TDR measurements and simulations in high lossy bentonite materials

Abstract

The measurement of moisture distribution in bentonite barriers in salt mines is absolutely essential in order to monitor fluid ingress and record data for long-term security analyses. The aim of this investigation was to apply a TDR measurement system using flexible flat band cable sensors in the harsh environment of a salt mine. The measurement of the dielectric material properties of sodium-bentonite sand mixtures moistened with tap water and concentrated NaCl solutions was the basis for the development of the measurement system. If the sensor was surrounded by a material mixture with strong losses it was found that both the pulse travel time and the complex wave impedance depended on the real part of permittivity and the loss factor. The step responses of the TDR sensors recorded in experiments and in electromagnetic field simulations were used to show the pulse travel time versus moisture content using tap water and concentrated NaCl solution.