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• A numerical model for duct-ventilated embankments driven by temperature difference is developed. • The effects of duct structure on its cooling performance are analyzed. • Ducts can greatly reduce the effect of snow thermal insulation on the cooling performance of a crushed-rock layer. In pan-Arctic permafrost regions, longitudinal ventilation ducts are often installed in embankments to cool the underlying permafrost and thereby ensure road stability. However, the current design methods for embankments with longitudinal ventilation ducts (ED) normally simplify the conjugate heat transfer process between the duct wall and air in the duct. In this study, based on the chimney effect and the theory of fluid flow and heat transfer, we propose an improved numerical method for evaluating the cooling performance of the ED. Using this method, we conduct an assessment of the influences of duct configuration on the efficiency of ventilation duct cooling in winter. The results indicate that increasing the diameter of the duct and the height of the duct outlet can effectively improve the radial cooling range of the ventilation duct. However, the cooling performance of the ventilation duct becomes worse when the length of the duct is increased. To address the limited cooling performance of the ED, we design a crushed-rock interlayer embankment installed with longitudinal ventilation ducts (CED). It is found that the CED is more effective at maintaining the long-term thermal stability of the road in a typical pan-Arctic permafrost region when compared to the ED and the crushed-rock interlayer embankment. Furthermore, a cost analysis of the four different embankment designs reveals that the CED is a financially viable option for embankment construction in permafrost regions. [ABSTRACT FROM AUTHOR]

Field surveys focusing on the crack damages in paved embankment of the Qinghai-Tibet Highway were carried out at 17 sections. Some severe cracks were found in the road embankment constructed on the permafrost ground affecting the smooth operation of the highway. Road orientation, thaw settlement, crack width and length were measured at the typical crack sections. Besides, embankment slope surface temperatures were monitored at two road sections, and the temperature difference as high as 10 °C was observed in the cold winter time. Three scenarios were employed in the numerical modeling to assess the impact of climate warming, embankment slope surface temperature, and embankment itself on the underlying permafrost evolution process. Thereafter, a method was introduced to obtain the thaw settlement of the road embankment according to the simulated thawing front depth. The results indicate that the thaw settlement difference across the road embankment width is the main cause results in the crack damages. This uneven thaw settlement can be amplified due to the presence of the original ground slope. Additionally, climate warming intensified the underlying permafrost degradation and accelerated the thawing front penetrating into the subgrade permafrost. In summary, road orientation, original ground slope, climate warming, and underlying permafrost type are major but not the sole causes for the crack damages of the paved embankment in the Tibetan permafrost environments. It is recommended that steep slope and ice-rich permafrost ground should be avoided in the early design of the highway embankment. • Field surveys focusing on the crack damages of the Qinghai-Tibet Highway were carried out. • A 10 °C temperature difference between the embankment slopes was observed in the winter time. • Three scenarios were designed to assess the permafrost evolution underneath the road embankment. • A method was introduced to obtain the thaw settlement of the road embankment. [ABSTRACT FROM AUTHOR]

Abstract A laboratory experiment was performed to investigate the thermal effect of rainwater infiltration into a one-half scale replicated road embankment built on artificial permafrost subjected to four 15-day freeze-thaw cycles and several rainfall events during thaw periods in a cold environmental chamber. The ground temperature, water content, and heat flux were monitored at different depths at three key locations in the road subbase. Based on the experimental results, the rainwater infiltration has a significant heating effect on the shallow subbase layers down to a depth no more than 30 cm. The heat transfer in the road embankment is directly correlated to the amount of rainfall. Moreover, rainwater infiltration has different heating effects according to the locations in the road subbase. The most important heating effect is underneath the embankment slope, the second one in the embankment shoulder, and the third one underneath the concrete pavement. The changes in temperature, moisture, and heat flux in the road subbase due to the rainwater infiltration are delayed and attenuated with the increase in depth. Even if the road subbase was frozen at these depths, moisture changes in the road subbase as deep as 60 cm were observed. The volumetric unfrozen water content in the road subbase and subgrade depends on the ground temperature and exhibits hysteretic behavior during cooling and warming cycles. The observed variations in heat flux are related to the changes in temperature and moisture in the road subbase. For road embankments located in permafrost environments, the thermal effect of rainwater infiltration into the road subbase may lead to permafrost degradation at depth. Highlights • The rainwater has a significant heating effect on the shallow road subbase. • The heat transfer in the road embankment is directly correlated to the rainwater amount • Rainwater infiltration has different heating effects according to the locations in the road subbase. [ABSTRACT FROM AUTHOR]

Abstract The crushed-rock interlayer (CRI) has been used to cool the railway embankment subbase and subgrade of the Qinghai-Tibet Railway (QTR) in permafrost regions. However, in addition to the climate change, aeolian sand clogging has been affecting this mitigation techniques aimed to increase heat extraction and reduce subsurface heat penetration by air convection through the voids of the CRI. Its long-term performance is evaluated herein using a numerical modelling. Simulation results demonstrate an unclogged CRI can mitigate permafrost warming for the first 20 years with a simulated increase in average air temperature by 0.052 °C a−1. But after sand clogging, including both filling of voids in the CRI and covering of embankment slopes, its cooling performance is weakened. In such conditions, permafrost table is increasing and the permafrost is warming up under different mean annual air temperature (MAAT) of −4.5, −5.5, and −6.5 °C. The water content of the aeolian sand can also affect the cooling effectiveness of CRI. A 1 m-thick dry sand cover can induce an increase in ground temperature. But wet sand layer can mitigate and delay the effect of climate change on the permafrost degradation. The sand-control measures and additional engineering techniques should be adopted to prevent the long-term thermal stability of the QTR in sandy permafrost zone of Qinghai-Tibet Plateau. Highlights • Crushed-rock interlayer can counteract impacts of climate warming on permafrost degradation. • Performance of crushed-rock interlayer embankment declines after aeolian sand clogging. • Warm ice-rich permafrost is sensitive to climate change and aeolian sand clogging scenarios. [ABSTRACT FROM AUTHOR]