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The thermal state of permafrost in the present and future is fundamental to ecosystem evolution, hydrological processes, carbon release and infrastructure integrity in cold regions. In 2011, we initiated a permafrost monitoring network along the China–Russia crude oil pipeline (CRCOP) route at the eastern flank of the northern Da Xing'anling Mountains in Northeast China. We compiled an integrated dataset of the ground thermal state along the CRCOP route consisting of meteorological data near the southern limit of latitudinal permafrost, ground temperature (GT) data in 20 boreholes with depths of 10.0–60.6 m, soil volumetric liquid water contents (VWCs) and 2D electrical resistivity tomography (ERT) data at different sites. Results demonstrate a permafrost warming during 2011–2020 in the vicinity of the southern limit of latitudinal permafrost, as manifested by rising GTs at almost all depths in response to climate warming. Local thermal disturbances triggered by the construction and operation of CRCOPs have resulted in significant permafrost warming and subsequent thawing on the right-of-way (ROW) of the pipelines. This permafrost thaw will persist, but it can be alleviated by adopting mitigative measures, such as an insulation layer and thermosyphons. The in situ observational dataset is of great value for assessing the variability of permafrost under the linear disturbances of the CRCOPs and related environmental effects, for understanding hydro–thermal–mechanical interactions between the buried pipelines and permafrost foundation soils, and for evaluating the operational and structural integrity of the pipeline systems in the future. The dataset is available at the National Tibetan Plateau/Third Pole Environment Data Center (10.11888/Cryos.tpdc.272357; Li, 2022). [ABSTRACT FROM AUTHOR]

Thermal infrared remote sensing technology based on unmanned aerial vehicle (UAV) was applied to estimate the spatial distribution of ground surface temperatures on permafrost slopes and evaluate the thermal influence of nearby engineering infrastructure. This paper presents a method that uses a miniature UAV with a thermal infrared sensor to collect thermal images with high temporal-spatial resolution. Moreover, spatial analysis is used to effectively evaluate the relationship between engineering infrastructure and permafrost slopes in the Qinghai-Tibet Engineering Corridor (QTEC), China. To test the method, aerial measurements were collected from 11:00 to 17:00 in July and August of 2017 at two permafrost slopes along the QTEC, where the Qinghai-Tibet Highway (QTH), Qinghai-Tibet Railway (QTR), and electric towers were built on permafrost slopes. The differences of ground surface temperature between the highway and the surrounding soil were largest at 11:00 and 17:00; the differences were smaller at noon to approximately 15:00 when the difference was minimal, and the differences began to increase after 15:00. The distances of the thermal influence of the highway, railway, and electric towers on the surrounding permafrost slopes are approximately 12-14, 8-10, and 2-4 m, respectively. The results indicate that the degree of influence of engineering structures on permafrost slopes is as follows: QTH > QTR > electric towers. This study is the first to use UAV-based thermal infrared remote sensing to evaluate the thermal dynamics of permafrost slopes along the QTEC. These results may provide new insights into the future design, construction, and maintenance of engineering structures on permafrost slopes. [ABSTRACT FROM AUTHOR]

The Qinghai-Tibet Engineering Corridor (QTEC) in China may reflect the changes in the alpine ecosystem of the Qinghai–Tibet Plateau (QTP) that are driven by global climate change combined with intensive human activities. We used the normalized difference vegetation index (NDVI) as an indicator of alpine vegetation activity and the permafrost active layer thickness (ALT) as an indicator of permafrost dynamics to understand the impacts of climate change, human activity, or their combination on the alpine ecosystem in the QTEC. Based on the types of frozen ground, we separated the QTEC into northern, permafrost, and southern zones. The surface air temperature increased by 0.28 °C per decade from 1982 to 2010, and the rising trend of air temperature was most prominent in the permafrost zone (P < 0.05); the total precipitation exhibited a significant increase of 15 mm per decade (P < 0.05). The level of human activity in the QTEC rose slowly before 2000 and rapidly after 2000. The NDVI trends over the QTEC increased over the past thirty years, but the NDVI declined in some areas from 2001 to 2010, especially in the southern QTEC. The permafrost in the QTEC continued to thaw, and the ALT increased. Our results indicated that the QTEC experienced a significant warming and wetting trend. The increased precipitation improved the alpine vegetation activity across much of the QTEC, and the increased air temperature accelerated the thawing of permafrost. However, the construction and operation of the Qinghai–Tibet Railway since 2001 and 2006 promoted an influx of residents and tourists, boosted the local economy, and resulted in the deterioration of the alpine vegetation, particularly in the southern QTEC. Moreover, our results suggested that improvement of alpine vegetation cannot necessarily prevent permafrost degradation caused by warming. [ABSTRACT FROM AUTHOR]

An R package was developed for computing permafrost indices (PIC v1.3) that integrates meteorological observations, gridded meteorological datasets, soil databases, and field measurements to compute the factors or indices of permafrost and seasonal frozen soil. At present, 16 temperature- and depth-related indices are integrated into the PIC v1.3 R package to estimate the possible trends of frozen soil in the Qinghai-Tibet Plateau (QTP). These indices include the mean annual air temperature (MAAT), mean annual ground surface temperature (MAGST), mean annual ground temperature (MAGT), seasonal thawing-freezing n factor (nt=nf), thawing-freezing degree-days for air and the ground surface (DDTa=DDTs=DDFa=DDFs), temperature at the top of the permafrost (TTOP), active layer thickness (ALT), and maximum seasonal freeze depth. PIC v1.3 supports two computational modes, namely the stations and regional calculations that enable statistical analysis and intuitive visualization of the time series and spatial simulations. Datasets of 52 weather stations and a central region of the QTP were prepared and simulated to evaluate the temporal-spatial trends of permafrost with the climate. More than 10 statistical methods and a sequential Mann-Kendall trend test were adopted to evaluate these indices in stations, and spatial methods were adopted to assess the spatial trends. Multiple visual methods were used to display the temporal and spatial variability of the stations and region. Simulation results show extensive permafrost degradation in the QTP, and the temporal-spatial trends of the permafrost conditions in the QTP are close to those of previous studies. The transparency and repeatability of the PIC v1.3 package and its data can be used and extended to assess the impact of climate change on permafrost. [ABSTRACT FROM AUTHOR]

Due to the vulnerability of permafrost environment to climate changes, permafrost in the Qinghai-Tibet Plateau (QTP) is experiencing thickening of the active layer and warming ground temperatures that together have a significant influence on the ground motion characteristics. A series of in situ wave velocity tests were carried out in permafrost regions along the Qinghai-Tibet Railway (QTR) and the characteristics of shear wave velocity of frozen soil were summarized. Then, the ground motion responses in permafrost regions were simulated, and the impact of permafrost change on the seismic site response was discussed. Moreover, the dynamic response of the traditional embankment at the Beiluhe site in permafrost regions was studied. The changes of ground motion parameters were significantly impacted and showed reproducible changes with different active layer thicknesses and permafrost thicknesses. The ground motion amplification coefficients increased with the increase of active layer thickness, and the amplification coefficients were greater in a warm season than that in a cold season. Furthermore, the active layer thickness had little influence on the characteristic site period, and the variation of the characteristic site period with the permafrost thickness showed the logarithmic variation characteristic. Compared with the soil profile away from the center of the railway subgrade, the acceleration under the embankment showed a significant increase due to the overlying subgrade embankment. The increase in amplitude was about 29%, which illustrated that the deformation of the soil under the embankment became greater and may be more prone to damage during the seismic loading. [ABSTRACT FROM AUTHOR]

Based on the monitoring data from 13 typical monitoring sites along the Qinghai-Tibet Highway, the degradation characteristics of the permafrost under asphalt pavement and natural ground surface were analyzed with considerations of climate warming and engineering disturbance. Results indicated that the mean annual thawing indexes (MATI) and mean annual freezing indexes (MAFI) of asphalt pavement ranged from 895 to 2,540 °C days and from 290 to 1,097 °C days, respectively, while the MATI and MAFI of natural ground ranged from 144 to 1,550 °C days and from 127 to 1,544 °C days, respectively. In warm seasons, average temperatures of asphalt pavement were 0.76-8.58 °C higher than that of natural ground, while in cold seasons, average temperatures of asphalt pavement were 0.22-4.19 °C lower than that of natural ground. Both natural permafrost table and artificial permafrost table were continuously declining through 1995-2011. Under the effect of climate warming, the active layer thickness (ALT) increased about 0.44 m, with an average increasing rate of 3.42 cm a in cold permafrost regions [the mean annual ground temperature lower than −1.0 °C (MAGT < −1.0 °C)], while in warm permafrost regions (MAGT > −1.0 °C), the ALT increased about 0.68 m, with an average increasing rate of 5.72 cm a. Under the effect of engineering disturbance, the ALT increased 1.38 m in cold permafrost regions, with an average increasing rate of 12.28 cm a, while in warm permafrost regions, the ALT increased 1.32 m, with an average increasing rate of 11.18 cm a. Meanwhile, changes in permafrost temperature under asphalt pavement were different from that under natural ground. The warming rate in permafrost under asphalt pavement at 6, 10 and 15 m depths was 0.024, 0.022 and 0.02 °C a, respectively, while the three values under natural ground were 0.016, 0.013 and 0.013 °C a. From these results above, it can be concluded that influences from climate warming on permafrost degradation in warm permafrost region were greater than that in cold permafrost region, and influences from engineering disturbance on permafrost degradation in warm permafrost region were less than that in cold permafrost region. [ABSTRACT FROM AUTHOR]

Abstract: Dynamic response characteristics and stability of embankment are of primary importance for railroad operation in permafrost regions. The strong motion tests are carried out on a traditional sand gravel embankment at the Beilu River segment along the Qinghai–Tibet Railroad, and the acceleration waveforms at the shoulder and the slope toe of the embankment, when passenger train and freight train pass, are collected through strong motion tests. There is an obvious attenuation effect during the waveform transfer process from the shoulder to slope toe, and the natural frequency of the embankment is between 30–40Hz. Based on the tests in situ, the nonlinear dynamic finite element analysis is applied for numerical simulations on dynamic response of the traditional sand gravel embankment to train load, and the influences of underlying active layer on the dynamic response of the embankment at different seasons are analyzed. The results show that the vibration attenuation of the train load is obvious at different seasons, which presents a linear decrease tendency in summertime, but a nonlinear decrease tendency in wintertime. Both of the two decrease tendencies mainly occur within the soil layer above the permafrost table, but the attenuation effect in summertime, when the active layer is thawed, is slightly greater than that in wintertime when the active layer is frozen. Soil deformation induced by train vibrations occurs mainly above the permafrost table in summertime, but in wintertime, it mainly occurs above the natural surface. Meanwhile, the amount of deformation at the same location in summertime is far more than that in wintertime. [Copyright &y& Elsevier]

The phylogenetic relationships of European and African Barbus and their West Asian relatives in Cyprininae remain largely unresolved. Consequently, little is known about the drivers of their evolution, including the possible association of uplifting of the Qinghai-Tibetan Plateau (QTP) with the early divergence of the subfamily. We use complete sequence data of the mitochondrial DNA gene encoding the protein cytochrome b ( Cytb) to hypothesize the phylogeny of 85 species belonging to 47 genera in the Cyprininae plus 6 species from the Leuciscinae. We employ 6 other species from Cypriniformes as outgroup taxa and estimate divergence times. Our results indicate that European Barbus sensu stricto lineage including Aulopyge shares a common ancestor with specialized and highly specialized schizothoracins and the genera Cyprinion and Scaphiodonichtys. The common ancestor appears to have originated in the Qinghai-Tibetan Plateau (QTP) region about 19.4-17.8 Ma. Barbus sensu stricto lineage appears to have originated about 16.6-15.5 Ma. Small to medium sized African Barbus sensu lato appear to have had an Oriental origin about 19.1-15.3 Ma and are closely related to Asian Puntius. West Asian Carasobarbus lineage including large African Barbus sensu lato might have originated about 9.94 Ma, also in Oriental Realm and has a close relationship to Asian Neolissochilus and Tor. The large-sized Barbus sensu lato appear to have diverged from Carasobarbus about 7.7 Ma. Finally, the Cyprininae appear to have radiated rapidly into nine lineages and many sublineages from about 27.8 to 17.8 Ma, close to the time of the second-stage tectonic movements of the QTP. Our analyses provide evidence that the uplifting of the QTP drove early diversification of the Cyprininae. Our extensive sampling of species involving all of the important areas results in clear evolutionary scenario for the Cyprininae. [ABSTRACT FROM AUTHOR]

The phylogenetic relationships of European and African Barbus and their West Asian relatives in Cyprininae remain largely unresolved. Consequently, little is known about the drivers of their evolution, including the possible association of uplifting of the Qinghai-Tibetan Plateau (QTP) with the early divergence of the subfamily. We use complete sequence data of the mitochondrial DNA gene encoding the protein cytochrome b ( Cytb) to hypothesize the phylogeny of 85 species belonging to 47 genera in the Cyprininae plus 6 species from the Leuciscinae. We employ 6 other species from Cypriniformes as outgroup taxa and estimate divergence times. Our results indicate that European Barbus sensu stricto lineage including Aulopyge shares a common ancestor with specialized and highly specialized schizothoracins and the genera Cyprinion and Scaphiodonichtys. The common ancestor appears to have originated in the Qinghai-Tibetan Plateau (QTP) region about 19.4–17.8 Ma. Barbus sensu stricto lineage appears to have originated about 16.6–15.5 Ma. Small to medium sized African Barbus sensu lato appear to have had an Oriental origin about 19.1–15.3 Ma and are closely related to Asian Puntius. West Asian Carasobarbus lineage including large African Barbus sensu lato might have originated about 9.94 Ma, also in Oriental Realm and has a close relationship to Asian Neolissochilus and Tor. The large-sized Barbus sensu lato appear to have diverged from Carasobarbus about 7.7 Ma. Finally, the Cyprininae appear to have radiated rapidly into nine lineages and many sublineages from about 27.8 to 17.8 Ma, close to the time of the second-stage tectonic movements of the QTP. Our analyses provide evidence that the uplifting of the QTP drove early diversification of the Cyprininae. Our extensive sampling of species involving all of the important areas results in clear evolutionary scenario for the Cyprininae. [ABSTRACT FROM AUTHOR]

A new soil moisture content sensor coupled with a new matric potential sensor that can operate in the subfreezing environment was used to measure the moisture content and soil matric potential dynamics of Qinghai-Tibetan silty clay. Combined with nuclear magnetic resonance (NMR) technique and thermal resistor temperature probe, the characteristics of unfrozen water content and soil matric potential, and their relationships with temperature were analyzed. The results show that initial water content has an impact on the freezing point and unfrozen water content. The decrease in the initial water content results in a depression in the freezing point. The Qinghai-Tibetan silty clay has more similar unfrozen water content characteristic to clay than to silt. There is approximately 3% of unfrozen water content retained when the soil temperature drops to −15°C. The change of soil matric potential with temperature is similar to that of the unfrozen water content. The matric potential value of the saturated silty clay is approximately −200 kPa when the soil temperature drops to −20°C. The measured matric potentials are significantly lower than the calculated theoretical values based on the freezing point depression. Moisture migration experiment indicates that soil matric potential controls the direction of moisture movement and moisture redistribution (including ice and liquid water) during the soil freezing. [ABSTRACT FROM AUTHOR]

Abstract: Based on the observation data of the two-phase closed thermosyphon and insulation combinational test embankment of the Qinghai–Tibet Railway, variations of permafrost table, thermal regime changes, heat budget and heat exchange of the combinational embankment were analyzed. As control groups, natural ground and a traditional soil embankment were also analyzed. Considering thermal asymmetry in the north and the south slopes, comparisons of ground temperature and heat budget in the north and the south slopes were made. The results showed that permafrost table dropped slowly but continuously under the natural ground, rose at first then dropped beneath the traditional soil embankment, and kept a longer period of rising underneath the combinational embankment. Also warming with small magnitude occurred under the natural ground. Under the traditional soil embankment (northern slope), cooling happened in the upper part while warming existed in the lower part. Universal significant cooling was resulted in under the combinational embankment after the application of the thermosyphon. An asymmetric thermal regime was demonstrated under both of the traditional soil embankment and the combinational embankment. The former presented an asymmetric degradation in the permafrost, and the latter presented an asymmetric evolvement. For the natural ground, the ground surface absorbed heat, and heat from ambient layers partly accounted for permafrost degradation. For the traditional soil embankment (northern slope), the embankment surface released heat, and heat from ambient layers mastered the permafrost degradation. Controlled by the cooling process caused by the thermosyphon, heat exchange of the combinational embankment was different from the former ones. The thermosyphon absorbed heat from ambient layers, cooled embankment, and its underlying layers. At the same time, it altered the embankment surface from heat releasing way to heat absorption way. And, for the combinational embankment, cooling effect in the northern slope was better than in the southern slope. The consequence was partly attributed to lower air temperature in the northern slope, and the thermosyphon cooled the ground to a lower temperature and its working duration was longer, correspondingly. And it was partly attributed to the application of insulation board. [Copyright &y& Elsevier]

Temperature changes and deformations were monitored on various embankment types on the Qinghai-Tibet Railway. Some of these embankments utilized permafrost protection techniques such as duct ventilation, crushed-rock embankments, crushed-rock protected slopes, or thermal-insulation treatments. Some embankments were built conventionally without considering permafrost protection. It was found that the majority of the deformations on both the permafrost-protected and the conventionally built embankments were due to deformation of warm frozen layers closely related to the temperature changes in the underlying permafrost. However, it was found that building embankments with permafrost protection reduced the magnitude of the settlements. After 2–3 years, deformation of all the embankments with permafrost protection countermeasures became smaller and smaller, whereas deformation was still increasing in the conventional embankments, where the settlement in the underlying permafrost could reach a considerable level, and could be a potential trigger for embankment failure. This should be taken into consideration in the railway engineering project on the Qinghai-Tibet Plateau. [ABSTRACT FROM AUTHOR]

It is vital to study the regional heat fluxes in the Tibetan Plateau Area. In this paper, the characteristics of down- and upward short wave radiation fluxes, down- and upward long wave radiation fluxes, net radiation flux, soil heat flux, sensible heat flux, and latent heat in the areas of CAMP/Tibet [coordinated enhansive observating period (CEOP) Asian-Australia Monsoon Project (CAMP) in Tibetan Plateau] are analyzed. Some new concepts about the characteristics of radiation flux budget and land surface energy budget are obtained. [ABSTRACT FROM AUTHOR]

Many of the unprotected tower footings along the Qinghai–Tibet Power Transmission Line (QTPTL) were buried by open excavation in thaw-unstable permafrost. Their thermal stability was of concern due to climate warming and human-induced thermal disturbances. On the basis of ground temperature measurements during the last three years, the tower foundation soils were stable during the studied period from 2011 to 2013 in spite of appreciable impacts of engineering construction of tower footings on the thermal regimes of the surrounding and underlying permafrost. The thaw front near a typical concrete footing was 0.67 m to 1.74 m deeper than that at adjacent natural, undisturbed sites in summer, and ground temperatures near such footings were lower than those at nearby natural sites in winter. This thermal enhancement (TE) effect of concrete footings lengthened the duration of freezing and thawing of the surrounding soils, deepened the permafrost table near the tower foundations, and subsequently adversely affected the thermal stability of the tower foundation soils. Numerical modeling was used for simulating the long-term thermal stability of the foundations soils and impacts of the TE effect, ice contents, mean annual ground temperature (MAGT), embedding depths of tower footings, and climate warming on ground thermal regime. Under the scenario of climate warming by 2.6 °C within the next 50 years, the active layer thickens and permafrost temperatures at depths rise progressively with time. The ice contents and MAGT of permafrost remarkably would affect the degradation rate of permafrost around the footings. The TE effect of the footings thickened the active layer by at least 1 m relative to natural sites 20-m away from the footings. The thaw settlement of tower foundation soils could present higher risk for the unprotected footings with a shallow (< 5.8 m) embedment in warm and ice-rich permafrost soils under a warming climate. In the end, some recommendations and suggestions were made. [ABSTRACT FROM AUTHOR]

Abstract: In K 0 consolidation, i.e. laterally confined compression, the axial pressure creates some plastic work on the soil samples. Part of this plastic work is dissipated by friction between soil grains. The other part is stored as free energy (SFE) in the soil. When the soil micro-structure is disturbed, SFE is either accumulated or released. In this paper, formula for SFE is deduced under K0 conditions. Lanzhou loess and Qinghai–Tibet silty clay were used as study objects. After freeze–thaw, changes in mechanical properties of the two soils lead to the changes in SFE. It is found that freeze–thaw has different effects on the soil density, and thus on SFE. They are increased for the soils with low original dry unit weight, and decreased for the soils with high original dry unit weight. [Copyright &y& Elsevier]

Abstract: To evaluate the thermal protection effects of the insulation treatment, a 307 m long railway test section was constructed on the Qinghai–Tibetan plateau in 2001. Over 5 years observation data were collected and analyzed. The results showed that there was an obvious temperature difference between the top and the bottom of the insulation. The temperature of the deep permafrost rose for both the expanded polystyrene (EPS) and polyurethane foam (PU) sections due to the embankment construction. Because the soil temperature at the depth of 0.5 m below the south facing slope was much higher than that of the north facing slope and was a few degrees higher than that of the embankment surface, the permafrost temperature under the south facing slope rose, and the permafrost temperature under the centre of the embankment remained unchanged, and the permafrost temperature under the north facing slope dropped. Accordingly, the artificial permafrost table under the center of the embankment did not change, while the artificial permafrost table under the northern slope rose, and the artificial permafrost table under the southern slope declined. The experiment indicated that the insulation method was suitable for permafrost regions with low embankment surface temperature and it was not suitable for warm permafrost regions with high embankment surface temperature. [Copyright &y& Elsevier]

Two-phase closed thermosyphons are extensively used for cooling foundation soils of tower footings in permafrost regions along the Qinghai-Tibet Power Transmission Line (QTPTL). In this paper, the working period of these thermosyphons is firstly determined by field observations. Then, a 3-D numerical heat transfer model is constructed to study the long-term cooling effects of thermosyphons and thermal performance of foundation soils. The numerically simulated results show a significant cooling of foundation soils near thermosyphons in cold season approximately from late October to early May, and a rapid shift of the thermosyphon cooling to the footing side due to greater thermal conductivity of the concrete footing. As a consequence, a colder bulb would develop under the footing, increasing the bearing capacity of foundation soils. In warm season from the mid-May to mid-October, the maximum thaw around the footing would be greater than that in the natural ground due to better heat transfer through the concrete footing. During a 50-year operational period, foundation soils under the footing would roughly go through about four thermal stages under a combined effect of the thermosyphon cooling and climate warming: a rapid cooling stage in the first to 5th year, a stable stage in the 6th–15th year, a rapid warming stage in the 16th–35th year and a slow warming stage after the 35th year. During the operational period, the maximum thaw around the footing would be less than the embedding depth of the footing (5.8 m), meeting the design criterion for thermal stability of foundation soils. [ABSTRACT FROM AUTHOR]

The increasing number of engineering activities on the Qinghai-Tibetan Plateau, along with a warming climate, tend to induce significant thermokarst processes. However, thermokarst lake development on the plateau and the long-term influence of thermokarst dynamics on the surrounding permafrost have not been fully understood. Based on the moving mesh method, we developed a dynamic model of lake growth with phase change to investigate the morphologic processes of a thermokarst lake and its long-term influence on the local permafrost thermal regime. Our numerical results indicated that lake expansion due to thermokarst development was fairly rapid, and it depended on many factors including lake-bottom temperature and permafrost temperature. The depth and radius of the simulated lake increased gradually from the end of May to the end of the following January, and remained stable from February to May due to the lower lake-bottom temperature. Our results also showed that lake expansion was not very sensitive to climate warming in the first 50 years after the formation of a thermokarst lake, but the lake expansion was clearly affected by a warming climate in the long run (200 years). The development of a thermokarst lake is shown to significantly enhance the thermal effects on the surrounding permafrost. Compared with a fixed-boundary thermokarst lake, an active (moving-boundary) thermokarst lake caused greater thermal disturbance to the permafrost around and beneath it. [ABSTRACT FROM AUTHOR]

Preliminary field observations along the Qinghai–Tibet Power Transmission Line (QTPTL) show that foundation soils of some shallow footings (with an embedding depth of 3.7 m) with thermosyphons in permafrost regions still suffer substantial and rapid thaw settlement in warm seasons. In this paper, a series of numerical simulations on the long-term thermal performance of foundation soils of these shallow footings are carried out. The simulated results show that thermosyphons could do effectively cool foundation soils at depths 2.5 to 8.0 m under the footing. However, in warm season from mid-May to mid-October, the rapid warming of shallow foundation soils near the footing caused by heat transfer through the concrete footing could not be prevented. The maximum thaw around the footing could be as much as 1.0 m deeper than that in the natural ground. Under a warming climate, the maximum thaw around the footing would go deeper than the embedding depth of the footing with four thermosyphons in very warm (≥− 0.5 °C) permafrost regions and with two thermosyphons in warm (≥− 1.0 °C) permafrost regions during a 50-year operational period. To retard thaw penetration around the footing, a combined cooling method of thermosyphons and insulation boards is proposed for foundation soils. Numerically simulated results show that the additional placement of the boards on ground surface could prevent the rapid warming of shallow foundation soils and effectively reduce the maximum thaw around the footing. The method could also effectively delay permafrost warming under the footing. Thus, it is recommended to be used at shallow footings in very warm, ice-rich permafrost regions along the QTPTL. [ABSTRACT FROM AUTHOR]

Abstract: The retrogression and thermal regime of a thaw slump affecting the stability of a slope along the Qinghai–Tibet Highway in China were studied over the last twenty years. The thaw slump was initiated in 1992 and the retrogression rate at the headwall slowed down somewhat in the recent years following the thermal stabilization of the affected area. According to field observation and monitoring, while the ground temperature was still not stabilized after the occurrence of the thaw slump, the depth of the permafrost table was usually shallower in the recently disturbed area than in the undisturbed area away from the thaw slump. However, due to a positive heat budget in the disturbed area, the ground temperature was increasing and the permafrost table was deepening. Moreover, since the ground temperature is higher close to the headwall than in the undisturbed area, lateral heat flux occurs in the thaw slump area inducing more retrogression at the headwall. However, as soon as the vegetation invaded the bare ground surface of the disturbed area, the ground temperature was decreasing in the disturbed area over the past two years and stabilization of the disturbed area was occurring. Following the stopping of the headwall retrogression and the decrease of the lateral heat flux, the ground temperature near the headwall is also decreasing. [Copyright &y& Elsevier]