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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]

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]