Modelling electromagnetic properties of saturated sand and clay

Abstract

Dielectric spectra of sand–water and clay–water mixtures differ in that the real permittivity of sand–water mixtures is almost constant over the 1 MHz to 1 GHz frequency range while the real permittivity of clay–water mixtures decreases with increasing frequency, a phenomenon termed the dielectric dispersion. A theoretical model is established for clay minerals so that the mechanisms controlling dielectric dispersion can be analysed and the dielectric dispersion magnitude can be quantified. Interfacial polarisation is the most important mechanism accounting for dielectric dispersion. Bound water polarisation also contributes to dielectric dispersion but its influence is small. The magnitudes of the contributions of these two polarisation mechanisms to the total dielectric dispersion magnitude are primarily determined by the total specific surface area. The model is successfully applied for dielectric spectrum analyses of saturated Ca-bentonite, Na-bentonite and kaolinite.

Keywords:

• dielectric dispersion
• specific surface area
• electrical conductivity
• real permittivity