Sonde électromagnétique pour la mesure de teneur en eau des matériaux poreux. Application aux argilites : caractérisation et modélisation

This paper focuses on the relation between electromagnetic properties of clayrock and its water content, in view of radioactive waste repository monitoring. Final aim is to improve off-the-shelf Time Domain Relfectometry sensing lines, which is basically sensitive to electromagnetic properties of the host material, clayrock in our case. Such parameters are poorly known. In a first time, we developed a new laboratory dielectric measurement device, consisting of a coaxial transmission line, enabling characterization of intact clayrock permittivity over the 50 MHz - 1 GHz frequency range. The study has shown a large variation of complex permittivity with (i) water content, the parameter of interest and (ii) frequency, which could be accurately fitted by a Cole - Cole model. In a second time, we proposed an analytical modeling of the TDR probe using these results as input electromagnetic parameter. Finally, some synthetic data were obtained, they was used to perform an inversion process: which consists to reach accurate estimation of the electromagnetic parameters starting from synthetic measurements. This stage has been made through both use of the analytical and Cole - Cole modeling in the same approach: the five parameters of the Cole-Cole model are least mean square estimated from a frequency sweep containing at least five frequencies.