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In order to accurately understand the relationship between soil structure and climate feedback in the frozen soil area of Mu Us Sandy Land, China, and to explore the key control factors for the structural stability of soft rock and sand compound soil under freeze-thaw environment, the indoor freeze-thaw simulation experiment was applied. The results show that the freeze-thaw period, clay content, organic matter and their interactions have significant effects on the stability of composite soil aggregates. After 10 freeze-thaw cycles, the aggregate content in the 1:0, 1:1, 1:2, and 1:5 composite soil with a diameter greater than 1mm decreased by 55%, 34%, 44%, and 57%, while the aggregate content with a diameter less than 1mm increased by 91%, 70%, 66%, and 87%, and the aggregate composition of each particle size is mainly concentrated in the range of 0.25-0.5 mm. Under freeze-thaw conditions, the changes of clay and aggregate content in different proportions of composite soil is the same, all showing 1:1>1:2:>1:5, and 1:1 composite soil with >0.25mm aggregate content is the highest. Under freeze-thaw alternations, 1:1, 1:2 and 1:5 composite soil aggregates (<0.5 mm) showed a significant positive correlation with soil organic matter, while there is no significant correlation between large aggregates (>1 mm) and soil organic matter. In conclusion, the freeze-thaw cycle reduces the structural stability of composite soil aggregates, and clay are the key controlling factors for the formation and structural stability of composite soil aggregates. [ABSTRACT FROM AUTHOR]

Frozen soil may cause structures to have different damage statuses, as revealed by earthquakes in northeastern China. ABAQUS (2019), a numerical simulation software application, was adopted to systematically and deeply study the structural seismic response, considering seasonal frozen soil–structure interaction under different ground motion intensities and soil ambient temperatures. The results showed firstly that the variation in soil ambient temperature had a great influence on the seismic response of the structure, as indicated by the damage status of the structure obtained through numerical simulation. Secondly, through further analysis of the numerical simulation results, the influence amplitude of different soil temperatures on the structural seismic response was quantitatively analyzed and systematically summarized. Finally, the structural seismic damage with negative ambient temperature could be significantly lower than that with positive temperature normally. Additionally, such an internal change mechanism was also objectively analyzed to verify the reliability of the conclusion. [ABSTRACT FROM AUTHOR]

Freeze–thaw (FT) erosion intensity may exhibit a future increasing trend with climate warming, humidification, and permafrost degradation in the Qinghai–Tibet Plateau (QTP). The present study provides a reference for the prevention and control of FT erosion in the QTP, as well as for the protection and restoration of the regional ecological environment. FT erosion is the third major type of soil erosion after water and wind erosion. Although FT erosion is one of the major soil erosion types in cold regions, it has been studied relatively little in the past because of the complexity of several influencing factors and the involvement of shallow surface layers at certain depths. The QTP is an important ecological barrier area in China. However, this area is characterized by harsh climatic and fragile environmental conditions, as well as by frequent FT erosion events, making it necessary to conduct research on FT erosion. In this paper, a total of 11 meteorological, vegetation, topographic, geomorphological, and geological factors were selected and assigned analytic hierarchy process (AHP)-based weights to evaluate the FT erosion intensity in the QTP using a comprehensive evaluation index method. In addition, the single effects of the selected influencing factors on the FT erosion intensity were further evaluated in this study. According to the obtained results, the total FT erosion area covered 1.61 × 106 km2, accounting for 61.33% of the total area of the QTP. The moderate and strong FT erosion intensity classes covered 6.19 × 105 km2, accounting for 38.37% of the total FT erosion area in the QTP. The results revealed substantial variations in the spatial distribution of the FT erosion intensity in the QTP. Indeed, the moderate and strong erosion areas were mainly located in the high mountain areas and the hilly part of the Hoh Xil frozen soil region. [ABSTRACT FROM AUTHOR]

The soil freeze/thaw (FT) state has emerged as a critical role in the ecosystem, hydrological, and biogeochemical processes, but obtaining representative soil FT state datasets with a long time sequence, fine spatial resolution, and high accuracy remains challenging. Therefore, we propose a decision-level spatiotemporal data fusion algorithm based on Convolutional Long Short-Term Memory networks (ConvLSTM) to expand the SMAP-enhanced L3 landscape freeze/thaw product (SMAP_E_FT) temporally. In the algorithm, the Freeze/Thaw Earth System Data Record product (ESDR_FT) is sucked in the ConvLSTM and fused with SMAP_E_FT at the decision level. Eight predictor datasets, i.e., soil temperature, snow depth, soil moisture, precipitation, terrain complexity index, area of open water data, latitude and longitude, are used to train the ConvLSTM. Direct validation using six dense observation networks located in the Genhe, Maqu, Naqu, Pali, Saihanba, and Shandian river shows that the fusion product (ConvLSTM_FT) effectively absorbs the high accuracy characteristics of ESDR_FT and expands SMAP_E_FT with an overall average improvement of 2.44% relative to SMAP_E_FT, especially in frozen seasons (averagely improved by 7.03%). The result from indirect validation based on categorical triple collocation also shows that ConvLSTM_FT performs stable regardless of land cover types, climate types, and terrain complexity. The findings, drawn from preliminary analyses on ConvLSTM_FT from 1980 to 2020 over China, suggest that with global warming, most parts of China suffer from different degrees of shortening of the frozen period. Moreover, in the Qinghai–Tibet region, the higher the permafrost thermal stability, the faster the degradation rate. [ABSTRACT FROM AUTHOR]

The treatment of chromium-contaminated soil in seasonal frozen soil areas has been the subject of recent interest. Polyurethane (PU), as a polymer material with excellent freeze–thaw resistance and abrasion resistance, has the potential to solidify Chromium-Contaminated soil in seasonal frozen soil areas. However, there is a lack of research on the mechanism of PU involved in solidifying/stabilizing chromium-contaminated soil in seasonal frozen regions from the perspective of pore structure and functional group coordination bonds. In this study, the leaching behavior of PU with different contents under different freeze–thaw cycles was analyzed, and the mechanism of PU in seasonal frozen regions was explored from the perspective of pores and functional groups by combining various microscopic characterization methods. The results show that PU can effectively resist the deterioration of chromium-contaminated soil after freeze–thaw cycles and can better prevent the harm of secondary leaching. The leaching concentration of chromium ion is only 1.09 mg/L, which is below China's regulatory limits. PU is beneficial for inhibiting the expansion of ice crystals in chromium-contaminated soil in seasonal frozen soil areas. PU solidifies chromium by physical encapsulation and complexation reactions. The amide functional groups, methyl-CH3 and isocyanate groups in PU play a leading role in the complexation with chromium. Although the freeze–thaw cycle will destroy the coordination bond between the PU functional group and chromium, chromium cannot break through the bond of PU film. This study confirmed the feasibility of using PU to solidify Chromium-Contaminated soil in seasonal frozen soil areas, which can provide research support and reference for in situ engineering in the future. [ABSTRACT FROM AUTHOR]

It is necessary to further investigate the spatial considerations, temporal characteristics, and drivers of change affecting the beginning and end of soil freezing and thawing, including the maximum depth of the seasonal freezing (MDSF) and the active layer thickness (ALT) in Northeast China. Hourly soil temperature, among other data, from 1983–2022 were investigated, showing a delay of about 6 days in freezing. In contrast, thawing and complete thawing advanced by about 26 and 20 d, respectively. The freezing period and total freeze-thaw days decreased by about 29 and 23 days, respectively. The number of complete thawing period days increased by about 22 days, while the MDSF decreased by about 25 cm. The ALT increased by about 22 cm. Land Surface Temperature (LST) is the main factor influencing the beginning and end of soil freezing and thawing, MDSF and ALT changes in Northeast China; air temperature, surface net solar radiation, and volumetric soil water content followed. The influence of the interacting factors was greater than the single factors, and the interactive explanatory power of the LST and surface net solar radiation was highest when the soil started to freeze (0.858). The effect of the LST and the air temperature was highest when the soil was completely thawed (0.795). LST and the volumetric soil water content interacted to have the first explanatory power for MDSF (0.866) and ALT (0.85). The results of this study can provide scientific reference for fields such as permafrost degradation, cold zone ecological environments, and agricultural production in Northeast China. [ABSTRACT FROM AUTHOR]

Heilongjiang Province, the largest commercial grain base in China, experiences significant challenges due to the environmental effects on its soil. The freezing and thawing cycle in this region leads to the transport of water and heat, as well as the exchange and transfer of energy. Consequently, this exacerbates the flooding disaster in spring and severely hampers farming activities such as plowing and sowing. To gain a better understanding of the freezing and thawing mechanisms of farmland soil in cold regions and prevent spring flooding disasters, this study focuses on Heilongjiang Province as a representative area in northeast China. The research specifically investigates the frozen and thawed soil of farmland, using a large-scale low-temperature laboratory to simulate both artificial and natural climate conditions in the cold zone. By employing the similarity principle of geotechnical model testing, the study aims to efficiently simulate the engineering prototypes and replicate the process of large-span and long-time low temperatures. The investigation primarily focuses on the evolution laws of key parameters, such as the temperature field and moisture field of farmland soil during the freeze–thaw cycle. The findings demonstrate that the cooling process of soil can be categorized into three stages: rapid cooling, slow cooling, and freezing stabilization. As the soil depth increases, the variability of the soil temperature gradually diminishes. During the melting stage, the soil's water content exhibits a gradual increase as the temperature rises. The range of water content variation during thawing at depths of 30 cm, 40 cm, 50 cm, and 80 cm is 0.12% to 0.52%, 0.47% to 1.08%, 0.46% to 1.96%, and 0.8% to 3.23%, respectively. To analyze the hydrothermal coupling process of farmland soil during the freeze–thaw cycle, a theoretical model of hydrothermal coupling was developed based on principles of mass conservation, energy conservation, Darcy's law of unsaturated soil water flow, and heat conduction theory. Mathematical transformations were applied after defining the relative degree of saturation and solid–liquid ratio as field functions with respect to the relative degree of saturation and temperature. The simulated temperature and moisture fields align well with the measured data, indicating that the water–heat coupling model established in this study holds significant theoretical and practical value for accurately predicting soil temperature and moisture content during the spring sowing period, as well as for efficiently and effectively utilizing frozen soil resources in cold regions. [ABSTRACT FROM AUTHOR]

Based on multi‐source data, including observation, analysis, model calculation, satellite remote sensing, and scenario estimation data, this study has systematically analysed the warming and dry–wet change characteristics of the Yellow River's upper reaches in the last 60 years. The causes and features of the current warming and humidification and their impact on surface water resources are also discussed. This study found that since 1961, the average temperature in the Yellow River's upper reaches has increased at a rate of 0.37°C/10a, which is more significant than the increases observed for the world, China, and even northwest China in the same period. At the beginning of this century, the rate of change in precipitation in the Yellow River's upper reaches reversed direction from decreasing to increasing, with a significant increase (35 mm/10a) since 2000. Therefore, climate change has shown a significant warming and humidification trend in the upper reaches of the Yellow River. From the dynamic change perspective, the Yellow River's upper reaches were warming and drying in each climatic period from 1961 to 2010; however, the tendency towards dryness slowed period by period. In contrast, the region showed consistent warming and humidification from 1991 to 2020. From the perspective of multiple time scales, the change in average temperature is mainly dominated by the multi‐decadal scale. In contrast, precipitation is dominated by interannual change. The increase in the multi‐decadal component in average temperature and precipitation explains the current warming and humidification. Precipitation changes in the upper reaches of the Yellow River Basin are mainly affected by the westerly circulation, the East Asian summer monsoon, and the South Asian summer monsoon circulation systems. However, precipitation was affected by different circulation factors on different time scales. On an interannual scale, it was mainly affected by the South Asian summer monsoon circulation. On an interdecadal scale, it was mainly affected by the westerly wind and the East Asian summer monsoon circulation. On a multi‐decadal scale, it was jointly influenced by the westerly wind, the East Asian summer monsoon, and the South Asian summer monsoon circulation. Under the control of multi‐decadal synergistic enhancement of the westerly, the East Asian summer monsoon, and the South Asian summer monsoon circulations, the vertical field shows an abnormal upward movement. There has been a significant abnormal easterly and southerly airflow that transports water vapour, and cold air is transported along the northwest airflow at the back of the Mongolian cyclone, which makes the climate in the upper reaches of the Yellow River more humid. The warming and humidifying of the upper reaches of the Yellow River has significantly increased runoff and lake area and significantly degraded the frozen soil. The surface water budget in the Yellow River's upper reaches has significantly responded to the current warming and humidification. The actual surface evapotranspiration and surface runoff increased significantly, but the net surface water budget still showed a decreasing trend. The increase in precipitation did not change the surface water deficit. [ABSTRACT FROM AUTHOR]

Climate warming exacerbates the degradation of the mountain cryosphere, including glacier retreat, reduction in snow cover area, and permafrost degradation. These changes dramatically alter the local and downstream hydrological regime, posing significant threats to basin-scale water resource management and sustainable development. However, there is still a lack of systematic research that evaluates the variation of cryospheric elements in mountainous catchments and their impacts on future hydrology and water resources. In this study, we developed an integrated cryospheric-hydrologic model, referred to as the FLEX-Cryo model. This model comprehensively considers glaciers, snow cover, frozen soil, and their dynamic impacts on hydrological processes in the mountainous Hulu catchment located in the Upper Heihe river of China. We utilized the state-of-the-art climate change projection data from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) to simulate the future changes in the mountainous cryosphere and their impacts on hydrology. Our findings showed that the two glaciers in the Hulu catchment will completely melt out around the years 2045–2051. By the end of the 21st century, the annual maximum snow water equivalent is projected to decrease by 41.4 % and 46.0 %, while the duration of snow cover will be reduced by approximately 45 and 70 days. The freeze onset of seasonal frozen soil is expected to be delayed by 10 and 22 days, while the thaw onset of permafrost is likely to advance by 19 and 32 days. Moreover, the maximum freeze depth of seasonal frozen soil is projected to decrease by 5.2 and 10.9 cm per decade, and the depth of the active layer will increase by 8.2 and 15.5 cm per decade. Regarding hydrology, runoff exhibits a decreasing trend until the complete melt-out of glaciers, resulting in a total runoff decrease of 15.6 % and 18.1 %. Subsequently, total runoff shows an increasing trend, primarily due to an increase in precipitation. Permafrost degradation causes the duration of low runoff in the early thawing season to decrease, and the discontinuous baseflow recession gradually transitions into linear recessions, leading to an increase in baseflow. Our results highlight the significant changes expected in the mountainous cryosphere and hydrology in the future. These findings enhance our understanding of cold-region hydrological processes and have the potential to assist local and downstream water resource management in addressing the challenges posed by climate change. [ABSTRACT FROM AUTHOR]

Downward solar radiation (DSR) and air temperature (Ta) have significant influences on the thermal state of frozen ground. These parameters are also important forcing terms for physically based land surface models (LSMs). However, the quantitative influences of inaccuracies in DSR and Ta products on simulated frozen ground temperatures remain unclear. In this study, three DSR products (CMFD‐SR, Tang‐SR, and GLDAS‐SR) and two Ta products (CMFD‐Ta and GLDAS‐Ta) were used to force an LSM model in an alpine watershed in Northwest China, to investigate the sensitivity of simulated ground temperatures to different DSR and Ta products. Compared to a control model (CTRL) forced by in situ observed DSR, ground temperatures simulated by the experimental model forced by GLDAS‐SR are obviously decreased because GLDAS‐SR is much lower than in situ observations. Instead, simulation results in models forced by CMFD‐SR and Tang‐SR are much closer to those of CTRL. Ta products led to significant errors in simulated ground temperatures. In conclusion, both CMFD‐SR and Tang‐SR could be used as good alternatives to in situ observed DSR for forcing a model, with acceptable errors in simulation results. However, more care need to be paid for models forced by Ta products instead of Ta observations, and conclusions should be carefully drawn. [ABSTRACT FROM AUTHOR]

With the rapid development of China's economy, the linear traffic infrastructure in the permafrost region has also developed rapidly. Many engineering problems in pile-supported bridges are caused by the freeze–thaw cycles and seismic activity on the roadbed when linear traffic passes over the frozen ground. Therefore, this study focused on the seismic response of a pile-supported bridge in frozen ground. A three-dimensional (3D) nonlinear finite-element (FE) model was established based on a pile-supported bridge, and various modeling techniques and methods were presented in detail. Specifically, the p−y curves in the frozen or unfrozen soil were calculated based on the experimental results from modeling the soil–pile interactions. Based on the computed results, the seismic response of a pile-supported bridge structure in the frozen ground was comprehensively investigated and compared with that in the unfrozen ground. The effect of the frozen ground on the seismic response of a bridge structure was systematically explored. The modeling technique and the derived insights could be significant for pile-supported bridges in frozen ground. [ABSTRACT FROM AUTHOR]

Microtremor recording tests using an accelerometer were carried out in this paper with the aim of characterizing the effects of seasonally frozen soil on the seismic site response, including the two-direction microtremor spectrum, site predominant frequency, and site amplification factor. The study selected eight typical seasonal permafrost sites in China for site microtremor measurements during both summer and winter seasons. Based on the recorded data, the horizontal and vertical components of the microtremor spectrum, HVSR curves, site predominant frequency, and site amplification factor were calculated. The results showed that seasonally frozen soil increased the predominant frequency of the horizontal component of the microtremor spectrum, while the effect on the vertical component was less noticeable. It indicates that the frozen soil layer has a significant impact on the propagation path and energy dissipation of seismic waves in the horizontal direction. Furthermore, the peak values of the horizontal and vertical components of the microtremor spectrum decreased by 30% and 23%, respectively, due to the presence of seasonally frozen soil. The predominant frequency of the site increased by a maximum of 35% and a minimum of 2.8%, while the amplification factor decreased by a maximum of 38% and a minimum of 11%. Additionally, a relationship between the increased site predominant frequency and the cover thickness was proposed. [ABSTRACT FROM AUTHOR]

A water delivery system can be gradually away from the normal state of the canal operation in northern China in winter. Water diversion projects can be launched to meet the harsh requirement on the large and medium-sized city's residents living water and industrial water consumption, as the guaranteed rates increased. However, the existing mechanical model of the canal with the water delivery cannot fully consider the difference between the freezing and underwater non-freezing areas in winter, particularly for the continuity of soil. It is a high demand to combine the difference in shear stiffness between frozen soil and non-frozen soil. Pasternak model with two parameters can be expected to consider the soil continuity in the freezing area, whereas, the traditional Winkler model can be adopted in the non-freezing area. By contrast, the Winkler model with only a few parameters can be easily calculated for definite physical significance. In this study, the combined Winkler-Pasternak model was proposed for the frost-heaving mechanical analysis of the trapezoidal canal with water delivery in winter. Taking a trapezoidal canal with water delivery in winter in the Manas River basin in Xinjiang of western China as a prototype, the real normal frost-heaving amount, and subsidence deformation of the canal lining plate were also calculated using the improved model, Winkler and Pasternak model. Then, the bending moment was calculated with the upper surface stress of each section of the lining plate. The results indicate that the lining plate was divided into three parts of frost heave, subsidence and frost heavesubsidence transition section. Three models better represented the basic change trend of normal displacement of the lining plate. Meanwhile, the improved model was in better agreement with the measurement. A comparative analysis showed that the improved model was much more accurate than the traditional Winkler model in the freezing area, whereas, some errors but trivial differences were compared with the Pasternak model in the non-freezing area. Furthermore, the improved model shared the excellent performance of the Winkler model, such as simple calculation, clear physical meaning, and few required parameters. The bending moment of sections decreased rapidly in the freezing area with the increase of groundwater depth. The risk of frost-heaving damage to the canal lining plate was dramatically reduced at the groundwater level by appropriate drainage measures. The position in the frozen soil area of the lining plate easy to crack was located at 10.0%~23.3% of the lining plate length away from the waterline. The optimal operation conditions were adopted in the ice-free water delivery of the trapezoidal canal in winter. The improved model can be also applied to the ever-increasingly common situation of water delivery with the ice cover. The finding can provide a strong reference to design the frost heave resistance of the trapezoidal canal with water delivery in winter. [ABSTRACT FROM AUTHOR]

Uneven frozen heave can cause some damage to the canal lining structure, particularly in the frozen soil in the north cold region of China. The frost-heaving damage of canal lining is closely related to the lining-frozen soil contact action. Some relations of contact consist of the contact surface, such as the freezing constraint, and friction slip. The lining stress can also depend directly on the separate conditions. However, the current simulation of the lining-frozen soil contact is mostly focused on the steady state. It is still lacking in the experimental verification of the mechanical parts. Taking the integral U-shaped canal frost heaving damage experiment in the Hetao irrigation area as the prototype, this research aims to construct the canal frost heave model with/without the contact relationship. Finite element (FE) software ABAQUS was selected to simulate the frostheaving damage process of the model. Two models were evaluated to compare the experimentally monitored data from the subsoil temperature field, layered frost heave displacement, and soil stress. A systematic analysis was made to determine the stress state and damage mechanism of the canal lining. The experimental and simulation were integrated to clarify the influence of lining-frozen soil separation and sliding process on the frost-heaving damage of the canal. The results show that the simulation considering the contact model was more consistent with the field test conditions, compared with no contact. There were the basically same distributions of temperature field between the experiment and simulation with/without contact. Specifically, the simulated freezing depths of the shady and sunny slopes increased by 2.44% and 1.68%, respectively, whereas, the freezing depth of the canal bottom decreased by 4.26%, compared with the experimental. Small errors were found between the experimental and simulated subsoil and lining normal frost heave displacement. The consideration of contact posed a weak limiting effect on the canal slope subsoil freezing. The average relative errors were 7.1% and 13.9% between the simulated and experimental data with/without contact, respectively. Moreover, the simulated stress peak at the side slope reached 3.3 times of the contact model. The voids were generated between the canal bottom lining and the foundation soil in the experimental and the considered contact model. By contrast, there were continuously increasing tensile stresses in the simulations without considering contact. The separation and sliding process between the lining-frozen soil contact surface were visualized dynamically to combine the considered contact model with the experiment. The lining at the bottom of the canal was the first to separate from the subsoil after the onset of frost heave, due to the inhomogeneity of the subsoil frost heave. There was no transferred contact stress. After that, relative sliding occurred between the lining and the frozen soil at the side slope. As such, the originally restrained lining stress was released. More importantly, the frost heave displacement of the lining was still increasing in the process of stress release. The sliding process changed the stress development trend from the "force increase" to the "force release". The peak values of normal stress were reduced by 903% and 164% on the upper and lower surfaces of the lining under the releasing force of the simulated slip in the considering contact model, compared with the simulation without considering contact. Meanwhile, the peak value of tangential force was reduced by 248% on the lower surface. All peak stresses occurred on the slightly shady slope at the bottom of the canal, where the frost-heaving damage was more likely to occur. The finding can provide a strong reference for the design and structural optimization of the frost heave prevention of canals in cold regions. [ABSTRACT FROM AUTHOR]

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The salinization of farmland soil is exacerbated during the freeze–thaw (FT) process, endangering agricultural production. The change of soil salt ions results in the formation and development of soil salinization. The objectives of this study were to investigate the migration characteristics of salt ions during the FT process, identify the effects of inconsistencies in ions transport on the development of soil salinization chemical properties. A six-month field observation was conducted from November 2020 to April 2021 in the Hetao Irrigation District, China, a typical seasonally frozen soil area affected by salinization. Soil salt ions, soil moisture content (SMC), soil temperature, and pH were measured. Soil salt content (SSC), sodium adsorption ratio (SAR) were calculated. The ions accumulated in the frozen soil layer during the freezing period in the order of Cl− > Mg2+ > Ca2+ > Na+ > SO42−, and accumulated in the topsoil during the thawing period in the order of Cl− > Na+ > Mg2+ > Ca2+ > SO42−, while the change in HCO3− was mostly the opposite. The FT process changed the main salt anions from sulfate to chloride. After the FT process, the topsoil was endangered by high salinization, excess Cl− toxicity, and a potential alkalization threat. This study has great guiding significance for the management and control of soil salinization before spring sowing in saline areas. [ABSTRACT FROM AUTHOR]

The Sichuan–Tibet Railway (STR) is currently under construction and serves as an important transportation route in western China. Identifying potential geohazards along the route is important for project construction. However, research on the frozen soil of the Western Sichuan Plateau, and on frozen soil identification using interferometric synthetic aperture radar (InSAR) is relatively negligible. As a low-cost, all-weather spatial geodesy tool, InSAR is frequently used for geohazard identification. We selected a study area located along the Litang section of the STR, starting from Litang County in the east and extending 60 km to the west. The geological conditions along the line are complex, with numerous fault zones and hidden danger points for landslide. To identify unstable slopes along the line, distribute scatterer InSAR (DS-InSAR) was used to obtain surface displacement information from 2018 to 2021. Based on the displacement information obtained from the ascending and descending orbit images from Sentinel-1, a spatial density clustering method identified 377 and 388 unstable slopes in the study area, respectively, of these, 132 were consistent. The identified unstable slopes were mostly located in areas with a relatively high altitude and moderate slope. The Luanshibao landslide, which is a typical landslide in the study area, had notable signs of displacement, where the displacement rate along the back edge of the landslide can reach 20 mm/a. An inversion method for the seasonal frozen soil area distribution was proposed based on the periodic subsidence and uplift model and time-series monitoring data; the calculated seasonal freeze–thaw amplitude exceeded 20 mm. Further analysis revealed a 2-month lag in the response of the freeze–thaw phenomenon to the air temperature. This study demonstrated that DS-InSAR offers optimal surface displacement data, which can provide an important basis to identify engineering geological hazards. [ABSTRACT FROM AUTHOR]

The Lanlin 750-kV electrical transmission line is 162.45 km long and traverses more than 3.27 km in highly frost-susceptible soil in Lintao County, China, possibly inducing several engineering problems related to frozen soil in the transmission tower foundation. To study the frost heave characteristics of a reinforced concrete foundation in a seasonally frozen alpine region, in this study, physical model tests were performed on independent reinforced concrete foundations under highly frost-susceptible soil conditions and verified via numerical simulations. The temperature field evolution, tangential frost heaving force, unfrozen water content, and frost heave of highly frost-susceptible soil in an open water-refill environment and under dead load were investigated. The influences of surface temperature, overburden loads, and the buried depth of the groundwater level on the frost heave, tangential frost heaving force, and vertical displacement of the foundation were considered in the numerical simulations. Results showed that when the soil is close to the surface, the response of the temperature field is fast and the range of temperature variations is wide. The tangential frost heaving force was the largest in the middle and upper areas of the foundation, reaching a maximum value of 2.18 kN; moreover, the frozen depth and frost heave were 210.42 and 7.20 mm, respectively. The variation curves of the unfrozen water content were similar at all depths, and the replenished water content increased linearly with time. The numerical simulation results showed that the surface temperature considerably influences the frost heave deformation of the foundation, the dead load has a substantial restraining effect on the tangential frost heaving force and vertical displacement of the foundation, and the groundwater level influences the frost heaving ratio and the increment rate of frost heaving force. The fitting degree between the experimental and simulation results was good. Finally, measures for controlling frost heave to guide engineering practices were proposed based on the experimental study and numerical calculation. [ABSTRACT FROM AUTHOR]

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Salinization in frozen soil has posed a serious threat to the emergence and growth of crops in the next growing period. It is of great importance for the accurate detection of the content and composition of soil salt during the freeze-thaw period. Fortunately, the spectral data can be used to monitor the soil salinity during the crop growing period, particularly for the soil under an unfrozen state. However, the monitoring models under the unfrozen state cannot suitable for the frozen soil, due to the variation in the soil reflectance during freezing. In this study, an inversion model was established for the soil water-soluble salt ions in the frozen state using hyperspectral technology. A systematic analysis was made to compare the accuracy of the model in the frozen and unfrozen states. The soil samples were first collected with different salinity gradients from the Jiefangzha Irrigation Area of Hetao Irrigation District in the Inner Mongolia of China. The contents of major water-soluble salt ions (i.e., HCO3-, Cl-, CO32-, SO42-, K+, Na+, Ca2+, and Mg2+) were then measured in the unfrozen soil. The hyperspectral reflectance of soil samples was also measured by the ASD FieldSpec 3 instrument. Secondly, the soil samples were then frozen at -15°C for 12h. After that, the above-mentioned hyperspectral reflectance and ion contents were measured once again after freezing. The raw spectral data was also processed using standard normal variable (SNV) for the subsequent model construction, in order to make the hyperspectral curves smoother. Thirdly, two-thirds of the soil samples were used for the modeling (n = 78), while one-third for the validation (n = 39). The concentration gradient method was utilized to ensure the statistical characteristics of the modeling and the validation sets resembled that of the whole sample set. At the same time, the sensitive spectral intervals of each water-soluble salt ion were selected using variable importance in projection (VIP). The hyperspectral inversion model was formulated for the major water-soluble salt ions content with the sensitive spectral bands using partial least squares regression (PLSR), support vector regression (SVR), and extreme learning machine (ELM). Finally, the performances of these models were evaluated by the determination coefficient of calibration sets (RC 2), determination coefficient of prediction sets (RP 2), root mean square error (SRMSE), and residual predictive deviation (SRPD). The results showed that the VIP hyperspectral monitoring model managed to invert the most content of the water-soluble salt ions in the frozen soil, but the inversion accuracy of different ions varied greatly. Among them, the prediction accuracies of Cl-and K+ were extremely high with an RPD of above 2.5. There was a reasonably good prediction accuracy of SO42-, Ca2+, and Na+ (2.0

Seasonally frozen soil regions refer to those areas where soil is frozen for 15 days or more per year. More than half of land surface is occupied with the seasonal snow cover in China. The freeze-thaw process can significantly change the soil properties, as well as the water and heat transferring in the vadose zone. Among them, temperature and water vapor have posed a significant impact on the soil moisture, due to the soil subjected to the dry condition in most of the seasonally frozen regions (belonging to the arid and semi-arid areas). It is gradually recognized as the significant effect of vapor flow on the soil water movement for both freezing and non-freezing periods over the past several decades. It is a high demand to couple the water, vapor, and heat transport suitable for the actual conditions of seasonally frozen soil regions, in order to reveal the influencing mechanism of soil hydrological cycle. The coupled theory of water, vapor, and heat transport was firstly proposed by Philip and de Vries. The total soil water flux was then divided into four components, including the liquid water flux and water vapor flux driven by water potential and temperature gradients, respectively. Since then, extensive researches were also carried out to continuously improve on the coupled transport. Once the soil was frozen, the liquid water, vapor, and ice were coexisted in the unsaturated zone. Two aspects were also observed in the influence of phase changes between liquid water and ice on the coupled water, vapor, and heat transport. Several hydraulic parameters were calculated to determine the hydrological cycle, such as the soil freezing curve, and hydraulic conductivity for the liquid water. The spatial and temporal distributions of soil moisture in the vadose zone were dominated by the seasonally freeze-thaw process as well. The contents of unfrozen water and ice also changed significantly with the variations of soil temperature. Numerical simulation was gradually utilized in this research field with the ever-increasing computational capacity and simulation accuracy. Great challenges were still remained on the coupled numerical model, due to the influence from the ice-water phase change. An appropriate coupling model was crucial to the numerical simulation via the reasonable simplification. The underlying mechanism of coupled water and vapor flow was gradually revealed from the simulation using different models. Specifically, the vapor flux was one of the most important components in the soil water movement, usually accounting for 10%-30% of the total water flux. Furthermore, the vapor flux was depended mainly on the relatively low soil moisture and large temperature gradient in the shallow layer. The vapor flow was much more significant during the freezing period, due mainly to the impeded flow of liquid water in the presence of ice. Consequently, some research directions that needed to be strengthened in this field were proposed to deepen the theoretical fundamentals and the practical tasks in the seasonal frozen soil areas. Firstly, the condensation and accumulation of water vapor can greatly contribute to the vegetation under soil drought and freezing stress. It is of great significance to maintain the desert vegetation ecosystem, where the soil water is critical to the vegetation growth in the fragile ecological areas. The vegetation module can be combined with the coupled model water, vapor, and heat transferring. Further studies can be implemented to explore the specific impact of liquid water and vapor on the surface vegetation in seasonal frozen region. Secondly, the coupled transport of liquid water and vapor can also impact many engineering construction activities as well, such as the frost heave in the railway embankments that caused by the continuous liquid water and vapor transport from the deep soil layer. Finally, in-situ monitoring and simulation can be strengthened to reveal the detailed process of liquid and vapor transport below the surface impermeable layer. The finding can also provide the scientific basis for the disaster prevention and control during freeze-thaw process. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil freeze depth variations greatly affect energy exchange, carbon exchange, ecosystem diversity, and the water cycle. Given the importance of these processes, obtaining freeze depth data over large scales is an important focus of research. This paper presents a simple empirical algorithm to estimate the maximum seasonally frozen depth (MSFD) of seasonally frozen ground (SFG) in snowy regions. First, the potential influences of driving factors on the MSFD variations were quantified in the baseline period (1981–2010) based on the 26 meteorological stations within and around the SFG region of Heilongjiang province. The three variables that contributed more than 10% to MSFD variations (i.e., air freezing index, annual mean snow depth, and snow cover days) were considered in the analysis. A simple multiple linear regression to estimate soil freeze depth was fitted (1981–2010) and verified (1975–1980 and 2011–2014) using ground station observations. Compared with the commonly used simplified Stefan solution, this multiple linear regression produced superior freeze depth estimations, with the mean absolute error and root mean square error of the station average reduced by over 20%. By utilizing this empirical algorithm and the ERA5-Land reanalysis dataset, the multi-year average MSFD (1981–2010) was 132 cm, ranging from 52 cm to 186 cm, and MSFD anomaly exhibited a significant decreasing trend, at a rate of −0.38 cm/decade or a net change of −28.14 cm from 1950–2021. This study provided a practical approach to model the soil freeze depth of SFG over a large scale in snowy regions and emphasized the importance of considering snow cover variables in analyzing and estimating soil freeze depth. [ABSTRACT FROM AUTHOR]

At present, it is in the peak period of infrastructure construction in western China, and due to the natural climate, the soil has been frozen for a long time, but there is little research on frozen red clay at present. Therefore, it is necessary to further study the mechanical properties of frozen red clay. In this paper, taking the remolded red clay as the test material, the change characteristics of uniaxial compression and uniaxial creep of frozen soil under different test factors are studied by artificial freezing method, and the damage theory is introduced to analyze the test results. The results of uniaxial compression test of frozen soil show that temperature has a great influence on the uniaxial compressive strength, and the compressive strength increases with the decrease of temperature, and the damage theory is introduced. It is found that the initial damage stress increases with the decrease of temperature, while the initial strain changes little with temperature. A damage constitutive equation which can well reflect the whole damage process of frozen red clay is established. The experimental research results of this paper can provide some theoretical reference for the engineering of soil quality for freezing red clay. [ABSTRACT FROM AUTHOR]

The evolution of the average freezing depth and maximum freezing depth of seasonal frozen soil and their correlations with the average winter half-year temperature in Heilongjiang Province in China are analyzed. Linear regression, the Mann–Kendall test, and kriging interpolation are applied to freezing depth data from 20 observation stations in Heilongjiang Province from 1972 to 2016 and daily average temperature data from 34 national meteorological stations collected in the winters of 1972–2020. The results show that the average freezing depth decreases at a rate of 4.8 cm (10 yr)−1 and that the maximum freezing depth decreases at a rate of 10.1 cm (10 yr)−1. The winter half-year average temperature generally shows a fluctuating upward trend in Heilongjiang Province, increasing at a rate of 0.3°C (10 yr)−1. The correlations between the average and maximum freezing depths and the winter half-year average temperature are −0.53 and −0.49, respectively. For every 1°C increase in the average temperature during the winter half of the year, the average freezing depth decreases by 3.85 cm and the maximum freezing depth decreases by 7.84 cm. The average freezing depth sequence mutated in 1987, and the maximum freezing depth sequence mutated in 1988. The average temperature in the winter half-year displayed multiple abrupt changes from 1972 to 2020. The spatial variations in the average and maximum freezing depths are basically consistent with those in the average winter half-year temperature. These research results provide a theoretical basis for the design and site selection of hydraulic structures in cold areas and for regional development and agricultural planning. Significance Statement: The freeze–thaw balance in the frozen soil environment has been disrupted in recent years, and various degrees of degradation have occurred in the frozen soil. The degradation of frozen soil will further aggravate the greenhouse effect, which in turn will affect the accumulation of water in the soil and will have a significant impact on local agricultural production. This article uses Heilongjiang Province in China as an example. The results show that 1) the temperature in the winter half-year has exhibited an upward trend in recent years, 2) the temperature in the winter half-year has a considerable impact on the frozen soil environment, and 3) the response of the spatial distribution of frozen soil to temperature changes in the winter half-year is revealed. [ABSTRACT FROM AUTHOR]

An elastic foundation beam theory can be used to properly and effectively deal with the interaction between soil and structure. The theory application has also been gradually promoted in the frost-heaving mechanical analysis of frozen soil engineering structures in recent years. However, the existing Winkler model cannot consider the continuity of frozen soil. It is very necessary to presuppose the distribution of tangential freezing force. In this study, the governing differential equations were presented for the normal and tangential directions. The Pasternak shear layer was also introduced to connect the adjacent soil springs and contact interface layer between the frozen soil and concrete lining plate. Then, the frost-heaving mechanical model of the trapezoidal concrete lining canal was established using the two-parameter Pasternak elastic frozen soil foundation. The model was effectively connected with the SL23-2006“Specification for Design of Anti-freeze of Canal Engineering”. The frost-heaving mechanical analysis was applied to the concrete lining canals with the deep groundwater table. The computational accuracy of the frost-heaving mechanical model was improved significantly, where the shear layer was introduced to describe the interaction between the Winkler soil springs. The distribution of tangential freezing force was incorporated into the elastic foundation beam theory through the introduction of the contact interface layer. As such, there was no need for an improved model for the distribution of tangential freezing force. Taking the trapezoidal main canal of the Jinghui irrigation area in Gansu Province of China as the prototype, the improved model was applied to calculate the normal frost-heaving displacement of each point on the concrete lining plate. A comparison was then made on the Winkler model, the Finite Element Model (FEM) and test values. The comparative analysis indicated that there was consistent overall variation and tendency in the presented model, Winkler model, and FEM simulation. The critical test points were set on the concrete lining plates. The two-parameter elastic foundation beam model was much more consistent with the test values than those in the Winkler model and FEM. Furthermore, the two-parameter elastic foundation beam model was reduced to the Winkler model, when the shearing factor of frozen soil g was equal to 0. These results demonstrated the rationality and reliability of the presented model. The presented model was also applied to calculate the tangential displace and tangential freezing force of each section of the concrete lining plate. A parameter analysis was then carried out for the tangential contact stiffness. Among them, different tangential contact stiffness was set as the contact surface layer between concrete lining plates and frozen soil. Consequently, there was a nonlinear distribution in the section tangential displace and tangential freezing force along the concrete lining plates. A general decreasing trend was found in the tangential displace of each section with the increment of tangential contact stiffness. The distribution of tangential freezing force showed that “when one side is relatively large, then the other side is small”. In addition, there was a linear and uniform distribution of tangential freezing force, when the tangential contact stiffness was smaller. By contrast, the more nonlinear and non-uniform distribution was observed with the increase of tangential contact stiffness. The finding can provide a strong reference to designing the frost heave damage resistance of canals. [ABSTRACT FROM AUTHOR]

In cold locales, the thermal conductivity of soil porous media varies according to their composition and the phase state of the substance contained within the pore space. During the winter, water and other media in the soil pore space freeze-thaw, resulting in their phase state, composition, distribution, and significant thermal conductivity changes. There are some shortcomings in the current research regarding the thermal conductivity change pattern of unsaturated ice-containing soils. In this paper, the representative elementary volume (REV) selection method is given for unsaturated ice-containing soil with porosity as a representative state variable. Under the condition of freeze-thaw, two thermal conductivity REV analysis models for unsaturated ice-containing soil are established: a simplified volume-weighted average REV model and a fine volume-weighted average REV model; accordingly, a macroscopic thermal conductivity analysis model is given. The computational analysis is carried out with an actual unsaturated ice-containing soil example. The influence of the application of frozen soil in China is examined for its effect on the variation law of the thermal conductivity of porous medium. The variation characteristics of thermal conductivity of permafrost soil with related parameters (porosity, water ratio, moisture percentage, ice content, and tortuosity) are discussed. The model built in this paper provides novel concepts and methods for analyzing the thermal conductivity characteristics of unsaturated soil, as well as enhancing and advancing the analysis. [ABSTRACT FROM AUTHOR]

The impact of soil freezing‐thawing processes on August rainfall in Southern China (SC) during 1979–2008 and related physical mechanisms are investigated using the coupled land‐atmosphere model Grid‐Point Atmospheric Model version 2.0—Community Land Model version 2.0 (GAMIL2.0‐CLM2.0). The moisture‐budget analysis is employed to quantify the contributions of different factors to the change of precipitation in SC. The results indicate that the vertical moisture advection and its dynamic component play an essential role in the long‐term trends of August rainfall. The possible physical mechanism is that the model which includes the supercooled water simulates much higher soil/air temperature in August, especially in the north of 40°N, which is not only weakened the meridional thermal contrast but also induced an anomaly "north high–south low" circulation pattern in the middle and high latitude of Eurasia. Both resulted in the 200 hPa zonal winds weakening, and 850 hpa northerly wind southward moved. Meanwhile, a convergence anomaly cyclone is initiated in the lower troposphere over SC regions, accompanied by enhanced ascending and strong moisture flux convergence, which is beneficial to the increased precipitation. This study provides a new interpretation of the "southern flooding" during 1979–2008 from the point of frozen soil changing. Key Points: The coupled land‐atmosphere model (Grid‐Point Atmospheric Model version 2.0‐Community Land Model version 2.0) with the consideration of supercooled water reproduces the trend of the August rainfall in Southern ChinaThe dynamic processes of the vertical moisture advection play a vital role in the long‐term trend of the August rainfallThe decreasing soil ice content has contributed to the wetter of Southern China in August over 1979–2008 [ABSTRACT FROM AUTHOR]

Silty clay can be found in the alpine region of the Qinghai province, China, where it is subject to annual freeze-thaw cycles. To investigate the static mechanical properties of silty clay modified by basalt fiber and basalt powder under the action of freeze-thaw cycles, triaxial compression tests and scanning electron microscope tests were conducted on the soil. The test results revealed that varying the number of freeze-thaw cycles resulted to different effects on the soil mechanical strength, which tended to increase after 2 cycles, but then tended to decline when subjected to 5–10 cycles. After 20 freeze-thaw cycles, soil strength reached a dynamic equilibrium state. The shear strength of basalt fiber soil and basalt powder soil increased by 7.55% and 5.12%, respectively, compared with that of normal soil under 30 freeze-thaw cycles. Subsequently increasing of the number of freeze-thaw cycles differentially affected the cohesion and internal friction angle of normal soil and admixture soils, and these soils gradually tended to stabilize at a mechanical strength higher than the initial value. Basalt fibers reinforced the soil to a higher degree than basalt powder at a dosage of 0.4% based on dry soil mass. The stress-strain curves of the three soil types can be simulated using the hyperbolic model. The results of the study can provide some theoretical reference for practical engineering in seasonal frozen soil areas. [ABSTRACT FROM AUTHOR]

To study the long-term stability of the large-scale freezing project, the longest subway connecting channel constructed by the artificial freezing method in China is taken as the background. The uniaxial compressive strength test, triaxial shear test, and triaxial creep test of artificial frozen soil under different temperatures were carried out by using the MTS 370.25 mechanical testing machine. A series of triaxial creep tests for artificial frozen soil under different stresses and temperatures were carried out. Based on the creep test results, a fractional-order constitutive model of frozen silt with sand was proposed. Comparing the calculated results with the tested ones, it is found that the proposed fractional-order model can simulate the properties of frozen silt with sand very well. Compared with the other creep models of frozen soil, the proposed model here has higher accuracy and strong stress sensitivity. Through the simulation of the connecting channel construction and comparison with the observed data in site, the effectiveness of the model is verified, which further verifies that the model has important guiding significance for the freezing project. [ABSTRACT FROM AUTHOR]

The study of artificial ground freezing temperature field is a necessary means to grasp the development status of frozen walls. The effective freezing radius of the frozen soil column is usually calculated by the measured data of the temperature measuring hole, and then the intersecting time of the frozen walls is predicted. The location of the temperature measuring holes is random and the number of designs is small. The weak points in the blind area of the monitoring cannot be grasped in time, resulting in the consequence that local observation replaces the overall temperature field of the frozen walls. In order to accurately judge the closed condition of the frozen wall, the longitudinal temperature measurement was carried out for the frozen apparatuses. According to the heat conduction of the frozen soil column, a mathematical model for calculating the transient temperature rise of a single hole frozen soil column after short-term cooling stop is established. It used the Maple mathematical calculation software to digitize and graph the formula, which reveals the relationship between the temperature distribution of the frozen soil column and the radius and time. According to the relationship between the above parameters, the minimum frozen column radius is determined to locate the weak position of the frozen wall. Finally, taking the Xipang air shaft of Dongpang Mine in China as an engineering case, theoretical calculation and analysis of the longitudinal temperature data of all freezing apparatuses are carried out. The results show that the 18# ~ 22# and 8 # ~ 10 # freezing holes are the weak points of the frozen wall, and the groundwater flow scours the frozen wall, resulting in a "gap" at these positions. The study effectively solved the problem that the abnormal groundwater flow affected the closure of the freezing wall, and provided a theoretical basis for the treatment of water inrush accident of the frozen wall. [ABSTRACT FROM AUTHOR]

The snow melting and frozen soil thawing processes in spring could lead to the significant anomaly in soil moisture (SM) over the Tibetan Plateau (TP), which has a strong influence on the interaction between land and atmosphere, and influencing the subsequent summer precipitation in China. However, there is distinct bias in SM in model simulation, influencing the surface energy and mass balance. In this study, the impacts of assimilating spring SM over the TP with indirect soil nudging (ISN) scheme on the simulation of summer precipitation in China are investigated. The results show that using the ISN method can reduce the spring SM bias over the TP, which further decreases the root mean square error (RMSE) of summer precipitation simulation, especially in South China, North China, northeast China, and the middle and lower Yangtze River. Compared to the experiment without assimilation, the assimilation of spring SM evidently modulates the distribution and intensity of surface sensible and latent heating over the TP, which leads to the change of Rossby wave train's (RWT) shape and propagation direction over the TP and the downstream region, affecting the general circulation over East Asia. Specifically, the upward movement over the TP gets stronger and leads to the position of 200 hPa westerly jet which shifts to west and is closer to ERA5 reanalysis; meanwhile the location of the 500 hPa western Pacific subtropical high (WPSH) and the distribution of water vapor in Eastern China are also corrected. As a result, the precipitation simulation biases are alleviated. This study suggests that decreasing SM bias caused by the snow melting and frozen soil thawing can be an effective approach to improve the seasonal prediction skills of precipitation in China. [ABSTRACT FROM AUTHOR]

The land surface temperature (LST) in permafrost regions in the Northeast permafrost on March 22 (spring), June 24 (summer), September 21 (autumn), and December 24 (winter) in 2019 were retrieved based on the AMSR2 brightness temperature data. An in-depth analysis of the temperature retrieval accuracy between different types of frozen ground, vegetation cover, and during the four seasons of the day or night was conducted. The results show that: (1) The retrieval accuracy of the four seasons lowers in the seasonal order of summer > autumn > spring > winter, and the accuracy of data at the night was better than that of the day; (2) The retrieval accuracy of different vegetation cover types lowers in the order of grassland > agricultural land > forest land, and; (3) The retrieval accuracy of different frozen ground types lowers in the order of the zone of seasonal frost > zone of isolated patches of thawing permafrost > zone of island permafrost zone > continuous permafrost zone. [ABSTRACT FROM AUTHOR]

The cryosphere plays a major role in earth's climate system. Most cryospheric assessments focus on one or more of its components and their response to climate change. However, to date, there has not been a comprehensive evaluation of the entire global cryosphere. We therefore determine such a holistic estimate and quantify changes to the hemispheric and global cryosphere due to climate change, by synthesizing sea ice, snow cover, and frozen ground extents into one global cryospheric extent data set. The 1981–2010 climatology of daily global cryospheric extent ranges from 45.7 ± 0.7 × 106 to 87.2 ± 2.0 × 106 km2 (9.0%–17.1%), from 13.3 ± 0.8 × 106–66.3 ± 1.7 × 106 km2 (5.2%–26.0%) in the Northern Hemisphere (NH), and from 17.9 ± 0.3 × 106 to 33.6 ± 0.4 × 106 km2 (7.0%–13.2%) in the Southern Hemisphere (SH). The monthly maximum cryospheric extent of 85.84 ± 1.91 × 106 km2 occurs in December, whereas minimum occurs in July with 45.92 ± 0.70 × 106 km2. During 1979–2016, global cryospheric area extent lost approximately 87 ± 11 × 103 km2/yr, with a decrease of 102 ± 9.7 × 103 km2/yr in the NH that was partly offset by an increase of 14.6 ± 4.4 × 103 km2/yr in the SH. The first day of cryospheric cover was delayed by 3.6 days at a rate of 0.95 days/decade, and the last day advanced by 5.7 days, at a rate of 1.5 days/decade. The duration and number of cryospheric cover days decreased by 8.7 days and 7.6 days over the study period, respectively. These variations of global cryospheric extent are correlated with rising air temperatures. Our findings highlight the importance of assessing the cryosphere as a whole, and provide a way to quantitatively estimate its overall changes. Plain Language Summary: Changes in river floods are of worldwide concern due to their massive socio‐economic impacts. Understanding the reasons of changes in this hazard is a prerequisite for managing the associated risks efficiently. Potential reasons include climate change, river regulations and changing land management practices. In some countries, such as China, the recent rapid socio‐economic development has led to dramatic modifications of the river and land system. Existing studies suggest that flood changes in China are mainly a result of land use change and the construction of reservoirs. Here we demonstrate, based on the most comprehensive flood database to date, that climate variations dominate the spatial pattern of changes in annual flood peak discharge in China, despite the intense human alterations over the past four decades. Flood trends of human‐modified and neighboring near‐natural watersheds are generally similar. Regional flood increases are mainly associated with increasing precipitation due to changes in the East Asian Summer Monsoon, tropical cyclones and the subtropical westerly jet. Regional flood decreases are due to decreased soil moisture in the North China Plain. Our results highlight the need for flood management policies to go beyond local measures and adapt to the effects of climate change. Key Points: Holistic changes in global cryospheric extent have not previously been quantifiedEach year, global cryospheric area extent decreased 87 ± 11 × 103 km2Climate change resulted in a decline of the duration and number of cryospheric cover by two or more days/decade [ABSTRACT FROM AUTHOR]

As a new tunnel presupport construction technology, the freeze-sealing pipe roof method (FSPR) has been successfully applied to the Gongbei Tunnel Project for the first time in China. To overcome the practical difficulties of this new method in the freezing construction process, such as welding difficulties of the profiled freezing tube, refrigerant leakage, and long construction period, based on the principle of an equal cooling capacity, an improved design of freezing tube was proposed. By designing three different pipe configurations and using scaled model tests and numerical simulation, the feasibility of the improvement and the difference in the freezing temperature field were studied. The research results show that the improved design with double circular freezing tubes exhibited a lower temperature and a higher cooling rate during the test, and the time required to meet the freezing design requirements was significantly shortened. Finally, a composite structure of "pipe roof and frozen soil curtain" with a better carrying capacity and water sealing performance was formed. It was recommended to strengthen the temperature monitoring at the pipe wall in the preliminary stage of the freezing construction to ensure the water sealing effect between the pipes. In the later stage, attention should be paid to monitoring the thickness of the frozen curtain and reducing excessive frost heave through technical means such as cooling capacity control. The improvement and configurations proposed in this research could effectively replace profiled freezing tubes in the original project, better adapt to horizontal freezing projects of similar curved tunnels, achieve the freezing goal faster, and provide a reference for the promotion of the FSPR. [ABSTRACT FROM AUTHOR]

The study of the mechanical properties of frozen saline soil is one of the key issues in addressing the design of infrastructure in cold regions. This research focuses on the supersulfated saline soil of the Ningxia Yellow River Irrigation Area in China, conducting triaxial tests under negative temperatures (−5, −10, −15 °C, and − 20 °C) with varying water contents (12%, 16%, 20%). Based on fractional calculus theory and incorporating an exponential decay factor, this study proposes a novel fractional-order constitutive model for a unified description of the softening and hardening behaviors in frozen saline soil. The model treats frozen saline soil as a composite blend of ideal solids and ideal fluids in varying proportions, taking into account the material's inherent time-dependency and non-linear stress-strain relationships. Finally, the validity of the model is verified by the calculated values of the model and the triaxial tests. The results indicate that, based on preliminary judgment, due to the presence of salt solutes, a large amount of liquid water remains in the supersulfated saline soil at temperatures ranging from 0 to −10 °C, forming an unstable state called "warm frozen saline soil". The mechanical properties of frozen saline soil depend on the relative content of unfrozen water, ice crystals, and salt crystals and the formation of ice and salt crystals significantly enhances the strength of frozen saline soil. The computational results of the improved fractional constitutive model align well with experimental results, effectively describing the stress-strain relationship of frozen supersulfate saline soil. In the model, the parameter κ functions analogously to an elastic modulus and exhibits a linear relationship with temperature, and the parameter α characterizes the strain hardening of saline soil, while β describes its softening behavior. The proposed fractional constitutive model, with only three parameters having clear physical significance, is convenient for practical engineering applications. • A fractional-order constitutive model of saline frozen soil is proposed. • The mechanical properties of supersulphate saline frozen soil are studied. • The fractional-order constitutive model can describe the process of strain softening and hardening uniformly. [ABSTRACT FROM AUTHOR]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Frozen soil processes are of great importance in controlling surface water and energy balances during the cold season and in cold regions. Over recent decades, considerable frozen soil degradation and surface soil warming have been reported over the Tibetan Plateau and North China, but most land surface models have difficulty in capturing the freeze–thaw cycle, and few validations focus on the effects of frozen soil processes on soil thermal characteristics in these regions. This paper addresses these issues by introducing a physically more realistic and computationally more stable and efficient frozen soil module (FSM) into a land surface model – the third-generation Simplified Simple Biosphere Model (SSiB3-FSM). To overcome the difficulties in achieving stable numerical solutions for frozen soil, a new semi-implicit scheme and a physics-based freezing–thawing scheme were applied to solve the governing equations. The performance of this model as well as the effects of frozen soil process on the soil temperature profile and soil thermal characteristics were investigated over the Tibetan Plateau and North China using observation sites from the China Meteorological Administration and models from 1981 to 2005. Results show that the SSiB3 model with the FSM produces a more realistic soil temperature profile and its seasonal variation than that without FSM during the freezing and thawing periods. The freezing process in soil delays the winter cooling, while the thawing process delays the summer warming. The time lag and amplitude damping of temperature become more pronounced with increasing depth. These processes are well simulated in SSiB3-FSM. The freeze–thaw processes could increase the simulated phase lag days and land memory at different soil depths as well as the soil memory change with the soil thickness. Furthermore, compared with observations, SSiB3-FSM produces a realistic change in maximum frozen soil depth at decadal scales. This study shows that the soil thermal characteristics at seasonal to decadal scales over frozen ground can be greatly improved in SSiB3-FSM, and SSiB3-FSM can be used as an effective model for TP and NC simulation during cold season. Overall, this study could help understand the vertical soil thermal characteristics over the frozen ground and provide an important scientific basis for land–atmosphere interactions. [ABSTRACT FROM AUTHOR]

Linear engineering across cold regions has a negative effect on the stability of underlying permafrost. The permafrost degradation affected by engineering activities would induce ground thaw settlement; hence, the feedback from ground alternation would damage the engineering structure conversely, which is detrimental to both engineering safety and the surrounding environment there, especially differential thaw settlement in patchy permafrost. To detect the engineering influence of gas pipeline on permafrost environment, a series of field monitoring was conducted and a numerical model considering the phase changing was introduced to simulate the thermal dynamic of underlying frozen soil and estimate the effect of several countermeasures chosen to alleviate the thermal disturbance from the pipeline. The results show that frozen soil was unstable and easy to degrade because of thermal disturbance from the pipeline—the active layer thickness is 1.5~2.0 m while the maximum thawing depth under the pipe goes over 7.0 m. Both cooling gas temperature and applying insulation layer would alleviate the permafrost degradation, but in different degrees of effect. The former did not have a significant alleviation for permafrost degrading, especially in the short term, while the latter was more effective during the whole life. [ABSTRACT FROM AUTHOR]

According to simulations, permafrost area in the Tienshan Mountains has decreased by about 1.73 × 104 km2 (or 20.91%) from the 1960s to the 2000s, and the freeze state of seasonally frozen ground (SFG) exhibited delaying freeze, advancing thaw, shortening freeze days and shallowing freeze depth. River discharge has changed largely, especially for winter and minimum monthly discharge. The rivers with low catchment permafrost coverage tended to have the highest increasing rates in winter discharge, minimum monthly discharge, winter discharge ratio (proportion of winter discharge contribution to total annual flow) and minimum monthly discharge ratio (proportion of minimum monthly discharge contribution to total annual flow). Gradually increasing correlations of maximum seasonally frozen depth (SFD) with the hydrological variables may indicate that the response of river discharge to frozen ground change is a long-term process. Possibly a result of frozen ground degradation, summer precipitation may strengthen the influences on low flow. [ABSTRACT FROM AUTHOR]

Many highways and railways in western China are built on permafrost roadbed. Frost heave and thaw settlement might cause diseases to frozen soil roadbed, such as deformation and cracking. For long-term operation, frozen soil roadbed should be kept stable and durable. Therefore, this paper analyzes the distribution law of temperature field of roadbed in permafrost regions, under the effect of thermal stability. Based on the thermodynamic properties of permafrost, the authors analyzed the influence of engineering geological factors, roadbed structural factors, and natural environmental factors on the thermal stability of frozen soil roadbed. Next, the antifreeze mechanism of frozen soil roadbed was described, together with the calculation methods for the relevant parameters. Afterwards, the temperature field of the roadbed with low thermal conductivity insulation material was analyzed by two methods, namely, steady-state thermal analysis and transient thermal analysis, and the solving process of roadbed temperature field was explained in details. The proposed analysis method and solving algorithm were proved valid through experiments. The research results provide a reference for the reasonable design of frozen soil roadbed. [ABSTRACT FROM AUTHOR]

The modeling of seasonally frozen soils is significant for understanding the hydrological process in cold regions. The water and heat transports of two seasonally frozen sites in northern China were simulated with the process-oriented CoupModel, and a more efficient Monte Carlo based method was employed to identify the uncertainties in multi-site calibration. Results showed that water and heat measured at different sites could be explained by 15 merged parameters including FreezepointFWi ( d 1 ), EquilAdjustPsi ( ψ eg ), AlbedoKExp ( k a ), RoughLBareSoilMom ( z 0 M ) etc. with common ranges to some extent and three parameters MinimumCondValue ( k min , u c ), WindLessExchangeSoil ( r a , max - 1 ), and SThermalCondCoef ( s k ) related to soil hydraulic conductivity, surface aerodynamic resistance and snow thermal conductivity respectively were identified to be site-dependent with site-specific ranges. The promotion in performance indices of interest variables indicated that the proposed systematic method had the potential to improve the multi-site simulation of heat and water in frozen soils based on CoupModel. However, the range ratios and posterior distributions of the merged parameters indicated the model structural uncertainty in CoupModel. And the comparison of the simulated variables between two sites demonstrated that the model structure uncertainty originated from the lack of consideration for the detailed processes related to ice cover and freezing point depression induced by soil solute. More detailed information on study sites as well as consideration of more detailed processes in frozen soil water-energy balance will expand the scope of model application in cold regions. [ABSTRACT FROM AUTHOR]

Canals, as the preferred form of water conveyance, play an important role in the agricultural irrigation and long-distance water diversion projects in arid regions. However, the arid regions are mainly distributed in the seasonal permafrost regions in China, namely arid-cold regions. Due to the interaction between the canal seepage and frost heave, the freeze-thaw aging damages are more severe and common. The field investigation shows that the failure forms of canals include seepage, swelling, uplift, overhead, instability and collapse, and limit the safe operation and performance of canals seriously. In this study, the research progresses of the theories and technologies of anti-seepage and anti-frost heave for canals in arid-cold areas were summarized. Firstly, the mechanism of freeze-thaw failure and failure mode for canals was analyzed by indoor unit experiments, model experiments and field monitoring. Secondly, the engineering mechanical models of canal frost heaving failure were introduced based on limit equilibrium theory, such as material mechanics model and elastic mechanics model. Thirdly, multi-field coupling numerical models were developed including coupled heat-mechanics model, heat-water-mechanics model and the interaction model between frozen soil and canal lining. Lastly, the development processes of anti-seepage and anti-frost heave technologies for canals were expounded from four aspects: 1) the thermal insulation and preservation technologies against the external low temperature on soil and heat loss; 2) the anti-seepage and drainage technologies to reduce water content and water migration in soil; 3) soil replacement with sand or gravel technologies; 4) force release technologies by section structure optimization. With the increase of canal scale and upgrading demand for disrepair canals in harsh environment, the frost heaving failure mode was complex. The research frontiers and technical difficulties in this study mainly included: 1) the multi-field coupling failure mechanism and failure mode in the complex environment, such as solar radiation, freeze-thaw cycles and salinization, and operation conditions, such as water conveyance in winter with or without ice cover and water level dropping; 2) further development of multi-field coupling simulation model based on coupled heat-water-mechanics model covered the following aspects: canal thermal boundary with solar radiation and convective heat transfer model considering section form; canal damage model of freeze-thaw deterioration considering frost heaving and thawing of soil to analyze canal slope collapse; viscoplastic damage model for contact surface according to experiment on interfacial strength and stress-strain characteristics of lining-separated ice-frozen soil under freeze-thaw cycles; effects of salt on parameters of moisture field, thermal field and mechanical field and coupled heat-water-mechanics-salt model; 3) the canal failure criterion determination including strength, stiffness and stability of structures combined with field monitoring and numerical model, then modified the engineering mechanical model from the aspects of frost heaving force and adfreezing force distribution and foundation coefficient, and eventually formed a set of design method using engineering mechanical model to design and numerical model to check; 4) moisture, temperature and displacement changes under different anti-seepage and anti-frost heave measures of canals and standardization design combined with experiments, failure criterion and numerical model; 5) the dynamic disaster process and prevention and control technologies of canals determination by the following methods: classified variables such as environmental factors, operating conditions, section forms and failure forms of canals based on the field monitoring data and numerical simulation results, and then established the relationship between the variables by neural network and other algorithms. Finally, the future research directions were discussed and included: 1) complement of the design theory and method for anti-seepage and anti-frost heave; 2) establishment of dynamic evolution forecasting model for disaster chain in the whole life cycle. These may help to provide guidance to scientific design and efficient operation of water conveyance canals in arid-cold areas. [ABSTRACT FROM AUTHOR]

The significant changes in the cryosphere have produced a series of effects on the cryospheric hydrological processes. This paper comprehensively reviews the recent 20 years, especially the new progress in the research on the changes in cryospheric hydrological processes in China, which mainly include glacial meltwater, snow melt runoff, and frozen ground hydrology. The main progresses in the study on changes in glacial melt water manifest as: a comprehensive study on glacial meltwater at different scales was carried out, it was found that the glacial meltwater showed continuously increase, and whether the "peak point" of the glacial meltwater have appeared has scientifically identified and some basic understandings has obtained, and the modelling on glacial melt water process had made significant progress. In the study on snowmelt runoff changes, the snowmelt runoff contribution rate to river runoff in various basins were basically grasped by estimating the snowmelt runoff and found that the snowmelt runoff changes in China vary greatly, and it increased in some basins while decreased in some basins. The changes in the start melting period in China are universal with other basins in the world, and the prominent feature is the advance of the peak value. In the study of frozen ground hydrology, the studies on the relationship between surface water, interflow in active layer soil, supra- permafrost water revealed the coupling mechanism of gravity and thermodynamics in the formation of runoff in permafrost regions. The impacts of permafrost change on surface runoff has already appeared, which mainly appears as increase in the winter ( dry season) runoff. It also found that the permafrost degradation has a direct replenishment effect on river runoff, and the amount of recharge may have reached a certain level in some basins. [ABSTRACT FROM AUTHOR]

At present, the tunnel design specifications in China do not provide a clear and systematic intelligent evaluation system of tunnel frost damage in cold regions. Based on the research results of 122 seasonal frozen soil tunnels in high-latitude areas of China, four key influencing factors of geohydrology, temperature, surrounding rock, and engineering measures were determined, the intelligent fuzzy comprehensive evaluation model was established, the weights of all factors were considered, and the intelligent evaluation technology system of tunnel frost damage in cold areas had been put forward. Meanwhile, the rationality of the intelligent model was verified by a specific engineering case. The research suggests that the intelligent evaluation model of tunnel frost damage proposed in this paper can accurately describe the relationship of influencing factors of tunnel frost damage in cold areas, the weight of each influencing factor is calculated by using analytic hierarchy process, and the main risk sources of tunnel frost damage in cold areas are found out. The intelligent evaluation model is an efficient and practical method for Intelligent prediction of frost damage. By using the subordinate function method, the improvement from qualitative analysis to quantitative index calculation is realized. The blindness of engineering analogy construction is avoided, and the scientificity and accuracy of renovation measures for frost damage have been improved. At the same time, the research results provide a theoretical basis for the improvement of the intelligent evaluation system of tunnel frost damage in cold regions. [ABSTRACT FROM AUTHOR]

To complement traditional methods of studying coarse roots (>2 mm in diameter) that are often destructive, laborious and point‐based, we tested a dual‐frequency ground‐penetrating radar (GPR) to non‐invasively map lateral coarse roots of shrubs (Caragana microphylla Lam.) in the sandy soil of a temperate semi‐arid shrubland. The dual‐frequency GPR system used in this study simultaneously collects data with two antenna frequencies (400 and 900 MHz). The GPR surveys were repeated in a grid (11 × 4.8 m2 with a total of 46 survey lines) in summer and winter. Both antenna frequencies and seasonal GPR surveys generated a consistent pattern of the distribution of lateral coarse roots, indicating reliable interpretation of GPR data for coarse roots mapping. The 400 MHz GPR and the winter survey detected more roots in the deeper soil (>0.6 m depth), whereas the 900 MHz GPR and the summer survey detected more in the shallower soil (<0.6 m depth). The higher wave velocity and lower degree of GPR energy attenuation in the frozen soil enhanced the detection of deep coarse roots. Combining root detection results obtained under all conditions revealed a higher distribution density of lateral coarse roots beneath a depression and at the depth of 0.4–0.6 m, but a lower abundance under the intershrub area (i.e. showing the avoidance of intershrub root overlap). These patterns were not evident in GPR images collected using a single frequency antenna in one season. Ground truthing confirmed that pairing GPR data collected at two frequencies improved the detection frequency of the number of lateral coarse roots. More field tests are required to validate the application of repeated dual‐frequency GPR surveys to detect and quantify coarse roots in other ecosystems. Highlights: The detection of lateral coarse roots by GPR needs to be further improved in field soils.Dual‐frequency GPR surveys were repeated in summer and winter to enhance coarse roots mapping.Combining seasonal dual‐frequency GPR data improved detection frequency of the number of roots.Topography and intershrub root competition influence the distribution of lateral coarse roots. [ABSTRACT FROM AUTHOR]

• Analyzes the spring drought in the cold region of Northeast China from 1980 to 2020. • Considering the impact of early spring snowfall, the spring drought was analyzed. • A novel cutoff radius approach for the PP information entropy model. Northeast China is an important grain-producing area, and spring is the sowing time for crops. Drought hinders crop germination and leads to crop failure. Spring drought analysis helps to understand the characteristics of regional spring drought and provides a reference for formulating disaster prevention and reduction measures. Considering the characteristics of seasonally frozen soil regions in northeastern China, sampling at a resolution of 0.5 degrees, accounting for the snow cover factors in the early spring, as well as precipitation, temperature, evapotranspiration, and soil moisture during the spring planting period, and uses the projection pursuit information entropy model to analyze the spatial and temporal variability of spring drought in Northeast China. In the model, a new method was proposed to calculate the cutoff radius by adjusting the radius size with the parameter. The optimal parameters were ultimately determined using the Shapiro-Wilk test, Kolmogorov-Smirnov test, and Epps-Pulley test. The results are as follows: drought is relatively severe in the eastern parts of Inner Mongolia, as well as in the northwest of Liaoning. The central and northern parts of Inner Mongolia, the northern and northeastern parts of Heilongjiang, the southeastern parts of Jilin, and the eastern parts of Liaoning are relatively humid, while the drought situation in other regions is relatively moderate. Regional spring drought shows an increasing trend, and most regions show statistical significance. Areas with high temperatures and low precipitation, as well as low snow cover in the early spring, are prone to spring drought. Moist regions are characterized by high precipitation, low evapotranspiration, and abundant snow resources. [ABSTRACT FROM AUTHOR]

Artificial ground freezing (AGF) technology is sometimes adopted to reinforce the surrounding soil to ensure the safety of subway tunnels during construction in the eastern coastal areas of China. The mechanical characteristics of frozen soil are subjected to change due to the incorporation of chlorine salt, and the soil strength decreases significantly with an increase of salt content. The mechanical properties of frozen silty clay have been rarely investigated due to the coupling effect of temperature, strain rate, and salt content. In this study, before the application of AGF, a series of unconfined compressive strength (UCS) tests and the consolidated-undrained static triaxial compression tests were conducted on frozen silty clay to investigate the influence of salt content, temperature, and strain rate on the mechanical properties of frozen soil. From the stress-strain curves of the UCS test, strain-hardening and strain-softening behavior were identified as a result of the influence of different temperatures and salt contents. Regression analysis was performed to discriminate the effect of each individual factor and their coupling effect. The results reveal that soil UCS logarithmically increased with a decrease in relative temperature and strain rate. Both UCS and static triaxial strength linearly decreased with an increase in salt content. The influence of salt content on the strength of frozen soil was discussed and compared with previous researches. Furthermore, an elastic-plastic constitutive model was proposed to characterize the stress-strain behavior in which the effects of strain rate and salt content were included. At last, with consideration of salt content, a modified constitutive model was proposed to describe the strength and deformation behavior of frozen silty clay. • UCS was extracted and constitutive model was established with consideration of temperature, strain rate, and salt content • The frozen chloride soil strength is predicted by superimposing the coupling effect of salt content and confining pressure • The sensitivities of the strength and deformation behavior of NaCl saline soils to salt content are characterized [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]

• A new thermo-hydro-mechanical coupled model for freezing unsaturated porous media is proposed. • The temperature-dependent soil-water characteristic curve is included. • The model was implemented in FEM and validated using laboratory and field data. This study presents a new fully coupled thermal-hydraulic-mechanical (THM) model for variably saturated freezing soil, which examines the freeze–thaw (F-T) actions. The model is derived based on the general form of continuum mechanics for porous media. The mass balance equations cover the conservations of the total water and dry air, where liquid water, ice, and vapor are involved in the total water balance equation. The effective stress law for the unsaturated frozen soil is included in the model to quantify poromechanical behaviors. The pore pressure contains components from pore water pressure, pore air pressure, and ice pressure. A new model for characterizing the unfrozen water content based on temperature and air-water capillary pressure is proposed. The THM formulation is based on multidimensional derivation, thus is versatile to be extended to cases including warm temperature conditions or large deformation behavior. The model was implemented in a 2D finite element package and validated by a set of published laboratory experimental data. The numerical code is also applied to simulate the freeze–thaw actions in highly unsaturated loess located in the northwest of China, where the quasi-distributed fiber optic sensing data is collected for field-scale validations. Our simulated thermal-hydro-mechanical responses match well with in situ monitored results and confirm that freezing-induced heaving is still significant in such highly unsaturated soil. [ABSTRACT FROM AUTHOR]