Apparatus for Coupled Effects of Suction, Temperature, and Stress on Thermal Conductivity of Unsaturated Sand

A suction-controlled thermo-mechanical apparatus was developed to measure thermal conductivity of unsaturated sand at different temperatures (5 degrees C to 75 degrees C) and isotropic net normal stresses (35 to 400 kPa). Coupled effects of temperature and stress level on thermal conductivity of unsaturated sand are investigated. Increases in confining stress cause an increase in thermal conductivity of the sand and are hysteretic with loading direction. Thermal conductivity increases appreciably as stress and temperature increase at intermediate degrees of saturation (S similar to 0.3 to 0.75). Maximum thermal conductivity occurs at 75.5 degrees C and 400 kPa when S= 0.54 where the value of thermal conductivity is about twice that at 5 degrees C and 35 kPa. The results indicate that the apparatus has the capability to effectively measure thermal response of near-surface sand under ranges of naturally occurring changes in temperature, stress, and moisture content.