A Simple Approach to Monitor Soil Moisture Dynamic in Vapour Equilibrium Cell

Abstract

Vapour equilibrium technique (VET) is usually used to determine the water retention curve of soils. It is a suction-controlled technique where the soil specimen is allowed to reach the suction equilibrium in a desiccator where the relative humidity is controlled by a chemical solution. The suction equilibrium condition is deemed to have been reached when its soil moisture content does not change with time. Therefore, VET requires continuous monitoring for moisture content of the testing soil without disturbing the water vapour exchange process. The aim of this study is to present the electrical resistivity (ER) method that can be used to measure the moisture content of the specimen in VET without disturbance. The ER method is able to monitor the changes of soil moisture with time, and to successfully determine the time at which the soil moisture reaches the equilibrium state. The total suction equilibrium condition was validated independently with the suction measurements using a WP4C water potential meter. The results show good agreement between the total suction equilibrium condition determined by the proposed ER method and the WP4C measurements.