Search

In recent decades, numerous membrane structures have been built in the cold regions of China. Nevertheless, uneven snow distribution and snow sliding from the edge of roofs cause frequent collapsing, which threatens people's lives and properties. To prevent the collapsing of membrane structures, we present an automatic snow-melting membrane roof based on an electrical–thermal system (ASMR-ETS) in this paper. ASMR-ETS is environmentally friendly, clean, and can be used for eliminating snow that accumulates on membrane roofs. The most important task in designing ASMR-ETS is the determination of its feasibility. A thermal simulation method for the snow-melting process is described in this paper. The surface temperature was obtained using the commercial software ABAQUS. The applicability and rationality of the thermal simulation were verified via snow-melting experiments. The heating wire spacing and heating wire power were set as heating wire parameters. The wind velocity, solar irradiation, ambient temperature, and snow thickness were selected to be the climatic conditions. The surface temperature of ASMR-ETS was simulated, and the snow-melting performance (snow-free area ratio and coefficient of variation of temperature) was analyzed for different heating wire parameters and climatic conditions. According to the simulation results, increasing the wind velocity and snow thickness decreases the snow-free area ratio and improves the coefficient of variation of temperature, whereas solar irradiation and ambient temperature showed an opposite effect. Furthermore, the snow-melting performance of the membrane structure was studied, and different layout schemes of the heating wire were considered. The results show that ASMR-ETS is practical and can therefore be used to clear snow on membrane structures. • An automatic snow-melting membrane roof with an electrical–thermal system is proposed to remove snow on membrane structures. • A thermal simulation model is established to analyze thermal transportation on the ASMR-ETS. • The snow-melting experiment is carried out to prove the applicability of the proposed thermal simulation. • The surface temperature of ASMR-ETS is simulated and the snow-melting performance of six key pamof siis analyzed for different heating wire parameters and climatic conditions. • The snow-melting performance of the membrane structure is analyzed by comparing different layout schemes of the heating wire. [ABSTRACT FROM AUTHOR]

The transport of ice particles beneath a stable ice cover (referred to as cover load transport), and the processes leading to ice deposition and erosion are highly dynamic and complex. Based on the strong analogous relationship between bed load and cover load transport processes, knowledge from bed load transport research can be used when developing experiments for cover load transport processes. This paper presents a detailed experimental study of cover load transport rate in a laboratory flume with simulated ice particles and a simulated ice cover. The effect of the particle shape and size on cover load transport rate is quantified using the buoyant velocity and its velocity coefficient. The critical dimensionless flow strength is identified as an important parameter which determines the incipient motion of the under cover ice particles, and was calculated using hydraulic measurements obtained through laboratory experiments. A new cover load transport formula is introduced based on regression analysis of experimental data for a wide range of dimensionless flow strength conditions. The impact of incoming ice supply rate on the under cover ice transport rate was also investigated by altering the ice supply rate to the flume. A control volume analysis of ice discharge underneath the ice cover is used as the approach to quantify the dimensionless ice transport rate at different sections of the flume. The concept of equilibrium ice transport rate is introduced based on the experimental observations with variable incoming ice supply rates. The experimental observations on the impact of incoming ice supply were supported by an analysis of field data from Hequ Reach, China (Sun et al., 1986; Wang, 1992). The introduction of a cover load transport formula developed exclusively with simulated ice particles that have similar physical properties to ice forming in a natural environment, and the discussion on equilibrium ice transport rate are important contributions to advance the present understanding on under cover ice transport processes. • Cover load formula using simulated ice with similar properties as ice in the natural environment. • Equilibrium ice transport concept introduced based on variable ice supply rates. • Critical dimensionless flow strength determines the incipient motion. • Relevant to further studies related to numerical modeling of ice transport. [ABSTRACT FROM AUTHOR]

Hydropower resources have been developed to the cold regions in the west of China recently, wherein the dam will be subjected to high frequency of repeated freeze-thaw action during the construction process in winter, and thus will cause safety and stability problems of these projects. According to the actual construction situations of Lianghekou hydropower station located in Sichuan Province, one-side freezing and two-side thawing tests of unsaturated core-wall soil samples in a closed system are carried out, and the evolution of temperature, water and displacement as well as their interaction are tested and analyzed. The results show that with the increasing of freeze-thaw cycles, water migration results in a decrease of water content in the unfrozen zone and an increase in the frozen zone, and the water concentration area is formed in the soil column. Simultaneously, a deeper freezing depth accompanied with a shorter thawing duration after 10 freeze-thaw cycles is observed through the temperature field results, whereas a steady fluctuation of the deformation field is showed after the 7th freeze-thaw cycle. Moreover, based on the test results and exiting researches, a thermo-hydro-mechanical coupling model for unsaturated soils subjected to cyclic freeze-thaw action is proposed, in which both the permeability and compressibility are inextricably related to the void ratio, and vary in different calculated areas. Additionally, the effects of number of cycles on initial conditions and model parameters are also considered. Comparisons with the experimental data demonstrate the validity and adaptability of the proposed model in describing the freeze-thaw process of unsaturated soil. Through the combination of experiments and numerical simulation, the freeze-thaw process can be more clearly understood, and related engineering problems can be predicted with the help of the mathematical model in this paper. • One-side freezing and two-side thawing tests of unsaturated soil are carried out. • A thermo-hydro-mechanical coupling model in freeze-thaw process is proposed. • The thermo-hydro-mechanical coupling mechanism is revealed by simulations. [ABSTRACT FROM AUTHOR]

Temperature changes may cause irregular soil uplift or thawing settlements in frozen soil areas, potentially affecting the safe operation of High-Speed Railways (HSR). Analyzing and predicting these deformation characteristics is thus critical. However, the conventional forecasting and analysis techniques rarely considered factors such as dynamic parameter variations, uncertainties, and measurement errors, which hinder accurate regional scale forecasting. To bridge this gap, this paper introduces a novel time-series coupling method, which integrates post-processing deformation from Interferometric Synthetic Aperture Radar (InSAR) with a frost heave model (FHM), facilitated by the ensemble Kalman filter (EnKF) assimilation algorithm. We obtained deformation observations along the HSR using Persistent Scatterer InSAR (PS-InSAR) technology in combination with time-series post-processing techniques. Considering the causative factors for deformation, we structured the FHM. By integrating FHM with observational data using the EnKF algorithm achieved an efficient upgrade of the posterior distribution of model parameters. This integration significantly improves the predictive accuracy, it facilitates an efficient update to the posterior distribution of model parameters, leading to enhanced prediction accuracy of our model. Our experimental results indicate that the effectiveness of this approach, with observational data assimilation into FHM reducing the average Root Mean Square Error (RMSE) to a mere 0.247 mm. Concurrently, both the Normalized Reduction Error Index (NER) and the Assimilation Efficiency Factor (EFF) values surpassed 0.60 and 0.84 respectively. These underlines signify a successful update of our model parameters, which in turn elevates the accuracy of future deformation predictions, thereby promising safer railway operations. • a time series coupling method based on data assimilation is proposed by considering the triggering factors of deformation. [ABSTRACT FROM AUTHOR]

Abstract Earthen dams are widely applied in the cold regions of northern China. However, the frost-heaving damage of concrete face slabs on the dam slopes is very serious under the dual effect of ice sheets and frost action during winter seasons. For this problem, a theoretical model is still lacking in the engineering design for water conservancy projects in cold regions. Starting with the study of the frost-heaving damage of concrete face slabs of earthen dams, this paper analyzes the damage types of the slabs under the effect of the static ice pressure and frost action, and clarifies the mechanism of the frost-heaving damage. The calculation method of the normal frost-heaving force of concrete face slabs is put forward, and a mechanical model suitable for the frost-heaving damage of concrete face slabs of earth-filled dams is established based on the mechanical analyses and engineering practice. The mechanical model can well explain the failure of frost heaving, extrusion and tensile strength of concrete face slabs under the double effect of the ice sheet and frost action, and a checking method for frost-heaving destruction is given. Finally, the mechanical model is used for the numerical analysis for an engineering example. The calculated results show that the model is reasonable and reliable, and it can provide theoretical basis for the design of concrete face slabs of earthen dams in cold regions. Highlights • The frost-heaving damage mechanism of the concrete face slabs of earthen dams in cold regions. • A mechanical model for analyzing the frost-heaving damage of the slabs is established. • A method for calculating the normal frost-heaving force of frozen soils is proposed. • The phenomenon of penetrating cracks of the slabs can be explained by the model. [ABSTRACT FROM AUTHOR]

Abstract: The design and building of a pipeline in permafrost regions challenge engineers and scientists in many regards, and the geohazards resulting from the (differential) frost heaving and thaw settlement of the pipeline foundation soils present one of the most daunting tasks. The China–Russia Crude Oil Pipeline, a spur line from the Siberia–Pacific Pipeline System, presented unique scientific and engineering problems because of: 1) extensive presence of the more ice-rich permafrost in boreal forests and swamps; 2) an insistence on a buried construction mode because of concerns about the potential for frequent forest fires and other safety issues; 3) great uncertainties in the temperatures of oil being transported although the given estimated oil temperature of −6.4 to +3.6°C entering the Mo''he Pump Station, and the estimated oil temperatures could vary from about −6 to +10°C along the southward pipeline route; 4) the limited lead time for detailed surveys on engineering geology along the pipeline routes and for engineering design; 5) very much limited investment and a limited number of engineers experienced in designing and building a major pipeline in an area where about one-half of its length would be impacted by generally warm (−3 to 0°C) permafrost. Nevertheless, the pipeline engineers and permafrost scientists strived to economically build and satisfactorily operate the first major crude oil pipeline in the boreal ecosystem in China. The major results on the formation mechanisms and mitigative measures for the (differential) frost heave and thaw settlement were presented in the eight papers in this special issue on permafrost pipeline, and one additional paper on the Golmud–Lhasa Oil Products Pipeline on the Qinghai–Tibet Plateau was also included. They may provide insights to the understanding of pipeline–permafrost interactions and benefit the future design and construction of pipelines in similar northern environments. [Copyright &y& Elsevier]

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]

The destruction of channel lining under frost action in seasonally frozen regions has become a prominent factor restricting water transportation in western regions of China, which has also caused a lot of waste of water resources. A novel assembled channel lining for reducing frost heave destruction was presented in this paper. The assembled channel and a normal channel with the trapezoidal section were carried out in the laboratory, considering different water level storage in the high-temperature period. The results revealed that the freezing depths in the channel was quite different, and the order from large to small is the channel embankment, center of the bottom and slope toe. Meanwhile, compared to the variation of water level, the influence of water storage in the channel on the frost heave deformation is more significant than that in the absence of water in the channel. The triangular prism block with the large cross-section set at the slope toe of the assembled channel not only has the insulation effect and a specific anti-seepage function at the channel foundation soil to a certain extent, but also connects the independent concrete plates one by one with the loop-end buckle groove to make the channel deformation uniform under the frost heave. Therefore, the assembled channel could be considered as a novel channel structure to prevent and reduce the frost heave damage in seasonally frozen regions. • An assembled channel lining for preventing the frost heave damage of channel was presented firstly. • The experiment between the assembled channel and normal channel with the trapezoidal section were carried out in laboratory. • The triangular prism block has the insulation and anti-seepage function at the channel foundation soil to a certain extent. [ABSTRACT FROM AUTHOR]

An in situ test was conducted to investigate the short-term mechanical behavior of frozen soils along the Qinghai–Tibet Highway, in China, using the pressuremeter. This paper uses the plane elasticity theory and the radial expansion equation of cylindrical hole in infinite elastic medium provided by Lame´ to interpret the test data. The initial horizontal pressure, the critical plastic load and the limit pressure are reduced from the pressuremeter testing curves, and then, the pressuremeter modulus and the shear modulus are worked out. This paper also analyses the relationships between the mechanical parameters and the soil temperature and the water contents, respectively, and gives out the approximate formula. At the same time, some inevitable problems encountered during the operating of test are discussed. [Copyright &y& Elsevier]

An appropriate probabilistic description of snow loads is important in reliability analysis. Probability distributions for annual maximum ground snow loads are studied in detail in this paper based on the samples of snow loads on the ground, which are simulated by a snowmelt model. Then, selection of probability distribution function and parameter estimation method for ground snow loads is found to have a great influence on reliability assessment results. The reliability of members of steel roof structures subjected to snow load at four representative sites in China is investigated. The reliability indices of studied roofs are found not to be enough to reach the target value 3.2. The possible reason is that characteristic value of snow loads on the ground specified in Chinese load code is not conservative and the partial factor 1.4 for snow loads on roofs is not enough. To ensure designed roofs subjected to extreme snow loads a target reliability index 3.2, large partial factors for snow load that varies with COV of ground snow loads are expected to be used. [ABSTRACT FROM AUTHOR]

Embankment deformation is a key consideration in high speed railway construction. Frost heave due to temperature and moisture variation is critical to consider in areas of seasonally frozen ground. This paper examined ground temperatures, frost heave, and moisture content in 2013–2014 at two sites along the embankment of the Harbin-Dalian Passenger Dedicated Line (HDPDL) railway. The railway is in seasonally-frozen ground of Jilin Province, China. The embankment at one site (K977) was built on the undisturbed ground surface while the other was in a cut section (K1004). Displacement measurements over one year indicated that frost heave of 14 mm at K977 and 25 mm at K1004 occurred in ballast during the freezing season. During the annual freeze-thaw period, soil moisture content varied drastically in the upper 0.6 m. The frost depth and freezing index were strongly and positively correlated during the freezing season. Soil moisture content was regarded as the primary control on the amount of frost heave, while frost depth was secondary. Furthermore, water vapor diffusion may have been an important contributor to the formation of near-surface ice. At K1004 site, the maximum recorded deformation was large and exceeded the 15 mm Chinese standard for maximum allowable heave. This suggested that high ground water level increased the amount of frost heave. [ABSTRACT FROM AUTHOR]

The freezing index (FI) is an important index used in investigations of climate change, frozen ground degradation and frost heave resistance engineering design. In view of the fact that the deterministic effects of latitude and elevation are not considered in the frequency calculation of FI, we proposed an index-freezing method that considers the certainty effects of both elevation and latitude by referring to the index-flood method in this paper. The correlations between the FI and certainty factors (elevation and latitude) were obtained by multiple regression analysis. The effects of latitude and elevation were then removed by nondimensionalisation, and dimensionless FI sequences were subsequently obtained. Finally, the index-freezing method was verified by regional probability analysis. Using the daily average temperature data recorded at 10 major meteorological stations over the 1960–2020 period in Ningxia, the calculation process of the FI and its frequency distribution were provided. The results showed that the proposed FI method can not only remove the certainty effects of elevation and latitude but can also consider the uncertainty associated with interannual FI variations, thus providing more scientific, reasonable and accurate results. The generalised extreme value (GEV) distribution is the optimal frequency distribution of the nondimensional regional FI. The estimation errors of the missing data tests were mostly within 10%, and the residual sum of squares (RSS) and root-mean-square error (RMSE) values were also lower than those obtained through spatial interpolation, thus indicating that the interpolation precision of the proposed FI method was optimal. • Multiple regression analysis is able to decompose of certainty and uncertainty factors of freezing index time series recorded at multiple stations. • The GEV distribution is the optimal frequency distribution of the regional freezing index in Ningxia Province, China. • Missing data tests prove that the errors of the interpolation are mostly within 10%. • Regional analysis of freezing index is able to make up for the lack of observational data. [ABSTRACT FROM AUTHOR]

Rapid permafrost thawing triggered by heat release from the buried warm-oil pipeline would result in the instability of the pipeline, posing a potential risk of an oil spill in permafrost regions. Therefore, how to precisely control the ground temperature to mitigate pipeline foundation permafrost from thawing is of significant importance. Thermosyphon is a widely-accepted and extensively-used countermeasure against permafrost thawing in permafrost engineering. This paper presents 3-year (2015–2018) monitored data of ground temperature and geophysical survey results conducted by electrical resistivity tomography in April 2018, to investigate the thermal stabilizing effect of thermosyphons installed nearby the China-Russia crude oil pipeline (CRCOP) and the influencing factors. Furthermore, numerical simulation tests were conducted to evaluate their long-term cooling applicability and to optimize their layout parameters. Field observations show that the thermosyphons can cool down and even freeze the thawed soil layers around the CRCOP, prohibiting the infiltration of water into the thawing front to some extent and effectively mitigating the rapid thawing of permafrost beneath the pipeline. The performance of the thermosyphons is greatly influenced by the method and time of thermosyphon installation, as well as layout parameters including the number and longitudinal spacing. Two pairs of thermosyphons with a shorter spacing are unable to control the thawing of the underlying permafrost due to the non-anticipated higher oil temperature, the thermal erosion of water ponding, and climate warming. The simulated results indicate that thermosyphons perform well in the first 5 years after installation. Thermosyphon lowers the mean annual temperature of soils surrounding it by about 2 and 1.4 times when the evaporator section length is increased by 50% and the longitudinal spacing is decreased by 0.5 m, respectively. The application of thermosyphons has proven its strength for thermally stabilizing the pipeline foundation permafrost along the CRCOP. • 3-year ground temperature data and geophysical survey results are presented. • Thermosyphon can mitigate the rapid thawing of permafrost beneath the pipeline. • Thermosyphons performs most significantly in the first five years. • Lengthening thermosyphon and decreasing spacings are favorable for the better cooling effect. [ABSTRACT FROM AUTHOR]

In order to achieve the purpose of sealing water between adjacent jacked pipes in construction of long-distance and large-section tunnel, an innovative method called Freeze-Sealing Pipe Roof (FSPR) was applied to the Gongbei tunnel, which is a key part of Hong Kong-Zhuhai-Macau Bridge in China. Since the pre-constructed jacking pipes provides great convenience for flexible placement of freezing tubes inside, it is crucial to study the temperature field of different freezing states. This paper first established a new mathematical model considering radial offset of jacking pipe according to the practical engineering, and then the analytical solution to steady-state temperature field was also derived. Moreover, temperature distribution of four typical cross-sections were analyzed to evaluate the freezing effect on different paths. Results show that the analytical results are in good agreement with the numerical results, and the quasi-double-circle freezing model can be well applied to the practical problem of radial offset. Soil between steel pipes will be lowered to a sufficiently low temperature and form a fairly reliable water-sealing curtain. By designing the radial offset between freezing tubes in solid and hollow pipes, the freezing effect can be better ensured. The conclusions have important guiding significance for design and construction of FSPR method in future projects. • Temperature field of a special double-circle-piped freezing model is solved analytically. • The boundary separation property of the harmonic equation is used to solve the heat conduction problem. • The accuracy of complex analytical expressions is verified by numerical simulation. • Water sealing effect of FSPR method considering radial offset of jacking pipes is analyzed. [ABSTRACT FROM AUTHOR]

The role of vapor flow in unsaturated freezing soils is unclear, and usually ignored when analyzing water migration. Indeed, vapor flow is seldom considered in geotechnical design. On the other hand, frost heave damages were recently observed in a cold and arid region in China, where the groundwater table is about 20 m deep, and cannot be explained using the classical frost heave theory which focuses on the coupled flow of heat and liquid water. This paper presents a new approach for modeling moisture and heat movement in unsaturated freezing soils, in which the phase change of evaporation, condensation of vapor flow are taken into account. The method enables numerically stable solutions with energy and mass conservation. The performance of the proposed model was evaluated by a series of laboratory freezing experiments, which involve a 60 cm long soil column subjected to different initial conditions and boundary temperatures. It is shown that the proposed model is capable of effectively simulating the freezing process of an unsaturated soil. The vapor flux is shown to be significant, especially at the end stage where the freezing process is stabilized. Parametric analysis was carried out to clarify the role of vapor in moisture migration. The results show that vapor flow apparently contributes to ice formation and generally accounts for more than 10% of total water flux. The percentage of vapor flux in total flux (vapor flux ratio) positively relates to temperature gradient and freezing depth, but negatively relates to initial water content. Relations between vapor flux ratio and hydraulic parameters are less clear. [ABSTRACT FROM AUTHOR]

Permafrost in Northeastern China has significantly degraded due to global warming, deforestation and urbanization in the last few decades. The frost heave and thaw subsidence induced by freeze-thaw cycles of deep seasonal frozen ground have caused serious damage to infrastructures. The Shiwei-Labudalin (Shi-La) Highway is an important infrastructure connecting Shiwei town and Labudalin town of Argun city, Inner Mongolia, which passes through the areas covered by deep seasonal frozen ground or isolated patchy permafrost. In this paper, we mapped the long-term linear displacement trend and amplitude of seasonal displacement of the Shi-La Highway and its nearby areas, with an ascending Sentinel-1 dataset acquired from September 2016 to April 2020. Seasonal displacement amplitudes of 5–20 mm are widely detected in low-lying areas (e.g., the basin of the Gen and Derbugan rivers). The time lags between frozen ground displacement and temperature variations generally range from 10 to 80 days while larger values of 100–120 days caused by soil moisture or land cover difference are also observed. Linear creep displacement rates greater than −20 mm/yr are detected on mountainous slopes and sections of the Shi-La Highway in the line-of-sight (LOS) direction. Our results provide a method for evaluating highway stability in cold regions, which is helpful to highway route selection and design in Northeastern China. • Map displacement of frozen ground in northern Inner Mongolia using InSAR. • Freeze-thaw related and creep movement were identified on Shi-La highway. • Time lags between displacement and temperature are 10–120 days in flat areas. [ABSTRACT FROM AUTHOR]

In recent years, the construction of cold-region tunnels has increased in western China. However, the studies of the analytical elasto-plastic solution for the stress and deformation of surrounding rock in cold-region tunnels are limited. To solve this engineering problem and propose new theoretical insights for analysis and design, the elasto-plastic calculation model for surrounding rock in cold-region tunnels is established in this paper. In this model, the entire surrounding rock is divided into four zones, namely, the unfrozen elastic zone, the frozen elastic zone, the frozen plastic zone and the support zone. The frozen surrounding rock is assumed to conform to the ideal elasto-plastic model and the Mohr–Coulomb yield criterion. The stress and deformation fields in each zone are solved according to continuity conditions. A case is introduced to obtain the distribution of stress and strain in the surrounding rock of cold-region tunnels. The reason that the circumferential stress is less than the radial stress in the unfrozen zone is explained and the range of that is also addressed. Moreover, the location in which no displacement is generated is determined in the freezing circle. The produced high stress is mainly influenced by the linear frost strain. The results of stress field and strain field are verified by the existing elastic solution. At last, parameter analysis is performed to obtain the influence of the related parameters on plastic radius and the surrounding rock stresses at the inner and outer edges of the freezing circle. The results can guide for numerical simulations and field engineering practice. [ABSTRACT FROM AUTHOR]

Natural gas hydrate (NGH) is considered one of the most promising alternative energy sources in the 21st century. The exploitation and decomposition of NGHs could cause geological disasters and eco-environmental problems related to climate warming, seawater blue tides, submarine landslides, drilling platform collapses, slope instability, etc. Thus, an investigation of the eco-environmental effects of NGH exploitation and decomposition has scientific and practical significance. In this paper, the electrical characteristics of NGH reservoirs before and after NGH trial production in the Muli permafrost area of the Qilian Mountains are comparatively examined for the first time. The electrical structure models before and after NGH trial production are obtained through two-dimensional and three-dimensional inversion of the NE audio-magnetotelluric (AMT) sounding profile around production test well SK2. Notably, the electrical structure of the NGH reservoir changes greatly. The research indicates that (1) after NGH trial production, the formation resistivity increases remarkably within 200 m and burial depths in the range of 120– 340 m around the production test well; (2) the main reason for the increasing resistivity after trial production is the Joule-Thomson effect caused by depressurization production and the endothermic effect of NGH decomposition, which lead to the formation of ice-bearing strata; afterwards, we explain the formation process of ice-bearing strata after NGH trial production; and (3) we speculate that the formation stability is not adversely affected after NGH trial production. These findings and research results can provide guidance for subsequent geoenvironmental safety risk assessments of NGH development in permafrost areas. • Two AMT profiles are comparatively studied before and after NGH trial production. • The resistivity of NHG reservoir increases significantly after trial production. • Joule-Thomson effect and depressurization endothermic action is the main reason for ice-bearing strata formation. • The formation stability is not adversely affected after NGH trial production. [ABSTRACT FROM AUTHOR]

Abstract: In order to solve the freezing damage problem of tunnel in a cold region, an innovative tunnel lining ground heat exchangers (GHEs) heating system was introduced in China for the first time and applied to Linchang tunnel in Inner Mongolia. This new-type system utilized the tunnel linings as heat exchanger to extract geothermal energy from the surrounding rock in the middle part of the tunnel so as to heat tunnel lining and the drainage system at the tunnel entrance. As for the thermal analysis and design of it, the classical line heat source model and “hollow” cylindrical heat source model for borehole GHEs are not applicable. Therefore, a new line source model was put forward in this paper, which considered both composite medium and time-dependent boundary conditions. Its analytical solution was obtained using the superposition principle and finite integral transfer method. The calculated results from the new model were validated by the experimental data of thermal response tests. Furthermore, the new model was applied to analyze the impact factors of heat transfer performance for design optimization, including the ground temperature as well as the flow rate and the inlet temperature of heat carrier liquid. It was proven that the new model can provide adequate tools for the design of tunnel lining GHE heating system. [Copyright &y& Elsevier]

Abstract: Engineering construction in cold regions and artificial ground freezing projects require an understanding of the mechanical properties of frozen soils. An understanding of properties such as strength and deformation are important for engineering design purposes. In the past decades of years, because of the increase of the engineering, such as the Qinghai–Tibet Railway (QTR), the Qinghai–Tibet Highway and the Golmud–Lhasa Oilpipe (GLO), constructed in frozen soil regions on the Qinghai–Tibet Plateau, the study on the material properties of frozen soils in China was being developed quickly, and numerous research results were achieved. This paper summarizes these research fruits in four aspects: (1). Strength property of frozen soils, (2). Deformation behavior of frozen soils, (3). Constitutive models for frozen soils, (4). Dynamical property of frozen soils. This summary would be helpful for their convenient application in practical engineering, as well as for supplying foundation and developing direction of mechanical property research on frozen soils. [Copyright &y& Elsevier]

Abstract: In cold region, precipitation, air temperature and snow cover significantly influenced soil water and heat transfer, and thus freezing–thawing processes of active soil layer. On the basic of physical processes of water and heat balances and their transfers in the snow covered soil, a water-heat coupling model for snow cover and its underlying soil layers was established in this paper. Numerical solution of the model was conducted by a full-implicit finite volume method. Observation data of snow cover depth, soil water content and active soil depth at two typical sites in the northeast of Three-River Source Region of China were selected for model calibration and validation. The results indicate that the model can capture soil freezing–thawing processes at the two sites. Simulated results reveal that variations of soil water content, soil temperature and soil freezing depth depend on climate conditions of air temperature, precipitation and snow cover as well. In comparison of the simulated results at two sites, we know that thick snow cover hinders temperature transfer from air to soil, resulting in prolonging the time lag between air and soil temperatures, decreasing variations of soil temperature and soil water content and reducing soil freezing depths of active soil. [Copyright &y& Elsevier]

Abstract: A thawing ditch existing in permafrost region along the Qinghai–Tibet Railway is studied with their geological features, failure characteristics, ground temperatures, and influence on permafrost roadbed in this paper. The failure shows surface subsidence and horizontal slip on the shoulder. Integrated analysis from the field-monitored data show that the thawing ditch totally subsided more than 11cm from January 2008 to (month) 2010 and the average was close to 6cm a−1. The active layer on both shoulders of the thawing ditch has been slipped inward, and the max horizontal displacement in 0.5m depth was 5–6cm a−1. The warm season is the main period of the failure expanding in scale, especially from August to October. The mean annual ground temperature in shallow layer was about 0.9°C higher in the thawing ditch bottom than in the natural ground (remove about 20m) during the past two years (2008–2009). Due to the vegetation covered on the thawing ditch was destroyed, and the heat absorbed exceeds obviously heat released. The estimated result using the data in 2008 and 2009 shows that the input of heat into the permafrost below the thawing ditch was about 114,000kJ m−2 and was more than the output of 88,000kJ m−2 in twoyears. The heat absorbing starts in mid April, ends at the beginning of November, and lasts over 230days. In addition, the lateral thermal erosion of thawing ditch would influence the surrounding permafrost and damage the adjacent engineering infrastructure. The approximate calculation shows that about 90,000kJ heat was transported from thawing ditch to adjacent permafrost in 2009. Therefore, the permafrost beneath the thawing ditch has been degrading, warming, and declining in stability. [Copyright &y& Elsevier]

Abstract: China is developing DC ice-melting method for the de-icing of overhead transmission lines after the ice storm in 2008. Melting ice apart, the Joule heat produced by DC heats the conductor. It is significant to investigate the temperature characteristic of the ice-melting conductors in order to protect the conductor from being damaged by overheating. This paper puts forward a model to simulate the temperature-rising process of ice-melting conductor, and the results have been investigated in the artificial climate chamber. Our research shows that the ice-melting process can be divided into two stages, namely pre-ice-shedding and post-ice-shedding, and temperature characteristics of conductor of the former is dissimilar from that of the latter. In the first stage, the direct reason of the conductor temperature-raising is air-gap, and conductor temperature is affected by ice thickness, while in the second stage, it is influenced by wind velocity and ambient temperature. The conductor temperature of both stages can be adjusted by changing current density. [ABSTRACT FROM AUTHOR]

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: The Chinese-Russian Oil Pipeline (CROP), from Mohe to Daqing has a length of about 965km and traverses the Da Hinggan Mountains and part of Song(hua)-Nen(jiang) Plain in Northeastern China. This paper attempts to estimate some of the important elements concerning the environmental hazards and contingency plans along the pipeline. The first part reviews the potential impacts of the Mohe-Daqing Pipeline on the cold regions environment. It includes 1) the major environmental characteristics such as complicated permafrost, rugged terrain, harsh weather, and the diverse flora and fauna, vegetation the pipeline passes through; 2) the consideration of route selection; 3) potential environmental impacts of the CROP on the environmental factors; 4) countermeasures to alleviate changes to the local environment during the design, construction and operation stages. The second part presents the risk of oil spills, the subsequent environmental challenges after the start of operation of CROP, and contingency plans in response to potential oil spills. [Copyright &y& Elsevier]

Abstract: The proposed China–Russia Crude Oil Pipeline (CRCOP) will be subjected to strong frost heave and thaw settlement of the surrounding soil as it traverses permafrost and seasonally frozen ground areas in Northeastern China. The freezing–thawing processes, the development of the maximum frozen cylinder in taliks and thawed cylinder in permafrost areas, and the variations in the maximum freezing depths under the pipeline in taliks and thawing depths in different permafrost regions near Mo''he station, the first pumping station in China, were studied in detail using numerical methods in this paper. The inlet oil temperature at Mo''he station was assumed to vary from 10 to −6°C in a sine wave form during the preliminary design phase. Research results showed that the freezing–thawing processes of soils surrounding the buried pipeline had distinct differences from those in the undisturbed ground profile in permafrost areas. In summer, there was downward thawing from the ground surface and upward and downward thawing from the pipeline''s surface once the temperature of the oil rose above 0°C. In winter, downward freezing began from the ground surface but upward and downward cooling of the cylinder around the pipeline didn''t begin until the temperature of the oil dropped below 0°C. However, in the undisturbed ground profile, downward thawing from the ground surface occurred in summer and downward freezing from the ground surface and upward freezing from the permafrost table occurred in winter. The maximum thawing depths and thawed cylinder around the pipeline in warm permafrost enlarged with elapsing time and decreasing water content of the soils. In taliks, the maximum freezing depths and frozen cylinder around the pipeline kept shrinking with elapsing time and increasing water content of the soils. The freezing–thawing processes and development of the thawed and frozen cylinders around the pipeline were muted by any insulation layer surrounding the pipeline. Insulation had better thermal moderating on the heat exchange between the pipeline and the surrounding soils during the early operating period. But its role slowly weakened after a long-term operating. Research results will provide the basis for assessment and forecasting of engineering geological conditions, analysis of mechanical stability of the pipeline, foundation design, and pipeline construction and maintenance. [Copyright &y& Elsevier]

Abstract: The China–Russia Crude Oil Pipeline (CRCOP), 813mm in diameter, is designed to transport 603,000 barrels of Siberian crude oil per day across 1030km of frozen-ground. About 500 boreholes, with depths of 5 to 20m, were drilled and cored for analyses, and the frozen-ground conditions were evaluated. After detailed surveys and analyses of the permafrost conditions along the pipeline route, a conventional burial construction mode at a nominal depth of 1.5m was adopted. This paper discusses the principles and criteria for the zonation and assessment of the frozen-ground environments and conditions of engineering geology for the design, construction, and operation of the pipeline system based on an extensive and in-depth summary and analysis of the survey and exploration data. The characteristics of pipelining crude oil at ambient temperatures in the permafrost regions and the interactive processes between the pipeline and foundation soils were taken into account. Two zones of frozen-ground environment and conditions of engineering geology, i.e., seasonally-frozen-ground and permafrost, were defined on the basis of the regional distribution and differentiations in frozen-ground environments and conditions. Then, four subzones of the permafrost zone were classified according to the areal extent, taking into consideration the temperatures and thicknesses of permafrost, as well as changes in vegetation coverage. In the four subzones, 151 sections of engineering geology were categorized according to the ice/moisture contents of the permafrost, as well as the classes of frost-heaving and thaw-settlement potentials. These 151 sections are comprehensively summarized into four types for engineering construction and operation: good, fair, poor, and very poor, for overall conditions of engineering geology. The zonation, assessment principles and criteria have been applied in the design of the pipeline. They have also been used as the scientific bases for the construction, environmental management, operation and maintenance/contingency plans. [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: Field observations conducted on oil platforms in the Bohai Sea revealed that the offshore jacket structures, which can withstand the maximum static ice force, might suffer from severe vibrations when ice sheets pass through the legs of the structure. It has been proved that, when the natural frequency of narrow or flexible structures is close to or coincides with the predominant frequency of cyclical ice forces, severe ice-induced vibrations will be evoked. Excessive and consistent vibration will cause the discomfort of working crew, failure of deck facilities even structural fatigue failure. Therefore, it is imperative to seek economical ways to reduce the vibrations to an acceptable level. Based on full-scale tests and technical feasibility, the strategies of vibration mitigation are investigated and compared in this paper. The primary studies demonstrate that adding a Tuned Mass Damper (TMD, also called a Dynamic Vibration Absorber, DVA) is a feasible and practical approach to reduce vibrations. The efficiency of optimally designed TMD and one-directional conceptual TMD device has been presented in this study. Field ice load time history was used as loading scenario to assess the performance of TMD system. The results show that the supplemental device can favorably reduce the dynamic response of platform. [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]

Freeze shaft sinking is one of the main methods for the construction of vertical shaft in deep and thick topsoil. Freezing tube, frozen soil wall and shaft lining are the key to ensure the safety of freeze shaft sinking. Based on the on-site monitoring of the freeze shaft sinking project in Yuncheng coal mine in East China, this paper analyzes the variation law of freezing pressure, steel bar stress, concrete strain of the shaft lining, and frost heaving stress inside and outside the frozen soil wall in deep topsoil, and makes an in-depth analysis of the sudden change of the monitoring curves induced by the fracture of freezing tubes. The results show that: the freezing pressure in deep topsoil increases rapidly in early stage, reaching 66% - 86% of its' maximum value in 10 days, and tends to be stable after 30 days; the maximum freezing pressure generally approaches or even exceeds the initial horizontal earth pressure. The accumulation of frost heaving stress aggravates the stress and deformation of the frozen soil wall, freezing tube and shaft lining during shaft excavation, which is an important reason for the maximum freezing pressure to exceed the initial horizontal ground pressure and the fracture of freezing tube. The fracture of freezing tube causes local melting and weakening of the frozen soil wall, significantly affects the stress and deformation of the shaft lining, and induces the mutation of monitoring parameters. By means of monitoring the stress and deformation of shaft lining closely, it is feasible to judge and forewarn the fracture accident of freezing tube in time and take corresponding measures based on the sudden change of monitoring curves captured. • The variation laws of freezing pressure, stress and strain of outer shaft linging in freeze shaft sinking are obtained. • The control requirements of concrete early strength for outer shaft lining in deep topsoil are put forward. • A method for determining the external load of outer shaft lining for freeze shaft sinking in deep topsoil is proposed. • The variation law of frost heave stress inside and outside frozen soil wall in freezing and excavation is obtained. • The influence of freezing pipe fracture on shaft lining is obtained, which proves the feasibility of early warning. [ABSTRACT FROM AUTHOR]

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]

Abstract: An in situ testing of a selected railway embankment in Qingshuihe region, Tibet Plateau, is described where no artificial protection measure was employed. Based on the results obtained, characteristics of the distribution of geotemperature and settlement of the embankment are examined. An assessment of long-term stability of the embankment is made, and a kind of efficient engineering treatment is recommended in this paper. The study reveals: a) although the permafrost table did not move after embankment construction, the layer between ground surface and the permafrost table approached the phase-transition critical state, i.e. 0.0 °C. This layer is about 3.0 m thick, and is the major source of embankment settlement; b) the varying heat-absorption at different locations along the cross-section of the embankment leads to a differential settlement, and results in the longitudinal cracking; c) the settlement developed at a constant rate (about 0.06 m/year in the middle of the embankment) during the complete test period; d) the optimal railway embankment height differs from that for highways, and should be less. Further study of the optimal height should be carried out comprehensively and the results applied to engineering practice immediately, since this could not only keep the permafrost table stable but also limit the differential settlement to an acceptable level; e) asymmetrical protection measures should be employed to reduce the differential settlement and longitudinal cracking; f) it is most important that embankment construction in permafrost area be carried out during the cold season. [Copyright &y& Elsevier]

Abstract: Since the element free Galerkin method (EFGM) is based on moving least-squares (MLS) interpolants, it requires only a mesh of nodes and a boundary description, which are beneficial to some problems with the moving boundary conditions, such as the transient temperature field problems with phase change. Because freezing and thawing often takes place in embankments in cold regions, the phase transition must be considered in heat transfer calculation. Therefore, in this paper, the EFGM is presented to solve the thermal problem involving phase change in permafrost embankment. In the calculation, the latent heat is considered using the enthalpy-based method and the essential boundary condition is enforced by the Lagrange multipliers method. The EFGM code has been written in the FORTRAN language for obtaining the numerical solution. The result shows that, compared with the finite element solution, EFGM has more advantages such as better agreement with the observational data, high convergence rate, simple pre-processing and post-processing, etc. in a word, these analyses support the proposition for employing such a method for nonlinear temperature field involving the phase change in the actual railway project on permafrost. [Copyright &y& Elsevier]

According to the in situ measured data of the air temperature and ground temperature inside of Kunlun mountain tunnel on Qing–Tibet railway, China, the thawed extent of the permafrost surrounding the tunnel is very large, caused by the latent heat of the cast in situ concrete lining insulation during excavation in winter and other artificial activities. In this paper, taking the coupled effects of moisture transfer and heat conduction into account, a finite element formula of this problem is derived from the governing differential equations with phase change and moisture transfer equations using Galerkin''s solution. Using the computer program, predictions for the refreezing of Kunlun mountain permafrost tunnel are made. The analysis results show that the vault of Kunlun mountain tunnel would have been refrozen by 31 March 2004, the arch bottom by 30 September 2004 and the total tunnel by 30 September 2005, without insulation material. On the other hand, if the tunnel is fitted with insulation material, whose thermal conductivity is equal to 0.03 W/m.K and thickness of 0.05 m, the vault of Kunlun mountain tunnel would have been refrozen by 31 March 2004, the arch bottom by 31 December 2004, the left wall by 31 March 2006, and the right wall by 30 September 2006. Thus, insulation material will delay the refreezing of Kunlun mountain permafrost tunnel. The thawed extent of the permafrost surrounding the tunnel in cold regions caused by construction must be considered, and the time of the field observation should be extended, or observational results, such as their temperature and stress field, will greatly be different from results in stability. [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]

In this paper, a comprehensive measurement of air temperature in Zuomutai tunnel in China was conducted. Meteorological monitoring was performed at both outsides of the tunnel. The results show that the air temperature in the whole tunnel changes periodically with the ambient air temperature out of the tunnel in an approximately trigonometric function, even if the tunnel length is approximately 3000 m and the height is 7.1 m. The lowest temperature is lower than −8 °C. In winter, the air temperature outside the tunnel is lower than that inside the tunnel, which causes the dominant airflows from the low elevation portal to high elevation portal. It is contrary in summer. Therefore, the temperature changes in the sections at the two sides of the tunnel are different, and the temperature distributions are asymmetrical along the tunnel length. The air temperature at the tunnel vault is generally higher than that at the waist and side wall in winter, especially nearby the dominant airflow outlet. With the temperature rising, the temperature difference decreases. The sharp rises or drops of air temperature in the tunnel caused by the intermittent traffic winds or natural winds blowing to the tunnel are transient. The air temperature will soon return to the overall change trend. The results can provide references for frost-proof design in cold region tunnels. • A field air temperature measurement was conducted in a long cold region tunnel. • The temperature distribution characteristics and changing rules in the whole tunnel were revealed. • The influence factors of the air temperature in the tunnel were analyzed. [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]