water
perform other operations. Also insure that the tester
around the mineral particles.
handle is in safe position prior to placing the tester into
storage case.
1-18