@article{WagnerBoreRobinetetal.,
  author    = {Wagner, Norman and Bore, Thierry and Robinet, Jean-Charles and Coelho, Daniel and Taillade, Frederic and Delepine-Lesoille, Sylvie},
  title     = {Dielectric relaxation behavior of Callovo-Oxfordian clay rock: A hydraulic-mechanical-electromagnetic coupling approach},
  series = {Journal of Geophysical Research: Solid Earth},
  journal   = {Journal of Geophysical Research: Solid Earth},
  doi       = {10.1002/jgrb.50343},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170428-31681},
  pages     = {4729 -- 4744},
  abstract  = {Water content is a key parameter to monitor in nuclear waste repositories such as the planed underground repository in Bure, France, in the Callovo-Oxfordian (COx) clay formation. High-frequency electromagnetic (HF-EM) measurement techniques, i.e., time or frequency domain reflectometry, offer useful tools for quantitative estimation of water content in porous media. However, despite the efficiency of HF-EM methods, the relationship between water content and dielectric material properties needs to be characterized. Moreover, the high amount of swelling clay in the COx clay leads to dielectric relaxation effects which induce strong dispersion coupled with high absorption of EM waves. Against this background, the dielectric relaxation behavior of the clay rock was studied at frequencies from 1 MHz to 10 GHz with network analyzer technique in combination with coaxial transmission line cells. For this purpose, undisturbed and disturbed clay rock samples were conditioned to achieve a water saturation range from 0.16 to nearly saturation. The relaxation behavior was quantified based on a generalized fractional relaxation model under consideration of an apparent direct current conductivity assuming three relaxation processes: a high-frequency water process and two interface processes which are related to interactions between the aqueous pore solution and mineral particles (adsorbed/hydrated water relaxation, counter ion relaxation and Maxwell-Wagner effects). The frequency-dependent HF-EM properties were further modeled based on a novel hydraulic-mechanical-electromagnetic coupling approach developed for soils. The results show the potential of HF-EM techniques for quantitative monitoring of the hydraulic state in underground repositories in clay formations.},
  subject      = {Lehm},
  language  = {en}
}
@article{BoreWagnerLesoilleetal.,
  author    = {Bore, Thierry and Wagner, Norman and Lesoille, Sylvie Delepine and Taillade, Frederic and Six, Gonzague and Daout, Franck and Placko, Dominique},
  title     = {Error analysis of clay-rock water content estimation with broadband high-frequency electromagnetic sensors—air gap effect},
  series = {Sensors},
  journal   = {Sensors},
  doi       = {10.3390/s16040554},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170418-31248},
  pages     = {1 -- 14},
  abstract  = {Broadband electromagnetic frequency or time domain sensor techniques present high potential for quantitative water content monitoring in porous media. Prior to in situ application, the impact of the relationship between the broadband electromagnetic properties of the porous material (clay-rock) and the water content on the frequency or time domain sensor response is required. For this purpose, dielectric properties of intact clay rock samples experimental determined in the frequency range from 1 MHz to 10 GHz were used as input data in 3-D numerical frequency domain finite element field calculations to model the one port broadband frequency or time domain transfer function for a three rods based sensor embedded in the clay-rock. The sensor response in terms of the reflection factor was analyzed in time domain with classical travel time analysis in combination with an empirical model according to Topp equation, as well as the theoretical Lichtenecker and Rother model (LRM) to estimate the volumetric water content. The mixture equation considering the appropriate porosity of the investigated material provide a practical and efficient approach for water content estimation based on classical travel time analysis with the onset-method. The inflection method is not recommended for water content estimation in electrical dispersive and absorptive material. Moreover, the results clearly indicate that effects due to coupling of the sensor to the material cannot be neglected. Coupling problems caused by an air gap lead to dramatic effects on water content estimation, even for submillimeter gaps. Thus, the quantitative determination of the in situ water content requires careful sensor installation in order to reach a perfect probe clay rock coupling.},
  subject      = {Wassergehalt},
  language  = {en}
}