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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]

Reservoirs lined with concrete slabs are very common in the northern cold regions of China. Failures such as the rotation and the dislocation of concrete lining slabs are usually found in those ice-covered reservoirs each year in winter. In this study, the interaction processes between water, ice, and lining when water level changes in ice-covered reservoirs are evaluated based on the theory of beams on elastic foundation. In general, ice cover can generate a rotation effect (bending moment) on concrete lining slabs when water level changes in ice-covered reservoirs. Under such conditions, the bending moment at the ice edge increases with the increase of the ice cover width and thickness. Once the tensile stress at the interface between concrete slab and its base layer exceeds the tensile strength of the interface itself, the concrete slab separates from its base layer and the support condition of the ice cover changes from fix-supported to hinge-supported. Then the rotational failure of the concrete slab may occur due to the rotation effect acted by ice cover. The calculated rotation angle of the concrete lining slab is in agreement with the angle observed at a reservoir in northwest China. In addition, prevention measures such as concrete lining slabs with hydrophobic coating on the surface, concrete lining slabs with dark surface, anchoring concrete slabs to reservoir slope, and integral large-scale lining modules are proposed to mitigate such rotational lining failures in ice-covered reservoirs. The results can help to improve the performance and service life of reservoirs in cold environments. [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]

Aeolian sand is an important factor, which can affect the permafrost environment and infrastructures on the Tibetan Plateau. The thermal conductivity of aeolian sand is an important parameter for analyzing the thermal regime of the ground in cold regions. This paper presents the test results of the thermal conductivity of aeolian sand sampled from the Tibetan Plateau in unfrozen state with temperature 20 °C and in frozen state. The aeolian sand samples were measured with water content ranging from 3% to 15% and dry density ranging from 1400 to 1650 kg·m − 3 . The results show that the thermal conductivity increased with water content and dry density. Some methods that have been developed for calculating the thermal conductivity of soils are applied to predict the thermal conductivity of aeolian sand. However, these methods all have significant deviations. From the test data, a simple model is proposed as a function of the degree of saturation and the volume fraction of each phase to calculate the thermal conductivity of aeolian sand. The calculated results obtained from the proposed model agree well with the test data. The mean deviations are 2.15% and 4.28% for the unfrozen and frozen states, respectively. [ABSTRACT FROM AUTHOR]

Canals play an extremely important role in irrigation and conveyance of water. In cold regions, composite geomembranes are usually utilized as cushions in canals to mitigate frost heaving and seepage damages. In this study, a mechanical model for trapezoidal canals lined with double-layer geomembranes was developed to clarify the mechanisms of action of double-layer geomembranes for trapezoidal canals during freezing-thawing processes. The external and internal forces of a traditional concrete canal and two composite canals (i.e. a double-layer geomembranes canal and an anti-slip canal) were calculated using the mechanical model, and the tangential and internal forces on the slabs of three canals were compared, and analyzed. Furthermore, The reasons for the cracks in canal slabs and the sliding of slope slabs were explained using the freeze-thaw mechanical model. The results show that the tangential and internal forces in the double-layer geomembranes canal are minimal during the freezing period, while the tangential and internal forces in the traditional concrete canal are maximum. Conversely, during the thawing period, the anti-slip force of the anti-slip canal is larger than those of the double-layer geomembranes canal and traditional concrete canal subsequently. The mechanical model developed in this study will benefit the design of canals in cold regions. • The frost-heaving damage and collapse mechanisms of the slope slabs of canals in cold regions were explored. • A new composite canal in trapezoidal is proposed, including the double-layer geomembranes canal and the anti-slip canal. • A mechanical model was established to deal with the frost heaving and slab-slipping of a composite canal. • The causes of crack formation in canal slabs and the sliding of slope slabs were explained using the mechanical model. • Judgment criteria for the frost-heaving damage of concrete slabs and the collapse of slope slabs were proposed. [ABSTRACT FROM AUTHOR]

Aeolian sand is sometimes used as geomaterial in cold regions of China. This paper tries to investigate the unfrozen water, matric suction of aeolian sand, which is related to its thermal and mechanical properties. The pF-meter matric suction sensor coupled with 5TM moisture content sensor that can operate in the subfreezing environment was used to measure the moisture content and matric suction of aeolian sand under different conditions. Combined with thermal resistor temperature probe, the relationship between unfrozen water and temperature is analyzed. The results indicate a significant phenomenon of latent heat absorption and release at freezing and thawing points. In addition, the phenomenon of the supercooling was observed with a value of −1.96 °C during stepwise temperature change. Most water in the sand freezes at freezing point 0 °C under rapid and stepwise temperature change. There is approximately 3% of unfrozen water content retained when the sand temperature drops to −15 °C. The soil matric suction increases very slowly at the stable freezing stage. These results provide the theoretical support for future research on the moisture migration mechanism and engineering application of aeolian sand in cold regions. • Matric suction and unfrozen water of aeolian sand were studied. • Most water in aeolian sand freezes at freezing point 0 °C. • Significant supercooling effect was observed under the rapid freezing process. • Matric suction shows dramatic change at freezing and thawing points. [ABSTRACT FROM AUTHOR]