Measuring Thermal Conductivity of Unsaturated Sand under Different Temperatures and Stress Levels Using a Suction-Controlled Thermo-Mechanical Method

摘要

Soil thermal conductivity is a function of pore water saturation, temperature, and stress level. A suction-controlled thermo-mechanical (SCTM) method has been developed to measure thermal conductivity of unsaturated soils at different temperatures (5.5°C to 75.5°C), isotropic normal stresses (35 kPa to 400 kPa), and wetting conditions. The apparatus consists of three main testing systems, including temperature-control, pressure-control, and sensor and data acquisition systems. This method permits quantification of soil thermal conductivity under the influence of stress level and temperature (i.e. construction and environmental conditions). A poorly-graded sand is used to investigate the effects of temperature and stress level on thermal conductivity of unsaturated sands. The thermal conductivity increases appreciably as stress and temperature increases at intermediate saturations (S~0.3 to 0.75). Maximum thermal conductivity occurs at 75.5°C and 400 kPa when S=0.54, where the value of thermal conductivity is about twice that at 5.5°C and 35 kPa. Hysteresis in thermal conductivity with respect to wetting-drying and loading-unloading was also observed.