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An extended ordinary state-based peridynamic model was developed to investigate the crack propagation of surrounding rock due to tunnel excavation. The frost heave effect on the crack surface was described by an equivalent pressure density. Two numerical examples were conducted to verify the effectiveness and robustness of the proposed model. Moreover, the influence of frost heave pressure, buried depth and rock elastic modulus on damage characteristics of the surrounding rock was investigated. The results demonstrate that massive microcrack damage will be formed at the invert when the tunnel is excavated in a deeply buried rock mass or soft rock stratum. A peridynamic model of rock mass under excavation and frost heave was constructed. Damage characteristics of surrounding rock could be simulated efficiently. Frost heave load was exerted on the crack surface by an equivalent pressure density. The effects of frost heave load, buried depth and rock elastic modulus were studied. [ABSTRACT FROM AUTHOR]

The presence of an impervious cover layer inhibits the free evaporation of moisture in the soil during seasonal freeze–thaw cycles, leading to a phenomenon known as the pot cover effect. This can result in severe frost heave issues in airport runways, highway subgrades, railway subgrades, and other similar infrastructure. In this study, a disease investigation was conducted at a gas transmission station situated in an area with seasonally frozen soil. Meanwhile, the causes of moisture accumulation and frost heave in the lower part of concrete pavement slabs were analyzed. A coupled water–vapor–heat model for unsaturated frozen soil is then established to analyze the formation mechanism of the pot cover effect in the subgrade. Finally, the preventive effect of the impervious layer on moisture migration in the pot cover effect was analyzed. The results indicate that the pot cover effect causes a significant accumulation of moisture beneath the concrete pavement at the gas transmission station, resulting in a moisture content increase of 5%–35%. During the freezing period, the vapor of shallow soil migrates upward, while the liquid water remains unchanged. During the melting period, both vapor and liquid water migrate downward. The laying of the impervious layer can prevent moisture migration of the pot cover effect. When the impervious layer is placed on the freezing front (0°C), the prevention effect of the pot cover effect is the best. [ABSTRACT FROM AUTHOR]

The temperature dynamics of conjugated soils of a paleocryogenic soil complex on chalk deposits in the Orenburg oblast is studied. Temperature measurements are combined with the study of cryogenic characteristics. The freezing point of soil moisture has been measured in laboratory. The temperature field within the soil complex is most heterogeneous. In the fall–winter season, the soil of microhighs is colder than the soils of microlows and microslopes; however, the microslope warms up faster than the microelevation and microlow in the spring–summer season. The differences between the temperature of soils in the frozen layer of microhighs and microlows reach –4.5°C at the beginning of freezing (December 15, 2019 at a depth of 15 cm), –4.0°C at the end of winter (February 10–11, 2020 at a depth of 5 cm), and –6.5°C during thawing (March 21–23, 2020 at a depth of 5 cm). The differences in the temperature regime along the microrelief are accompanied by the differences in the moisture distribution along the profile and determine the manifestation of cryogenic processes. The soils of microhighs freeze deeper and lens-type cryostructure forms in the entire frozen layer; this is accompanied by frost heaving, cryogenic sorting of coarse fragments, and formation of a crust on the soil surface ensuring preservation of the microtopography and soil cover pattern of chalk polygons. Cryogenic processes determine the formation of a platy soil structure in microhighs. Freezing in microlows is blocked in the middle part of the profile because of relatively high soil temperatures and low soil freezing points. The cryogenic characteristics and processes described in microhighs are unobservable in microlows. [ABSTRACT FROM AUTHOR]

Freeze–thaw action leads to soil volume changes, which significantly influence the stability of earthen structures. The volumetric strain of soil is sensitive to the changes of temperature. Recent research has identified the potential application of microencapsulated phase change materials (PCM) as a temperature regulator to reduce thermal-induced volumetric strain in soil. However, the effect of PCM inclusion on the soil volumetric behaviour has not been clarified yet. In this study, soil samples to which 2% PCM was added were tested using a double-cell triaxial apparatus to investigate the influence of the PCM on the soil volumetric strain. To estimate and predict the volumetric behaviour of soil with PCM mixture subjected to freeze–thaw action, a numerical model based on the thermo-hydro-mechanical (THM) framework and large strain consolidation theory is adopted. The results of laboratory tests reveal that soil containing PCM exhibits lower frost heave during the freeze–thaw action. Compared with unamended soil, volumetric strain is reduced from 4.2 to 3.4% by adding PCM when soil temperature stabilised at − 6 °C. Meanwhile, the volumetric strain after thawing induced by thaw consolidation was 2.4% for unamended soil and 1.5% for soil with PCM. The computed result from THM model reveals that the thermoregulation effect of PCM can effectively decrease the rate of soil temperature change and therefore, both frost heave and thawing contraction is reduced. The rates of temperature change for soil with PCM were 24% and 10% lower than those of unamended soil during thawing and freezing, respectively. The decrease in the rate of soil temperature change is caused by the release of PCM latent heat and reduction in thermal conductivity of the soil mixture. [ABSTRACT FROM AUTHOR]

The phenomena of freezing damage in the cold regional tunnels have happened frequently. Therefore, in order to precisely calculate frost heaving force ( σ 1 ), based on the displacement method, a new analytical solution was proposed. The analytical solution presented in this paper was verified by the results of the model test and field measurement of σ 1 , the imperfect contact effect between frozen and unfrozen zones of surrounding rock was considered and the influence of the interaction between any two factors on frost heaving force was studied by means of orthogonal experiment and analysis of variance. The results show that: (1) the inner radius of lining ( r a ), excavation radius ( r 1 ) and freezing radius ( r f ) are highly significant for σ 1 and the interaction between the inner and outer radiuses of lining (i.e., changes of the size in inner and outer radius of lining) is also highly significant for frost heaving force ( σ 1 ); (2) the analytical solution presented in this paper can avoid the frost heaving force ( σ 1 ) with tensional property under the condition of the circular tunnel under hydrostatic pressure; and (3) sensitivity function shows that the larger Young's modulus of lining ( E I ), inner radius of lining ( r a ), freezing radius ( r f ), linear frost heaving rate ( β 0 ) and Young's modulus of frozen surrounding rock ( E II ) are, the more sensitive the factors E I , r a , r f , β 0 and E II are to σ 1 . It is expected that the results of this paper can give some novel insights for the anti-freezing design of tunnels. Highlights: Inner radius of lining is the more sensitive to frost heaving force. The interaction between the inner and outer radiuses of lining is highly significant. The ra, r1 and rf are highly significant for frost heaving force. The analytical solution can avoid frost heaving force ( σ 1 ) with tensional property. [ABSTRACT FROM AUTHOR]

In this paper, an experiment study was carried out to identify the fundamental behavior of geosynthetic-encased stone column (GESC) reinforced foundation under freeze-thaw cycles. Three loading tests under four freeze-thaw cycles were considered. A 10-m thick reinforced foundation unit consisted of four floating GESCs with 2.5-m underlain clay layer, and the foundations were preconsolidated to three different initial degrees of consolidation (U = 1.0, 0.6 and 0.3, respectively). The results showed that soil near GESCs had a larger frozen depth due to the excellent heat transfer ability of GESCs. An extra uneven subsidence of soil also appeared around GESCs. Voids could be found between foundation soil and the loading plate after thawing, which indicated that only GESCs carried the overburden pressure. The GESCs showed outward bending under lower initial degree of consolidation, while inward bending under higher one. A bulging failure was observed on frozen part of GESCs, especially at the connection of encasement in foundation with lower initial degree of consolidation. In the first freezing process, a rapid decrease in frost heave force was noticed, inferring the fracture of frozen soil. The stress on GESC was found to almost have no change until complete freezing, when the soil was freezing and the stress on soil exceeded that on GESC. Negative pore pressure was observed in the foundation soil, and the absolute value decreased with the increasing overburden pressure. Both the peak positive and negative pore pressures were reduced as the foundation was preconsolidated to a higher degree. The freeze-thaw cycles were also found to generate excess pore pressure in soil during thawing. Moisture migration was also analyzed using Electrical Resistivity Tomography (ERT) method, and the results showed that moisture tended to go upwards and outside the reinforced unit from thawing to freezing, while downwards and inside the unit from freezing to thawing. • This paper investigated the behavior of GESC-reinforced foundation under freeze-thaw cycles. • Significant differential settlement was observed in the foundation. • The deformation patterns of GESCs were influenced by the initial degree of consolidation. • Only GESCs carried overburden pressure by the rigid base during thawing, and SCR reduced to less than 0.5 during freezing. • Moisture migration was studied using ERT, and negative pore pressure was observed. [ABSTRACT FROM AUTHOR]

Engineering usually considers coarse-grained soils as non-frost swelling soils, but serious frost swelling still occurs in coarse-grained canal bases, which is directly related to the recharge conditions and the fine particle content in the soil. Little attention is currently paid to the effect of different fine particle contents on coarse-grained soil frost swelling, especially after the fine particle admixture content exceeds 16%. This paper considers the characteristics of coarse-grained soils in water conservancy projects with fines content between 0% and 50%. The coarse-grained soils with 5%, 15%, 25%, 35%, and 45% fines content were designed for freezing and swelling tests. The evolution of temperature and moisture fields and the amount of freezing and swelling of coarse-grained soils during the freezing process were studied by using servo-type freezing and swelling and thawing tester. The experimental results show that the cooling process of soil samples can be divided into a rapid cooling stage, a slow cooling stage, and a freezing stabilization stage. The cooling rate and the frost heave amount with increasing fines content showed a trend of first increasing and then decreasing. [ABSTRACT FROM AUTHOR]

Frost heave susceptibility is a key index for designing the subgrade fillings of high-speed railways in cold regions. The existing methods for assessing frost heave susceptibility are mainly empirical or semi-empirical, and most of them are defined based on the fine content of soils. This study attempts to propose a new criterion based on the analytical solution of frost heave in the soil. A number of experiments are used to validate the proposed analytical model, which shows that the computed value of frost heave matches well with the measured data. The proposed model indicates that frost heave is a proportional function of the square root of time. Thus, the slope R named frost heave classification index of the proportional function is defined as a new index for frost heave susceptibility classification. A value of R less than 0.21 corresponds to a non-frost heave susceptibility condition, a value greater than 1.18 corresponds to a high frost heave susceptibility condition, and a value in the range of 0.21 and 1.18 means a frost heave susceptibility condition. R is directly related to the boundary temperatures and soil–water and soil-freezing characteristics. The parameter study shows that reducing the values of SWCC fitting parameter α and cold end temperature Tc or increasing the values of permeability of frozen soil kf, the saturated volumetric water content θs, the unfrozen water content at the frost front θu and the residual volumetric water content θr increases the possibility of frost heave. Compared with the existing method, the new index has a clear theoretical basis, and the parameters are easily obtained. It may be a rational method for assessing frost heave susceptibility. [ABSTRACT FROM AUTHOR]

Frost heave, which is related to the variation in the hydrothermal interaction properties of soil, is the main factor causing the inhomogeneous deformation of structures in cold regions. The relevant requirement for describing frost heave is to obtain the soil freezing characteristic curve, which contains fundamental information for describing the hydrothermal behavior of frozen soil. In this study, the unknown parameters of the van Genuchten equation and the hydraulic conductivity of partially frozen soil were indirectly derived using the pulsed nuclear magnetic resonance (P-NMR) technique based on the soil freezing characteristic curve and Clapeyron equation. Based on continuum mechanics, a hydrothermal coupling model combined with the unknown parameters obtained from a P-NMR experiment was applied to quantify the hydrothermal performance of the frozen soil. The mathematical module of COMSOL Multiphysics was employed to solve the coupling equation numerically. To validate the proposed coupling model, water transfer experiments were conducted on silty clay in closed and open systems under freezing conditions in our laboratory. The measured experimental data were consistent with the prediction results, confirming the applicability of the coupling model of the frozen soil in predicting the hydraulic parameters based on the new soil freezing characteristic curve. [ABSTRACT FROM AUTHOR]

The degree of water saturation significantly affects the rate of rock deterioration caused by freeze–thaw weathering, which may trigger serious geological engineering hazards. This study aimed to explore the impacts of water saturation on freeze–thaw-induced deterioration of sandstone, and to improve our understanding of this damage mechanism. Sandstone specimens with varying degrees of moisture saturation were subjected to freeze–thaw tests, computed tomography scanning, and uniaxial compressive tests. The distribution of the areal porosity along the computed tomography slices, evolution of the pore volume, and changes in the pore network model parameters of the sandstone samples were visually and quantitatively characterised to assess the damage evolution. The results show that the parameters of the pore-fracture structure reflect the influence of saturation and cyclic freeze–thaw actions on rock deterioration. As the moisture saturation increased, the sandstone transformed from being dominated by pores with a radius ranging from 0 to 100 μm to being dominated by pores of 200–300 μm. The increase in the equivalent radii of pores caused the rock to be more susceptible to deformation and failure, whereas an increase in the number of throats represents a disruption of the cementation between the rock grains, making to rock more susceptible to freeze–thaw actions. Furthermore, the damage mechanisms of sandstone can be interpreted by volumetric expansion and hydrostatic pressure theory in a rapid freeze–thaw environment. The results of this study provide a comprehensive insight into the influence of water saturation on freeze–thaw-induced damage evolution of rocks in cold regions. Highlights: With the increase of water saturation, the radius of the dominant pores in the rock gradually expands. With the increase of saturation, the number of throats between connected pores increases, which disrupts the cementation between the rock grains, thereby making the rock more susceptible to freeze–thaw cycles. The frost heave force accelerates the coalescence of pores and prolong the pore closure stage in the stress–strain curves of the tested rocks. Volumetric expansion and hydrostatic pressure are jointly responsible for the damage caused by freeze–thaw cycles. [ABSTRACT FROM AUTHOR]

The dynamic mechanical behavior of frozen rock with a flaw is essential for plateau alpine region mining. However, the freezing temperature's strengthening and damage mechanism on dynamic strength is still unclear. Drop weight impact tests (single factor) and orthogonal tests (3 factors and 5 levels) were used to examine the influence of flaw dip angle (β), impact height (H), and freezing temperature (T) on the dynamic response of frozen sandstone in plateau alpine region. Different factors' effect on peak strain and failure mode was compared, as well as a significant analysis of three factors' influence on peak strain. The results reveal that with the increase of β, the ultimate strain (εu) of sandstone shows a 'M' type variation, while the linear increase of εu occurs with the increase of H and the decrease of T. At the same time, β and T have a substantial effect on εu, and T has a significant influence on the occurrence time of εu. In addition, tensile failure is the failure mode of sandstone with tensile cracks mainly parallel to the direction of impact. Moreover, a two-dimensional particle flow code was used to supply the stress–strain curve, cracking process, and energy absorption characteristics. The obvious rebound phenomenon can be observed, and the peak stress increases with the increase of H and decreases as β and T increase. Furthermore, the energy usage rate has a linear relationship with β and T, but it decreases first and then increases as impact energy increases. At the end, the effect of the strengthening mechanism of T on single-flaw sandstone dynamic strength and the damage evolution was discussed. The effect of pore ice is primarily responsible for the strength enhancement of frozen sandstone, but the frost heave damage at a certain T (− 20 °C) will inhibit the strength growth. The damage constitutive model based on logistic function can accurately describe the stress–strain properties of single-flaw frozen sandstone before εu. Highlights: The dynamic mechanical responses of single flaw frozen sandstone were studied by drop weight impact tests and numerical simulation. The influence of flaw dip angle, impact height and freezing temperature on peak strain, stress, and energy consumption were revealed. The strengthening mechanism of freezing temperature on dynamic strength was discussed. The frost heave damage formed at a certain freezing temperature (– 20 °C) will inhibit the growth of strength. [ABSTRACT FROM AUTHOR]

After the repeated freezing and dissolution of fractured rock masses in cold regions, the liquid present in the pores undergoes a water–ice phase transition, resulting in frost heave forces and damage to the internal structure of the rock mass. This causes the rock masses to continuously develop new cracks, which further expand and connect, leading to rock mass failure and ultimately reducing the overall stability of the rock mass in engineering projects. In this study, uniaxial compression tests, direct shear tests, and Brazilian splitting tests were conducted on rock after freeze–thaw cycles (FTCs), and the changes in the physical and mechanical properties of the rock under freeze–thaw conditions were obtained (this study used raw rock from an engineering project and processed it into symmetrical jointed rock samples). The roughness of the shear fracture surfaces was analyzed through 3D cross-sectional scanning experiments. Using statistical damage theory, the mechanism of freeze–thaw damage was analyzed, and a constitutive model for freeze–thaw rock damage was established. The research results can provide a theoretical basis and support for engineering safety and stability in cold regions. [ABSTRACT FROM AUTHOR]

In this paper, two centrifuge tests were conducted on geosynthetic-encased stone column (GESC) supported embankment to investigate the behavior under freeze-thaw cycles considering the effects of initial degree of consolidation and number of freeze-thaw cycles. The embankments with a height of 4.5 m supported by GESC-reinforced foundation with a thickness of 9 m in prototype were first consolidated to initial degrees of consolidation of 30% and 60%, respectively, and then subjected to three freeze-thaw cycles. The results showed that the foundation soil under the embankment toe experienced a higher degree of freezing than the soil outside the embankment with non-uniform frozen depths observed at different positions in soil under the embankment, and that multiple freeze-thaw cycles contributed to extra settlement in the foundation. Both the frost heave and thaw settlement appeared on GESCs prior to soil. During freezing, the stress on GESC increased first, while decreased rapidly when soil began freezing. The stress concentration ratio (SCR) reached nearly 1.0 before complete freezing. After the complete thawing of GESCs, the stress on GESC increased significantly. As the number of freeze-thaw cycles grew, the variation in settlement, stress and pore pressure was reduced. The final settlement on soil was greater in the foundation with lower initial degree of consolidation, as well as the SCR. The GESCs had larger deformation and showed outward bending under lower initial degree of consolidation, but inward bending appeared on GESCs under higher one. • This paper investigated the behavior of GESC-supported embankment under freeze-thaw cycles. • The frozen depths were found to vary in different positions, and frost heave and thaw settlement were observed. • The deformation modes of GESCs were different considering the initial consolidation degrees. • Stress on soil and GESCs experienced increase and decrease according to different timing nodes during freeze-thaw cycles. • Dissipation of excess pore pressure depended on the periods of freezing or thawing. [ABSTRACT FROM AUTHOR]

Geotextile offers numerous benefits in improving pavement performance, including drainage, barrier functionality, filtration, and reinforcement. Wicking geotextile, a novel variant in this category, possesses the intrinsic ability to drain water autonomously from soils. This paper details the development and application of a comprehensive multiphysics model that simulates the performance of wicking geotextile within a pavement system under freezing climates. The model considers the inputs of various environmental dynamics, including the impact of meteorological factors, groundwater levels, ground heat, and drainage on the pavement system. The model was firstly validated using field data from a long-term pavement performance (LTPP) road section in the cold region. It was subsequently applied to assess the impacts of wicking geotextile if it was installed on the road section. The model simulated the coupled temporal and spatial variations in soil moisture content and temperature. The simulation results demonstrated that wicking geotextile would create a suction zone around its installation location to draw water from surrounding soils, therefore reducing the overall unfrozen water content in the pavement. The results also showed that the installation of wicking geotextile would delay the initiation of frost heave and reduce its magnitude in cold region pavement. [ABSTRACT FROM AUTHOR]

Understanding the frost deformation characteristics of rock with varying water contents under freeze–thaw conditions is of great significance to engineering construction activity in cold regions. In this study, sandstone samples with different degrees of water saturation were first prepared and then submitted to cyclic freeze–thaw experiments. Temperature sensors and strain gauges were attached to the samples so as to trace the temperature and strain changes. The changes in the major principal strain and minor principal strain against the temperature were individually explored. It is found that the sandstones exhibit heterogeneous frost deformation behaviors during the freeze–thaw cycle, and the heterogeneity of frost deformation is more considerable in terms of the sandstone with a higher degree of saturation based on the strain ellipse analysis. The coefficient of linear thermal expansion (CLTE), maximum frost heave strain and residual frost heave strain tend to increase exponentially with increasing the degree of saturation. These three parameters, however, are different from one another along the minor and major principal strain directions, which further gives evidence of the heterogeneous frost-heaving features of the sandstone. Finally, the crystallization pressures within a single pore and over the entire sandstone volume were theoretically calculated. It is verified that the resulting stress translated by the crystallization pressure for the 80% or higher saturation degree exceeds the tensile failure threshold, which explains the mechanisms that more considerable frost-heaving damage and heterogeneous behaviors are caused in the sandstone with a saturation degree of 80% or higher. The findings in this study help schedule feasible ways of alleviating the freeze–thaw-induced damage of rock mass in cold regions. Highlights: Integrated strain and temperature measurements of the partially saturated sandstones during the freeze–thaw cycle. Heterogeneous frost deformation was found in the partially saturated sandstones. More considerable heterogeneous frost deformation was generated in the sandstone with a higher degree of saturation. [ABSTRACT FROM AUTHOR]

Frost heave can lead to both the ground uplifting and frost heave pressure under different circumstances, and cause many engineering problems. To describe the characteristics of frost heave under various thermo‐hydro‐mechanical (THM) coupling conditions and calculate both the frost heave amount and the frost heave pressure, the coupled THM process, as well as the phase change of the pore water, should be considered for freezing soil. In this paper, thermodynamic equilibrium conditions in saturated freezing soil were derived to account for the mechanical effect on the cryogenic suction and unfrozen saturation of pore water during phase transition. Then the governing equations were developed considering the water flow, heat transfer, stress equilibrium, phase change, ice segregation, and their complex interactions. Based on that, a numerical model considering fully THM coupling is presented within the framework of finite element provided by COMSOL. Both frost heave amount tests and frost heave pressure tests were simulated to verify the proposed model. Then the model was applied to subgrades with different types of soil and different boundary conditions, to reveal the characteristics of frost heave amount and frost heave pressure under different conditions, and at the same time to demonstrate the model's applicative prospect. [ABSTRACT FROM AUTHOR]

Heat transfer, moisture migration and water-ice phase change during the soil freezing process are important factors contributing to frost heave damage in geotechnical engineering. Firstly, the temperature variation characteristics of the samples were obtained using a temperature detection switch (TDS) acquisition system. Secondly, the NMR signal amplitude of the samples after one-dimensional unidirectional freezing under different initial conditions was measured using the GR-HSE sequence. Finally, the evolution of pore development and crack propagation in the samples before and after freezing was characterised using CT scanning technology. The results showed that there was no significant difference in temperature gradient between different regions of the samples, and the freezing depth increased with decreasing temperature. The redistribution characteristics of moisture in the samples after freezing were obtained through its correspondence with moisture content, which confirmed the phenomenon of moisture migration in frozen soil. The porosity of the samples significantly increased after freezing, and the damage in the laminar structure zone was more severe than that in the fibrous structure zone. There were significant differences in the quantity and volume contribution of pores at different particle sizes, and the proportion of pores with higher coordination number increased, promoting the degree of frost heave damage. [ABSTRACT FROM AUTHOR]

The resource utilisation of mine overburden in subgrade is an essential approach to accelerate environmental governance in mining areas. The present study focuses on investigating the mechanical properties and damage evolution of mine overburden under different environmental factors. The influences of water immersion, freeze–thaw cycles, water and salt migration on the road characteristics of mine overburden with different coarse grain contents (CGCs) were systematically studied and a cumulative damage model of mine overburden was proposed. The durability of mine overburden under the effect of the environmental factors was further compared. The results showed that mine overburden has less frost heave and can be utilised as subgrade filler in seasonally frozen region. With the increase of CGC of mine overburden, the resilient modulus and CBR gradually increase, and the UCS increases first and then decreases. The cumulative damage model of mechanical properties can effectively characterise the failure evolution of mine overburden. The infiltration of sulphate solution turns the mine overburden filler into weak frost heaving soil. The mine overburden with a CGC of 40% – 60% can be selected to improve the environmental adaptation. The wrapping method is recommended to reduce the impact of negative temperature and moisture on mine overburden subgrade. [ABSTRACT FROM AUTHOR]

Liquid nitrogen (LN2) fracturing technology is a novel waterless fracturing technology that has significant potential for application in the development of coalbed methane. However, the changes in the microstructure after coal samples are treated with LN2 freeze thaw are poorly understood. Therefore, a combination of mercury intrusion porosimetry and micro-computed tomography (micro CT) was employed to investigate the evolution of pore and fracture structure of coal samples treated with LN2. The experimental results showed that the pore volume and average pore size of coal samples increase after LN2 freeze thaw. After 12 freeze thaw cycles, the change in pore volume of micropores and minipores of coal samples was not significant, while the pore volume of mesopores and macropores increased significantly before LN2 freeze thaw. The specific surface area of the pores in different size ranges of coal samples increases with the increase in the number of LN2 freeze thaw cycles; the structure of micropores and miniopores were damaged by thermal stress and frost heave force during LN2 freeze thaw; and the pore size gradually increases to form mesopores and macropores. Micro-CT images of coal samples after LN2 freeze thaw indicated the primary fractures of coal sample expanded and generated a large number of secondary fractures. The primary and secondary fractures are interconnected and ultimately form penetrated fracture enhancing the connectivity of fractures, enhancing the connectivity of the fracture structure. The key finding study is expected to provide a theoretical basis for LN2 fracturing. [ABSTRACT FROM AUTHOR]

Railways constructed in cold regions can experience localized frost heave in the winter as well as track softening during the spring thaw. These phenomena are great challenges for road and railway foundations on seasonally frozen ground and must be considered by railway operators. To address these problems, temporary wooden shims can be used to smooth existing tracks; reductions in train speeds may also be mandated. The degree of susceptibility of a given section of a track to frost can be determined by considering the main preconditions allowing heave and frost to occur. This study reviews several frost susceptibility surveys that show the correlation between soil properties and laboratory results of frost heave tests. A summary of treatment methods for frost action is presented and a straightforward design procedure is provided to first evaluate the frost susceptibility of soils and the frost hazard potential in Canada as well as predict the frost penetration depth, and then select the appropriate frost-treatment method based on previous studies and standards. The outcome of this study is a five-step tool that can be applied by Canadian engineers to first evaluate the frost susceptibility degrees of soils based on the soil properties in each province and then select the appropriate treatment method considering the frost hazard potential. [ABSTRACT FROM AUTHOR]

Freeze–thaw cycles in seasonal permafrost areas are a dominant cause of road damage. Therefore, the roadbed fill must be frost-resistant. In this study, taking the experimental section of the asphalt concrete pavement structure of the Zhangcheng Expressway in the seasonally frozen soil area of Hebei Province as an example, three working conditions were selected: a low embankment with a waterproof geotextile partition layer, a low embankment with a gravel layer + extruded polystyrene (XPS) board, a high embankment with a gravel layer + two pieces of cloth, and a waterproof geomembrane. After 2 years of tracking and analysis of the measured data, the subgrade temperature distribution law was derived in terms of time and depth to obtain the freezing depth under each working condition. The experimental results showed that the gravel bedding layer, XPS plate, and geosynthetic materials had a significant effect on the prevention and mitigation of road disease, and therefore, their application must be promoted. [ABSTRACT FROM AUTHOR]

Frost heave in coarse-grained soils caused by vapour transfer has attracted much attention, but little experimental or numerical evidence has been reported thus far. A series of laboratory experiments is carried out by a frost heave apparatus and an X-ray micro-computed tomography instrument. The only water supply mechanism to the tested specimen is vapour transfer. The results indicate that considerable frost heave occurs in coarse-grained soil specimens with a zero fines content. The ratio of frost heave to the initial height can reach 13·8% and 25·1% at 14 days and 18 days, respectively. Ice crystals first grow in pores causing the soil particle to rotate and move, and the soil porosity to increase. With continued ice crystal growth, they eventually become connected and form an ice lens. If a constant temperature gradient is applied, only one horizontal ice lens is formed, which differs from the layered ice lenses observed in fine-graded soils. A new numerical model is developed to simulate ice formation and frost heave in coarse-grained soils, which considers the process of vapour transfer and desublimation. The predicted frost heave results agree well with the measured results. This study provides a novel explanation for the frost heave mechanism in coarse-grained soils. [ABSTRACT FROM AUTHOR]

To protect pavement in cold regions, insulation layers have been used in pavement construction. The insulation layer blocks the heat exchange, resulting in different pavement temperature distributions at different layers. Pavements in cold regions are subject to frost heave, thaw weakening, and freeze–thaw cycling, and the moisture content of unbound materials is affected by the temperature of the pavement. Therefore, the base and subgrade temperature can affect the pavement performance, and the insulation layer influences the performance of the pavement. This work aims to demonstrate the capability of the machine learning method to predict the pavement temperature of the base and subgrade layers in the presence of insulation layers. Pavement temperature measured from sensors embedded in the pavement at the IRRF test road and environmental factors collected from a weather station were used to train machine learning models. The results obtained from machine learning models indicated that the air temperature and day of the year were the most robust input prediction parameters at each depth. Machine learning models outperformed the existing model and proved that it could be a method to improve pavement temperature prediction with insulation layers, especially when the base layer temperature is below 0°C. [ABSTRACT FROM AUTHOR]

Tunnels are among the main components of transport infrastructure systems and as such must be protected against damage. As damage is particularly prevalent in cold climates, tunnels in Gangwon province, the coldest region of South Korea, were investigated in this research. The temperatures inside three tunnels (one short tunnel and two medium-length tunnels) were measured during the winter season (November to March) using iButton sensors installed on the surface of the tunnel linings at a height of 2 m from the ground. The long-term temperature data measured in this way were analysed and the results showed that January was the coldest month. The minimum and maximum daily air temperatures most frequently appeared during 3–6 a.m. and 2–4 p.m., respectively. The highest temperature gradient was found to occur 30 m from the entrance or exit. The temperatures inside the tunnels were significantly affected by external wind induced by vehicle traffic volumes compared with the natural wind direction, the wind velocity and rainfall. It is concluded that tunnel damage caused by frost heave and freeze–thaw action can be reduced by frequent inspection and evaluation. [ABSTRACT FROM AUTHOR]

This study takes the aeolian sand concrete as a research object, uses the relative dynamic elastic modulus to study its macro characteristics, and combines nuclear magnetic resonance、scanning electron microscope to study its pore characteristics and micro morphology under the action of prestress, freeze-thaw and salt intrusion. The results show that with the increase of the amount of aeolian sand, the dynamic elastic modulus of aeolian sand concrete shows a pattern of first decreasing, then increasing, and then decreasing; when no prestress is applied, the porosity of aeolian sand concrete first increases, then decreases, and then continues to increase. Among them, the porosity of aeolian sand concrete with a 40% content of aeolian sand decreases by 0.06% compared to that with a 0% content of aeolian sand, and decreases by 0.003% compared to that with a 60% content of aeolian sand; with the increase of prestress, the porosity of aeolian sand concrete with the same amount of aeolian sand increases gradually with the increase of damage degree. The porosity of concrete with 40% aeolian sand content increases by 0.33% when the damage degree is 0.0 compared to 0.3, with a 6.31% increase in the number of multi damage pores; under the coupling effect of multiple factors, when the amount of aeolian sand is 40%, the damage degree of the four groups of aeolian sand concrete before and after the coupling effect is 0.0, 0.1, 0.2, and 0.3, respectively, increases by 25.8%, 32.2%, 73.8%, and 85.8%, respectively; under the coupling effect of multiple factors, the content of aeolian sand is 60%, the damage degree is 0.2 and 0.3 groups, and the content of aeolian sand is 20%, the damage degree is 0.3 groups, which does not meet the standard requirements; under the coupling action of stress, freeze-thaw, salt intrusion and the amount of aeolian sand, the filling effect of aeolian sand on the internal pores of aeolian sand concrete decreases first, then increases, and then decreases with the increase of the amount of aeolian sand. The filling effect is further weakened after the action of stress. After the superposition of freeze-thaw and salt intrusion, the coupling effect of water and salt solution in frost heaving medium makes the variation law and range of physical and chemical characteristics of aeolian sand concrete show a great difference. [ABSTRACT FROM AUTHOR]

To protect pavement in cold regions, insulation layers have been used in pavement construction. The insulation layer blocks the heat exchange, resulting in different pavement temperature distributions at different layers. Pavements in cold regions are subject to frost heave, thaw weakening, and freeze–thaw cycling, and the moisture content of unbound materials is affected by the temperature of the pavement. Therefore, the base and subgrade temperature can affect the pavement performance, and the insulation layer influences the performance of the pavement. This work aims to demonstrate the capability of the machine learning method to predict the pavement temperature of the base and subgrade layers in the presence of insulation layers. Pavement temperature measured from sensors embedded in the pavement at the IRRF test road and environmental factors collected from a weather station were used to train machine learning models. The results obtained from machine learning models indicated that the air temperature and day of the year were the most robust input prediction parameters at each depth. Machine learning models outperformed the existing model and proved that it could be a method to improve pavement temperature prediction with insulation layers, especially when the base layer temperature is below 0°C. [ABSTRACT FROM AUTHOR]

Frozen ground covers vast areas worldwide and about 75% of the land area in the Northern Hemisphere undergoes seasonal freezing and thawing processes. It has been well acknowledged that freeze–thaw cycles (FTCs) and temperature rise in cold regions have significant effects on the hydraulic, thermal, and mechanical properties and processes of foundation soils of infrastructure, which subsequently affect its stability and durability. Numerous efforts have been devoted to mitigate the capillary rise (transport of liquid water under matric potential gradient) to the freezing front that builds up as ice and leads to frost heave, in addition to reducing temperature rise of the frozen ground beneath foundations in order to alleviate thaw settlement. However, increasing more studies have shown that the "canopy effect" would lead to the frost heaving damage and threaten engineering safety given that the capillary rise is minimized and temperature rise is controlled. The "canopy effect" as a result of water vapor transmission through soils or other porous construction materials during ground FTCs that increases ice content beneath the impermeable layer of infrastructure. At present, there is a lack of in-depth and comprehensive understanding of the processes, magnitude, and significance of canopy effect. Therefore, the objective of this study was to review the progress in research on water vapor transport processes in the soil during FTCs, their dominant factors, experimental setup, and control measures. Pros and cons of available water–heat–vapor measurement methods and mechanisms of frost heaving because of water vapor transmission are discussed. Water vapor transmission models are inventoried, the shortcomings of the currently available research are discussed, and future perspectives on water–heat–vapor transmission are also given. [ABSTRACT FROM AUTHOR]

The damage caused by the frost heaving pressure on the surrounding rocks and lining structure of cold-region tunnels is always common, which can seriously threaten the safety and stability for cold-region tunnels. Although many achievements of frost heave pressure model have been obtained, two factors have been often ignored, which are in-situ stress and freeze-thaw cycles. Therefore, the calculation mechanical model of cold-region tunnels is established and the expression of frost heaving pressure considering frost heaving effect and in-situ stress is derived based on the elastic theory. The relationship between the elastic modulus of surrounding rocks and the number of freeze-thaw cycles was fitted by experimental data and the calculation formula of frost heaving rate of rocks considering their porosity change caused by freeze-thaw cycles is derived. Based on that, the calculation method of frost heaving pressure considering in-situ stress and freeze-thaw cycles is proposed. The example analysis results show that frost heaving ratio and frost heaving pressure gradually increase with freeze-thaw cycles, which are eventually subjected to a steady value. Simultaneously, the frost heaving pressure acting on lining increases with in-situ stress for tunnels in cold regions and some effective insulation measures should be applied to prevent frost damage. [ABSTRACT FROM AUTHOR]

The Lanolin 750 kV electrical transmission line traverses more than 102.86 km through seasonally frozen regions, causing many engineering problems for transmission tower foundations. In this work, physical models of reinforced concrete independent foundations in soils with different frost heave grades were used to simulate the frost heaving performance in seasonally frozen alpine regions. The test results were used to evaluate the tangential frost heaving force calculated based on different specifications. The results showed that the tangential frost heaving force and frozen depth increased with the temperature decrease. Moderately frost-susceptible soils also increased the tangential frost heaving force and frozen depth. Based on technical standards, the main differences between the calculated and the test values were the variable load component and effective frozen depth coefficients. Correcting the coefficient values resulted in a closer agreement between the test and the calculation results. [ABSTRACT FROM AUTHOR]

During the freezing process, water migration is a decisive factor for the estimation of frost heave and thaw-settlements of fine and mixed-grain soils. One-dimensional freezing tests with and without a water supply were carried out. The influence of different temperature gradients of a saturated clay on parameters such as water intake, frost heave, and thaw-settlements is discussed here. A new approach is presented to describe the rate of water intake, which consists of three parameters. This study shows that all three parameters were influenced by the temperature gradient. This approach helps predict frost heave and thaw-settlement in cold regions. [ABSTRACT FROM AUTHOR]

In order to study the effect of moisture content and fiber content on the frost heaving and thawing settlement of subgrade soil improved by fiber under freezing and thawing cycles, the indoor unidirectional freezing and thawing tests were carried out, the changes of moisture field, frost heaving rate, thawing settlement coefficient, temperature field and freezing temperature in the whole process of freezing and thawing under different moisture content and fiber content were obtained. The results showed that: 1) during the unidirectional freezing and thawing process of the sample, the water phase transition became smaller and smaller with the increase of the depth, and the water content was not consistent after the freeze-thaw process. The moisture redistribution of soil samples with different initial moisture content after freezing-thawing cycles was obvious, and the moisture distribution of soil samples with different fiber content after freezing-thawing cycles was basically similar. With the increase of fiber content, the degree of water migration decreases. 2) In the range of 8%-16% moisture content, the maximum vertical displacement of freezing reached1. 19 mm, and the maximum vertical displacement of thawing reached 2. 56 mm. When the moisture content reached 12%, the frost heave rate and thawing settlement coefficient tended to be stable. In the range of 0% -0. 5% fiber content, the maximum vertical displacement of freezing reached 1. 10 mm, and the maximum vertical displacement of melting reached 2. 85 mm. 3) with the increase of fiber content, the latent heat of phase transformation became more obvious, and the soil freezing temperature first decreased and then increased. The lowest freezing temperature was -1. 95 ℃ when the fiber content was 0. 3%, and the longest time to reach the freezing temperature was 14. 1 min. The results of this study can provide reference for railway and engineering construction in silty sand areas in the west of China. [ABSTRACT FROM AUTHOR]

A method for an a priori estimation of the frost heave ratio for clayey soils, considering the degree of their water saturation upon a closed system of freezing, is proposed. The proposed approach involves the introduction of a new parameter in the mechanics of frozen soils, namely, the frost heave index of clayey soils, which characterizes the degree of frost heaving of soil relative to the maximum height of the frost heave of soil that is fully saturated with water. An introduced parameter is used in the final formula to estimate the frost heave ratio of clayey soils. Laboratory experiments were performed to determine the height of frost heaving of clayey soils with a variation in their moisture and porosity to verify the proposed approach. A comparison of the experimental and calculated results showed a suitable convergence sufficient for the practical use of the formula to determine the frost heave ratio in a closed system of freezing. An example of a calculation to justify antiheaving measures using the proposed estimation of the frost heave ratio is given. [ABSTRACT FROM AUTHOR]

The environmental conditions of the Arctic are vulnerable to the effects of climate change. We focus on the territory of the Yamalo-Nenets Autonomous Okrug (YaNAO). The objective of this study is to project mid-21st century climate-driven changes in the state of climate and the natural environment in the YaNAO. For this purpose, the CMIP6 data models with the climate change scenario SSP5-8.5 were used. Climate change directly affects the statistics of extreme events and climatically driven phenomena, such as frosts and thaws, as well as avalanches and slush flows. Climate change causes changes in the Arctic environment, primarily due to permafrost degradation, leading to important modifications in events such as mudflows, cryogenic landslides, abrasion, erosion, suffusion, frost heave, solifluction, thermokarst, and others. In some cases, the intensity and area of these processes increase, such as heaving processes and thermokarst becoming more active by 2050. In other cases, the solifluction processes decrease in the south part of the YaNAO due to the discontinuous or sporadic permafrost distribution. Projected climatic changes will inevitably lead to the restructuring of the geosystems in YaNAO, creating risks for infrastructure in economically active territories. [ABSTRACT FROM AUTHOR]

In order to investigate the stress characteristics of ballastless track under high latitude, and multi-source and multi-field extreme temperature conditions. Based on the finite element theory and the elastic foundation beam–plate principle, a finite element model of the ballastless track considering the limit convex abutment, gel resin, and interlayer bonding is established. The mechanical characteristics of the ballastless track under the slab–CAM layer bonding state, mortar separation, freeze–thaw degradation and forced deformation of the foundation are studied. Considering the deterioration of materials, the bending moment and reinforcement of track structures in cold regions are checked and calculated. The studies show that under the action of negative temperature gradient load, the edge of the track slab is subjected to tension, and structural separation occurs at the edge of the slab. When the interface between the track slab–CAM layer is poorly bonded, the bearing capacity can be improved, and the amount of separation can be reduced by increasing the structural stiffness of the CAM layer. Under the action of freeze–thaw cycles, the material performance deteriorates seriously, the separation between the track structures intensifies, the baseplate is seriously powdered and cracked, and the maximum tensile stress exceeds 6 MPa. The CAM layer and the baseplate are weak structures, and the foundation frost heave occurs at the expansion joint of the baseplate, which is the frost heave condition. Under freeze–thaw deterioration, the original reinforcement design of the substructure structure does not meet the requirements of structural cracks and reinforcement yield stress. In severely cold areas, the structural reinforcement scheme should be reasonably determined. [ABSTRACT FROM AUTHOR]

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

Seasonally frozen ground regions occupy approximately 55% of the exposed land surface in the Northern Hemisphere, and frost heave is the common global problem in seasonally frozen soil areas. Frost heave induces uneven deformation of ground and damages railways, road paving, and buildings. How to mitigate frost heave is the most important technical issue in this field that has provoked great interest. Here, using freezing experiments, we investigate the effect of anionic polyacrylamide (APAM) polymer on frost susceptible soil. The results demonstrate a so-far undocumented inhibition of frost heave by APAM in freezing soil, namely APAM (tested at concentrations from 0.0 wt% to 0.60 wt%) slows down the frost heave by a factor of up to 2.1 (since 0.60 wt% APAM can decrease frost heave from 8.56 mm to 4.14 mm in comparison to the control experiment). Moreover, it can be observed that the maximum water content near the frozen fringe decreased from 53.4% to 31.4% as the APAM content increased from 0.0 wt% to 0.60 wt%, implying a mitigated ice lens growth. Hydrogen bonding between APAM and soil particles triggers an adsorption mechanism that accumulates soil particles, and thus can potentially inhibit the separation and growth of the ice lens. Moreover, the residue of APAM due to hydrogen bonding-induced adsorption in the pores of granular media may narrow seepage channels (capillary barriers) and provide an unfavourable condition for water migration. The use of APAM can also increase the viscosity of the solution, which causes a greater water migration resistance. This research provides new insights into APAM-influenced frost heave (introducing APAM into the soil can induce bridging adsorption between APAM polymer segments and a particle surface), can enable engineers and researchers to utilise chemical improvement design and to consider suitable actions (e.g., by injecting APAM solution into a frost susceptible soil or using APAM-modified soil to replace the frost susceptible soil) to prevent frost heave from having a negative impact on traffic roads and buildings in cold regions. [ABSTRACT FROM AUTHOR]

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

This document is a discussion of a research paper titled "Experimental and Numerical Investigations of Frost Heave Characteristics of a Transmission Tower Foundation along the Lanzhou–Lintao Power Transmission Line." The authors conducted experimental and numerical studies on the behavior of the foundation of a transmission tower in frost-susceptible soils in Linto County, China. They investigated various conditions such as surface temperature, tangential frost heaving force, and water content distribution. The authors made recommendations based on their findings and addressed the results of both the experimental and numerical analyses. However, there are some areas in the presentation of the results that require further explanation or clarification. [Extracted from the article]

Considering that a jointed rock mass in a cold area is often affected by periodic freeze–thaw cycles and shear failure, definitions for the mesoscopic and macroscopic damage to a jointed rock mass under the coupling of freeze–thaw and shear are proposed, and the damage mechanism is verified according to experimental results. The results show that: (1) the jointed rock specimens increase macro-joints and meso-defects, the mechanical properties deteriorate significantly under freeze–thaw cycles, and the damage degree becomes more and more significant with the increases in freeze–thaw cycles and joint persistency. (2) When the number of freeze–thaw cycles is constant, the total damage variable value gradually increases with the increase in joint persistency. The damage variable difference in specimens with different persistency is distinct, which is gradually reduced in the later cycles, indicating a weakening influence of persistency on the total damage variable. (3) The shear resistance of non-persistent jointed rock mass in a cold area is determined by the coupling effect of meso-damage and frost heaving macro-damage. The coupling damage variable can accurately describe the damage variation law of jointed rock mass under freeze–thaw cycles and shear load. [ABSTRACT FROM AUTHOR]

Cryogenic LN2 fracturing is one of the environmentally friendly waterless fracturing technologies that promote the fracture complexity of shale gas reservoir. The water-ice phase transition under freezing condition causes frost heave in saturated shale. The effect of moisture in shale should be taken into account during cryogenic damage process. Therefore, the differences of cracking characteristics between dry and saturated shales were studied in this paper. A laboratory triaxial and high temperature fracturing system was developed for nitrogen fracturing dry and saturated shale after LN2 injection. The influence of moisture on breakdown pressure was studied under different confining pressures (3 MPa, 6 MPa, 9 MPa, and 12 MPa) and bedding directions (parallel bedding and vertical bedding). The experimental results demonstrated that when the confining pressure increased from 3 MPa to 12 MPa, the breakdown pressure of dry parallel bedding after LN2 preconditioning decreased 7.12 MPa, 6.06 MPa, 4.58 MPa, and 3.11 MPa, respectively. Therefore, LN2 preconditioning could damage shale resulting in a lower breakdown pressure, but the effect of cryogenic damage decreased with the confining pressure increasing. The moisture in shale had little impact on nitrogen fracturing without LN2 injection because the breakdown pressure difference between dry and saturated shales was small. However, the breakdown pressure of saturated shale after LN2 preconditioning was always lower than that of dry shale. The breakdown pressure of saturated parallel bedding shale after LN2 injection decreased 8.62 MPa, 7.67 MPa, 6.08 MPa, and 4.63 MPa, respectively, with the confining pressure increasing from 3 MPa to 12 MPa. The breakdown pressure difference between dry and saturated shales was impacted by the migration of unfrozen water and frost heave. In addition, the extent of cryogenic damage varied substantially between different bedding directions. When the confining pressure was 3 MPa, the breakdown pressure of saturated parallel bedding shale reduced by 69.18% after LN2 preconditioning, but that of saturated vertical bedding shale only decreased by 22.49%. The tensile strength of shale had a greater influence on the breakdown pressure. According to the Brazilian disc test results, the tensile strength of matrix was much higher than that of bedding planes. As a result, it is useful to wet the shale in order to reduce the breakdown pressure. The fracturing direction of horizontal drilling should be consistent with the bedding direction for better cryogenic fracturing effect. [ABSTRACT FROM AUTHOR]

A highly efficient and accurate mapping relationship model of subgrade disease and track geometry is significant for determining criterion of subgrade deformation and evaluating operation safety of High-speed Railway. In this paper, an innovative spatial mapping relationship model (SMRM) is proposed for describing track spatial geometry under subgrade disease of differential settlement and frost heave. Starting from analysing the theoretical interaction mechanism between subgrade and ballastless track, and presenting the flowchart of SMRM and its implementation process are described in detail. The good accuracy and applicability of SMRM method is verified based on the finite element model (FEM) and scale model experiment. The results indicate that it can better simulate the spatial characteristic of above mapping relationship than traditional theoretical model and avoid complicated and time-consuming FEM analysis process. It has high accuracy and reliability for the most application scenarios. The proposed method also can analyse the influences of others' diseases on track geometry as long as the disease description function is available. [ABSTRACT FROM AUTHOR]

The analysis of frost heave in unsaturated subgrade soils should consider the coupled movement of liquid water, vapor, and heat, accompanied by phase transition of water, vapor, and ice. In this paper, the equilibrium relationship of the three phases of water in soils was comprehensively considered, and the water head and vapor density were determined under frozen and unfrozen conditions from the perspective of thermodynamics. Based on that, the governing equations of mass and energy conservation were then derived and a new transient finite element model was developed, considering the behavior of the phase change and coupled hydrothermal transport under frozen as well as unfrozen conditions. Since the discontinuities between the frozen and the unfrozen zones may bring difficulties to the numerical solution, two kinds of smoothing techniques were proposed to solve the discontinuities at the phase transition interface, which guaranteed robust convergence and enhanced computational efficiency. The model proposed was verified by comparing with some available test results and applied to analyze the frost heave process of unsaturated subgrade under impermeable road pavements, demonstrating the model's accuracy and applicative prospect. It is revealed that the movement of liquid water and vapor in the frozen zones may still exist, and its mechanism and performance are different from that in unfrozen zones. The significance of vapor migration on the subgrade frost heave is also emphasized. [ABSTRACT FROM AUTHOR]

Ground frost heaving can be caused by the implementation of freezing method. In order to explore the frost heaving effect in the water-rich and sand cobble stratum as well as its influence on the existing structure, the essence of the ground frost heaving was illustrated and the relationship between temperature and structural stress and strain was explained. And a three-dimensional coupling model was established based on the connection aisle project between Tawan station and Shiwan station of Luoyang transit line 1. changed in stratum􀆳s frost heaving effect, deformations and stress state of existing tunnels during freezing period were analyzed by numerical calculation. The results show that the cooling of the freezing pipe can freeze the water in the surrounding stratum, and the volume of soil expands, thus generating the surface uplift above the connected aisle. And the closer the horizontal distance to the center of connected aisle, the greater the uplift deformation value. The frost heaving of stratum has an influence on the existing tunnels, and there is a rise at the arch vault, a settlement at the arch bottom as well as a transverse deformation towards the inside of the tunnel at the arch haunches which is near the connected aisle. Meanwhile there is also stress concentration in the segment near the opening of connected aisle. The cooling rate and temperature diffusion rate in sand cobble stratum are relatively fast in the early period of this freezing, so the frost heaving effect of strata changes significantly. But at the later stage of freezing, growth ranges of both the frost heave deformation of the ground and the tunnel deformation decline to some extent, which is limited by the freezing scope. [ABSTRACT FROM AUTHOR]

A common issue for Canadian railway operators is the development of localized frost heave near railway culverts, which leads to nonuniform deformation of the track surface and degradation of the track geometry, damages the track component, and affects the quality of rides in railway operations. Frequent maintenance including placing wooden shims between rail and ties and often the reduction of train speeds are required to ensure safe operating conditions. Given the future expected climate patterns, freeze–thaw cycles are anticipated to become more frequent, and therefore, a greater understanding of their effect on the changing ground thermal regime under railway embankments is essential. This paper investigates the effects of culverts and insulation layers on changing the temperature regime of the ground during the winter–spring period through numerical modeling in TEMP/W (version 2019) two-dimensional (2D) and three-dimensional (3D) software. The model was calibrated using actual field measurements collected from an instrumented section of the track that has suffered from frost heaves at the proximity of a culvert. Using the results from 2D simulation, the effect of culverts on extending the frost zone, in both horizontal and vertical directions, was quantified. In addition, the effects of shape, installation depth, and the number of culverts on the frost penetration depth were discussed. Using TEMP/W 3D results, the most appropriate configuration to install the culverts was studied to minimize frost penetration. [ABSTRACT FROM AUTHOR]

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

Sandstone from the Longshan Grottoes in Taiyuan, China, was the research object of this paper. The sandstone samples were soaked in distilled water, Na2SO4 solution, and NaCl solution and subjected to freeze–thaw testing. Sandstone specimens were treated with 0, 5, 10, 15, 20, 25, and 30 freeze–thaw cycles. The mass ratio, P-wave velocity, surface hardness, uniaxial compressive strength, and other physical-mechanical features of rock samples were measured after different numbers of cycles. The results of mercury injection, scanning electron microscopy, and X-ray diffraction were combined to explore the damage mechanisms and characteristics of the rock samples under the combined action of chemicals and freeze–thaw cycles. It was found that the damage degree of sandstone increased logarithmically with the number of cycles, with Na2SO4 solution causing the most damage. Damage variables D of the samples soaked in distilled water, Na2SO4 solution, and NaCl solution after 30 freeze–thaw cycles were 3.89%, 6.51%, and 4.74%, respectively. The difference in damage between the solutions is caused by the combination of frost heave, dissolution, and salt crystallization, and the damage process generally occurs from the inside and the outside and is manifested as an increase in the number of macropores and the appearance of new pores. Freezing–thawing and salt action are important causes of the powdering and detachment of sandstone in the Longshan Grottoes. [ABSTRACT FROM AUTHOR]

A large amount of water accumulated below the runway of Shenyang Taoxian International Airport caused frost heaving, which resulted in a wide range of cracks on the pavement. From the geological and environmental conditions of the engineering field, the possibility of capillary water migration and rainwater leakage is excluded. In the process of exploring this fraction of water, we put forward the concept of "pot cover effect." The "pot cover effect" refers to the phenomenon that the water vapor in the overburden soil moves upward by temperature gradient and condenses into liquid water or decomposes into ice which accumulate under the overburden eventually. The existence of the phenomenon of "pot cover effect" was confirmed by laboratory experiments, and the phenomenon also recurred in the field experiments. The long-term impacts of the "pot cover effect" will inevitably lead to water accumulation in the shallow soil of the airport runway, and eventually induce pavement disasters. Contraposing to the mechanism of "pot cover effect," we proposed the method of setting a separation layer in soil to block water vapor migration. Furthermore, the optimal depth of the separation layer was analyzed by numerical simulation of heat-water-mechanics coupling. The effective impacts of the separation layer on preventing "pot cover effect" are verified by field experiments. Eventually, the method of setting a separation layer was applied to the design of Beijing Daxing International Airport to prevent the disasters caused by "pot cover effect." [ABSTRACT FROM AUTHOR]