Evaluation of TDR-Measured Water Content for Dry-Out Curves of Sand Using a Modified Tempe Cell Test

Modified tempe cells equipped with time-domain reflectometry (TDR) sensors can measure dry-out curves for sands over the complete range of saturation. The water content measured from TDR sensors is estimated from directly measured dielectric constant and electrical conductivity using empirical calibration relationships. However, the commonly used calibration equations were developed from test data in conditions different from the tempe cell test. In this study, a tempe cell with a self-fabricated TDR sensor was used to evaluate the TDR-measured water content estimated from Topp's equation and one-step method. The tempe cell was placed on two digital scales to record mass change and, thus, the water content change during the test. ASTM fine-graded sand of two different densities was tested for dry-out curves of dielectric constant and electrical conductivity. The results show that both empirical relationships can not perform satisfactorily for both tests over the complete range of saturation, and a new calibration relationship is needed to improve water content measurement from TDR sensors for tempe cell test.