A new experimental setup for the determination of drying soil–water characteristic curve and coefficient of permeability using the continuous evaporation method and osmotic tensiometers

Soil-water characteristic curve (SWCC) and coefficient of permeability (k) are amongst the most crucial soil properties in unsaturated soil mechanics for soil moisture conservation. The direct measurement and prediction of such properties are important to engineering applications, but they are complicated. This study developed a new experimental setup (the OT permeameter) using osmotic tensiometers (OTs) and the continuous evaporation method. The proposed OT permeameter could directly measure SWCC and k up to 1000 kPa suction within one to two weeks. Moreover, the proposed setup is fully automated and data processing was minimal. In addition, a new general equation has been developed to predict and best fit the unsaturated k measurement. The proposed equation uses a minimal number of parameters that carry physical meaning and provides an intuitive and easy way to predict and best-fit k measurement. The accuracy and robustness of both the proposed OT permeameter and prediction equation were evaluated using published data and experimental data from this study.