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With the construction of railways on plateaus, the slab tracks of railways are facing rigorous temperature challenges and adverse thermal effects. This paper analyzed the temperature field and thermal effects of the CRTS III slab track on plateaus. Firstly, the pivotal thermal parameters of the geotextile and rubber pad of the slab track were obtained by tests. Subsequently, a coupled thermal-fluid-solid model for the CRTS III slab track on plateaus was established, followed by experimental validation. Based on the model, the temperature field and thermal effects of the slab track on Tibetan Plateau were revealed. The main conclusions are as follows: the thermal conductivity, specific heat capacity, and heat flux of the rubber pad and geotextile were very small, resulting in poor heat conductivity. The temperature of the track on plateaus showed obvious non-uniformity along both lateral and vertical directions, and changed with time significantly. Compared with that on the plain, the CRTS III slab track on the plateau had low temperature and large temperature variations. Compared with the conventional simplified temperature load, the spatial temperature field can fully reflect the non-uniform thermal effects of the slab track on plateaus. The method and conclusions presented in this paper can provide scientific guidance for the construction, operation, and maintenance of railways on plateaus. • The thermal parameters of rubber pad and geotextile of the CRTS III slab track were obtained by tests. • The thermal-fluid-solid model for the CRTS III slab track on cold plateaus was established. • The temperature field characteristic of the CRTS III slab track on cold plateaus was revealed. • The influence of spatial temperature fields on the thermal effects of the slab was explored. [ABSTRACT FROM AUTHOR]

Permafrost under road embankments often degrades more seriously than that under natural ground surfaces due to the influences of both climate warming and road embankment. In a companion paper, we analyzed the states of permafrost degradation under road embankments in the five typical regions along the Qinghai–Tibet Highway (Yu et al., 2013a). In this paper, the states of permafrost degradation under natural ground surfaces, near the road embankments, are analyzed based on up to 15 years of in-situ geothermal data, while that under road embankments are also further analyzed. On this basis, the states of permafrost degradation and related processes are compared between the natural ground surfaces and road embankments. Possible influences of climate warming and road embankment on permafrost degradation are discussed. The results show different characteristics of permafrost degradation under natural ground surfaces and road embankments. The contributions of climate warming and road embankment on the thermal regime of permafrost may vary during the process of permafrost degradation. [ABSTRACT FROM AUTHOR]

Abstract: In allusion to the problems of the frozen soil engineering geology, the roadbed stability with climate change in construction of the Qinghai–Tibet Railway (QTR), this paper provides overview of the frozen soil engineering problems before and during the QTR constructions. Based on the experiences and lessons learned from the road construction in permafrost areas, the authors recommended that the principle of “positive cooling” of the railroad roadbed by lowering permafrost temperatures should be used in the design of the QTR, rather than that of “passive protection” of permafrost through increasing thermal resistance of the roadway, such as simply increasing fill thickness and/or using thermal-insulation materials. This is especially important for the road sections in warm, ice-rich permafrost areas. In addition, this paper reviews several methods for “cooled roadbed” by controlling radiation, convection and conduction through modifying roadway structure and using different fill materials. Meanwhile, the authors also provide information on some existing problems and future monitoring programs along the QTR. [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]

A series of dynamic triaxial experiments have been conducted to study the dynamic properties of the frozen soil from the subgrade along the Qinghai-Tibet Railway. Under long term cyclic loading, the effects of initial stress state and stress level on cumulative permanent strain and critical dynamic stress were studied in the paper. The results indicate that the influence of dynamic amplitude on the curve of cumulative permanent strain versus cyclic loading number is significant. Besides, based on the shakedown concept, curves of cumulative permanent strain versus cyclic loading number under different initial mean stress and deviatoric stress can be separated to three possible categories of plastic shakedown, plastic creep and incremental collapse. In addition, the critical dynamic stress of frozen soil under specific condition is obtained, and the analysis on critical dynamic stress at different stress state is presented. Therefore, this study could provide an innovative approach for permanent deformation behavior analysis. Furthermore, it is important for practical design and evaluation on stability of frozen soil in the subgrade. [ABSTRACT FROM AUTHOR]

Recognizing the status of permafrost thawing and providing information for permafrost treatment in the Tibetan Plateau is a key problem. In this paper, a GPR experiment is designed to explore effective geophysical attributes for characterizing and evaluating the impact of key factors on permafrost thawing. A new algorithm for the assessment of rapid relative water content is also presented. After processing the GPR data, the weighted average frequency attribute, sweetness attribute and relative wave impedance attribute, which better characterize the effect of different factors on permafrost thawing, are selected. The weighted average frequency attribute can distinguish the thawing front and evaluate the extent of thawing in addition to the completely thawed fringe; the sweetness attribute can help to characterize thawing in water ice mixed with permafrost and evaluate the impact of free water on permafrost below the thawing front. The relative wave impedance attribute highlights the completely thawed fringe and other smaller internal stratifications in the permafrost thawing zone. Using the rapid relative water content assessment algorithm, it is easy to evaluate the extent of thawing using only GPR data. In addition, a thermokarst lake strengthens the degree of permafrost thawing. Permafrost thawing accelerates on sunny slopes. This study shows that roadbeds inhibit permafrost thawing and that a thermosyphon significantly inhibits permafrost thawing. [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]

Active-layer thickness's distribution is a key parameter for permafrost area studies. In the past, the factors of vegetation, soil water content usually were employed to forecast the spatial distribution of active-layer thickness. But in coarse material distribution area, the above method is often unsatisfactory due to the failure in accurate acquisition of biomass and soil water content. In this paper, a simple method was recommended to be used for calculating of active layer thickness distribution, which is suitable for all kinds of soil texture. Our study analyzed the relationship between ground surface layer permittivity and the thawing depth of the active layer in a permafrost area that was undisturbed by subsurface water flow or local melting. Ground surface layer permittivity is confirmed as having a strong correlation with soil moisture content and biomass of the vegetation cover. We used the direct ground wave velocities from GPR detecting results to compute the dielectric permittivity. Our conclusion is that in our specific study area, a power function relationship existed between the ground surface layer permittivity and the thawing depth of the active layer. [ABSTRACT FROM AUTHOR]

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]

With global warming and increasing engineering activities, one effective approach to mitigating frost hazards in warm permafrost regions is proactive cooling of foundations soils. Thermosyphons are important proactive cooling engineering measures. Evaluating the effectiveness of thermosyphons is necessary for engineering design and stability analysis of tower foundations. Based on field monitoring data, the current paper presents the analysis on the evaporator temperatures, the effectiveness of thermosyphons, and the characteristics in changing hydrothermal regimes of foundation soils along the Qinghai–Tibet Power Transmission Line (QTPTL) from Golmud, Qinghai Province to Lhasa, Tibet Autonomous Region, China. The results showed that thermosyphons effectively cooled the surrounding soils from early October to early May of the next year. In cold seasons (from October to the next May when thermosyphons were working), the evaporator temperatures changed synchronously with air temperature, and the temperature differences along the evaporator were relatively small (less than 3 °C). At the monitoring site, with the help of thermosyphons, the backfilled soils around the tower foundation re-froze completely and the thermal disturbance caused by the construction activities disappeared after the first cold period from mid-November 2010, when the foundation was constructed, to early May 2011. Due to the functioning thermosyphons, the cooling effect of the thermosyphons on foundation soils in cold seasons not only offset the warming effect of the building and operating of tower footings, but also progressively cooled the foundation soils during the first four operating years from 2011 to 2014. The more remarkable heat release was mainly because the cooling process in every year began much earlier. This resulted in the extension of the cooling period and the shortening of the warming period, resulting in an ongoing cooling of the foundation soils. As a result, the bearing capacity of the foundation soils was improved and sustained. Numerical simulations may be conducted in future to evaluate the necessary quantity and design layout of the thermosyphons around a tower foundation. [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: Embankment settlement is closely related to the process of degrading of underling permafrost. Previous studies have focused on the process of permafrost degradation under natural ground surfaces, and the degradation process under roadway embankments has yet to be investigated. With the influence of climate warming, this study becomes more and more important in the analysis of embankment settlement. In this paper, based on the in-situ geothermal data of up to 15years of 5 typical sections along the Qinghai-Tibet Highway (QTH), the characteristics of permafrost degradation are extensively investigated. According to the characteristics, the trends of thawing and temperature rise in the process of permafrost degradation are analyzed. Corresponding to the tendencies, four stages are defined according to the mean annual ground temperature (MAGT). Combining the features of permafrost degradation in each stage with the in-situ data of embankment settlements along QTH, the sources of the embankment settlement are identified. The main results are as follows. The permafrost degrades extensively in the five typical sections with different characteristics. With the increase in MAGT, the thawing rate firstly increases and then fluctuates as temperature rise rate increases and then decreases at MAGT of about −0.5°C. The four stages are divided: initial degradation stage, for MAGT≤−2.5°C; the intensive degradation stage, for −2.5°C0°C. When MAGT is less than about −1.2°C, the main contribution of total settlement is probably thawing settlement, with the negligible creep of permafrost; when MAGT higher than −1.2°C, creep of permafrost starts to have an increasing share in the total settlement. [Copyright &y& Elsevier]

Abstract: The temperature field of permafrost embankments is a key factor to determine the embankment stability. On the basis of observed climate data and field-temperature values in Beiluhe on the Qinghai–Tibet Plateau, this paper uses statistics methods to set up a regression equation between the temperature at shallow ground depth (0.5m) and the net radiation on embankment horizontal surface. There is a good linear relation between the temperature and the net radiation after the phase difference is removed. Moreover, an empirical formula consisting of the shallow-ground temperature of (0.5m) and the direct solar radiation is proposed. It is also suitable for the area having high elevation at the Beiluhe site. These formulas combining with the law of documents and materials suggest that there exists an obvious linear relation between the temperature on horizontal surface and the direct solar radiation. However, there is hardly linear relation between the temperature and the direct solar radiation on embankment slopes. The key factor is that the railway embankment slope has a relatively heavier gradient. The slopes with heavier gradient have different heat transfer characteristic during a specific year. In summer, the sun is shining straight on the ground, which results in a relatively lower direct solar radiation on slopes; however, because of diffuse radiation and higher temperatures of the horizontal surface, temperatures on slopes are relatively higher. In winter, the direct solar radiation on shady slopes is even zero, meaning that there is almost no direct solar radiation. Thus, the relations between the temperature and the direct solar radiation on slopes are more complicated. [Copyright &y& Elsevier]

Abstract: The 1076-km-long Golmud–Lhasa oil product pipeline is located closely parallel to the highway constructed 20years earlier within the relatively narrow north–south engineering corridor crossing the treeless central area of the Qinghai–Tibet Plateau. Much of the corridor is at elevations exceeding 4500m and high-elevation, generally warm permafrost is encountered in more than one-half of the length. The pipeline, transporting mostly diesel, motor and aviation fuels at ambient temperatures, is 159mm in diameter, has a wall thickness of 6mm and was buried in a trench at a nominal depth of between 1.2 and 1.4m. The soils encountered, mostly periglacial sands, silts and gravels, often have elevated saline contents and are subject to severe wind erosion and occasional monsoon flash flooding conditions. During its first quarter century of operation, the pipeline suffered at least 30 significant leaks and four pipeline ruptures. About 337km of the pipeline was extensively rehabilitated, including relocations or replacements in major problem areas and, where feasible for an existing pipeline, improvements in pipeline protection during 2001–2004. It was supposed to safely operate for another 30years with proper checks and needed repairs. This paper provides a review on the history of the permafrost and cold regions environmental problems of the pipeline, and their major rehabilitation, repairs and problems in the future, which might have useful implications for similar oil product pipeline at high elevations or permafrost regions. [Copyright &y& Elsevier]

Abstract: Based on dynamic triaxial test at low temperature of the frozen clay from the Beiluhe permafrost subgrade along the Qinghai–Tibet Railway (QTR), residual deformation laws and dynamic subsidence prediction model of permafrost subgrade under train traffic were studied. First, time history curves of residual strain of frozen soil are obtained and analyzed under different temperatures, frequency, confining pressure and moisture content. And conclusions can be drawn that the axial strain rate is greatly affected by the amplitude of dynamic stress, as well as increases with dynamic to static stress ratio and temperature rising, while it decreases with the raise of frequency and moisture content. Hereby, the power functions were adopted to fit the relationships of axial dynamic strain rate vs. stress ratio, temperature, frequency, and moisture content, respectively. Simultaneously, the permafrost dynamic subsidence mechanism was interpreted rationally and the variation of fitting parameters was discussed. Furthermore, the long-term traffic loading subsidence model was established through observing the axis residual strain time histories of frozen specimens under the longtime cyclic loading and adopting the amendment of vibratory number of times. The model can comprehensively consider the effects of stress state, temperature, moisture content, and confining pressure of frozen soil, as well as the vibratory frequency and vibration number of longtime cyclic loading. Consequently, the model can be applied to the train-induced subsidence forecast investigation of permafrost subgrade. The paper has an important significance for rational safety evaluation on long-term operation of permafrost regions railway such as QTR. Meanwhile, the investigation provides basic data for the further research on dynamic damage constitutive model of frozen soil under train traffic and the gradual improvement of railroading criterion in cold regions. [Copyright &y& Elsevier]

Abstract: Analyses of characteristics of vibration response of track structure from train traffic and its attenuation laws, based on the field monitoring of the vibration acceleration response of rail, sleeper, and embankment at the Beiluhe permafrost testing section along the Qinghai–Tibet railway in China, are performed in this paper. The reasonable fitting formula of attenuation relationship of embankment vibration is put forward in a negative exponential function form. The quantitative understanding of the vibration property is obtained according to the statistic of the two well-defined eigenvalues of vibration acceleration response, as well as the analysis of the acceleration time histories and the corresponding frequency spectra. The results suggest that: the effect of rail gap on the maximal vertical vibration response of rail is not evident; vibration response of sleeper near the rail gap is obviously larger than that of other sleepers, especially having intensive shock pulse, and the maximum is more than three times that of the vibration response of the sleeper lying in the very middle of the two rail gaps from one compartment passing by; the rail vibration energy concentrates within 10Hz, and the rail predominant frequencies mainly correlate with train speed and bogie spacing; the dominant frequencies of the embankment vibration, varying from 40 to 70Hz for the embankment shoulder and reducing with the distance increasing from the track, are influenced chiefly by train speed and sleeper spacing. The results mentioned above have important significance for rational cognition of vibration response characteristics of track structure at permafrost site, and moreover for the dynamic stability evaluation for the long-term operation of the Qinghai–Tibet railway. Meanwhile, the investigation provides basic data for the further research on the rail transit dynamics and the improvement of railroading criterion in cold regions. [Copyright &y& Elsevier]

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: In this paper, a frozen soil parameterization scheme is developed based on the Common Land Model. We modify a frozen soil parameterization scheme using soil matric potential to define maximum liquid water content when soil temperature is below the freezing point; the simulation performance is validated using the data from Maqu station on the Tibetan Plateau from 2005 to 2006. The simulated results indicate that the modified frozen soil parameterization scheme allows the liquid water to exist when the soil temperature is below the freezing point, and the simulated soil liquid water content is significantly improved. The simulated soil temperature is also improved because of the successful simulation of the soil liquid water content. The distribution of energy from the modified model is closer to the observed data. Also, the simulated latent heat flux from the modified model increases and the simulated soil heat flux descends compared with the original model. [Copyright &y& Elsevier]

Abstract: Under the impact of potential climate warming and human engineering activities, the Embankment with Crushed Stone Slope Protection (ECSSP) needs further countermeasures to protect the underlying permafrost along the Qinghai–Tibet railway in warm (−1 to 0 °C) permafrost regions according to the observed in situ data. In this paper, a new strengthening countermeasure, the Embankment with Shading Board and Crushed Stone Slope Protection (ESBCSSP), is proposed to cool the foundation soil and to protect the warm permafrost. The crushed stone layers placed on the side slopes of the embankment have an apparent “thermal semi-conductor” effect by intensive natural convection of pore air in the winter and a “heat shield” effect in the summer. The shading boards erected on crushed stone slope protection can shade the ground surface from the sun to lower its surface temperature, and can keep snow from covering the crushed stone layer in the winter, which can enhance the cooling effect of the crushed stone layer. Based on the processes of natural convective and conductive heat transfer in porous media, systemic numerical tests were performed to study the cooling effect of the ESBCSSP, and to propose the reasonable range in thickness, height and grain size of the crushed stone slope protection. [Copyright &y& Elsevier]

Desertification in Qinghai-Xizang (Tibet) Plateau is part of Chinese desertification. In the past decades, due to the climate warming, the climate condition in Qinghai-Xizang (Tibet) Plateau has been relatively dry. This has resulted in permafrost degradation and other environmental problems. In addition, the vegetation and the soil layer were also destroyed by unreasonable economic activities. Cultivated and grassland lands have become deserted. Nowadays, the desertification is still expending. In this paper, the factors affecting the desertification in Qinghai-Xizang (Tibet) Plateau were examined, and the desertification as well as its relationship with permafrost degradation was also discussed. [Copyright &y& Elsevier]

This paper presents a new frozen soil parameterization in the land surface scheme (LSS). A modified approximation Stefan solution is incorporated in the framework of the land surface model-SiB2 to calculate the frost/thaw depth over time and to estimate the soil moisture and temperature profiles during the freeze/thaw cycle. The structure of the soil model in Simple Biosphere Model 2 (SiB2) is kept, but the governing equations of water balance and surface heat balance are modified to account for soil freezing/thawing. The model is calibrated and validated using the GEWEX Asian Monsoon Experiment (GAME)-Tibet observations at MS3608 site, Tibetan Plateau. First, the original SiB2 without frozen soil parameterization is calibrated using the observations in summer; an optimized parameter set for the short grassland in the Tibetan Plateau was obtained. Then, the modified SiB2 with frozen soil parameterization is validated using the soil moisture and temperature observations in winter. The results show that the new model estimates the frost depth precisely with an error less than 9% and predicts the soil temperature reasonably and phase transition time realistically. It also improves the soil moisture estimation in the surface layer and the root zone significantly. The mean absolute errors of simulated soil moisture using the new model are 0.020 and 0.013 in the surface layer and root zone, respectively, far below than those without using the frozen soil parameterization. [Copyright &y& Elsevier]