Determination of in situ moisture content in soils from a measure of dielectric constant

There are currently several electromagnetic sensors commercially available for determining in situ moisture content. All of these sensors work in a similar manner. A known electrical signal is sent into the soil. The signal measured back from the soil is expressed in the form of a complex dielectric constant that is directly related to the amount of water present in the soil. As the real component of the dielectric constant of water is four to eight times greater than most soils, changes in water content directly affect the sensor output. Soil calibration models specific to the various soil types are developed by plotting measurements of the real component versus gravimetric moisture contents. The subsequent linear regression line then becomes the soil-specific model. The focus of this study was to compare linear calibration models developed for various soil samples, with various geotechnical properties. The intent was to develop a generalized calibration model for the electromagnetic sensor. The generalized model will allow moisture content to be determined in situ, regardless of the soil type. The results of this study was the development of a generalized soil model that predicts the in situ moisture content for fine grain soils as well as the soil-specific models. In general, this study provides a framework for developing methodology to predict other in situ geotechnical parameters from measurements of the complex dielectric constant.