The measurement of unfrozen water content by time domain reflectometry: results from laboratory tests

A new technique for determining the volumetric unfrozen water content of frozen soils is reported, which uses time domain reflectometry (TDR) to measure the dielectric property. Using precise temperature control, the technique, which was developed previously by others for unfrozen soils, has been successfully applied to the measurement of unfrozen water contents of frozen soils. Curves of the dielectric property versus temperature show a close similarity to unfrozen water content curves, for a variety of soils. Results from experiments on ice–water mixtures and from combined TDR–dilatometry experiments on frozen soils suggest that an empirical relationship obtained by Topp, Davis, and Annan may be applicable to frozen media as well as unfrozen soils. Using this relationship, dielectric values were converted to unfrozen water content values, and the results agreed very closely with published data for similar soils, determined by other methods. For silt loams, agreement is typically within ± 1½% in volumetric water content, and for clays ± 3 %. Some of this difference is undoubtedly due to soil sample variations.