Search

The Qinghai-Tibet (QT) Plateau Engineering Corridor is located in the hinterland of the QT Plateau, which is highly sensitive to global climate change. Climate change causes permafrost degradation, which subsequently affects vegetation growth. This study focused on the vegetation dynamics and their relationships with climate change and human activities in the region surrounding the QT Plateau Engineering Corridor. The vegetation changes were inferred by applying trend analysis, the Mann-Kendall trend test and abrupt change analysis. Six key regions, each containing 40 nested quadrats that ranged in size from 500 × 500 m to 20 × 20 km, were selected to determine the spatial scales of the impacts from different factors. Cumulative growing season integrated enhanced vegetation index (CGSIEVI) values were calculated for each of the nested quadrats of different sizes to indicate the overall vegetation state over the entire year at different spatial scales. The impacts from human activities, a sudden increase in precipitation and permafrost degradation were quantified at different spatial scales using the CGSIEVI values and meteorological data based on the double mass curve method. Three conclusions were derived. First, the vegetation displayed a significant increasing trend over 23.6% of the study area. The areas displaying increases were mainly distributed in the Hoh Xil. Of the area where the vegetation displayed a significant decreasing trend, 72.4% was made up of alpine meadows. Second, more vegetation, especially the alpine meadows, has begun to degenerate or experience more rapid degradation since 2007 due to permafrost degradation and overgrazing. Finally, an active layer depth of 3 m to 3.2 m represents a limiting depth for alpine meadows. [ABSTRACT FROM AUTHOR]

To analyse the damage characteristics of thermosyphon embankments in a permafrost region, the Qingshui River section along the Qinghai-Tibet Highway (QTH) was used as a case study in which a field investigation and drilling were performed. The field soils were sampled, and their water content, dry density and compaction degree were tested in the laboratory. Based on the measured temperature data of the thermosyphon embankment, damage characteristics and possible associated causes were analysed. The major damage found in thermosyphon embankments was a longitudinal crack, which developed 1.0 to 2.0 m away from the thermosyphon. In partial sections, waves and other damage also occurred. The damage was primarily attributed to the non-uniform temperature distribution, which resulted in a non-uniform distribution of the mechanical properties of the embankment filling. Under a heavy traffic load, stress concentration phenomena occurred at the freezing-thawing interface that gradually developed into a longitudinal crack with increased highway operation. The embankment damage history, rainfall seepage, ponding near the embankment and freezing-thawing cycles further accelerated the development of damage along the thermosyphon embankments. According to the characteristics and causes of thermosyphon embankment damage, precisely computing the cooling efficiency of thermosyphon in the design stage is necessary to prevent freezing-thawing interface waves resulting from excessive cooling effectiveness, to reduce thermal erosion from ponding near the embankment by improving embankment drainage systems, and to set necessary structural measures at thermosyphon embankments that can improve their strength. [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: The two-phase closed thermosyphon (TPCT) is a passive high-performance thermal transfer device that can efficiently decrease the ground temperature. However, only a few studies focus on the quantization of working efficiency of thermosyphons. Thus, in this study, based on data obtained from an experimental TPCT embankment on the Qinghai–Tibet Highway from 2004 to 2012, the ground temperature fields of the TPCT embankment were obtained, and the horizontal and vertical ground temperature characteristics were analysed. The results showed that the TPCT embankment exhibited better thermal stability than that of a traditional embankment. The artificial permafrost table was elevated to or maintained at the original natural level due to the cooling effect of the TPCT. To quantitatively analyse the cooling effect of the TPCT embankment, a thermal budget evaluation method is proposed. The calculated results revealed the dynamic working state of the thermosyphon during its service period. The annual average energy of the TPCT transferred in a year was generally determined to be between 1500MJ and 2000MJ. The results of this study could provide a method to evaluate the TPCT embankments and provide technological support in designing the TPCT embankments in permafrost regions. [Copyright &y& Elsevier]

Abstract: In this work, a two-dimensional unsteady model for analyzing the roadbed temperature in permafrost regions of the Qinghai-Tibet Plateau (QTP) is developed and the heat transfer processes of comprehensive earth-atmosphere coupled system are simulated by the numerical method. In the computation, the surrounding air environment of ground surface is brought into the research model and the corresponding unsteady and non-uniform influence factors of earth-atmosphere coupled system are also considered to obtain reasonable simulation results. Meanwhile, the model is validated with monitored data at a depth of 0.5m in different roadbed positions. Based on the above model, the spatial and temporal temperature distributions of the roadbed surface in Wudaoliang region are determined. Then the influences of the system parameters, such as the ambient temperature, wind speed, roadbed height and route trends, on the local temperature distribution are investigated. The results show that, temperature of surface regions exhibits a periodic sinusoid trend and always higher than the ambient air temperature. For different surface regions, the temperature of asphalt pavement keeps the maximum value and the natural ground surface has an abrupt step change in temperature at beginning of April and end of October. The variation of ambient air temperature has little influence on annual average temperature of permafrost roadbed surface. The deviations between the surfaces'' annual average temperature increase and their average values are less than 1%. Annual average temperature of various surfaces decreases as the wind speed and the roadbed height increase. Furthermore, the annual average temperature of leeward slope (also sunny side) along EW direction is the highest one among all three route directions and such temperature decreased systematically from SW45° direction to SN direction. However, the annual temperature of upwind slope (also shady side) is just contrary to the leeward slope. [Copyright &y& Elsevier]

Abstract: As far as the railway embankment in permafrost regions is concerned, its mechanical properties are closely related to soil temperature. Especially for the embankment in the warm permafrost regions (mean annual ground temperatures range from 0–−1.5 °C), its stability will change greatly with minor temperature variations. The Qinghai–Tibet Railway (QTR) is approximately 1142 km long, of which 275 km are underlain by warm permafrost. Furthermore, the Qinghai–Tibet Plateau (QTP) is in an active seismic zone. Thus, the seismic stability, liquefaction, and deformation of the embankment of QTR are critical issues on safe operation. However, there are few papers concerning about the seismic response of railway embankment in permafrost regions. This paper will propose a thermal-dynamic coupled model, and the model and its specific analytical procedure can be described as follows. Firstly, based on the governing differential equations of transient temperature field with phase change, the temperature distributions of railway embankment are computed and analyzed by numerical method. Then, since the mechanical properties of frozen soil are effected by temperature, the dynamic consolidation equations of Biot, whose parameters are relative to temperature, are deduced in detail by adopting dynamic consolidation theory. Lastly, by using this numerical model, the seismic response of the QTR embankment is simulated, and the characteristics of seismic response, such as excess pore water pressure, stress and displacement, are analyzed in detail. Meanwhile, the seismic stability of this embankment is evaluated. The results show that this numerical model is able to simulate seismic response of embankment in permafrost regions. [Copyright &y& Elsevier]