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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]

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]

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]

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]

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]

This article presents a study of water-heat coupled problems of frozen soil along the Mohe-Daqing crude oil pipeline with thermosyphons. It is known that the Mohe-Daqing pipeline goes through four different kinds of frozen soil classified by ice content in soil. To determine the region with high tendency of permafrost thawing, the temperature field and water content field of the four types of frozen soil were first investigated in this paper. Taking freezing and thawing risk, typical geological condition and other factors into consideration, the soil temperature field of pipeline located at the permafrost swamp area was calculated numerically. Comparative study was also carried out for soil temperature field with and without thermosyphons to investigate the cooling effect of thermosyphons. It is evident that thermosyphons have great influence on temperature drop of permafrost, and this influence is especially magnificent in winter. In contrast to soil temperature without thermosyphons, installing the thermosyphons could reduce the soil temperature right beneath the pipeline by approximately 4°C. Numerical results, which have been validated by field data, are of great guiding significance for construction and operation safety of pipelines buried in cold regions. [ABSTRACT FROM AUTHOR]

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]

Copyright of Plateau Meteorology is the property of Plateau Meteorology 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.)

The surface displacement by seasonally freezing bulge and thawing subsidence are the main hazards for engineering construction in permafrost regions, especially for the Qinghai-Tibet railway. One of the main problems is how to monitor the frozen ground's displacement in the process of construction and protection of the Qinghai-Tibetan railway. The technology of Permanent Scatterers (PS) has been successfully used to detect the long-term subsidence at urban areas. For detecting the subsidence of the frozen earth on Qinghai-Tibet Plateau, this paper extended the capability of the technology of PS to investigate deformation phenomena in vegetated area. The paper analyses an interferometric phase model, and presents improved PS algorithms for separating different components in interferometric phase. The proposed technique is implemented using ENVISAT ASAR images to detect the deformation over permafrost region of Qinghai-Tibet Plateau. The results are in concordance with results provided by a traditional ground levelling, which encourages future development using the Permanent Scatterers method to analyse deformation of the frozen earth on Qinghai-Tibet Plateau. [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]

Yangbajain contains the largest geothermal energy power station in China. Geothermal explorations in Yangbajain first started in 1976, and two plants were subsequently built in 1981 and 1986. A large amount of geothermal fluids have been extracted since then, leading to considerable surface subsidence around the geothermal fields. In this paper, InSAR time series analysis is applied to map the subsidence of the Yangbajain geothermal fields during the period from December 2011 to November 2012 using 16 senses of TerraSAR-X stripmap SAR images. In the case of the TerraSAR-X data, most orbital fringes were removed using precise orbits during the interferometric processing. However, residual orbital ramps remain in some interferograms due to the uncertainties in the TerraSAR-X orbits. To remove the residual orbital ramps, we estimated a best-fit ‘twisted plane’ for each epoch interferogram using quadratic polynomial models based on a network approach. This method removes most of the long-wavelength signals, including orbit ramps and atmospheric effects. The vertically stratified component (Topography Correlated Atmospheric Delay, TCAD) was also removed using a network approach. If the influence of seasonal frozen ground (SFG) is not taken into consideration, our results show that the subsidence rate around power plant I (the south plant) is approximately 20 mm/yr with a peak of 30 mm/yr. The subsidence rate around power plant II (the north plant) is approximately 10 mm/yr, when accounting for the influence of SFG on the power plant and its surrounding ground surface. Our results show that ground motion is caused by seasonal frozen ground and is strongly related to the temperature change. [ABSTRACT FROM PUBLISHER]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering 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 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]

It is absolutely necessary to quantify the hydrological processes in earth surface by numerical models in the cold regions where although most Chinese large rivers acquire their headstreams, due to global warming, its glacier, permafrost and snow cover have degraded seriously in the recent 50 years. Especially in an arid inland river basin, where the main water resources come from mountainous watershed, it becomes an urgent case. However, frozen ground’s impact to water cycle is little considered in the distributed hydrological models for a watershed. Took Heihe mountainous watershed with an area of 10,009 km2, as an example, the authors designed a distributed heat-water coupled (DWHC) model by referring to SHAW and COUP. The DWHC model includes meteorological variable interception model, vegetation interception model, snow and glacier melting model, soil water-heat coupled model, evapotransporation model, runoff generation model, infiltration model and flow concentration model. With 1 km DTM grids in daily scale, the DWHC model describes the basic hydrological processes in the research watershed, with 3∼5 soil layers for each of the 18 soil types, 9 vegetation types and 11 landuse types, according to the field measurements, remote sensing data and some previous research results. The model can compute the continuous equation of heat and water flow in the soil and can estimate them continuously, by numerical methods or by some empirical formula, which depends on freezing soil status. However, the model still has some conceptual parameters, and need to be improved in the future. This paper describes only the model structure and basic equations, whereas in the next papers, the model calibration results using the data measured at meteorological stations, together with Mesoscale Model version 5 (MM5) outputs, will be further introduced. [ABSTRACT FROM AUTHOR]

This paper presents a case history study of a tunnel in the cold plateau region of China. It describes the permafrost distribution of the mountain in which the tunnel is located and the observed air and surrounding rock temperatures in and outside the tunnel. By comparing these measured temperatures, it is found that the effect of the thermal insulation doors, installed at both ends of the tunnel, raises the air temperature in the tunnel higher than the antisnow shelter installed at both ends of the tunnel. The thermal insulation doors are thought to be better than the antisnow shelters in preventing the tunnel from being damaged by frost action. [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]

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]

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 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]

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]

This paper presents new field observations that assist in further defining the extent of Last Permafrost Maximum (LPM) permafrost and frozen ground in north China. In that respect, this region is specific by its arid environment and continental position. Bedrock exposures and sand and gravel pits were examined along a south-north transect from southern Ordos as far as the vicinity of Dongsheng District, Ordos City on the Ordos Plateau (North China). Attention focussed upon the recognition of sand-wedge remains and possible cryoturbations. Two types of wedge structures were recognized: type A wedges extend to depths in excess of 3.0 m and are thought to have formed under conditions of continuous permafrost. Type B wedges are restricted to the upper 1.5 m and are thought to reflect discontinuous permafrost and/or deep seasonal frost. OSL dating of wedge infills indicates that type A wedges formed between 23–19 ka and younger type B wedges formed until the early Holocene. It is now possible to delineate a more exact position of the boundary between continuous permafrost and discontinuous permafrost and/or deep seasonal frost on the Ordos Plateau during the LPM. This boundaries occur between Dongsheng and Jinbian at 37°-39°N. • Precise location of southern limit of continuous permafrost during the Last Permafrost Maximum (c.19-23 ka) in north China. • Narrow zone of discontinuous/sporadic permafrost during the Last Permafrost Maximum (c.19-23 ka) in north China. • Permafrost extent in N China at LPM was specific by its aridity, continentality and proximity to the Siberian High Pressure. [ABSTRACT FROM AUTHOR]

Abstract: Snow cover is a common and relatively stable land cover condition in winter for cold north regions in China. Snow cover has significant effects on water and heat transfers in frozen soil; it needs to be considered in the study of frozen soil water–heat coupled movements. On the basis of previous research results and physical process analysis of water and heat movements in snow cover and soil, a snow cover–soil union water–heat coupled movements model is established in this paper. The numerical simulation was conducted by using a finite difference method. The results indicate that the simulated values have a similar trend to the measured values and the numerical simulation had big relative errors. However, the average absolute errors of the total and liquid moisture content in frozen soil were all less than 4%, and that of the frozen soil temperature was 1.37 °C. The errors of the numerical simulation were still within the acceptable range. Thus, the snow cover–soil union water–heat coupled movement model constructed in this paper is rational. [Copyright &y& Elsevier]

The delineation of the southern boundary of the latitudinal permafrost in the north of China in the period of late Pleistocene, i.e. the last glaciation maximum (LGM), has been hampered for two reasons. Firstly, previous studies were limited to the eastern part of the north of China, and, secondly, the ages of the permafrost had not been determined systematically. In this paper, we suggest that the southern boundary of the high latitudinal permafrost in the north of China is bounded by approximately 38-40°N (eastern part) and 37-39°N (western part) lines of latitude based on our interpretation of periglacial phenomena and their implication to the environment during the late Pleistocene, and this southern boundary is plotted for the first time. Also, we reconstrnct the migration of the southern latitudinal permafrost boundary and the environment after LGM. It is proposed that two cold stages occurred in the LGM at 26 kaBP and 23-13 kaBP, when the annual mean temperature was 8 -12°C lower than at present. [ABSTRACT FROM AUTHOR]

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

• A combined opto-electronic sensing approach was proposed for soil multivariables. • Loess thermo-hydraulic behaviors in freezing-thawing were deciphered by field data. • The laboratory-obtained soil freezing point is applicable to field investigations. • Importance of in-situ soil-freezing characteristic curve acquisition is emphasized. • Frozen soil matric suction considering ice is the driving force of water migration. Frost damage in mid-latitude loess regions is mainly caused by the coupled soil water and heat transfer during freezing-thawing (FT) processes. In this paper, to better understand the thermo-hydraulic (TH) behaviors of seasonally frozen loess, field monitoring and assessment were performed on the Loess Plateau, China with a quasi-distributed opto-electronic sensing system. This system successfully captured the spatiotemporal variations in multivariables of seasonally frozen soil in near real-time, including in-situ soil temperature, unfrozen water content, and ice content. The monitoring datasets collected during the 2020/2021 winter offer unique insight into the TH behaviors of freezing point (FP) depression, in-situ soil-freezing characteristic curve (SFCC), and cryosuction. The findings highlight the importance of acquiring SFCCs under natural boundary conditions and confirm the applicability of laboratory-obtained FP in determining in-situ soil freezing depth. Furthermore, the study reveals that soil matric suction, considering the presence of ice, is the primary driving force of water migration during FT. Finally, errors in field monitoring are discussed, which arise from two aspects: the special features of loess and imperfections in monitoring schemes. This assessment of the coupled TH responses to climate changes in loess offers valuable theoretical guidance for optimizing engineering construction schemes and mitigating geohazards in mid-latitude loess regions. [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 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]

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The freeze-sealing pipe roof (FSPR) method, which combines the pipe roof method (PRM) with the artificial ground freezing (AGF) method, has been successfully utilized for the first time in the Gongbei Tunnel Project in China. During the construction process, there have been practical problems such as difficulty in welding of the profiled freezing-tube, easy leakage of refrigerant, and working environment pollution, which bring difficulties to the tunnel construction and may affect the further promotion of this new method in the future. To address these problems, a method of placing double circular freezing-tubes on the inner wall of the hollow pipe and wrapped with cement mortar was put forward to replace the welding profiled freezing-tube in the actual project. By designing a scaled model test, the feasibility and freezing effect of this improved design were verified. The corresponding numerical calculation model was established to study the distribution characteristics and differences of temperature field under two different configurations. The research results show that the Configuration 2, with the improved design, presents a lower temperature and a higher cooling rate; the limiting-tube could limit the excessive development of the frozen soil wall within a certain range, to avoid the adverse impact of frost heave on the ground building structure. Under the premise of meeting the design requirements for freezing, the freezing time of Configuration 2 at the centerline between the pipes and the vertical line of the hollow pipe is 33% and 46% shorter than that of Configuration 1, respectively. Finally, the average thickness of the frozen soil wall at the right side of the hollow pipe, the vertical direction of the hollow pipe, and between the pipes increased 33%, 17%, and 13% in Configuration 2, respectively. The improved design proposed in this paper is not only more convenient in production and installation but is also demonstrated to provide improved freezing effects, providing a strong guarantee for the further popularization and application of the freeze-sealing pipe roof method. [ABSTRACT FROM AUTHOR]

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

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]

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]

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

Abstract: This paper discusses the spatial and temporal change of different frozen soil types from 1980s to 2000s, and the impacts of frozen soil change on rangeland productivity and sustainable livelihood in the source regions of Yangtze and Yellow Rivers employed numerical model and GIS technology. Authors use the analytical framework of adaptation of animal husbandry according to national, regional, community and household scales, and release three key instruments of cryospheric change adaptation, including adaptive capacity of the policies, adaptive capacity of the people, and adaptive capacity of the grassland ecosystem. Analysis result shows that there is clearly a need, to develop institutional processes that support policy analysis to draw on existing information, that facilitate multidisciplinary research on topics of policy relevance, and that link the accumulation of credible cryosphere scientific evidence with policy making. Finally, Authors suggest that further support to mainstream climatic and cryospheric change concerns in adaptation policies and strategies of animal husbandry must include a focus on: (1) Formulating ecological compensation policy and mechanism for grassland ecosystem maintenance; (2) Strengthening vocational training, long-term essential-qualities-oriented education to improve indigenous people''s professional skills and abilities; (3) Strengthening development of livestock replacement industries to broaden employment channels of indigenous people; (4) Strengthening the consciousness of ecosystem maintenance, improvement the social civilization level for indigenous people; (5) Continuous implementation the Ecological Protection and Restoration Program in the Three-River Source Region in national scale. [Copyright &y& Elsevier]

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

Abstract: This paper reports the development of a decision tree algorithm to classify the surface soil freeze/thaw states. The algorithm uses SSM/I brightness temperatures recorded in the early morning. Three critical indices are used as classification criteria—the scattering index (SI), the 37 GHz vertical polarization brightness temperature (T 37V), and the 19 GHz polarization difference (PD19). The thresholds of these criteria were obtained from samples of frozen soil, thawed soil, desert, and snow. The algorithm is capable of distinguishing between frozen soil, thawed soil, desert, and precipitation. In-situ 4-cm deep soil temperatures on the Qinghai–Tibetan Plateau were used to validate the classification results, and the average classification accuracy was found to be 87%. Regarding the misclassified pixels, about 40% and 73% of them appeared when the surface soil temperature ranged from −0.5 °C to 0.5 °C and from −2.0 °C to 2.0 °C, respectively, which means that most misclassifications occurred near the soil freezing point. In addition, misclassifications mainly occurred from April to May and September to October, the transition periods between warm and cold seasons. A grid-to-grid Kappa analysis was also conducted to evaluate the consistency between the map of the actual number of frozen days obtained using the decision tree classification algorithm and the reference map of geocryological regionalization and classification in China. The overall classification accuracy was 91.7%, and the Kappa index was 80.5%. The boundary between the frozen and thawed soil was consistent with the southern limit of seasonally frozen ground from the reference map. The statistics show that the maximum area of frozen soil is about 6.82×106 km2 in late January, accounting for 69% of total Chinese land area. [Copyright &y& Elsevier]

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

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

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]

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

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

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]

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]

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]

• Properties of hydraulic conductivity of dispersive soil had been rarely reported. • Permeability of dispersive soil is proposed to be characterized by k max and k rs. • Increasing soil salinity leads to an exponential increase in k max but not in k rs. • Effect of freeze-thaw cycles on k max and k rs is not monotonous. • Correlations of osmotic and matric suctions to k max are respectively positive and negative. The hydraulic conductivity of soil is a fundamental parameter that should be obtained both in hydrological and geotechnical studies since it relates to a series of hazards in earthen engineering projects, whereas investigations on dispersive soils, especially those distributed in cold regions, have rarely been reported. This study aims to explore the characteristics of permeability by using a dispersive soil from northeastern China, as well as the effects of soil salinity and freeze-thaw on the variation in hydraulic conductivity. Indoor constant-head permeation tests were conducted on artificially prepared specimens, and initial soil suctions were measured by the filter paper method to assist the analyses. The results demonstrated that the hydraulic conductivity decayed with permeation time until reaching relative stability, and both maximum and relatively-stable values (k max and k rs , respectively) should be adopted for comprehensively characterizing the permeability of dispersive soils. Increasing salt content increased the k max exponentially, and the inflection salt content was approximately 1.5%, from which a sharp increase in k max appeared; the k rs showed a slight increase with initial salt contents as well. Freeze-thaw yielded nonmonotonic changes in the permeability as k max peaked at 5 freeze-thaw cycles; the variation in k rs was similar. The osmotic suction positively correlated with k max but did not fully contribute to the sharp increase in k max since it increased linearly with the salt content without mutation points. The number of freeze-thaw cycles influenced the relationship between the osmotic suction and k max. The matric and osmotic suctions posed opposite impacts on the permeability. More importantly, detailed discussions for the underlying mechanisms of the abovementioned novel observations were illustrated. These results may serve as good references for understanding the features of the permeability of dispersive soils in seasonally frozen regions domestically or worldwide. [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]