The influence of pavement type on the thermal stability of block-stone embankments in the warm permafrost region

Based on long-term, continuously monitored data of an expressway, this paper analyzes the influence of pavement types on thermal stability of block-stone embankments with variations of temperature, heat flux, heat budget change, freeze-thaw cycles, permafrost table, and thawing plate area. Results show that closer to the ground, the annual average temperature of the block-stone embankment with asphalt concrete is 0.04–1.99 °C higher than that of cement concrete pavement. Due to the distinct endothermic characteristics of the pavement materials, a block-stone layer with asphalt concrete pavement exhibits a higher temperature and heat budget than cement concrete pavement, causing varied rates of permafrost table's downward movement, in other words, different growth rates of active layer thickness or thawing plate area. Moreover, the freezing and melting processes of block-stone embankment with different pavements have inconsistent onset times, durations, and offset times. Compared with ordinary embankment, the existence of block-stone layer can greatly raise or slow down the declining of permafrost table, and light-colored cement concrete pavement is more conducive to the thermal stability of embankment. The central active layer and asymmetric thawing plate of the block-stone embankment with cement concrete pavement grows more slowly than that of the asphalt concrete pavement, but this growth has not been eliminated. Rather, it continues at 17.75 cm/a and 8.55 m2/a, compared to 26.75 cm/a and 12.41 m2/a for asphalt concrete pavement. Thus, the block-stone embankments, whether constructed with asphalt concrete pavement or cement concrete pavement, did not entirely ensure the thermal stability. Some reinforcement measures or a composite embankment structure should be adopted to improve the thermal stability of expressway embankments in the warm permafrost region.