Frozen Soil Region Research Articles

Effect of frost heave deformation of bridge foundation on operation safety of high-speed railway

The frost heave deformation of the bridge foundation in seasonal frozen soil regions threatens the safe operation of high-speed trains. The first high-speed railway in extremely cold zones, the Harbin-Dalian Line, is used as the background in this study, and finite element analysis (FEA) is used to investigate the impact of freezing temperature and moisture content on the frost heave force and deformation of the bridge foundation. Furthermore, the dynamic response of the train crossing the frost heave deformation region of the bridge foundation is analyzed based on finite element (FE) and multi-body dynamics co-simulation. Conclusively, the frost heave threshold of the bridge foundation is proposed in accordance with the limit of the train’s dynamic response indicators. The results indicate that the normal frost heave stress at the bottom section of the cap is distributed in a “W” shape along the lateral direction of the cap. The magnitude of the stress at the edges of the cap and the inner hole of the pile foundation is relatively large. the frost heave deformation is negatively and positively linked with the fluctuations of temperature and moisture content, respectively. The train's vertical acceleration grows gradually as the pier's upward deformation increases, while there is no discernible relationship between the train’s lateral acceleration and the pier’s upward deformation. Additionally, variations in the train speed and the pier’s upward deformation are positively correlated with the derailment coefficient and wheel load reduction rate. To enable the high-speed railway’s operation safety, it is proposed that the deformation threshold of frost heave be 14.4 mm.

Mechanical and Microscopic Properties of Copper-contaminated Soil Solidified with Calcium Carbide Residue, Metakaolin, and Desulfurization Gypsum under Freeze-thaw Cycles

The solidification/stabilization effect of heavy metal contaminated soils in frozen soil regions may be weakened. A novel binder comprising calcium carbide residue, metakaolin, and desulfurization gypsum was used to solidify and stabilize copper-contaminated soil subjected to freeze-thaw (F-T) cycles. The unconfined compressive strength (UCS), F-T cycles, scanning electron microscope (SEM), X-ray diffraction (XRD), and pH tests were conducted to investigate the characteristics of UCS, deformation, pH value, and microscopic mechanism of contaminated soils. The results demonstrated that the UCS of contaminated soils decreased with the increasing F-T cycles and Cu2+ concentration; the strength loss rate increased first and then decreased as the F-T cycles increased. The failure strain rose first and then reduced with the increase of F-T cycles, and increased with the rise of Cu2+ concentration. There was a considerable correlation between UCS, failure strain, and deformation modulus E50. The pH value decreased with the increasing F-T cycles and Cu2+ concentration. The microscopic characteristics indicated that the formation of hydrated calcium silicate and ettringite was the fundamental reason for the enhanced UCS. Besides, heavy metals could be solidified and stabilized by chemical precipitation, physical encapsulation, and ion exchange. The effect of F-T cycles could significantly damage the internal structure of contaminated soils, and the frost heaving force could loosen the soil skeleton structure, leading to the deterioration of the mechanical properties.

Experimental Investigation of Interface Characteristics between Geogrid and Coarse-Grained Soil in a Seasonally Frozen Area

In seasonally frozen soil regions, the influence of temperature change on reinforced-soil engineering cannot be ignored. In particular, the mechanical properties of the reinforced-soil interface have an important impact on the overall stability and long-term service performance of reinforced soil engineering. To explore the interface characteristics and reinforcement mechanism between geogrids and coarse-grained soil under negative temperatures, this paper takes the typical coarse-grained soil in Xinjiang as the material and carries out a direct shear test of the reinforcement–soil interface under different normal stresses, water contents and temperatures. The curve characteristics of the shear displacement-shear stress, the change trend of the peak shear stress and the formation mechanism between the geogrid and coarse-grained soil interface under freezing and nonfreezing conditions are thoroughly analyzed. The formation mechanism of the dilatancy characteristics of the reinforced-soil interface is explained by combining the Mohr-Coulomb strength criterion and apparent friction coefficient. It is concluded that the trend of the shear displacement-shear stress curve between the geogrid and coarse-grained soil interface under the nonfreezing state and freezing state is basically the same. In a state of low normal stress, the curve has no obvious peak, which is closer to the ideal elastic-plastic double linear model. In a state of high normal stress, the curves have more obvious peaks, and the curve type is closer to the elastic-strain softening type. In the nonfreezing state, the shear strength of the reinforcement–soil interface has a great correlation with the water content, which is different in the freezing state. The main sources of the difference are the cementation of pore ice in the soil skeleton in the frozen state, the improvement of the strength of the soil particles themselves, and the further interlocking effect of the geogrid on the soil. In comparison with the reinforced coarse-grained soil under the nonfrozen state, the shear strength under the frozen state is significantly improved. In comparison with coarse-grained soil reinforced by geogrids in the nonfreezing state (0 °C), the shear strength of the frozen state (−5 °C) is significantly improved. Under normal stresses of 40 kPa, 60 kPa, and 80 kPa, when the water content is 2%, the corresponding peak shear stress increases by 19.39%, 21.71% and 11.34%, respectively. When the water content is 4.5%, the corresponding peak shear stress decreases by 29.98%, 16.17%, and 13.83%. When the water content is 7%, the corresponding peak shear stress decreases by 50.85%, 18.64%, and 21.96%. The apparent friction coefficient between the geogrid coarse-grained soil interface in the nonfrozen state and frozen state decreases with increasing normal stress. With the decrease in temperature, the dilatancy phenomenon of the reinforced soil composite is more obvious. The research results can provide a reference for the construction of reinforced engineering in seasonal frozen soil areas.

Vegetation Growth Status and Topographic Effects in Frozen Soil Regions on the Qinghai–Tibet Plateau

The Qinghai–Tibet Plateau (QTP), which is known as Earth’s “Third Pole”, is a driver of global climate change, and long-term monitoring of QTP vegetation can reveal changes attributable to climatic and human influences. Previous research monitoring vegetation on the QTP focused primarily on spatiotemporal variations of vegetation indices, while few studies have considered fractional vegetation cover (FVC) in relation to topographic and frozen soil factors. We used MODIS-EVI, digital elevation models, and frozen soil data to investigate topographic effects on vegetation growth status in different soil types on the QTP during 2000–2020. (1) FVC showed a trend of increase during 2000–2020, and the FVC on the QTP decreased from the southeast to the northwest in spatial distribution. FVC in permafrost regions was the lowest, followed by seasonal frozen soil areas; FVC in unfrozen areas was the highest. (2) With increasing elevation, FVC of permafrost, seasonal frozen, and unfrozen soil areas showed downward trends for each aspect. In seasonal frozen soil areas, at elevation ≤4000 m (>4000 m), FVC of sunny (shady) slopes was greater than that of shady (sunny) slopes. In permafrost regions, except at elevations of 3000–4000 m, FVC of shady slopes was greater than that of sunny slopes. In unfrozen soil areas, at elevation >4000 m, FVC of sunny slopes was obviously greater than that of shady slopes. (3) With increasing slope, FVC in seasonal frozen and permafrost soil (unfrozen soil) regions showed a trend of increase (decrease). In seasonal frozen soil areas, FVC of sunny (shady) slopes was greater than that of shady (sunny) slopes on slopes ≤6° (>6°). In permafrost regions, FVC of sunny slopes was less than that of shady slopes. With increasing slope, the influence of aspect became more obvious. In unfrozen soil areas, FVC of sunny slopes was slightly greater than that of shady slopes. Topographic effects especially the elevation and slope effects might significantly affect the spatiotemporal variations of vegetation growth status in frozen soil regions on the QTP.

Effect of Freeze-Thaw on Mechanical Properties of Loess with Different Moisture Content in Yili, Xinjiang

Various geological disasters such as collapses, landslides, and mudslides occur frequently in Yili, Xinjiang. The loess in this area provides a basis for the occurrence of landslides and other disasters. At the same time, Yili Valley is typically a seasonally frozen soil region. The freeze–thaw cycle is an essential disaster-inducing factor. However, scholars have lain a research emphasis on the material source of the Yili Loess, while lacking a systematic investigation of the degradation mechanism of the soil’s physical and mechanical properties under the freeze–thaw action. Therefore, it is prudent to investigate the changes in mechanical properties of loess in this region under the freeze–thaw cycle. In this study, focusing on a typical loess landslide in Yili, some in situ soil samples were collected to conduct related physical and mechanical tests. According to the maximum dry density and optimum moisture content of the loess in the region, four different groups of soil samples with varying moisture contents were prepared and subjected to different freeze–thaw cycles. The changes of apparent individual characteristics under freeze–thaw cycles were observed, and a consolidated undrained (CU) shear test was carried out to obtain the changes of shear strength indices of loess samples with varying moisture contents under freeze–thaw cycles. The results showed the obvious development of characteristics during freeze–thaw cycles, with the growth of many frost and ice crystals. At the freezing stage, the growth of ice crystals led to hexagonal peeling bodies on the surface layer. At the thawing stage, a rapidly melting network ice crystal pattern imposed a thermal thawing disturbance on the surface rock soil. After multiple freeze–thaw cycles, the soil’s peak strength dropped significantly and the internal friction angle changed slightly, but the cohesion was adversely affected, with frequent fluctuations. The present study enhances the research level of loess’s mechanical and strength properties under freeze–thaw cycles and provides a theoretical foundation for preventing loess landslides in this region.

Frost resistance and mechanical degradation characteristics of cement-stabilized macadam under the long-term freezing–thawing cycles

• Three different cement contents and removal of two different fine particle sizes of cement-stabilized macadam (CSM) were tested. • The mechanical strength characteristics were degraded by long-term freezing−thawing cycles. • The removal size of larger fine particles had adverse effects on the strength and degradation rate of CSM. • The increase in the cement content led to an increase in the frost resistance and strain energy density of CSM. • The initial elastic modulus determined using unconfined compressive strength tests could be applied to characterize the stiffness of CSM for high-speed railway lines. The high-speed railway subgrade in seasonal frozen soil regions should be able to resist long-term freezing and thawing cycles. In consideration of cement-stabilized macadam (CSM) as the subgrade surface material needs to have resistant to freeze–thaw strength deterioration. This study aimed to evaluate the mechanical degradation characteristics of CSM under the long-term freezing-thawing cycles by the unconfined compressive strength tests. Three different cement contents (3 %, 5 %, and 7 %) and removal of two different fine particle sizes (0.1 and 0.25 mm) of CSM were studied and analyzed. The number of freezing–thawing cycles was set to 0, 1, 3, 5, 7, 10, 15, 20, 30, 40, and 50, respectively. Based on the unified calculation model of strength deterioration, evaluation index of frost resistance, and analysis of strain energy density failure, C 5 P 0.1 could be used in seasonal frozen soil regions. If the subgrade bed had requirements for permeability, fine particles with larger sizes could be removed. The results indicated that, first, the strength of fine particles with larger size removal was smaller and the strength deterioration was faster under the same cement content. Second, when the cement content was higher, CSM showed better resistance to freezing–thawing strength degradation. Further, when the cement content increased, the increase in the amplitude of strain energy density varied significantly; the increasing effect was the best when the cement content increased from 3 % to 5 %. Finally, the initial elastic modulus of the Duncan-Chang hyperbolic model was used to characterize the stiffness of CSM in the high-speed railway subgrade bed. This study revealed the mechanical degradation characteristics of CSM under the long-term freezing–thawing cycles with different cement contents and removal sizes of fine particles. The findings were useful for understanding the mechanical behavior of CSM under the long-term freezing–thawing cycles.

Discussion on pile axial load test methods and their applicability in cold regions

The measurement of pile axial load is of great significance to determining pile foundation design parameters such as skin friction and end bearing capacity and analyzing load transfer mechanisms. Affected by the temperature and ice content of frozen ground, the interface contact relationship between pile foundation and frozen soil is complicated, making pile axial load measurements more uncertain than that in non-frozen ground. Therefore, it is necessary to gain an in-depth understanding of the current pile axial load test methods. Four methods are systematically reviewed: vibrating wire sensors, strain gauges, sliding micrometers, and optical fiber strain sensors. At the same time, the applicability of the four test methods in frozen soil regions is discussed in detail. The first two methods are mature and commonly used. The sliding micrometer is only suitable for short-term measurement. While the Fiber Bragg grating (FBG) strain gauge meets the monitoring requirements, the Brillouin optical time-domain reflectometer (BOTDR) needs further verification. This paper aims to provide a technical reference for selecting and applying different methods in the pile axial load test for the stability study and bearing capacity assessment of pile foundations in cold regions.

Engineering Disaster Investigation and Recurrence of the Covering Effect in a Petroleum and Gas Station in Seasonally Frozen Soil Region

The impermeable engineering surface layer in the cold regions blocks the water and heat exchange between the foundation soil and the atmospheric environment. Especially in cold areas with significant temperature differences, the moisture in the foundation soil accumulates at the bottom of the structure layer to form a covering effect. This will exacerbate the occurrence of engineering freeze-thaw diseases. This paper conducts a disease survey of the Guanshan oil and gas station site, which is located in a seasonally frozen soil zone. The ponding and freeze-thaw diseases under the concrete cover are analyzed. The formation process of the pot covering effect in the lower part of the concrete surface layer was reproduced through indoor tests. In addition, a water-vapor-heat coupling model of unsaturated soil was established, which quantitatively produced the formation process of silty clay covering under the concrete slab. The results show that (1) in-situ monitoring demonstrated that the water content of the roadbed soil from 0 to 50 cm below the concrete slab gathered significantly, with the water content increasing by 5 to 30%. (2) Under the action of the indoor time-varying covering effect, the moisture content of silty clay will increase with the number of freezing-thawing cycles, with a maximum migration amount of 6%. (3) Seasonal temperature changes lead to the accumulation of water in the subgrade surface, and the maximum accumulation amount is 32%. (4) During the freezing period, the liquid water and vapor water in the subgrade migrate to the surface layer of the subgrade. As a result, the moisture content of the subgrade surface layer increases, while the melting period is the opposite. The above research results can provide theoretical support and scientific countermeasures for engineering design and disease control in cold regions.

Experimental and analytical investigation on frost heave characteristics of coarse-grained soils under closed and open systems

Coarse-grained soil is widely used in the seasonal frozen soil region as subgrade filler. However, substantial frost heave has been observed in coarse filler in high-speed railway embankments. To investigate the frost heave characteristics of the coarse-grained soil in a deep seasonal frozen soil zone, indoor tests were carried out under water supply and no water supply conditions. The effect of water, fineness, and temperature on frost heave behavior is studied experimentally. The relationship between the freezing rate and frost heave of coarse-grained soils was analyzed. The results show that the freezing process of the filler can be divided into the rapid cooling stage, phase transition stage, slow freezing stage, and freezing stability stage. In the closed system, the increase of the fine-grained soil does not affect the cooling process, while the moisture content significantly affects the whole process. In the opened system, both the fine-grained soil content and the ambient temperature affect the cooling process. When the ambient temperature decreased from −5°C to −15°C, the duration of the phase transition stage decreased by almost 17 h, whereas when the fine-grained soil content increased from 2.7 to 16%, the duration of the phase transition stage increased by only 5 h. In both opened and closed systems, the development of the frost heave is closely related to the cooling process. Approximately 95% of frost heave occurs during the phase transition stage and slow freezing stage. Frost heave develops most rapidly in the phase transition stage, with approximately 85% of the frost heave amount occurring in this stage.

Shaking table test and numerical simulation of shallow foundation structures in seasonal frozen soil regions

Frozen soil layers can induce the formation of double or multilayers on the ground. Such formations change the dynamic characteristics and dominant period of soil, directly influencing the stability and safety of upper buildings. In this paper, the frozen soil-structure interaction system in cold region was taken as the research object. The frozen soil model was made artificially, and two kinds of structure models with different natural frequencies were designed. Through a series of shaking table tests and finite element numerical analysis, the influence of structural natural frequency, soil frozen depth and seismic load on the seismic response of structure were studied. The test results indicate that ground freezing could weaken the soil–structure interaction effect and the nonlinear development of the soil structure. The effect of peak acceleration amplification of the ground is significant close to the surface. The acceleration amplification coefficient of the ground surface decreased as the freezing depth increased, which indicates that the freezing of the ground suppressed the acceleration response of the ground surface. If the peak frequency of a seismic wave is close to the natural frequency of the structure, it can significantly amplify the seismic response of the structure. Owing to the interaction between the soil and the structure, the degree of liquefaction of the ground varied with different structures. Subsequently, a nonlinear finite element program was used to establish the dynamic calculation model of frozen soil-structure interaction system considering the gradient change of stiffness of frozen soil and the dependence of frozen soil on temperature. On the basis of validating the numerical model rationality, the seismic response of frozen soil-structure interaction system under horizontal seismic excitation was further explored. The analysis results show that the seismic response of the structure increased significantly with amplitude excitation; the greater was the freezing depth, the greater was the seismic response of the structure, The influence of the frozen ground on the seismic response of structures in the design of structures in frozen soil areas should be considered. In summary, the dominant period of the ground, the dynamic characteristics of a structure, the type of seismic wave, and the degree of liquefaction of the ground have a significant influence on the seismic response of the structure. Therefore, considerable attention should be paid to the influence of frozen soil on the dynamic characteristics of a structure in frozen soil regions.

Effects of Freeze–Thaw Cycles on Volume Change Behavior and Mechanical Properties of Expansive Clay with Different Degrees of Compaction

Freeze–thaw (F-T) cycles are one of the main deterioration factors for the performance of expansive clay in seasonally frozen soil regions. This study designed a unidirectional environmental boundary loading device for F-T cycle tests. Laboratory tests were conducted to quantitatively evaluate the effects of the F-T cycle on volume change behavior and mechanical properties of expansive clay with different degrees of compaction below the canal in Xinjiang. The SEM image processing was performed with the Image-Pro Plus image processing software to get pore parameters. The results showed that during the F-T cycle, the volume change of the sample gradually changes from contraction to expansion as the degree of compaction increases. As the degree of compaction increases, the hardening characteristics of the expansive clay are weakened, and the F-T cycle promotes the softening of the stress–strain relationship. The first F-T cycle resulted in a significant decrease of failure strength, and the failure strength of different compaction degrees decreased by 56.07%–67.54% after seven cycles. The failure strain and resilient modulus of the samples are attenuated to varying degrees after F-T cycles. The correlation rate between the porosity and the attenuation rate of the failure strength is 0.719–0.882, the corresponding weight reaches 0.419–0.445, and there is an excellent linear relationship between them. The research offers some important insights into the construction and maintenance of expansive clay engineering such as the Xinjiang Canal.

Dynamic Responses of a Pile with a Cap under the Freezing and Thawing Processes of a Saturated Porous Media Considering Slippage between Pile and Soil

The freezing/thawing stratification effect of seasonal factors or artificial disturbances in frozen soil regions has an important influence on the vertical vibration of the pile–soil–cap system. Taking into account the slippage between the pile and soil, a simplified layered analytical model of the vertical vibration of the pile–soil–cap system in a double-layered stratum under the freezing and thawing processes of a saturated porous medium was established, and the analytical solution of the dynamic response on the top of the pile cap was obtained. In this model, frozen saturated porous media and Biot’s porous media theory were used to simulate frozen soil and unfrozen soil, respectively. The validation of the slippage model was first verified by comparison with the results of the existing model tests. This was followed by a dynamic model test of the pile–soil–cap system in a self-made, ground-freezing system. In comparison with the analytical results and the experimental results of model tests under the freezing/thawing processes, the validation of the present model is further verified. A comprehensive parametric study reveals that the parameters of the frozen or thawed soil layer have significant effects on the amplitude–frequency curve of the vertical vibration of the pile foundation.

Migration Law of LNAPLs in the Groundwater Level Fluctuation Zone Affected by Freezing and Thawing

Freezing and thawing can cause dynamic fluctuations of the groundwater level, resulting in the migration and retention of LNAPLs. However, this process is difficult to observe visually, and a suitable simulation method for its quantitative calculation is lacking. In this study, a numerical simulation is established by coupling the HYDRUS-1D software and the TOUGH program to realize dynamic simulation of the entire process of soil temperature changes, water migration, water level fluctuation, and redistribution of LNAPLs during the freeze–thaw process. The results of the study show that the process of soil freezing and thawing causes water migration, which in turn causes groundwater level fluctuation, leading to the migration and redistribution of LNAPLs within the water level fluctuation zone. In this process, the soil particle size and porosity control the response degree and speed of the water level under freezing and thawing and the spatiotemporal distribution of LNAPLs by affecting the soil temperature, capillary force, and water migration. The migration ability of free LNAPLs is determined by their own density and viscosity; the retention of residual LNAPLs is affected by soil porosity and permeability as well as LNAPL viscosity. The results of this study can not only be used to develop a simulation method for the migration and retention mechanism of LNAPLs in cold regions but also serve as a scientific and theoretical basis for LNAPL pollution control in seasonal frozen soil regions.

The Study of Influence of Freeze-Thaw Cycles on Silty Sand in Seasonally Frozen Soil Regions

Freeze-thaw cycles can cause varying degrees of damage to expressway, in order to study the influence of freeze-thaw cycles on silty sand of expressway in Qinghai seasonal frozen soil regions, triaxial compression tests were carried out on silty sand under different initial freeze-thaw temperatures and freeze-thaw cycles. The stress-strain curve, secant modulus, cohesion, internal friction angle, dynamic shear modulus, and dynamic damping ratio of soil after freeze-thaw cycles were analyzed and studied. The experimental results show that the number of freeze-thaw cycles has different effects on the stress-strain curves at different initial freezing temperatures. With the increase of freeze-thaw cycles, the secant modulus of soil increases and changes in wave shape. The cohesion decreases and the internal friction angle decreases nonlinearly. The dynamic shear modulus and damping ratio do not change significantly. The change of freeze-thaw cycles will also affect the physical structure of the soil itself. The change of freeze-thaw cycles will also affect the physical structure of the soil itself. It will change the mosaic form of soil particles, the shape of soil particles, the size of soil particles and pores, and also make the redistribution of water in the soil.

Influence of subgrade filling types on covering effect in seasonally frozen soil area

The existence of a large area of expressway pavement in seasonally frozen soil region causes the moisture in roadbed filler to migrate upward and accumulate under the action of external temperature gradient and road barrier which aggravates the frost heave and thaw settlement of the subgrade. The formation process of subgrade covering effect in seasonally frozen soil area is reproduced by laboratory experiment. The water-vapor-heat model of unsaturated soil is established to simulate the formation process and difference of different subgrade filling cover effect in a certain area of Lanzhou. The results show that under the effect of seasonal temperature changes， soil water accumulates to the bottom of the impervious layer， and the accumulation phenomenon intensifies with freezing-thawing cycles. When the subgrade fillings are sandy soil， silty soil and silty clay， the maximum frozen depths are 1.21， 0.97 and 0.89 m， respectively， due to the difference in thermal conductivity and soil moisture diffusivity of the fillings. Water vapor migration dominates the water transport in shallow ground， which is most significant in silty soil. Water accumulations of sandy soil， silty clay and silty soil subgrade are 0.68%， 2.86% and 12.56%， respectively. The accumulation depth becomes shallower in turn. It is important to prevent and control the subgrade hazards caused by water vapor migration in the existing subgrade engineering. <fig fig-type="abstract-image" id="F1" orientation="portrait" position="float"><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="SP.J.1249-2022-39-1-59/733994E6-A745-493b-B2C8-B61D2BDE06B2-F001.jpg"/></fig>

Analysis and Evaluation on Residual Strength of Pipelines with Internal Corrosion Defects in Seasonal Frozen Soil Region

In order to study the residual strength of buried pipelines with internal corrosion defects in seasonally frozen soil regions, we established a thermo-mechanical coupling model of a buried pipeline under differential frost heave by using the finite element elastoplastic analysis method. The material nonlinearity and geometric nonlinearity were considered as the basis of analysis. Firstly, the location of the maximum Mises equivalent stress in the inner wall of the buried non-corroded pipeline was determined. Furthermore, the residual strength of the buried pipeline with corrosion defects and the stress state of internal corrosion area in the pipeline under different defect parameters was analyzed by the orthogonal design method. Based on the data results of the finite element simulation calculation, the prediction formula of residual strength of buried pipelines with internal corrosion defects was obtained by SPSS (Statistical Product and Service Solutions) fitting. The prediction results were analyzed in comparison with the evaluation results of B31G, DNV RP-F101 and the experimental data of hydraulic blasting. The rationality of the finite element model and the accuracy of the fitting formula were verified. The results show that the effect degree of main factors on residual strength was in order of corrosion depth, corrosion length, and corrosion width. when the corrosion length exceeds 600 mm, which affects the influence degree of residual strength will gradually decrease. the prediction error of the fitting formula is small and the distribution is uniform, it can meet the prediction requirements of failure pressure of buried pipelines with internal corrosion defects in seasonally frozen soil regions. This method may provide some useful theoretical reference for the simulation real-time monitoring and safety analysis in the pipeline operation stage.

Soil temperature dynamics and freezing processes for biocrustal soils in frozen soil regions on the Qinghai–Tibet Plateau

The relationship between soil temperature and its variations with different types of land cover are critical to understanding the effects of climate warming on ecohydrological processes in frozen soil regions such as the Qinghai–Tibet Plateau (QTP) of China. Biological soil crusts (biocrusts), which cover approximately 40% of the open soil surface in frozen soil regions, exert great impacts on soil temperatures. However, little attention has been given to the potential effects of biocrusts on the temperature characteristics, dynamics and freezing duration of soil in frozen soil regions. To provide more insight into this issue, an automatic system was used to monitor soil temperatures and dynamics at depths of 5, 30, 50 and 100 cm beneath bare soil and two types of biocrustal soils (soils covered with two types of biocrusts) on the QTP of China. The results showed that biocrusts play an important role in controlling the dynamics of soil temperatures. Biocrusts cause a 0.6–1 °C decrease in the mean annual temperature of soils down to a depth of 100 cm. The extent of the decrease in soil temperature was dependent on biocrust type, and dark biocrust showed a greater reduction in soil temperature than light biocrust. In addition, reductions in soil temperatures of biocrusts mainly occurred in daytimes of the thawing period, and this prolonged the freezing duration in the top 100 cm by approximately 10–20 days. The results of this study indicate that biocrusts maintain lower temperatures in the thawing period and slow the thawing of frozen soil in the spring, which helps to maintain the stability of the frozen soil. This information may aid understanding of the function of biocrusts in the frozen soil regions under global warming conditions.

WITHDRAWN: Heating Method and Artificial Heating Supply Pipe of Railway Active-Temperature Control Embankment in Seasonally Frozen Soil Regions

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Resilient modulus and cumulative plastic strain of frozen silty clay under dynamic aircraft loading

This paper describes an investigation into the factors influencing the resilient modulus and cumulative plastic strain of frozen silty clay. A series of dynamic triaxial tests are conducted to analyze the influence of the temperature, confining pressure, frequency, and compaction degree on the resilient modulus and cumulative plastic strain of frozen silty clay samples. The results show that when the temperature is below − 5 °C, the resilient modulus decreases linearly, whereas when the temperature is above − 5 °C, the resilient modulus decreases according to a power function. The resilient modulus increases logarithmically when the frequency is less than 2 Hz and increases linearly once the frequency exceeds 2 Hz. The resilient modulus increases as the confining pressure and compaction degree increase. The cumulative plastic strain decreases as the temperature decreases and as the confining pressure, frequency, and compaction degree increase. The research findings provide valuable information for the design, construction, operation, maintenance, safety, and management of airport engineering in frozen soil regions.

Experimental and numerical investigation on thermal-moisture-mechanical behaviors on a new anti-frost cutting bed of high-speed railway in deep seasonally frozen ground regions under extreme climate

Cutting damages caused by frost action seriously threaten the safe operation of railways in cold regions. This paper uses worth of monitoring data to examine the temperature, unfrozen water, and deformation behaviors of a new High-speed Railway (HSR) anti-frost cutting bed in a deep seasonally frozen ground region. A frost numerical model is established to study the effectiveness of the anti-frost cutting bed under extreme weather conditions. The influence of snow cover on the soil water-heat state and the causes of slope instability in cold regions are also discussed. Results demonstrate that the frost depth of the cutting top is less than that of the cutting center and that the sensitivity of different soil layers’ unfrozen water content to ground temperature changes are delayed in turn. Frost heave mainly occurs in the initial freezing and freeze–thaw alternating periods at the ground surface. Greater infiltration of rainwater or snow melt will lead to a greater peak frost value. Slopes in frozen soil regions are thus prone to instability and collapse at the freeze–thaw interface. These findings will help to improve understandings of thermal-moisture-mechanical behaviors for cutting beds with spatiotemporally in deep seasonally frozen ground regions, thereby potentially improving HSR operation quality.