Basins around the Asian Water Tower benefits more than one billion people in Asia and plays a vital role in global economic development. However， the water resources of the Asian Water Tower have changed dramatically under the background of climate warming. Meanwhile， the water demand of human activities is increasing rapidly. For all that， changes in supply and demand side make the water stress risk more prominent. In order to understand the Current situation and future changes of water stress in basins of the Asian Water Tower， here based on the runoff and water withdrawal data of the global hydrological model in the Inter-Sectoral Impact Model Intercomparison Project （ISIMIP）， the research establishes an index to evaluate the water stress status and possible future changes in 21 basins around the Asian Water Tower. We conclude that the water stress of the 21 basins of the Asian Water Tower showed an overall upward trend during 1971—2010. Especially， the basins with high or above average water stress levels， including Indus， Tarim and Huanghe. In the future scenario， the change of water stress in the 21 basins of the Asian Water Tower will initially increase， and then different basins will show three trends under different scenarios， involving continuous increase （2 basins）， stabilization （5 basins） and decline （14 basins）. Human activities of water withdrawal play a crucial part in the change of future water stress. Among them， the basins in South Asia and Southeast Asia with increasing water stress， such as Brahmaputra and Mekong， water scarcity and security of them pose a significant risk in the future.
The freeze-thaw front within active layer is the interface between the frozen and the unfrozen soil layers during the freeze-thaw process， and the hydrothermal parameters of the soil layers on both sides of freeze-thaw front are significantly different. Therefore， the accurate simulation of the freeze-thaw front movement in the land surface model is essential to improve models both in simulating the hydrothermal characteristics of permafrost and simulating the energy-water balance of the land surface. In this study， the simulation depth of the Noah-MP land surface model was extended to 20 m， and the 4 soil layers of the Noah-MP land surface model was increased to 19 soil layers， and the organic matter scheme and vegetation root scheme were introduced. After these modifications， in order to strengthen the ability of the Noah-MP land surface model on simulating freeze-thaw front， the Stefan method was coupled. Then， the simulation effect of the augmented Noah-MP land surface model on the hydrothermal process of the Xidatan permafrost site was evaluated. Two experiments， CTL experiment （coupled Stefan method） and STE experiment （not coupled Stefan method）， were conducted to simulate the soil temperature and soil liquid water content of 0~20 m in 2012， and the simulation results were verified by the observed daily soil temperature and soil liquid water of 0~3.2 m and the observed yearly ground temperature of 3 m， 6 m and 10 m. The results showed that the freeze-thaw front （0 °C isotherm） obtained by interpolation of soil temperature simulation values had obvious step-like characteristics， and its maximum freeze-thaw depth was larger than the measured. Coupling Stefan method enhanced the ability of Noah-MP model to simulate the freeze-thaw front， so that the model was able to better simulate the change trend and maximum depth of the freeze-thaw front. At the same time， coupling Stefan method also improved the simulation of soil temperature. The mean RMSE and the mean MBE of the soil temperature in the soil layers of 0~3.2 m decreased to 0.89 ℃ （decreased by 44%） and -0.13 ℃ （decreased by 86%） respectively， and yearly ground temperature of 3~20 m was closer to the measured. And it also improved the simulation of the soil liquid water content. The mean RMSE and the mean MBE of the soil liquid water content in the soil layers of 0~3.2 m decreased to 0.06 m3·m-3 （decreased by 33%） and -0.01 m3·m-3 （decreased by 67%） respectively， and the soil water melting time of 20 cm， 40 cm， 80 cm and 120 cm in the active layer was closer to the observed. It can be seen that coupling the Stefan method that can better model the movement process of freeze-thaw front in the land surface model can greatly improve the simulation ability of the model， which is one of the effective ways to improve the land surface process model. The results of this study can provide a reference for improving the simulation of the land surface model in the permafrost area. This study will provide a reference for improving the ability of land surface model to simulate hydrothermal processes of permafrost.
Lakes are sensitive indicators of climate change， and studying their dynamic changes was of great significance to reveal global climate change and water resources utilization and management. Based on Landsat-5/7/8 satellites and high-resolution remote sensing images， the temporal and spatial characteristics of lake area change during 1989—2021 in Dorsodong Co-Mitijiangzhanmu Co in source region of the Yangtze River were analyzed， and the response of glacial lake and glacier to climate change was discussed. The results showed that during 1989—2021， the average area of Dorsodong Co-Mitijiangzhanmu Co was 1 011.37 km2， which expanded from 872.07 km2 in 1989 to 1 119.5 km2 in 2021， with an average expansion rate of 8.62 km2⋅a-1. In terms of interdecadal variation， the lake area expanded most obviously in the early 21th century， especially in the northern， northwestern and southern parts of the lake. Growth was slowest in the 1990s. From 1990 to 2020， the area of Geladandong Glacier shrank from 797.85 km2 in 1990 to 766.19 km2 in 2020， a decrease of 31.66 km2， with a reduction rate of 1.106 km2⋅a-1. Between 2015 and 2022， the glacier area decreased by 19.55 km2. From 2005 to 2010， the glacier area decreased by 1.50 km2. Glacier retreat accelerated from 0.51 km2 in 1990 to 2.20 km2 in 2010. Before 2004， glacial meltwater caused by rising temperature was the main factor of Dorsodong Co-Mitijiangzhanmu Co lake area change， with an average contribution of 66.8%. After 2004， precipitation played a leading role in the change of Dorsodong Co-Mitijiangzhanmu Co lake area. The average contribution rate of precipitation to lake area change was 57.8%. Through the analysis of net evaporation， it can be found that the net evaporation of Bangor， Shenza and Amdo all showed a downward trend year by year， especially the net evaporation of Shenza Station showed a significant downward trend， and the decline rate was 7.8 mm⋅a-1. Therefore， it can be found that the net evaporation of Dorsodong Co-Mitijiangzhanmu Co area decreased， and the lake area also increased with the decrease of evaporation. From the perspective of mass balance and lake water volume change， the correlation between mass balance and lake water volume in Geladandong Glacier was 0.69， indicating that glacier mass loss contributes to the increase of lake water volume. The mass balance of Geladandong Glacier lost the most in 2016， the lake area increased by 16.4% and the lake water volume increased by 3.16 Gt compared with 2000. In 2005， the glacier was in a state of accumulation， the lake area was only 0.67% compared with 2000， and the lake water volume increased by 0.9 Gt compared with 2000. From 2000 to 2004， the lake area expanded by 5.1%， and the glacial meltwater was about 4.56 Gt. From 2005 to 2016， the lake area expanded by 6.9%， and the glacial melt water was about 1.94 Gt. It can be seen that the contribution rate of glacier loss to lake from 2000 to 2004 was about 80%. After 2004， the contribution of glacier loss to lake water volume will reach 40%.
Debris flows pose a significant geological hazard， inflicting severe damage to infrastructure such as buildings and roads in eastern region of the Qinghai-Tibet （Xizang） Plateau. Considering the background of global warming， the likelihood of potential debris flow occurrences in the mountainous areas of the Qinghai-Tibet Plateau is expected to rise. Therefore， a quantitative assessment of debris flow susceptibility assumes great importance as the primary approach for implementing regional disaster reduction and prevention measures. The formation of debris flows is influenced by source conditions， terrain conditions， and water conditions. In this study， we focus on the variability of source and terrain conditions while temporarily assuming constant water conditions within a small area. Specifically， we address the challenge of determining and quantifying source conditions by examining the freeze-thaw erosion type provenance in the Gonjo （Gongjue） area of eastern Tibet. Through detailed field investigations and comprehensive research， we calculate the freeze-thaw erosion intensity （DR） to represent the source conditions of debris flows. To evaluate debris flow susceptibility， we select eight factors related to source and terrain conditions， including freeze-thaw erosion intensity （DR）， elevation （H）， plane curvature （Pl_cv）， profile curvature （Pr_cv）， slope （Slope）， stream power index （SPI）， topographic wetness index （TWI）， and terrain characterization index （TCI）. The weight values of these eight evaluation factors are determined using the analytic hierarchy process （AHP） and principal component analysis （PCA） methods. The susceptibility of debris flow in Gonjo area of eastern Tibet is then evaluated using the weighted information method. Additionally， the study divides the watershed units into four groups based on different flow thresholds （5 000， 10 000， 20 000， and 40 000） and analyzes and compares the susceptibility evaluation results of each group. The evaluation results are further validated using the receiver operating characteristic curve （ROC） analysis. The main findings of this study are as follows： Firstly， among the selected evaluation factors， freeze-thaw erosion intensity （DR）， terrain characterization index （TCI）， and plane curvature （Pl_cv） exhibit the highest weight values， with their cumulative weights exceeding 0.5. This indicates that these three factors are more sensitive to debris flow formation in the study area and contribute significantly to debris flow susceptibility. Secondly， based on the susceptibility evaluation results of the four groups of watershed units， the group G2 （flow threshold 5 000） demonstrates the highest area under the curve （AUC） value， followed by groups G3 and G4， while group G1 exhibits the lowest AUC value. These results highlight the efficacy of employing the G2 group to divide watershed units when conducting debris flow evaluations in the study area and surrounding regions， as it yields relatively accurate evaluation outcomes. Lastly， the study establishes a debris flow susceptibility evaluation model incorporating freeze-thaw erosion type provenance and topographic hydrological factors， which yields satisfactory evaluation results. This indicates the viability of integrating freeze-thaw erosion intensity to characterize source factors and underscores the feasibility of a susceptibility evaluation system primarily driven by provenance and topography in Gonjo area of eastern Tibet. In conclusion， this study introduces novel methodologies and concepts for assessing debris flow susceptibility in the region， where freeze-thaw erosion phenomena are prevalent. The findings significantly contribute to the theoretical research and hold practical implications for guiding local authorities in disaster prevention and mitigation efforts.
Geoengineering， as a potential avenue for tackling climate change， seeks to address global climate change scenarios， manage the pace of global warming， and counteract human-induced impacts on the climate. This paper， utilizing bibliometrics， systematically dissects the trajectory of international research in the realm of geoengineering， shedding light on scientific and technological frontiers through metrics such as publication numbers， global collaboration， and frequently employed terms. In recent years， the overall global scientific research in the field of geoengineering has shown a growing trend， and countries such as China， the United States of America and the United Kingdom are in a world-leading position in this field， with strong scientific research level. Geoengineering research predominantly resides in the realm of model simulation and assessment at this juncture. A significant portion of the research lacks tangible， analyzed data， and some geoengineering methods and technologies probably pose potential threats to the natural environment and society. Solar radiation management technologies stand out as potentially menacing to global and regional climate patterns， while carbon dioxide removal technologies are marked by unintended environmental consequences and uncertainty regarding their long-term impacts on the Earth’s climate system. Furthermore， glacier geoengineering is emerging as a focal point in the cryosphere discipline and the broader field of global change. Applied research in this domain has commenced in polar ice caps and select mountain glaciers， guided by geoengineering principles. However， the majority of efforts involve numerical simulations and scenario design， with only a handful of field experiments conducted. Looking ahead， the trajectory of geoengineering research will pivot towards securing financial and technical support for experimental endeavors. This shift aims to enhance modeling capabilities and furnish empirical and theoretical foundational data for technical analyses. This evolution is expected to facilitate the transition of geoengineering from its current phase of model simulation to large-scale commercial demonstration. The development of geoengineering requires ethical and moral guidance， combined with energy transformation strategy in China， and may be based on international cross-disciplinary cooperation development and deployment to help protect the environment and improve human well-being.
Snow cover is one of the most active factors in the cryosphere， directly affecting the energy exchange between the atmosphere and the Earth. Snow depth （SD） is an important attribute to describe the temporal and spatial variation of snow cover， and is an important input parameter for models such as basin water balance， and the simulation of snow runoff. Passive microwave remote sensing utilizes the strong correlation between the differences in snow scattering characteristics and snow depth at different frequency brightness temperatures （BT） for snow depth inversion. It is widely used to study the temporal and spatial variations of snow depth at global or regional scales. However， due to the strong spatial and temporal heterogeneity of snow cover in mountainous areas， the spatial distribution is uneven， the temporal variation is different， so these passive microwave remote sensing snow depth products with coarse spatial resolution are greatly limited. Especially in the mountainous areas of the Qinghai-Xizang Plateau， due to the spatial discontinuity and heterogeneity， these data are insufficient to represent the snow conditions at a regional scale. This study is based on MODIS fractional snow cover dataset， and uses empirical fusion rules and snow decay curves to perform spatial downscaling on the two sets of snow depth products of "the long-term series of daily snow depth dataset in China". The first set of snow depth product， referred to as Che_SSMI/S products， is inverted from SMMR， SSMI， and SSMI/S， while the second set， Che_AMSR2 products， is inverted from AMSR-2 brightness temperature. Ultimately， the 500 m downscaled snow depth data （Che_SSMI/S_NSD and Che_AMSR2_NSD） of the Qinghai-Xizang Plateau were obtained. There are significant differences between the two sets of snow depth data after downscaling. Utilizing 6 scenes of Landsat-8 images， we conducted a comparative analysis of the downscaled snow depth data from the two sets， it was found that both sets of downscaled data had a high degree of agreement with the spatial distribution of snow cover in Landsat-8 images. The Che_AMSR2_NSD product was compared with the snow depth data of 29 meteorological stations and found that the data were closer to the measured snow depth data， the correlation coefficient （R） was 0.72 and the root mean square error （RMSE） was 3.21 cm， while the correlation coefficient between Che_SSMI/S_NSD and the measured snow depth is 0.67， the RMSE is 4.44 cm. It is speculated that the reason for this discrepancy may be due to the difference in the accuracy of the two sets of original snow depth products with brightness temperature data from different sensors. In addition， the experimental results show that the downscaled accuracy of passive microwave snow depth products is also affected by factors such as snow depth and snow cover period. The results show that the accuracy of downscaled snow depth is different at different snow depth and different snow cover periods. Specifically， when the snow cover is accumulation period and stable period， the downscaled accuracy of the two sets of snow depth products is higher， while when they are in the snow ablation period， the accuracy gradually decreases. The highest downscaled accuracy for both sets of snow depth products occurs， when the snow depth is less than 10 cm. Conversely， the accuracy of the snow depth is significantly reduced when the snow depth exceeds 30 cm， which may be due to the saturation issues in passive microwave snow depth inversion. Through the comparative evaluation of the two sets of downscaled snow depth products， it is helpful to understand the temporal and spatial distribution of snow depth more comprehensively over the Qinghai-Xizang Plateau， and provide snow depth data support for its application.
Analyzing the evolution characteristics of dissolved organic matter （DOM） in glaciers is an important basis for evaluating the biogeochemical effect of glacier melting on downstream ecological environment. However， the evolution characteristics of DOM in surface snow in winter and spring are still unclear. In this study， the surface snow of Dagu Glacier and glacial runoff in winter and spring was studied， and DOM in the surface snow was characterized at molecular level by using Fourier transform ion cyclotron resonance mass spectrometry （FT-ICR MS）. The results indicate that the chemical composition of DOM in the surface snow of Dagu Glacier during winter and spring exhibits a diverse range， primarily consisting of lipids， peptide-like， unsaturated compounds， and minor quantities of polyphenolic， condensed aromatics， and sugars compounds. The sources of these components include both microbial and terrestrial origins. The main source of DOM in spring runoff is terrestrial inputs， which is greatly affected by human activities. The molecular composition of DOM in surface snow in different seasons was analyzed， and it was concluded that the low temperature environment in winter was conducive to the enrichment of aliphatic， peptide-like and S-containing DOM molecules in surface snow， and the higher temperature in spring was conducive to the enrichment of peptide-like， unsaturated hydrocarbons and N- containing DOM molecules in surface snow. Comparing the molecular composition of DOM in spring runoff and surface snow， it was found that the content of heteroatomic DOM in runoff decreased， the content of aliphatic and peptide-like DOM from microbial source decreased， and the content of terrestrial sources of polyphenolic and condensed aromatics significantly increased， indicating that the biological activity of DOM in runoff decreased and the photoreactive activity increased. The continuous melting of glaciers leads to the influx of a significant amount of glacial meltwater into downstream water environments. This influx， combined with microbial activities and light reaction processes， results in an increased emission of greenhouse gas CO2 and intensifies the greenhouse effect.
Seasonally frozen soil is widely distributed in alpine mountains and its freeze-thaw process has profound effects on hydrological water resources and ecological environment. Research on the changes of freeze-thaw characteristic parameters and influence mechanism of seasonally frozen soil under the background of climate change can provide scientific basis for water resources management and ecological protection in alpine mountains. This study selected southern slope of the Tianshan Mountains as a typical area. Based on the observed daily data from 13 meteorological stations， including data of seasonally frozen soil （e.g. maximum frost depth， freezing period， starting date of soil freezing， and ending date of soil freezing）， air temperature， land surface temperature and precipitation， as well as reanalysis snow cover data since 1958， the spatiotemporal variations of freeze-thaw parameters of seasonally frozen soil and the driving mechanisms were analyzed using multiple linear regression statistics and spatial analysis. The results showed that： （1） The maximum frost depth of seasonally frozen soil ranged from 48.5（±11.4） cm to 96.8（±8.5） cm， the freezing period ranged from 102（±10） days to 141（±14） days， the multi-year average starting date of soil freezing were largely ranged from November 7 to November 19 and the multi-year average ending date of soil freezing ranged from March 1 to March 28. （2） The starting date of soil freezing was gradually postponed， while the ending date of soil freezing was advanced and the freezing period was shortened during 1950s—2010s. （3） The maximum frost depth showed a pattern of “higher altitude， deeper frost depth”， and it has increased significantly in the past decades in the central part of the study area. The freezing period has shortened significantly in most of the study area. （4） According to comparative analysis， temperature （air temperature and land surface temperature） is the dominant factor of the freeze-thaw parameters variation of seasonally frozen soil on south slope of the Tianshan Mountains， and the detailed impact weights are： air temperature accounts for （24.1±3.6）%， land surface temperature accounts for （12.1±3.1）%， precipitation accounts for （9.6±1.7）%， and snow cover accounts for （5.1±1.5）% by quantitative analysis.
The artificial ground freezing method is widely used in underground engineering in soft soil areas and has been rapidly developed. However， the complex stratigraphic distribution in soft soil areas and the rheological properties of frozen soil materials also bring challenges to the program design and engineering construction of the artificial ground freezing method under large-scale conditions. Based on the field surveys and the context of an estuary access project in Sanya with pipe curtain freezing method construction， considering the complexity of distribution depth on clay with different plastic states， the tensile and compressive properties of frozen fluid-plastic clay， hard-plastic clay and plastic-silty clay were studied by radial splitting and uniaxial or triaxial compression tests. The results show that the tensile properties of frozen undisturbed clays with three different plastic states are different under the radial splitting. The fluid-plastic clay and plastic-silty clay display weak strain-harden at -5 ℃， and weak strain-soften at -10 ℃ and -15 ℃， while hard-plastic clay exhibits strong strain-soften at three negative temperatures. The frozen undisturbed clays with three different plastic states show weak strain-soften under compression tests. For both the tensile and compressive stress-strain behaviors， the weak strain-harden and strain-soften behaviors of the frozen undisturbed clays with three different plastic states can be described by a modified hyperbola model of deviator stress and axial strain， and the strong strain- soften behavior can be described by a quadratic parabola model. Under the same negative temperature， the tensile strength of the fluid-plastic clay is the weakest and the deformation resistance is the strongest， the plastic-silty clay is secondary， and the hard-plastic clay has the strongest tensile resistance and the weakest deformation resistance. In the distribution range of initial tangential modulus on the frozen undisturbed clays with three different plastic states， it is largest for the plastic-silty clay， secondary for the fluid-plastic clay and smallest for the hard-plastic clay. However， the initial tangential modulus tends to increase with the decrease of temperature. The failure strain of hard-plastic clay has a tendency to increase with the increase of confining pressure， while the failure strain of fluid-plastic clay and plastic -silty clay is relatively discrete and irregular. The shear strength of fluid-plastic， hard-plastic clay and plastic-silty clay can be described by the linear Mohr-Coulomb criterion. The cohesion and internal friction angle of the three soils basically increase with the decrease of temperature. At the same temperature， the cohesive force of fluid-plastic clay is the smallest， the cohesive force of plastic-silty clay is close to that of hard-plastic clay， and for the internal friction angle， it is largest for the hard-plastic clay， secondary for the fluid-plastic clay and smallest for the plastic-silty clay. In this paper， the influence of plastic state on the tensile and compressive properties of frozen undisturbed clay is studied so as to provide data support and reference for the development of underground artificial freezing projects.
With the rapid growth in demand for clean energy sources like natural gas， the safe storage of liquefied natural gas （LNG） has emerged as a significant challenge. Due to its excellent mechanical properties， concrete has become an important engineering material for LNG storage structures. In recent years， the development of the LNG industry has also propelled research into the ultra-low temperature performance of concrete. The performance of concrete at ultra-low temperatures greatly differs from that at normal temperatures. Current studies indicate that the compressive and tensile strengths， as well as the elastic modulus of concrete， are significantly enhanced in ultra-low temperature environments. Scholars have developed various performance prediction formulas based on experimental results and have explained the mechanism behind the enhanced performance by considering the pore water-ice phase transition process. Ultra-low temperature freeze-thaw cycle experiment results show that concrete has poor frost resistance at ultra-low temperatures， with a significant reduction in mechanical properties after just a few freeze-thaw cycles. The existing conventional freeze-thaw testing methods do not meet the requirements for ultra-low temperature freeze-thaw conditions， and there is a lack of specific standards for testing and evaluating concrete performance under these conditions. Moreover， due to differences in testing equipment and procedures， it is difficult to reference related achievements. Therefore， there is an urgent need to systematically summarize the existing experiment result of concrete performance under ultra-low temperature freeze-thaw conditions， improve the relevant standards for concrete testing under special conditions， and facilitate the development of research on ultra-low temperature concrete through in-depth analysis of a large amount of experimental data. To this end， this paper comprehensively summarizes and analyzes the progress in research on ultra-low temperature concrete testing platforms， mechanical properties at ultra-low temperatures， the mechanism of freeze-thaw damage under ultra-low temperature and large temperature difference conditions， and approaches to enhancing frost resistance and durability， both domestically and internationally. Based on the understanding and contemplation of the current state， future research directions for ultra-low temperature concrete are proposed， aiming to provide references for experimental studies on ultra-low temperature concrete.
The mechanical properties of recycled micro powder engineered cementitious composites （ECCs） under various low-temperature conditions are investigated. The control variable method explores the ECC’s compressive and flexural strength concerning two low-temperature conditions： various freeze-thaw cycles and constant negative temperatures， with different types of recycled micro powders and replacement rates as variables. The effects of recycled micro powder type， replacement rate， number of freeze-thaw cycles， and negative temperature on the mechanical properties of ECC were analyzed. Moreover， two prediction models were presented to calculate their compressive strengths based on 3-6-1 and 3-3-1 BP neural network structures for two conditions of freeze-thaw cycle and constant negative temperature. Results show that the mechanical strengths of recycled concrete micropowder ECC are higher than those of recycled brick micro powder ECC under the same freeze-thaw conditions. With the increase in the replacement rate of recycled micro powder， a tiny decline and a sharp decline were observed， as well as a 20% loss of mechanical performance for 150 freeze-thaw cycles. However， the mechanical properties of the recycled micro powder ECC showed the opposite trend after experiencing constant low-temperature insulation. The recycled micro powder ECC mechanical strength showed an upward trend of 22%， from room temperature to -40 ℃ constant low-temperature state. The two BP neural network prediction models were established under low-temperature conditions with an average relative error of 1.43% and 1.28%， respectively. The maximum freeze-thaw cycles of recycled micro powder ECC with different mix ratios were predicted based on the mass loss rate and relative dynamic modulus.
The amplification or damping of seismic waves is impacted by the characteristics of the site， making it essential to use a precise site model for assessing seismic ground motion. To investigate the seismic ground motion properties of frozen soil sites in the western alpine region， a model is developed. This model is based on the principles of elastic wave propagation in both single-phase elastic media and frozen saturated porous media. Specifically， the model focuses on a free site of saturated frozen soil that is situated above bedrock and is subjected to P-wave incidence. By considering the case of plane P-wave incidence， an analytical solution for the seismic ground motion of this free site is derived. The seismic ground motion of a saturated frozen soil free site is analyzed for plane P-wave at different incidence angles using numerical calculations. The influence of physico-mechanical parameters， such as incident frequency， porosity， medium temperature， cementation parameter， and contact parameter， on the seismic ground motion is examined. The analytical results indicate that the frequency of plane P waves significantly affects the surface displacement of the free site of saturated frozen soil overlying bedrock. The horizontal displacement of the free site of saturated frozen soil overlying bedrock diminishes as the frequency of the P wave increases， but the vertical displacement of the surface increases with higher frequencies； An increase in porosity leads to an increase in the horizontal displacement of the free surface of saturated frozen soil on bedrock. The magnitude of this increase initially rises and then falls with the increase of the angle of incidence of the P-wave. Additionally， vertical displacement also increases， with the magnitude of the increase decreasing gradually as the angle of incidence increases； Decreasing the temperature of the medium reduces both the horizontal and vertical displacement of the surface of the saturated frozen soil free field on the bedrock， demonstrating the significant impact of the ice phase on the propagation of seismic waves in the frozen soil site； Poisson’s ratio affects the displacement of the surface of saturated frozen soil on the bedrock. As Poisson’s ratio increases， the horizontal displacement of the surface diminishes. As the incident angle of plane P wave rises， the magnitude of this increase initially increases and subsequently declines. An increase in Poisson’s ratio leads to a large rise in the vertical displacement of the surface of the free site of saturated frozen soil on the bedrock. The magnitude of this increase diminishes as the incident angle of the plane P-wave increases； An increase in contact parameters leads to a rise in the surface horizontal displacement of saturated frozen soil over bedrock. The amplitude of the increase first rises and then progressively diminishes. The vertical displacement of the surface grows while the amplitude of the increase steadily declines. In this paper， extending the fluctuation problem of single-phase elastic solid media， saturated soil media， or unsaturated soil media to frozen soil medium containing ice phases while considering the coupling effect of the phases in frozen soil is exceedingly significant for the study of seismic ground motion characteristics of frozen soil sites in the western alpine region. On the one hand， it can make a theoretical explanation for the ground motion of the earthquakes that have occurred in the western alpine region， and on the other hand， it can make a prediction of the ground motion characteristics of the future earthquakes that may occur in the frozen soil sites in the alpine region， so as to provide the theoretical basis for the work of seismic small zoning and engineering site selection. In addition， the study of seismic ground motions at frozen soil sites is at the same time a prerequisite for the study of seismic response of large structures and permafrost structure interaction in the western alpine region.
Freeze-thaw cycles significantly affect the water-heat-deformation interaction process of the soil-rock mixture. Therefore， this paper carried out the water-heat-deformation interaction and unconfined compressive strength test of the soil-rock mixture under unidirectional freeze-thaw cycles. Utilizing a unidirectional freeze-thaw cycling device， the soil-rock mixture sample with a rock content of 30% was prepared， and four freeze-thaw cycles were conducted according to the preset temperature change curve， with each cycle lasting 168 hours. Simultaneously， the mechanical properties of the sample both before and after freeze-thaw cycles were conducted， and the microstructural deterioration mechanism of the soil-rock mixture exposed to freeze-thaw cycles was investigated. The results show that the unidirectional freeze-thaw cycle has a significant effect on the temperature， moisture， and deformation variations in the treated sample. In the process of unidirectional freeze-thaw cycles， the melting rate of the soil-rock mixture is greater than the freezing rate. Meanwhile， the frost depth changes continuously during the freeze-thaw cycles and does not reach a stable state within the limited number of freeze-thaw cycles. The migration and redistribution of volumetric unfrozen water in soil samples occurred during the freeze-thaw processes. At the onset of the experiments， the volumetric unfrozen water content changes under the influence of temperature gradients， causing the liquid water to infiltrate downwards and leading to the accumulation of unfrozen water at the middle location of the sample， while the volumetric unfrozen water content at the top does not undergo drastic changes. Additionally， the first freeze-thaw cycle has a significant influence on the vertical deformation of the soil-rock mixture， and the net deformation of the sample increases first and then tends to be stable with the freeze-thaw cycles raised. Furthermore， the pore structure and internal arrangement of the soil-rock mixture are restructured during the unidirectional freeze-thaw cycles. The repeated expansion and contraction of soils accelerate the destruction of the skeletal structure， gradually reducing the attraction among soil particles and leading to the formation of new fractures. The unconfined compressive strength test shows that the compressive strength and deformation modulus of the sample decrease by 45.31% and 60.92%， respectively.
Plants are the engineers of the nature， they can effectively improve the strength of the soil and can enhance the stability of shallow soil slopes and minimizing surface erosion. for their mechanical reinforcement to soil. Therefore， they are widely used in slope protection. However， in the seasonal frozen soil regions of the central and western areas， the repeated freeze-thaw cycles of vegetation slopes lead to changes in soil mechanics under the dual effects of plant root reinforcement and freeze-thaw damage， introducing uncertainties in slope stability. Therefore， to explore the combined impact of freeze-thaw cycles and root distribution on soil， triaxial consolidation undrained （CU） tests were conducted under confining pressure from 25 kPa to 400 kPa， considering different freeze-thaw cycles （0， 1， 5 cycles） and root distribution （vertical uniform distribution： one root in each of the three layers； horizontal uniform distribution： three roots in the middle layer）. The materials were prepared with sands and sorbus pohuashanensis roots from Hailuogou in Minya Konka. To investigated the strength variations of root-containing soil under freeze-thaw cycles， stress-strain curves and pore pressure-strain curves were plotted respectively. Then the analysis of the stress-strain characteristics of the samples under different conditions was performed， and the total stress strength parameters and effective stress strength parameters were obtained from the shear strength envelopes. The results revealed that： （1） with the increase of freeze-thaw cycles， the peak strength of both the one-root-per-layer and three-roots-in-the-middle-layer samples gradually decreased， along with reduced cohesion and internal friction. Under low confining pressure （25 kPa）， the weakening effect of freeze-thaw cycles on root-containing soil strength was more pronounced. However， under high confining pressure， the strengthening effect of plant roots on soil strength remained significant. （2） Under different freeze-thaw cycles， roots can still enhance the soil's strength to a certain extent， and the arrangement of one root in each of the three layers showed the most significant enhancement effect. The roots contact with soil， which leads to irregular occlusions and “self-locking”， which has a positive effect on the enhancement of shear strength. （3） Under the same freeze-thaw cycle and confining pressure， samples with vertically distributed roots exhibited higher strength and cohesion， because the contact area was larger of roots placed in three layers along the height of the sample than the other distribution of samples. The distribution pattern of roots mainly influenced the soil's cohesion， with minimal impact on the internal friction angle. These findings can provide a theoretical basis for ecological slope protection in cold regions.
Under freeze-thaw cycle conditions， the water migration in subgrade structure was a pivotal factor contributing to the deformations associated with frost heave and thaw settlement in road structures. Many scholars had confirmed that the phenomenon of water migration and accumulation under the pavement structure layer under freeze-thaw action was widespread， and the action of water vapor migration cannot be ignored. However， there was a lack of quantitative understanding of the study of only water vapor migration， and there was a lack of experimental methods for studying only water vapor migration. At the same time， the outflow of liquid water under the pavement covering layer during the freeze-thaw process was an important reason for the sharp increase of water content in the gravel layer or unsaturated subgrade soil layer at the bottom of the covering layer. At present， there were relatively few studies on the outflow law of liquid water during freeze-thaw cycle. In order to explore the water-heat-vapor migration law of the subgrade structure under the freeze-thaw cycle， the subgrade structure of the actual project was simulated， including pavement structure layer， gravel layer and unsaturated subgrade soil layer， and the water migration test of liquid water and water vapor separation under the freeze-thaw cycle was carried out based on the semi-permeable membrane material. The water migration law under the freeze-thaw cycle was obtained by monitoring the hydrothermal change of the sample， the rise image of fluorescence， the change curve of water replantation and water collection. And the pore structure of soil column， the rate of rise and fall and the temperature gradient and other factors on the water vapor migration and liquid water outflow characteristics. The experimental results showed that the temperature change of a freeze-thaw cycle can be divided into five stages： rapid cooling stage， slow cooling stage， stable freezing stage， rapid heating stage and slow heating stage. Under the action of soil water potential， the water in the Maanobis bottle migrated upward in the soil column in the form of water-vapor mixture， and then changed to the form of water vapor when it reached a certain height. The amount of water vapor migrated at the bottom of the temperature-controlled plate and the crushed rock layer increased linearly during the whole freeze-thaw cycle. The amount of water vapor migration gradually increased with time， indicating that the action of water vapor migration in the process of water accumulation cannot be ignored. The outflow of liquid water from the bottom of the temperature control plate and the gravel layer was mainly concentrated in two stages of the freeze-thaw cycle： the first stage was the cooling stage， mainly condensate water， and the second stage was the melting stage， mainly melt water， which accounts for more than 70% of the outflow of liquid water in a freeze-thaw cycle. The small pore structure of silty clay resulted in water vapor migration mainly affected by volumetric gas holdup. With the increase of moisture content， the water vapor migration tended to decrease. However， sand had large pores， and the water vapor migration was mainly affected by the water vapor diffusion enhancement factor. With the increase of moisture content， the water vapor migration showed an increasing trend. The decrease of cooling rate led to a slow decline of the freezing front and reduced the closed effect of soil freezing on the water vapor migration channel. With the decrease of rising and cooling rate， the water accumulation at the bottom of the temperature control plate and the gravel layer increased. The larger temperature gradient led to the increase of water vapor diffusion coefficient and water vapor density gradient， which will lead to the increase of water vapor migration at the bottom of the temperature control plate and the gravel layer. Based on the above results， it was of great significance to reveal the mechanism of the increase of water content of subgrade soil under the condition of freeze-thaw cycle and the causes of road diseases.
Geosynthetics is widely used in civil engineering in cold regions， but the shear strength of the interface between soil and geosynthetics is weakly. Influenced by rainfall， irrigation and other factors， the soil undergoes wet-dry cycles in the shallow， which affects the shear strength of the interface between soil and geosynthetics. In this paper， based on the temperature-controlled direct shear apparatus， a series of experimental research on the shear characteristics of clay-composite geotextile interface under constant normal stress are carried out， and the test factors include the number of wet-dry cycles， temperature and normal stress. The results show that the shear stress-displacement curves at room temperature are all hardening type under different numbers of wet-dry cycles， and more visible at the higher normal stress. While the curve tends to soften at the decrease of temperature and the increase of numbers of wet-dry cycles. The wet-dry cycle has a deteriorating effect on the interface shear strength under room temperature conditions， especially the first wet-dry cycle. In contrast， the interface shear strength under negative temperature conditions shows an overall trend of increasing with the number of wet-dry cycles， and tends to stabilize after a certain number of cycles. Taking the condition of -6 ℃ as an example， the shear strength of the sample no longer increases after 5 wet-dry cycles. Under the action of wet-dry cycles， the change rule of interface cohesion and internal friction angle corresponds to the change rule of interface shear strength， but the change of interface cohesion is the main factor that causes the change of shear strength， that it is average increase more than 10% under different temperature after 10 wet-dry cycles. Through significance analysis of the influence variables of shear strength and their interaction， it is found that normal stress， freezing temperature and the number of wet-dry cycles have strong significant influence on the shear strength， and the interaction between normal stress and temperature， and the interaction between temperature and the number of wet-dry cycles also have significant influence on the shear strength.
The thermo-mass transfer and salt heave and frost heave characteristics of saline soil under temperature gradient are complex multi-physical field coupling problems. Understanding the salt heave and frost heave characteristics of sulfate saline soil under freezing conditions is crucial for soil salinization control， building durability and underground structure in sulfate saline soil areas. In order to explore the water-heat-salt-mechanics coupling mechanism of coarse-grained sulfate saline soil under freezing conditions， this paper conducts theoretical and experimental research on the water and salt migration and deformation characteristics of coarse-grained sulfate saline soil in a closed system during the freezing process. Saline soil is a multiphase continuous porous medium composed of solid， liquid and gas phases， and the water and salt content inside the soil will undergo phase change with the variation of temperature， which will lead to the change of the volume of the soil， thereby causing the deformation of the soil. The analysis of unidirectional freezing of sulfate soils involves the coupling effects of water and salt migration， heat transfer， ice-water phase transition， salt crystallization-dissolution， and soil deformation. Based on the thermo-elastic theory of unsaturated porous media and considering the phase transition of pore water and salt， a multi-field coupling model for water-heat-salt-mechanical fields in coarse-grained saline soil under unidirectional freezing condition was established. Numerical simulations were carried out for temperature， water content， salt content and displacement distributions in coarse-grained saline soil under unidirectional freezing condition. In the numerical simulation， we first set the initial conditions of the soil， including the water content， salt content and temperature of the soil. Then， according to the equations of the model， we obtained the distributions of temperature， water content， salt content and displacement of the soil during the freezing process through iterative calculations. Indoor tests were conducted by preparing fine sand with sulfate as soil samples under unidirectional freezing conditions. Temperature and water content distribution during the freezing process were measured using temperature and humidity sensors， and deformation of the soil was measured using displacement gauges. The results were compared with numerical results to verify the effectiveness of the theoretical model. The following conclusions are drawn from this paper. First of all， Through the comparison of SWCC fitting models for clay and sand， it was found that due to the larger particle size of sand and the larger pore structure of soil， water and salt can penetrate and migrate more easily. In the unidirectional freezing test， the migration rate of water and salt is faster. Secondly， during unidirectional freezing， the axial deformation characteristics of fine sand and clay are the same， showing a trend of first decreasing and then increasing， that is， the soil column will first undergo significant shrinkage deformation. Unlike clay， the duration of shrinkage deformation of coarse- grained saline soil is longer. Thirdly， the pressure exerted on the side walls of the soil column decreases as the height increases. This is due to the migration of water content from the warm end to the cold end， resulting in an increasing number of ice crystals at the cold end. The mass of the upper soil body increases， causing the lower soil body to be compressed. As a result， the porosity of the lower soil body decreases and its density increases， ultimately leading to a higher side wall pressure at the lower end compared to the upper end. At last， our research provides a new method for understanding the water and salt migration and deformation characteristics of coarse-grained sulfate saline soil during freezing. This method can not only be used for theoretical research， but also provide reference for deeper understanding of the disease mechanism of saline soil in cold regions and selecting appropriate prevention measures.
Saline soils are widely distributed in the cold and arid regions of northwestern China. The freezing temperature of soil is a critical temperature at which the physical properties of soil undergo significant changes. This temperature determines whether the soil is in a frozen state or not， and it has an effect on frost heave deformation. Additionally， the freezing temperature is a crucial parameter in calculating the freezing depth and is closely associated with the formation of segregated ice and the migration of water and salt in the soil. But due to the presence of salt， predicting the freezing temperature is challenging in saline soils， and consequently， accurately predicting the freezing temperature of saline soil is of significant importance for engineering damage treatment and providing practical references in engineering construction. The soil particle size and salinity affect the freezing temperature of soil. This paper proposes a freezing temperature calculation model applicable to sulfate saline soils with salt analysis and different salinity. The study investigates the variations in freezing temperature for sodium sulfate free solution， sodium sulfate saline soil， and quartz sand. In the beginning， based on the principles of equal increments of chemical potential at the solid-liquid phase equilibrium， and the influence of the solute in pore solution on water activity and ice crystal interface curvature effect was considered， and a freezing temperature prediction model was developed for aqueous solution， saline soils and quartz sand， respectively. Then， the freezing temperature was obtained through the freezing process tests on the saline soil with different salt contents. The experimental equipment includes a metal container with a lid， containing an inner diameter of 2.5 cm and a height of 3.5 cm， a temperature sensor， a vertical precision incubator， and a data collector. Finally， the accuracy and applicability of the model are validated by the root mean square error， significance level and the coefficient of agreement.
Some conclusions were conducted in this paper. The results indicate that the lower the initial moisture content in the soil sample， the stronger the capillary and adsorption effects on the soil surface， resulting in a lower freezing temperature. Additionally， when the water content of quartz sand exceeds its saturation water content and the water content of the soil surpasses its liquid limit， the freezing temperature of the pore solution tends to stabilize as the water content increases. The higher effective concentration of pore salt solution leads to the lower freezing temperature， and due to the influence of salt crystallization， the effective concentration initially increases with initial concentration. Specifically， when the concentration is less than 0.53 mol⋅kg-1， the freezing temperature decreases as the increasing of solution concentration. When the initial concentration is between 0.53 and 0.74 mol⋅kg-1， the solution concentration results increasing in salt crystallization， reducing the effective concentration and increasing the freezing temperature. When the concentration is above 0.74 mol⋅kg-1， salt precipitation is complete， the effective concentration remains constant， and the freezing temperature tends to stabilize. The smaller soil sample pore radius results in a greater influence of ice crystal interface curvature， which leads to a lower freezing temperature. Specifically， when the pore radius is less than 0.55 μm and greater than the critical pore radius of 0.003 μm， the freezing temperature of the soil sample decreases rapidly as the pore radius decreases. Above 0.55 μm， the extent of the influence of interface curvature on freezing temperature is greatest in clay， followed by silty clay， then silt， and least in quartz sand. This paper provides a practical model for temperature in saline heave deformation of saline soils and artificial freezing method， which provides theoretical basis for numerical simulation in hydro-thermal-saline coupling.
In order to investigate the basic rules of thermal conductivity of the soil， the transient planar heat source method was used to test the thermal conductivity of the soil during freezing. The variation of the thermal conductivity of soils at different temperatures， moisture content， and dry density physical indicators is studied. The mechanism by which the dynamics of these three physical indicators affect the thermal conductivity of the soil is analyzed. Based on the experimental data， six machine learning models， DT， RF， GBDT， AdaBoost， SVR and BPNN， were developed to predict the thermal conductivity of the soil. The predictive performance of six machine learning models and three empirical models is evaluated through four performance indicators. In addition， feature importance analysis is carried out based on RF and GBDT. The results indicate that there is no significant change in the thermal conductivity of the soil during the unfrozen phase. During the phase change stage， the thermal conductivity of soil exhibits a decreasing and increasing trend with decreasing temperature depending on the moisture content and dry density， respectively， with the increasing trend increasing with increasing moisture content. During the frozen phase， the thermal conductivity of the soil decreases as the temperature decreases due to the evaporation and migration of water from the soil sample during the test. The thermal conductivity of the soil increases with both dry density and moisture content. Based on the evaluation results， the performance of RF is better among the six machine learning models （RMSE=0.036， MAE=0.028， R2=0.993， AD=0.004）， significantly outperforming the three empirical models. Compared to empirical models， RF can also more accurately predict the thermal conductivity of soil in other regions. It is recommended to use RF to predict the thermal conductivity of soil during the freezing process. The analysis of feature importance highlights that moisture content， temperature， and porosity are significant factors that influence the thermal conductivity of frozen soil.
Given the complexity of frozen soil mechanics， establishing constitutive models that reasonably describe its mechanical behavior inevitably requires increasing the number of model parameters. The predictive accuracy of these models largely depends on the rational determination of these parameters. However， some parameters in frozen soil constitutive models cannot be directly determined through experiments or empirical equations. Therefore， parameter identification of frozen soil constitutive models based on limited experimental data holds significant engineering significance. Optimization algorithms provide effective tools for parameter identification in various engineering fields， and their application in geotechnical engineering has become increasingly widespread. Among them， genetic algorithm （GA） and particle swarm optimization （PSO） algorithm are two popular optimization algorithms. However， both algorithms have their own advantages and disadvantages. GA lacks target orientation， but possesses strong global search capability， while PSO is prone to local optima， but efficient information transmission. Therefore， this paper proposes a novel hybrid algorithm， the GA-PSO algorithm， which combines the strengths of GA and PSO while mitigating their respective weaknesses. In the GA-PSO algorithm， the incorporation of the elite preservation strategy within the GA computation step serves as advantageous information for the PSO computation step， preventing PSO from getting stuck in local optima. Conversely， the incorporation of the non-elite optimization strategy into the PSO computation step provides guiding information for the GA computation step to address the issue of lacking target orientation in the GA algorithm. The specific process involves global exploration of the solution space using GA calculation step while preserving elite individuals， followed by further optimization of poor fit individuals using PSO calculation steps. Validation results based on two standard test functions， i.e.， Griewank function and Restrigin function， illustrate that the GA-PSO algorithm exhibits superior global search capability and faster convergence speed in the solution space. Furthermore， The GA-PSO algorithm is applied to the parameter identification of the non-orthogonal elastoplastic constitutive model for frozen soil. The results of model parameter identification， as well as the comparison and validation of model prediction with test results， indicate that the GA-PSO algorithm is proficient in effectively identifying parameters of the non-orthogonal elastoplastic constitutive model for frozen soil， thereby enhancing the predictive accuracy of the model.
Due to the unclear development rule of freezing wall under seepage action and other reasons， the partial freezing method construction project relies on manual experience and lacks scientific prediction models， and is still far away from precise design and control. In order to explore the evolution law of freezing wall in coarse-grained soil layers during the freezing method construction under seepage， this article first establishes a numerical model for the freezing method construction， and verifies the effectiveness and applicability of the established model through indoor model experiments. Afterwards， considering five factors such as seepage velocity， freezing tube spacing， environmental temperature， moisture content， and thermal conductivity， an orthogonal numerical experiment was conducted to determine the main control factors for the formation of freezing walls， including time and thickness of freezing wall intersection. Finally， the development and evolution of freezing wall under influence of the main control factors were studied through numerical simulation. Based on the results， a prediction model is established for critical flow velocity， freezing wall thickness， and freezing wall intersection time， and provide a selection plan for the construction parameters of the freezing method. The research results indicate that： （1） A coupled soil freezing-thawing model established can effectively simulate the frozen soil process under seepage conditions， which can meet the needs of computation and analysis of freezing wall development process. （2） Based on the results of orthogonal numerical experiments， it was found that the contribution percentages of seepage velocity to the thickness of freezing wall and the intersection time are 78% and 52%， respectively， which is the dominant factor controlling whether a freezing wall can close and the final thickness. （3） When the seepage velocity exceeds a certain threshold， the freezing wall cannot be closed. This threshold is defined as the critical flow rate in freezing wall construction. When the freezing walls can be closed， thickness of the resulting freezing wall is mainly determined by flow velocity， and the two have an inverse exponential relationship. （4） The spacing between freezing pipes has little effect on the final thickness of freezing wall， but it has a great impact on freezing wall closure time. Furthermore， an inverse exponential relationship exists between them. （5） Given formulas of freezing pipe spacing， freezing wall thickness and closure time of freezing wall under conditions of 0~6 m·d-1 is provided， which can provide theoretical guidance for parameter selection and construction technology design of freezing method for coarse granular soil layer.
Warming and humidification trend of the Qinghai-Xizang Plateau is becoming increasingly severe， and the water vapor mass fraction in the air seasonally varies， resulting in changes in air physical parameters， enthalpy values， etc.， which may indirectly affect the heat transfer process of the crushed rock structural embankment. This paper analyzes the hydrothermal characteristics inside the crushed rock layer in dry and wet air under the same pressure conditions based on model experiments and air thermodynamics theory. The results indicate that under isobaric conditions， the temperature difference between dry and moist air is positively correlated with water vapor mass fraction， and the changing rate in water vapor mass fraction is 8% lower than the varying rate of temperature difference. The surface sensible heat flux of crushed rock considering the thermal influence of vapor was calculated based on the surface energy balance method， and it was found that the difference in sensible heat flux under the two air conditions is also positively correlated with water vapor mass fraction. At this time， the changing rate of water vapor mass fraction is 9.8% higher than the varying rate of sensible heat flux difference. After sunrise， the convective heat transfer difference between dry and moist air and the deep-layer rock mainly depends on the relative humidity of the air. After sunset， due to the large temperature difference between dry and moist air， it is mainly influenced by the temperature difference. When the water vapor mass fraction is at a low level， the changing rate in enthalpy difference between dry and moist air is about 87% higher than the changing rate in water vapor mass fraction， and the changing rate in enthalpy difference is about 21% higher than the rate of change in water vapor mass fraction. This phenomenon becomes more pronounced as the water vapor mass fraction decreases. The research results are of great significance for evaluating and predicting the long-term thermal stability of crushed rock structural embankment considering humid air conditions in permafrost regions.
The presence of large amounts of moraine soil in the Chada Gully of Xizang， China， with the development of the western regions， there will be numerous infrastructure projects built on moraine frozen soil foundations. To investigate the influence factors of frost depth and frost heave deformation of moraine soil in this area， carry out multi-factor and multi-level unidirectional freezing tests under the open system indoors through orthogonal design， having investigated the effects and magnitude of the significance of different factors on frost depth and frost deformation of moraine soils under unidirectional freezing conditions in an open system， at the same time， analyzed the redistribution of moisture in the moraine soil at different heights after freezing， and established the multivariate linear regression equations of multi-factors with the frost depth and frost heave deformation. The study shows that the most significant factors affecting frost depth and frost heave deformation are freezing side temperature and initial volumetric water content， respectively. The significant influence of each factor on frost depth is as follows： freezing side temperature>freezing time>freezing side cooling rate>initial volumetric water content>compaction， of which the freezing side temperature （negative temperature） and freezing time are positively correlated with the frost depth， and the other three factors have a small influence on it. The influence on frost heave deformation is as follows： initial volumetric water content>freezing side temperature>compaction>freezing time>freezing side cooling rate， and initial water content is positively correlated with the freezing side temperature and the frost heave deformation， compaction is negatively correlated with it， and the cooling rate and freezing time have less influence on it. Due to the large pores of the solid particles of the moraine soil， the freezing process moisture continues to migrate to the cold end， and free water and gaseous water form a poly-ice layer at the cold end. When the temperature of the cold end is low and the freezing time is long， there exists a freezing edge 3~8 cm above the freezing front， the soils here are saturated， with large amounts of free ice and free water， which is the key area for water migration and water-ice phase transition， when the bottom of the soil body is recharged， this area acts as a water storage zone further exacerbating the frost heave of the soil body. According to the orthogonal test results， a multiple linear regression equation was established to effectively predict the frost depth and frost heave deformation of the moraine soil in this area under the influence of multiple factors， and this equation can be utilized in the engineering field to quickly classify the freezing grade of the soil body. The results of the study have certain reference values for the safety evaluation and anti-freezing design of moraine soil projects in the relevant area.
The vast territory of China covers a diverse range of climate types and topographical features， providing intricate environmental conditions for the precipitation recycling process. This diversity presents challenges in categorizing and comparing different regions when analyzing the characteristics of precipitation recycle ratio. This study employs an optimized precipitation recycle ratio evaluation model to calculate the precipitation recycle ratio in China and investigates its variation characteristics and response to global warming. The findings reveal that from 1979 to 2020， China experienced notable regional and seasonal differences in precipitation recycle ratios， with the Qinghai-Xizang Plateau exhibiting the highest value. Regions with high values and increase of precipitation recycle ratio were mainly located in the inland humid areas of non-monsoon regions； However， in the arid and semi-arid eastern part of Northwest China， despite a generally lower precipitation recycle ratio， there was a significant upward linear trend. The empirical orthogonal function （EOF） results indicate that the first mode of precipitation recycle ratio is dominated by a negative phase before 2000， shifting to a positive phase afterward. A nine-year moving average of the precipitation recycle ratio suggests an initial increase followed by a decline. This study categorizes China into four precipitation recycle ratio regions based on the magnitude of precipitation recycle ratio and its positive or negative climate tendency rate： the precipitation recycle ratio is relatively high and shows an upward trend （Class I）， the precipitation recycle ratio is relatively high and shows a downward trend （Class II）， the precipitation recycle ratio is relatively low and shows an upward trend （Class III）， and the precipitation recycle ratio is relatively low and shows a downward trend （Class IV）. Eight representative regions were selected from the four regions to study the response of precipitation recycle ratio to global warming. In Class I and Class II， precipitation is mainly affected by local evaporation， while in Class III and Class IV， the relationship between precipitation and external water vapor transport is closer. Within the same class， the response values of internal and external circulation variables to global warming are different. Changes in evaporation and water vapor flux divergence will affect the response strength of the contribution of low-level flow and local evaporation to global warming. Studying the distinct responses of internal and external cyclic variables to global warming across different regions in China can enhance our understanding of climate change impacts and provide a scientific basis for formulating corresponding climate adaptation strategies.
Climate change is essential throughout the groundwater research field in cold regions， significantly impacting hydrological processes， ecological environment， and engineering geological and hydrogeological conditions in cold regions. This research field has attracted extensive attention from experts and scholars in different research fields. Until December 31， 2022， the research field has led to many research efforts in different directions. In order to understand the research status and development trends in this field， this paper was based on the literature data of CNKI， Web of Science （WOS）， and Science Direct （SD）， employing the following three methods： （1） CiteSpace， Originpro， and SCImago Graphica were used to conduct statistical and co-occurrence analyses of publications， authors’ writing age structures， institutions， and countries or regions to understand the research situation and status. （2） VOSviewer and Pajek were used to identify research topics and hot spots by keywords’ co-occurrence， clusters， and co-citation analysis. （3） Sixty representative papers were selected by VOSviewer and manual search and summarized to clarify this field’s leading research directions and development trends， combined with the locations of these papers’ study areas projected by ArcGIS. The results based on CNKI showed that the authors’ writing age structure was positively triangular， and the annual number of publications was on the rise， with 86 papers published in the past four years. There needed to be more cooperation among Chinese scholars and research institutions. Research hot spots based on CNKI focused on groundwater under the influence of the freeze-thaw cycle in permafrost areas in the following two aspects： （1） Engineering geological problems such as tunnel excavation， roadbed laying， and frost damage prevention and treatment， as well as ecological environment problems of alpine meadows and wetlands； （2） Response of groundwater regime to climate change in high-altitude mountainous areas. The results based on WOS and SD showed that authors’ writing age structure was trapezoidal， and the annual number of publications increased yearly， with 1 057 papers published in the past four years. Cooperation significantly existed among foreign scholars， scientific research institutions， and European and American countries. Besides， the Chinese Academy of Sciences and the United States Geological Survey contributed the most to the research field. Moreover， the United States， China， and Canada played a leading role in this field. Research hot spots based on WOS and SD focused on three core themes of groundwater， climate change， and permafrost， corresponding to the following three hot spots： （1） The groundwater age， water balance， water source， and groundwater flow path were studied using isotopes， hydrochemistry， and numerical simulation； （2） Hydrological input changes caused by climate warming affected the formation process of groundwater runoff and its interaction with surface water； （3） The mechanism of permafrost degradation， the release and migration of dissolved organic carbon， and the formation mechanism of permafrost landforms were primarily studied in cold regions of high latitudes. The development trend of this field should be studied closely around climate change， such as characteristics of groundwater regime in different aquifers and their response mechanism to climate change， the interaction between aquifer systems and groundwater under the influence of permafrost degradation， the mechanism of organic carbon release and migration in permafrost areas， and the interaction between groundwater and surface water in discontinuous permafrost areas. Recent advances suggest we continue studying aquifers’ types and hydraulic characteristics in high-altitude mountainous areas and engineering geology and ecological environments in high-latitude and low-altitude cold regions. Furthermore， we recommend continuing field investigations， improving hydrogeological data， strengthening numerical simulation research， and combining marginal or interdisciplinary research content boldly. This study can provide a reference for the sustainable utilization of water resources， ecological environment protection， and geological engineering problems in cold regions.
Slope aspect and position are important factors influencing the infiltration of soil moisture in slope active layer， but there is currently limited research on the infiltration characteristics of soil moisture in different slope aspect and position under the influence of freeze-thaw cycles in the active layer of permafrost region. This study establishes field experimental sites with different spatiotemporal conditions， enabling a more comprehensive analysis of the spatiotemporal variations in the soil moisture infiltration process within the active layer of permafrost region on the Qinghai-Tibet （Xizang） Plateau. We select the active layer soil on the slope surface of the alpine meadow in the Fenghuoshan basin， located in the hinterland of the Qinghai-Tibet Plateau， and set observation points at different slope aspects （sunny and shady slopes） and positions （top and middle of slopes） to analyze the infiltration characteristics and spatiotemporal differences of soil moisture on the slope surface during complete thawing period （July to August） and initial freezing period （September to October） of the active layer soil， and evaluate the applicability of different infiltration models in the study area. The results indicate that the infiltration characteristics of soil moisture in slope active layer in permafrost region exhibit significant spatiotemporal variations. The infiltration process of soil water can be divided into three stages： infiltration transient stage （0~30 min）， infiltration gradual stage （30~100 min）， and infiltration steady stage （>100 min）. The infiltration rate shows as follows： sunny slope > shady slope， top of slope > middle of slope， complete thawing period > initial freezing period， infiltration transient stage > infiltration gradual stage > infiltration steady stage. By using five models to simulate the infiltration process， the results show that the Horton model has the best simulation effect for the infiltration process of soil water in permafrost regions of the Qinghai-Tibet Plateau. However， the general empirical model and Jiang Dingsheng’s formula has almost identical fitting curves and statistical parameters for infiltration， but the model expressions are different. The simulation and analysis of soil moisture infiltration in permafrost region of Qinghai-Tibet Plateau in this study will provide data support for parameterization of land hydrological model under different spatiotemporal conditions.
The enhancement of tourism ecological efficiency in the five western provinces （regions） of China is pivotal not only for the high-quality development of the tourism industry itself but also for the ecological protection and green sustainable development of the western region. This paper， set against the backdrop of cryosphere tourism analysis and from the perspective of carbon emission constraints， constructs a framework for measuring the tourism ecological efficiency in these five provinces （regions） by focusing on inputs， expected outputs， and unintended outputs. Based on this， the super-efficiency SBM （slack-based measure） model is employed to assess the tourism ecological efficiency of these provinces from 2013 to 2021， and the grey relational analysis model is utilized to reveal its influencing factors. The findings indicate： （1） Overall， the tourism ecological efficiency in these five provinces （regions） is not high， among them， Gansu Province shows relatively higher efficiency， exceeding the overall average of the five provinces （regions）. （2） During 2013-2021， the overall tourism ecological efficiency in these provinces （regions） has shown a growth trend， with Xizang experiencing the most significant increase. （3） The level of economic development， infrastructure， carbon emission structure， cryosphere endowment， and environmental regulation are the main factors affecting tourism ecological efficiency. Among them， the cryosphere environment imposes notable constraints on other factors. With the enhancement of cryosphere projects， the flow of tourists， logistics， and capital in the western region will significantly improve， and the cryosphere endowment will gradually transform from a limiting factor into an economic advantage. By enhancing the efficiency of cryosphere tourism， it will effectively boost and improve the tourism ecological efficiency in the western provinces （regions） during the winter and spring seasons.
Glaciers， as an integral part of the cryosphere， are highly susceptible to both local and global climate change. Ice crevasses， which are prominent features on the surface of glaciers and the important channels for glacier meltwater， play a crucial role in understanding the condition， stability， internal stress and mass balance of glaciers. Mountain glaciers are subject to cloud cover and area limitation， and the spatial resolution of traditional satellite remote sensing data is low， which is difficult to be used for extracting ice crevasses， so there are fewer studies related to ice crevasses on mountain glaciers. In this study， the objective was to address the challenge of identifying and extracting glacier crevasses quickly and accurately. This research takes the mountain glacier： Baishui River Glacier No.1 in Yulong Snow Mountain in Lijiang， Yunnan Province as the research object， and takes the cloud-free orthophotos of the glacier surface with a resolution of 0.12 m in 2021 and 2022 acquired by aerial photography of the DJI M300RTK drone as the data source， and applies the U-Net Deep Learning Network to carry out the extraction of ice crevasses of the Baishui River Glacier No.1.
The results demonstrate that the U-Net network outperforms traditional methods such as the Canny operator and SVM algorithm in terms of crevasse extraction accuracy. The overall accuracy can be as high as 93%. Furthermore， the U-Net network exhibits strong generalization capabilities， which can be used to automatically extract unmanned aerial imagery from different time periods. From the perspective of spatial distribution of ice crevasses， the crevasses observed on BRG1 predominantly consist of transverse crevasses， splaying crevasses， and En échelon crevasses， which show the typical characteristics of mountain glacier ice crevasses in the low advection lifecycle. As the altitude decreases， there is a gradual transition from transverse crevasses to splaying crevasses. From the perspective of temporal change of ice crevasses， comparing the extraction results from different time periods reveals an increase in the number and average length of crevasses. This proves that the ablation of BRG1 is intensifying， and the glacier mass is gradually losing. The orientation of the ice crevasses was almost unchanged， indicating that the stress inside the glacier didn’t change dramatically. In summary， the study of intelligent extraction of ice crevasses based on UAV images and deep learning methods creates new possibilities for extracting ice crevasses from mountain glaciers， and can provide technical support for monitoring glacier changes and their relationship with climate change.
The presence of supraglacial debris profoundly influences the energy transfer processes between the atmosphere and glaciers， fostering the development of supraglacial ponds and ice cliffs， and significantly altering the glacier ablation processes and hydrological patterns. Modeling the interactions and feedback processes among climate， supraglacial debris， and glaciers by various parameters of debris deepens our understanding of the process and mechanism of debris-covered glaciers change， aiding in the accurate estimation and prediction of glacier mass balance， and then assisting in assessing the future evolution trend of glacier morphology. This paper systematically summarizes and compares various techniques for identifying the extent of debris cover， extracting glacier flow velocities， and obtaining physical parameters of supraglacial debris. Additionally， it introduces the principles and applications of glacier ablation models incorporating supraglacial debris cover effects. Furthermore， the limitations and future developments of these methods or models are discussed. Debris-covered glaciers situated in mountainous terrains with complex surface changes， posing several challenges for remote sensing methods to identify the extent of debris cover and extract glacier flow velocities： the existing supraglacial debris identification methods are still unable to overcome the influence of inherent disturbing factors； The flow velocity extraction methods should have a strong anti-interference ability， and the time baseline for paired images need to be as short as possible. The present state of research on debris-covered glaciers reveals significant data gaps in key parameters and data. Nevertheless， it is expected that these deficiencies will be addressed in the future， resulting in more refined models describing glacier dynamics and the change processes of supraglacial debris. Consequently， assessments and predictions of glacier mass balance， runoff， and other indicators are anticipated to become more realistic and accurate.
