COUPLED MEASUREMENTS OF WATER CONTENT AND ELECTRICAL CONDUCTIVITY IN DIELECTRICALLY LOSSY CLAY SLURRY USING A COATED TDR PROBE

概要

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Although time domain reflectometry (TDR) has been widely accepted as a non-destructive in-situ method with high reliability, the effective use of TDR for water content (w) and electrical conductivity (EC) measurements in clay slurry has not been established. We developed a Teflon-coated (TC) probe with a 0.05-mm thick fluorocarbon resin coating, and conducted a calibration experiment for kaolinite slurry to indicate its applicability to the measurements. The TC probe could estimate w from the observed effective dielectric constant (ε_<eff>) in the range of w≥47% with a ±6% error range. The ε_<eff> includes dielectric constant of two components: material under test (ε_m) and coating material (ε_<tef>). The relationship between ε_<eff> and w for this particular probe design cannot be directly applied to other coated probes because each probe has its own specific dielectric characteristic. We defined a function expressing the characteristic, that is ε_<eff> vs. ε_m, according to the testing in various fluid media. By applying the function, the observed data sets of ε_<eff> were transformed for a soil specific value (ε_m). Owing to the sufficient agreement of the ε_m values with those for the uncoated probe, we obtained the data sets of ε_m vs. w and its empirical expression for kaolinite slurry.