Factors Influencing the Application of Nuclear Techniques to Soil Compaction Control

The use of nuclear backscatter moisture -density gages for soil compaction control has gained a great deal of favor during the past several years . However, before this type of equipment can be applied to routine field control, several factors influencing the operation of the gage must be investigated. Various techniques for expressing nuclear results were studied, and the results indicate that the use of count ratio at constant high voltage should be adopted. This technique along with the use of standard calibration blocks provide for reproducibility of results and account for aging to some extent. These factors are especially important from the standpoint of recalibrating the gages . Results of tests performed on various materials and calibration blocks of different chemical composition indicate that material composition has a major effect on the development of calibration curves for the density gages . This was not found to be true for the moisture gages . Soil pH as an indication of soil type was investigated, and calibration curves based on this parameter were developed. The effect of grain size distribution resulted in a different calibration curve for coarse grained versus fine grained soils . Along with typical calibration curves, guidelines for field application were developed. A statistical decision theory based on a "t" test was also developed to aid in making a decision involving the validity of using a given calibration curve .