Frost Depth Research Articles

Calculation method and model tests of pile frost jacking for railway overhead contact systems in permafrost regions

One of the major challenges encountered in electrification reconstruction project of Golmud-Lhasa section of Qinghai-Tibet railway of China is ensuring the frost jacking stability of the pile foundation of overhead contact system mast (OCSM). To evaluate the resisting frost jacking performance of OCSM pile in permafrost regions, a theoretical model of OCSM pile in permafrost soils under the effect of frost heave was constructed based on superposition principle and deformation coordination relationship between the pile and soil. The model was solved by using the finite difference method combined with MATLAB. Then, large scale model tests were performed to investigate the thermodynamic behaviors of OCSM piles with different sections (equal section circular pile, straight cone cylindrical pile and curved cone cylindrical pile) in the permafrost soils under freeze-thaw actions, after which the theoretical model were validated. It was found that distribution curves of pile axial force obtained by the calculation method is basically consistent with model test results in the overall trend, implying that the calculation model is reasonable and feasible. During soil freezing, the pile is under tension as a whole, and the axial force is greatest near the depth of frost penetration. The maximum value of tangential frost-heave stress occurs near the ground surface. The total tangential frost heaving force of the curved cone cylindrical pile is the smallest, and the effect of resisting frost jacking is the best. These research results can provide a reference for resisting frost jacking design of OCSM pile in permafrost regions.

Further food for thought: higher tropical mountains revisited once again

D.H. Janzen argued that tropical mountains, for their heights, pose greater migration barriers than temperate mountains owing to lower temperature seasonality, and consequent greater niche and ecosystem specialization. These result in distinct altitudinal zonation under hardly varying temperature lapse rates. The Asian Far East alone provides an opportunity to test this hypothesis owing to latitudinal continuity of evergreen forests from equator to warm temperate zone. With data from four mountains, we find Janzen’s hypothesis broadly correct. The primary and most consistent mediator of forest zonation and therefore species’ habitat specificity is soil, itself indirectly mediated by climate. But declining habitat niche specificity does not proceed north along a continuum, instead in a series of latitudinal steps initiated by quite sudden habitat changes. Tropical montane forests are altitudinally floristically and structurally zoned by factors only indirectly mediated by temperature. Equatorial forests experience continuously wet climates and a frost line at c.4100 m. North of 8°N, temperature and rainfall seasonality increases and winter air frosts descend to c.2000 m. Upper montane forest becomes truncated, while lower montane forest continues to the frost line which remains constant in moist climates. The margin of the wet tropics is pushed north to 27°N by the Himalaya. Annual frost at c.2000 m here marks a narrow ecotone between tropical lower montane forest and warm temperate evergreen lucidophyll forest, a formation unique to east Asia. In equably moist South China, the lowland tropical-warm temperate (‘subtropical’) margin returns to the Tropic of Cancer and appears to be narrow at all altitudes. The temperate forests exhibit less distinct and inconsistent altitudinal zonation, instead manifesting an altitudinal floristic and structural continuum mediated by winter frost frequency and intensity.

Estimation of Soil Freeze Depth in Typical Snowy Regions Using Reanalysis Dataset: A Case Study in Heilongjiang Province, China

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.

Dynamics of soil freezing and thawing in the agroforestry landscape

The article presents the dynamics of soil freezing and thawing in the agroforestry landscape of the dry-steppe zone. These processes in winters with unstable snow cover have their own characteristics. The purpose of this study was to investigate the character of soil freezing and thawing in the agroforestry landscape under conditions of low snowfall winters. Observations were carried out in the winter period of 2020–2021 at the existing runoff-erosion research station in Volgograd. The dynamics of soil freezing and thawing was studied using Danilin freeze-thaw meters installed in the field and in the center of a four-row forest belt. Simultaneously, snow cover height was measured in triplicate with a snow measuring rod. The weather conditions were characterized by alternating thaws, which promoted snow cover melt, and frosts, which increased the depth of soil freezing. The formation of a 10-15 cm snow cover did not affect soil freezing. In the absence of snow on the background of a brief thaw, the lower boundary of the frozen layer in the field decreased by 11 cm compared to the forest belt, which even in the leafless state affected the inflow of solar thermal energy. Average freezing at the end of winter was 85 cm in the field and 67 cm in the forest belt. Thawing in the field was faster. During the first two weeks, the rate of soil thawing averaged 2.3 cm/day in the field and 1.3 cm/day in the forest belt. After that, the depth of freezing in the whole agroforestry landscape became equal. During the next two weeks, the thawing rate doubled. After complete soil thawing in the field in the forest belt, the thickness of the frozen layer averaged 32 cm.

Freezing and Thawing Processes of Highways in Kazakhstan

This paper presents the results of an experimental study of freezing and thawing patterns of highways in Kazakhstan. Special sensors measure temperature and moisture change every hour in automatic mode. The purpose of this work is to develop a methodology for determining the depth of freezing of subgrade soils of roads of Kazakhstan, and the task is to establish the pattern of cold temperature change (temperature “0 °C”) through certain points (sensors) at any time. In the upper part of the pavement (up to 30–40 cm), the temperature changes in annual and daily cycles. As the depth increases, the daily temperature fluctuations disappear, leaving only the annual fluctuation. At a depth of 180 cm and below, temperature fluctuations occur only in the annual cycle. The freezing rate varied from 14 cm/day to 0.33 cm/day. The maximum freezing depth was 227 cm. The descending branch of thawing occurs almost uniformly, with an average rate of 6.25 cm/day to a depth of 220 cm; the average rate of the ascending branch of thawing is 0.9 cm/day. Asphalt–concrete layers of the pavement and the upper part of the subgrade were in a frozen state for 151 and 166 days, respectively. In the subgrade at the beginning and end of the cold period, there are abrupt changes in moisture, which are explained by phase transitions of the second order: the transition from the liquid state to the solid (ice) at the beginning of the cold period and the transition of moisture from the solid state to liquid at the end of the cold period.

Experimental and numerical study of heating embankment utilizing solar energy in seasonally frozen regions

Frost heave has a significant influence on the stability of embankment in seasonally frozen regions, where the active heating embankment has become a new method for preventing and controlling frost heave. In this study, a field experiment was conducted based on a solar circulating heating embankment system (SCHES), and the heat collection performance of the SCHES and the heating effect of the soil were analyzed. Additionally, the numerical simulation of the coupled moisture-heat of the embankment under heating conditions was performed, and the heating effects of different buried forms and buried depths of the heat accumulation pipe (HAP) were discussed. The experimental results showed that the SCHES can provide a heating temperature of up to 70 °C and a mean heating flux of 87 W m−2 during the cold season. The heating action of the SCHES makes the temperature of the surrounding soil of HAP above 0 °C in cold season, which significantly reduces the freezing depth. The numerical results also show that the maximum freezing depth of the embankment can be reduced by 70%, the volumetric ice content can be reduced by more than 60%, and the heating embankment can reduce the frost heave deformation by more than 60% compared with the normal embankment. The buried form of the HAP is recommended to be the horizontal insertion on both sides and the horizontal insertion on sunny sides. The optimal buried depth is between 0.5 m ∼ 1.0 m when the HAP burial form is the horizontal insertion on both sides. As a preliminary study, the concept of the active heating embankment utilizing solar energy can provide a reference for the prevention and control of frost heave in seasonally frozen regions.

Assessment of frost and heating penetration in compacted clay layers of landfill top covers in temperate climate

Compacted clay (CC) layers are commonly used as hydraulic barriers in landfills, thanks to their impervious capacity. However, mechanical and hydraulic properties of CC can be significantly affected by temperature variations due to the heat produced by waste degradation as well as to external air temperature and weathering. Previous experimental tests show that the most detrimental occurrence is the cyclic freezing–thawing (FT) that can increase the hydraulic conductivity of CC up to one order of magnitude. This paper aims at assessing the temperature distribution in a landfill multilayered top cover in several scenarios of temperature solicitations, in order to evaluate the depth of frost penetration. For this purpose, a 2D hydro-thermal coupled finite element model representing a case study landfill top cover has been developed; each constituting layer has been characterized by physical and thermal properties acquired through direct measurements on sampled materials in unfrozen and frozen conditions. The model provides a reliable time description of the isotherm distribution within the layered top cover in several temperature scenarios typical of a temperate climate, thus estimating the penetration of the frost front as well as of high temperatures.

Problems of engineering geomorphology in the settlement zone of the Eg River valley: A case study of Aufeis in Erdenebulgan Soum, Khuvsgul Province, Mongolia

Aufeis formation in the winter season in settlements located in continuous, discontinuous, and isolated permafrost regions of Mongolia has become one of the urgent problems that must be solved in the settlement areas. In this study, the reasons for the formation of Aufeis in the settlement area of Erdenebulgan Soum, Khuvsgul Province, located in the Eg River valley, were clarified. In addition to the analysis of geomorphology and permafrost survey materials, the research was based on satellite image data and calculated using the methods of normalized snow index (NDSI) and snow water index (SWI). In the Eg River valley, the normative depth of seasonal freezing and thawing of subsoil ranges from 2.2-3.7 meters. Depending on the freezing of the winter season, there were long, short, and straight rows of cracks and fractures in the vicinity of river diversions, floodplains, terraces, or along the settlement zone. Over the past 10 years, the average size of the Aufeis area was 5555.8 m², and the average Aufeis volume was 5000.2 m³. In 2022, the Aufeis area increased sharply to 6,381.3 m², which can be related to that year's precipitation and soil temperature fluctuations. According to the area and volume classification of Aufeis in Mongolia, the research area belongs to the III class of medium-sized category, but it is exposed to the space of Aufeis distribution due to the improper expansion of the settlement area and wrong planning. According to the changes in the satellite map over the last 30 years, the diversion of the Eg River has caused the spatial distribution of the Aufeis to move towards the settlement area. This study is important for the planning of the spatial location of towns to determine the methods of pre-research and prevention of permafrost-related phenomena and engineering geomorphological problems.

Influence of snow cover on soil freeze depth across China

Using 1980–2014 observation data of 378 meteorological stations, this study quantified the correlations between snow cover and the annual maximum seasonally freeze depth (MSFD) across China and the contributions of snow cover to MSFD. Snow cover exhibited a weak effect on MSFD across China, which may be related to the thinness and short duration of the snow cover. Regional differences in the effects of snow cover on MSFD were relatively large, and the effects of snow cover were more significant than those of air temperature (characterized by the air-freezing index) at stations in Northeast China, northeastern Inner Mongolia, and the north of the Tianshan Mountains. In regions with a thin snow cover or short snow cover duration (SCD), the cooling effect of snow cover can dominate, but it only slightly influences MSFD owing to the short SCD. With increasing average snow depth (ASD) and SCD, the relative contributions of snow cover to MSFD gradually increased, peaking at SCDs of 120–140 days or ASDs of 8–10 cm, which is attributable to the increasing insulating effect. However, with further increase in ASD and SCD, the insulating effect decreases because of high albedo and the latent heat effect of snow melting. This decrease resulted in declining MSFD–snow cover correlations and snow cover contributions to MSFD. Compared with SCD, ASD has a greater influence on MSFD. By adding an ASD variable to the Stefan formula, this modified formula outperformed the conventional formula in MSFD estimation at SCDs of 60–140 days. This study demonstrated the importance of snow cover variables for soil freeze depth analysis and simulation in areas with large snow cover and further elucidated the effects of snow cover on soil freeze depth.

Numerical investigation of the temperature field and frost damages of a frost-penetration tunnel considering turbulent convection heat transfer

Accurate evaluation of tunnel temperature field plays an essential role in anti-freezing measures of cold-region tunnels. The aim of this study is to establish turbulence-based theoretical models for the temperature field of cold-region tunnels and to investigate the temperature field and frost damages of an actual cold-region tunnel with negative mean annual air temperature. A transient convection–conduction heat transfer model with turbulent flow and phase change was established. The proposed theoretical model was validated using model test results. The temperature field and frost damages of the Daban Mountain tunnel were investigated. The influence of global warming on the temperature field was also deeply discussed. The results indicate that for the Daban Mountain tunnel, the freezing circle develops to the radial surrounding rock and simultaneously develops along the longitudinal direction of the tunnel. Permafrost occurs at the tunnel entrance in the 7th year and along the whole tunnel in the 16th year. The formation rate and maximum freezing depth of permafrost is significantly influenced by the mean annual air temperature. The annual air temperature amplitude has significant effect on the formation rate of permafrost but little effect on the maximum freezing depth. Under global warming, the mean annual temperature of the surrounding rock decreases first and then increases. In the early years, the unfrozen surrounding rock freezes yearly and develops into permafrost. However, as the mean annual air temperature rises, the permafrost gradually degenerates into seasonally frozen rock and the maximum freezing depth decreases yearly.

Comprehensive Assessment of Seasonally Frozen Ground Changes in the Northern Hemisphere Based on Observations

AbstractSeasonally frozen ground (SFG) in the Northern Hemisphere (NH) plays a significant role in the earth system via changes in the freeze‐thaw cycle. Previous studies primarily focus on permafrost; however, the SFG response to climate change on a hemispheric scale is uncertain due to a lack of observations. We rectify this with a newly assembled comprehensive database of 1,220 stations with daily observations. To quantify the spatiotemporal characteristics of SFG in response to climate change, we calculate eight variables with these observations: the first date of soil freeze (FFD), freezing duration (FDR), maximum freeze depth (MFD), the date of maximum freeze depth (MFDD), the last date of soil thaw (TLD), thawing duration (TDR), freeze‐thaw duration (FTDR), and actual number of freezing days (AD). During the variables' common 1986–2005 period, MFD decreased 8.9 cm (9% change). FFD was later by 5.3 days (2% change), MFDD and TLD were earlier by 14.5 days (27% change) and 24.7 days (22% change), respectively, and FDR and TDR decreased by 9 days (11% change) and 4.6 days (10% change). FTDR and AD decreased 18.1 days (14% change) and 12.1 days (10% change), respectively. The spatial pattern of freeze‐thaw variables depends on latitude and elevation, and varies by climatic zone: FTDR increases, going from the warm temperate climate, to the arid climate, and the snow and polar climates. The variability in freeze‐thaw changes is mainly driven by air temperature and latitude, while precipitation, soil moisture, snow depth, and elevation are relatively insignificant at the hemispheric scale.

The effects of combined throughfall reduction and snow removal on soil physical properties across a drainage gradient in aspen forests of northern Minnesota, USA

Climate change is projected to alter precipitation patterns across northern latitudes, with decreased snow accumulation and summer rainfall predicted. These changes may alter soil physical properties such as soil strength, which would have implications for the feasibility of forest management activities. Reductions in summer and winter precipitation were simulated using a paired-plot design with throughfall reduction and snow removal as treatments across four soil drainage classes (well, moderately well, somewhat poor, and poorly drained) at each of three locations in northern Minnesota, USA. Snow removal caused large reductions in soil temperature and significantly deeper penetration of frost that varied by drainage class, where frost depth decreased with decreasing (wetter) drainage. There was a positive relationship between air freezing index and frost depth, where the rate of frost development was much higher in the snow removal treatment compared to the control (r2 of treatment = 0.8, slope = 0.093, p < 0.001; r2 of control = 0.18, slope = 0.012, p < 0.001). Throughfall reduction had limited effects on soil water content (SWC) and inconsistent effects on soil strength; relationships between SWC and strength were positive, negative, or non-existent. Based on these findings, changes in soil physical properties with altered precipitation are likely to manifest primarily in winter. Drainage class and air freezing index may be used to predict when sufficient soil frost is present for forest management activities to occur without detrimental effects to soil functions.

Current state and past changes in frozen ground at the Third Pole: A research synthesis

The thermal state of frozen ground and its changes are important for understanding environmental change and supporting related applications to the Earth’s Third Pole, which is a hotspot area for science research. However, challenges remain in data and modelling, meaning that much information is unavailable, especially for the entire Third Pole region. Here, we provided basic statistical data regarding the current state of frozen ground and its changes over the 1960s–2010s across the entire Third Pole by integrating nearly all currently available ground observation data and high-quality spatial data using machine learning models and existing high-quality frozen ground data products. The results show that the current (2000–2018) areal extents of permafrost and seasonally frozen ground in the Third Pole are approximately 1.27 × 106 km2 (1.15 × 106 to 1.39 × 106 km2) and 2.59 × 106 km2, accounting for 28% and 58%, respectively. The areal extent of permafrost region is approximately 50% (23%–93%) larger than that of permafrost area (land underlain by permafrost), especially in some early maps. The corresponding regional average of the mean annual ground temperature is approximately −1.51 °C (−1.75 to −1.27 °C) in the permafrost area. The regional average of active layer thickness overlying the permafrost and the maximum frost depth for regions of seasonally frozen ground are 235 cm (233–237 cm) and 92 cm, respectively. From the 1960s to the 2010s, on average, permafrost in the Third Pole warmed at a rate of 0.17 °C per decade, which was associated with increases in the maximum thaw depth at a rate of 4.42 cm per decade. The regional average of the maximum frost depth declined at a rate of 2.34 cm per decade over the same period. This synthesis highlights the differences between the two terms (permafrost region and permafrost area) and provides crucial information for frozen ground in the Third Pole with higher accuracy for the scientific community and the public.

Пропозиції щодо розширення номенклатури типів межових знаків для адміністративно-територіальних одиниць

The purpose of the work is to substantiate methodological approaches for the development of scientific and technological recommendations for determining the optimal types of boundary markers for the establishment (consolidation) of the boundaries of administrative-territorial units. Method. Methods of historical analysis of constructions of boundary signs are used for researches, in particular: influence on constructions of boundary signs of natural and climatic conditions; requirements of land cadastres in different historical periods; research of interdependence of the centers of geodetic points and properties of soil on a choice of the centers of boundary signs. Results. An expanded nomenclature of types of boundary markers is proposed, which takes into account the properties of local soils through which the boundary of the administrative-territorial unit runs, and proposals for the selection of appropriate materials for the manufacture of boundary markers to increase their shelf life. This will allow more efficient management of land resources of administrative-territorial entities. The developed proposals can be reflected in land management projects to establish (change) the boundaries of administrative-territorial units, in particular in the description of their boundaries. Scientific novelty and practical significance. The analysis of the types of boundary markers in combination with the available information about the soils of Ukraine shows that when choosing their types do not take into account the properties of the soils of the area through which the boundary of the administrative-territorial unit. As a result, it is not possible to identify boundaries on the ground, which in turn leads to inconsistencies between the authorities and inefficient use of land resources. To solve this problem, it is proposed to use well-developed scientific, technical and regulatory developments on the use of different types of geodetic points, which take into account the depth of freezing and physical and mechanical properties of the soil; the presence of groundwater in places of laying and their chemical state; wetlands and, accordingly, on their basis to offer an expanded range of boundary markers. The proposed types of boundary markers can be used for the boundaries of OTG, districts, cities and areas that run on land.

Predicting Frost Depth of Soils in South Korea Using Machine Learning Techniques

Predicting the frost depth of soils in pavement design is critical to the sustainability of the pavement because of its mechanical vulnerability to frozen-thawed soil. The reliable prediction of frost depth can be challenging due to the high uncertainty of frost depth and the unavailability of geotechnical properties needed to use the available empirical- and analytical-based equations in literature. Therefore, this study proposed a new framework to predict the frost depth of soil below the pavement using eight machine learning (ML) algorithms (five single ML algorithms and three ensemble learning algorithms) without geotechnical properties. Among eight ML models, the hyperparameter-tuned gradient boosting model showed the best performance with the coefficient of determination (R2) = 0.919. Furthermore, it was also shown that the developed ML model can be utilized in the prediction of several levels of frost depth and assessing the sensitivity of pavement-related predictors for predicting the frost depth of soils.

Study on the Change in Freezing Depth in Heilongjiang Province and Its Response to Winter Half-Year Temperature

Abstract 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.

Climatic influence on productivity of walking excavators and bulldozers in stripping in gold placer mining

The state and mineability of placer gold reserves and resources in the Russian Federation is reviewed. Judging from wide application of dragline excavators in peat cutting, it can be effective to use draglines in placer mining at depths up to 50 m due to the much lower cost of stripping compared to the other methods. In this case, it is possible to apply various schemes of direct dumping and wider employment of draglines in actual mining. It is noted that one of the highest influences on productivity of draglines and bulldozers during stripping is the presence of seasonal and perennial frost. Two groups of factors to decrease productivity of walking excavators and bulldozers at negative air temperatures are proposed. The conclusions are made about the difficulty of determining frozen ground cuttability due to the peculiarities of overburden sediment formation and because of deficient detailed studies into the properties of rocks, which govern their strength characteristics during freezing. The less labor-intensive method of calculating productivity reduction of walking excavators and bulldozers during stripping is proposed as the determination of hourly productivity reduction patterns by mathematical methods describing the random nature of phenomena, in particular, by the correlation method. The equations of the hourly productivity reduction of draglines and bulldozers depending on average monthly negative air temperature and the hourly capacity reduction factor as function of seasonal permafrost thickness and perennial permafrost cross-sections in overburden face are derived. It is noted that seasonal freezing governs reduction in productivity of excavators and bulldozers at the beginning of the warm period of the year until the permafrost is completely thawed. Stefan&rsquo;s formula is suggested, according to which it is possible to calculate the depths of seasonal freezing of peat depending on the average monthly air temperature quite reliably.

Research on Frost Heaving Characteristics of Hydraulic Tunnels’ Wall Rock in Cold Regions Based on Phase Transition and Water-Heat-Stress Coupling

In order to study the problem of frost damage to wall rock caused by hydraulic tunnels’ phase transition between water and ice at low temperatures in cold regions, a three-field coupling governing equation considering temperature, seepage and stress was deduced. Taking a water conveyance tunnel in Xinjiang as the research object, a three-dimensional frost heaving finite element model was established based on the deduced coupling equations using finite element software. By numerically simulating the process of frost heaving, the spatial distribution and variation law of the frozen area and frost heaving force were obtained. The present study showed that the frozen area of wall rock at the tunnel entrance is spatially distributed in a long-necked funnel shape, and the frost depth of the section gradually decreases along the depth of the tunnel. Due to the hysteresis of heat conduction, the peak point of the maximum freezing depth of wall rock appears after the minimum ambient temperature. The circumferential distribution law of frost heaving force in wall rock remains consistent with the depth, that is, the maximum frost heaving tension occurs at the arch top and arch bottom and decreases to zero in the circumferential direction, and then it turns into the frost heaving pressure which gradually increases to the maximum at the arch waist. Along the depth, at 20 m away from the tunnel entrance, the frost heaving force at the arch top, arch waist and arch bottom is divided into a steep decline zone and a slow decline zone. After being frozen for 30 to 150 days, the growth rate of the absolute value of the maximum frost heaving force at the arch top and arch bottom is about 1.5 times that of the arch waist. The frost heaving force has greater influence on the arch top and arch bottom than on the arch waist.

Response of Seasonally Frozen Ground to Climate Changes in the Northeastern Qinghai-Tibet Plateau

The effects of climate change on permafrost have been well documented in many studies, whereas the effect of climate change on seasonally frozen ground (SFG) is still poorly understood. We used the observed daily freeze depth of SFG and environmental factors data from the period 2007–2016 to examine the seasonal and inter-annual variation of SFG. We quantitatively evaluated the effects of environmental factors on SFG using a boosted regression tree analysis. The results show that, on a seasonal scale, the lower layer soil frost starts freezing in mid-November, with the maximum freeze depth occurring in late March (209 cm), and then begins to thaw in both the lower and upper layers. We identified four stages of the freeze-thaw cycle: the non-frozen phase, initial freezing, deep freezing, and thawing. Furthermore, the thawing process of SFG mainly took place in the upper layer, but the freezing rate of the lower layer from mid-November to early February was similar to the thawing rate of late April to late June. On the inter-annual scale, the maximum freeze depth showed a significant increasing trend (p &amp;lt; 0.05). However, the freeze-thaw duration declined significantly (p &amp;lt; 0.05), which was correlated with the decrease in the period when surface soil temperature is below 0°C. The mean soil temperature and soil heat flux were the most important environmental indicators affecting seasonal variation of SFG depth, and the cumulative negative air and soil temperatures were the dominant factors affecting inter-annual variation of maximum freeze depth. Our results might provide insight into predicting hydrological and ecological responses to future climate change in frozen-ground regions.

Assessment and projection of ground freezing–thawing responses to climate change in the Upper Heihe River Basin, Northwest China

Study regionUpper Heihe River Basin, Northwest China. Study focusWe investigated potential climate change under three Representative Concentration Pathways (RCP 2.6, 4.5, and 8.5) and their impacts on frozen ground in the upper Heihe River Basin using the ensemble climate data from eight general circulation models and the Soil and Water Assessment Tool (SWAT). New hydrological insights for the regionAir and ground freezing indices declined significantly during the baseline period (1976–2015), whereas the thawing indices increased, indicating the heat accumulation in study area. The frost depth, which refers to the potential frost depth of active layer in permafrost areas and the maximum frost depth in seasonally frozen areas, decreased significantly at the rate of 3 cm/10 yr. The SWAT-simulation and gray relational analysis revealed that soil water was controlled by precipitation and frost depth in spring and autumn. Compared to that of the baseline, the projected frost depth is projected to decline by 0.07–0.1 m during the near future (2020–2059) and 0.08–0.36 m for the far future (2060–2099). In addition, we developed a long-term warning system, which indicates that the degree of frozen ground degradation would be mild during the near future and would be severe for the far future under RCP 8.5. This study provides valuable insights into the protection of frozen-ground in the Upper Heihe River Basin.