Determination of the swelling characteristics of a soil using neutron and gamma density meters

Abstract

In-situ measurement of swelling characteristics of soils are required in soil physics and engineering studies. The combined use of neutron and gamma meters for making such measurements was evaluated. The regression of gamma ratio (ã) on neutron ratio (n) was calculated by combining the calibration equations of the neutron and gamma meters with the swelling characteristics of the different soil layers in a transitional red-brown earth. The slope of the calculated regression of ã on n was correlated with the extent of swelling in the soil layers. Close agreement was found between wet bulk densities calculated from measured ã and n values at two adjacent sites. These densities were also very similar to the wet bulk densities obtained from the calculated regression lines of ã on n for the transitional red-brown earth, allowing for soil heterogeneity of the field sites. Equations were derived for calculating the bulk density-moisture content relationship of a soil using the measured regression of ã on n, and the calibration equations for the neutron and gamma meters. Equations were also developed for calculating the moisture content and the dry bulk density at a given depth in a swelling soil from a single gamma count. The use of the measured regressions of ã on n to evaluate uniformity in swelling characteristics with depth in field soils is discussed. These regressions can also be used to determine the heterogeneity in swelling characteristics between field experimental sites of any soil.