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Soil and foundation engineers have for many years needed a technique for accurate and rapid determination of the moisture content and density of compacted fills. Delays in completion of the earthwork while the results of density and moisture measurements are being determined are a very real cost to contractors and owners. For these reasons developments by the Civil Aeronautics Administration, Cornell University and others in the measurement of soil moisture and density by the nuclear method have been of particular interest.
In the hope that instruments utilizing the nuclear method might expedite performance of numerous field moisture and density determinations on the O'Hare Field project in Chicago, one of the instruments manufactured by Nuclear Chicago Corp. has been used since August 1059. This paper describes some of the author's experiences with this equipment, including correlation data with the conventional sand cone method.
Initial correlation work between nuclear measurements of soil density and moisture indicated extremely poor results, with nuclear instruments consistently giving low readings for water contents, and giving errors as high as 17 lb per cu ft, referred to the sand cone densities. Subsequent work, however, has indicated that, by using calibration curves for moisture content and density which are prepared specifically for the soil types involved, the errors in moisture content can be reduced to approximately 2 per cent or less. By using revised calibration curves for the density measurements for the soil types involved, the nuclear instruments can be expected to give moist densities within approximately 5 lb of the densities obtained by the sand cone method.
President, Soil Testing Services, Inc., Chieago, Ill.