Analysis of Interfacial Water in Clay by High Frequency Dielectric Relaxation Spectroscopy

Geotechnical application of high frequency (radio to microwave) electromagnetic (HF-EM) techniques is based on the relationship between constitutive HF-EM material properties and soil structural or state parameters such as water content, density, temperature and stress strain state. An unresolved problem in the theoretical modeling of HF-EM properties is the interaction of the aqueous pore solution and mineral phases, especially in fine grained soils containing clay minerals. Against this background temperature (-2 to 25 °C) and frequency (50 MHz to 5 GHz) dependent dielectric material properties of two water saturated clays (illite-chlorite, montmorillonite) were measured with open ended coaxial line technique. The impact of dielectric relaxation processes below 1 GHz were analysed based on a master plot for the electrical modulus representation. In case of illite-chlorite the deviation from a Debye-type characteristic is small indicating that a Maxwell-Wagner effect dominates the interaction of the aqueous pore solution and soil particles. In contrast montmorillonite shows a significant deviation from Debye-type characteristics with asymmetrical relaxation time distribution. Hence, an additional HF relaxation processes are hidden behind the dominated Maxwell-Wagner process.