A crushed-rock embankment (CRE) with a high porous crushed-rock layer (CRL) can effectively cool the underlying permafrost through natural ventilation within the layer. However, in addition to the ambient conditions, the ventilation efficiency of the CRL and its cooling effect are significantly affected by the pavement width. In this study, the local wind flow around an embankment section was first analyzed based on field monitoring data. Then, considering climate warming, a 2-D coupled model of heat and mass transfer was established to investigate the wind characteristics and the cooling effects of the CRE with different pavement widths. The results showed that the pavement width exerted considerable impacts on the wind characteristics and cooling effects of the CRE. These impacts were evaluated via variations in the wind speed, the permafrost table, and the soil temperatures. An increase in pavement width can lower the wind speed within the CRL, which is adverse to the long-term thermal regimes of the embankment and the underlying permafrost. In addition, due to differential wind flows around the embankments, an asymmetric distribution of the soil temperatures beneath the windward and leeward sides of the embankments existed. Overall, it is hoped that the results of this study can provide informative references for the Qinghai–Tibet expressway that is constructed in permafrost regions.
1 January 2021 in Advances in Materials Science and Engineering
In the context of climate warming and the frequent wind‐sand hazards in the Qinghai‐Tibet Engineering Corridor (QTEC), the construction of the embankment will affect the thermal regime of permafrost underground. The influence of embankment construction on the variation of the permafrost table beneath it is different, especially for the regime with different mean annual ground temperatures (MAGTs). In this study, the effects of the unilateral sand particles deposition on the spatial distribution and temporal evolution pattern of temperature beneath the embankment are investigated through the numerical simulations, in which the heat transfer is considered. The model is validated by the field observed data of soil temperatures around an experimental zone built at the sand hazard area in Honglianghe, the interior of Qinghai‐Tibet Plateau (QTP). The simulated results indicate that the temperature field beneath the embankment is asymmetrically distributed under the condition of unilateral sand particles deposition. This asymmetry gradually weakened with the increase of operation time and the gradual adjustment of the permafrost temperature field. By comparing the permafrost table beneath the natural surface, the sand deposition center, and the middle of the embankment center, it could be found that the unilateral sand particles deposition has less effect on the degradation of the permafrost table in the center of the embankment. However, for the center of the sand deposition, the change of the permafrost table is larger with the increase of time and the corresponding rate of permafrost table degradation is higher than that without sand particles deposition, especially for the high‐temperature permafrost. In addition, with different sand thickness and width conditions, the effect of “narrow‐thick” form sand particles deposition on the temperature field beneath embankment is greater than that of “wide‐thin” form sand deposition. Hence, in order to reduce its impact on the long‐term thermal condition beneath the embankment, it is necessary to clean the thicker deposition sand particles at the toe of the embankment.