Temperature Effects on the Unsaturated Hydraulic Properties of Two Fine-Grained Soils and Their Influence on Moisture Movement under an Airfield Test Facility

The influence of temperature on soil engineering properties is a major concern in the design of engineering systems such as radioactive waste disposal barriers, ground source heat pump systems and pavement structures. In particular, moisture redistribution under pavement systems might lead to changes in unbound material stiffness that will affect pavement performance. Accurate measurement of thermal effects on unsaturated soil hydraulic properties may lead to reduction in design and construction costs. This paper presents preliminary results of an experimental study aimed at determining the effect of temperature on the soil water characteristic curve (SWCC) and the unsaturated hydraulic conductivity function (k_unsat). Pressure plate devices with volume change control were used to determine the SWCC and the instantaneous profile method was used to measure k_unsat. These properties were obtained for two fine-grained materials subjected to controlled temperatures of 5°C, 25°C and 40°C. The results were used to perform a sensitivity analysis of the effect of temperature changes on the prediction of moisture movement under a covered area. The findings were compared to field measured water content data obtained on the subgrade of FAA William Hughes test facility located in Atlantic City. Results indicated that temperature affected the unsaturated hydraulic properties of the two fine-grained materials used in the study. For the DuPont soil, the water retention at 5°C was higher than that for higher temperatures for suction levels lower than about 10,000 kPa; while the k_unsat functions were not statistically different. The County soil holds around 10% more moisture at 5°C than at 40°C for suction levels higher than about 1,000 kPa and the k_unsat function at 40°C was slightly higher than the function at 5°C. The finding from sensitivity analysis showed that the most accurate modeling was the modeling with unsaturated material properties at 40°C and the difference in unsaturated hydraulic properties did lead to some variations in modeling results.