Experimental Study on the Influence of Increased Summer Rainfall on the Hydrothermal Process within the Highway Embankments in Permafrost Regions

The Qinghai–Tibet Plateau shows an obvious trend of warming and humidification, and the increased rainfall is mainly concentrated in the summer. There have been few reports on the effects of summer rainfall variations on the hydrothermal states of embankments in permafrost regions. Therefore, based on an indoor embankment-scale model experiment, the effects of increased summer rainfall on the surface energy, temperature, and water fields of highway embankments in permafrost regions were investigated. The results showed that increased summer rainfall led to an increase in surface net radiation. However, the increase in summer rainfall led to a decreasing trend in the pavement temperature and shallow heat flux of the embankment, indicating that increased summer rainfall could effectively inhibit the increase in pavement temperature. Simultaneously, the increased summer rainfall also increased the shallow water content at different locations of the embankment in the following order: natural site > shoulder > slope > pavement. The maximum increase in water content at the natural site was 6.7% after a twofold increase in the summer rainfall. In addition, the temperature within the embankment exhibited a decreasing trend with an increase in summer rainfall. Compared to other parts of the embankment, although the increased summer rainfall led to a relatively small increase in water content in the lower part of the pavement, the asphalt concrete pavement had a higher temperature. Therefore, when rainfall acts as an energy cold pulse on the pavement, the temperature of the lower part of the pavement decreases more significantly than that of the other parts of the embankment. The increased summer rainfall affected the cooling range of different parts of the embankment in the following order: pavement > natural site > shoulder > slope. The increase in summer rainfall had a hysteresis effect that affected the water and temperature fields within the embankment in autumn.