On Reconstructing the Soil Shrinkage Characteristic Curve by Dielectric Spectroscopy

In this paper, we attempt to re-construct the soil shrinkage curve through electromagnetic measurements and modelling. In order to achieve this objective, broadband dielectric measurements based on vector network analyser (VNA) and open ended (OE) coaxial probe have been performed to measure the relative effective complex permittivity of soil during shrinkage over the 50 MHz - 3 GHz frequency range. A novel approach (Augmented Broadband Complex dielectric Mixture model - ABCM) has been used as kernel to model the spectrum in an inversion scheme. Water saturation and porosity have been estimated directly from the measured spectrum in order to retrieve the Soil Shrinkage Characteristic Curve (SSCC). Upon comparison of the reconstructed SSCC with the SSCC obtained from direct measurements of weights and volumes of soil, a reasonable degree of agreement has been observed in the initial portions of the curve (structural and normal shrinkage) prior to zero and residual shrinkage.