Determination of gravimetric water content of porous media based on time domain reflectometry

Abstract

Time domain reflectometry (TDR) has become the most commonly utilized method for calculating the water content of porous media due to its advantages of rapidity, safety, and non-destructiveness. Nonetheless, the dielectric constant of porous media with the same gravimetric water content varies considerably due to their different porosity, so the TDR method cannot be directly used to measure the gravimetric water content. Although the traditional thermo-gravimetric method has high measurement accuracy, sampling is cumbersome and measurement is time-consuming. Therefore, it is essential to develop an accurate and effective method to calculate the gravimetric water content of porous media. Based on the dielectric measurement results, a third-order polynomial fitting equation describing the relationship between volume water content and apparent dielectric constant of quartz sand is obtained by employing the least square method. Then a TDR method, which can eliminate the influence of gap through secondary compression, is proposed to calculate the gravimetric water content of porous media. The comparative experiment with the thermo-gravimetric method demonstrates that this method has high measurement accuracy, and provides an approach for predicting the gravimetric water content, bulk density, and porosity of porous media, which can be used in field and laboratory applications.