Subgrade moisture variations interim report IV Suggested nuclear depth gage calibration procedures

Abstract

An experimental procedure for calibration of nuclear depth moisture and density gages is described. Calibration of the gages was accomplished utilizing laboratory standards constructed of native Oklahoma soils. The soil standards were compacted to a known density and moisture content; one sand and two cohesive soils were employed. Calibration curves were derived by comparing instrument response with probes in the standards to the various densities and moisture contents of the standards. Previous work in the calibration area was reviewed and the effect of soil type on gage response was investigated. A satisfactory method of constructing laboratory standards was developed. The calibration curves for the gages indicated that soil type influences instrument response. Each soil had a separate and unique calibration curve for moisture content and for density. The use of dual-purpose standards, to calibrate both moisture and density gages, was proven desirable. Specific calibration curves are recommended for project use.