Microwave dielectric measurements for soil density and moisture content inference in engineering applications

Soil is a material of interest in a number of disciplines such as geotechnical, environmental, military and agricultural engineering. Precise knowledge of dielectric properties of soil provides information about the interactions between the soil and applied electromagnetic (EM) fields. Detecting anomalies of interest in heterogeneous soil media without enough information about the background media is very challenging, if not impossible. Dielectric properties are considerably intricate, can exhibit frequency dependent behavior, and correlate with many physical and chemical properties. Measuring dielectric properties can therefore be used to estimate those physical and chemical properties, if the correlation between the dielectric properties and other physical and chemical properties is well investigated and understood. In this study, laboratory measurements and theoretical modeling of dielectric properties of sandy soils are carried out. Dielectric property measurements are executed using a minimally invasive cross-borehole microwave measurement technique. An in-situ technique to measure dielectric properties of a sandy soil at different densities and moisture contents, and their frequency dependence over a wideband of frequency (0.4 GHz to 2.2 GHz) is implemented and evaluated. Then, the correlation between variations of dielectric and physical properties of the soil (e.g. density and water content) is studied. Dielectric mixing models were used to ascertain these correlations as a forward model for future inversion. Finally, a comparison between the forward model and experimental results was undertaken to seek the level of agreement.