Hydrothermal accumulation under asphalt pavement in cold regions

Water and heat changes are the main problems that plague the stability and service performance of roadbeds in cold regions. Though hydrothermal transfer and accumulation directly affect roadbed properties, these processes remain poorly understood as monitoring data are often collected over short time periods and large spacing in depth. This research compares water and temperature data collected from 2012 to 2015 to elucidate the physical mechanisms of hydrothermal accumulation under both asphalt pavement and original pavement. These thermal and physical mechanisms include differences in the freezing process (FP) and the thawing process (TP), water transport, condensation, and hydrothermal accumulation. For instance, when compared to the underlying layer, the thawing of the surface layer of asphalt pavement was delayed by 35 days because of differences in hydrothermal properties. During TP, liquid water content changes from 3.31%-13.2% to 15%-37.67%, and the unfrozen water content of the soil layers under the asphalt pavement was approximately 6.85%-12.34% higher than that of the soil layers under the original pavement. A layer with high water content and heat formed under the surface layer of asphalt pavement and provided the appropriate conditions for vapor transport and condensation. Soil layers thawed early in the preceding year, and this hydrothermal accumulation occurred on an annual basis. The annual minimum monthly average temperature was thus found to be increasing at the rate of 0.34 degrees C/y. As water content also accounts for heat accumulation and was found to be more sensitive to change than temperature, the results of this study can provide theoretical and technical data useful for highway construction and design in permafrost regions.