Determination of Moisture Diffusion Coefficient at Low Suctions Using Thermal Conductivity Sensors

Abstract

The main aim of this research is to determine the drying and wetting moisture coefficients in unsaturated soils at low suctions using thermal conductivity sensors. The performance of a geotechnical structure can be strongly influenced by the moisture conditions in the soil. The movement of water in unsaturated soils can be described by determining the diffusion coefficient of the soil. The diffusion coefficient can be determined by the analysis of suction changes with time in the soil. The suction measurements can be made using different techniques. In this research study, the suction measurements were conducted using thermal conductivity sensors and thermocouple psychrometers. Mitchell (1979) proposed an approach to determine the diffusion coefficient of the soil. Mitchell's proposal of one dimensional analysis using rate of moisture flow through soil provides a simple, economical and reliable framework for determining the drying and wetting diffusion coefficients in a geotechnical laboratory. The calibration and the operation of the thermal conductivity sensors and the thermocouple psychrometers are explained in detail in this research study. Using the two devices, the drying and wetting diffusion coefficients were determined and the comparison study has been conducted between the two approaches. With the reliable estimate of the diffusion coefficient, the moisture movement can be predicted in a soil mass