1-25. COMPUTE PERCENT COMPACTION

TM 5-6635-386-12&P The standard count is taken from Para 1-11. FIELD COUNTS STANDARD COUNT = RATIO 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). DRY WEIGHT OPTIMUM = % SOIL MAXIMUM DENSITY COMPACTION 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 DRYWIEGHT = % 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 storage case. 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 including natural standards and artificial (metal) 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 accordingly. 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. 1-18