Geohazards such as slope failures and retaining wall collapses have been observed during thawing season, typically in early spring. These geohazards are often attributed to changes in the engineering properties of soil through changes in soil phase with moisture condition. This study investigates the impact of freezing and thawing on soil stiffness by addressing shear wave velocity (Vs) and compressional wave velocity (Vp). An experimental testing program with a temperature control system for freezing and thawing was prepared, and a series of bender and piezo disk element tests were conducted. The changes in Vs and Vp were evaluated across different phases: unfrozen to frozen; frozen to thawed; and unfrozen to thawed. Results indicated different patterns of changes in Vs and Vp during these transitions. Vs showed an 8% to 19% decrease for fully saturated soil after thawing, suggesting higher vulnerability to shear failure-related geohazards in thawing condition. Vp showed no notable change after thawing compared to initial unfrozen condition. Based on the test results in this study, correlation models for Vs and Vp with changes in soil phase of unfrozen, frozen, and thawed conditions were established. From computed tomography (CT) image analysis, it was shown that the decrease in Vs was attributed to changes in bulk volume and microscopic soil structure.

The soils in the eastern region of Qinghai, China, are characterized by typical unsaturated loess with poor engineering properties, rendering them susceptible to geological disasters such as landslides. To investigate the mechanical properties of these soils, triaxial and direct shear tests were conducted, followed by simulations of deformation and stability under freeze-thaw cycles using the discrete element software MatDEM, based on the experimental data. The findings indicate that (1) the stress-strain curves from both tests typically exhibit weak strain-softening behavior, with increased matric suction enhancing shear strength; (2) in the direct shear test, both cohesion (c) and the angle of internal friction (phi) rise with matric suction, whereas in the triaxial test, cohesion increases while phi decreases; and (3) an increase in freeze-thaw cycles results in a gradual decline in slope safety factor, though the rate of decline diminishes over time. Additionally, initial water content and slope gradient changes significantly affect slope stability. These insights are essential for geohazard risk assessment and the formulation of prevention and control strategies in Qinghai and similar alpine regions.

During winter construction of earthworks such as earth dams and embankments, the structural properties of the soil may deteriorate due to freeze-thaw cycles. A new measure to combat freeze-thaw damage, incorporating phase change materials (PCMs) into the soil to regulate temperature, has been verified and applied in roadbed and pavement engineering. However, the law of deterioration from freeze-thaw cycles for this novel construction material is not clear yet. This study investigated the characteristics and mechanism of deterioration of clay mixed with paraffin-based PCM (PPCM-clay) through freezing and thawing using freeze-thaw tests, unconfined compression tests, permeability tests, and macro-micro structural analysis. The results show that the freeze-thaw resistance of PPCM-clay is better than that of pure soil. The amount of PPCM added is proportional to the effect of inhibiting soil strength and permeability degradation. Under the same number of freeze-thaw cycles, the compressive strength of PPCM-clay is greater than that of pure soil. Micropore expansion and frost heave are also not significant in PPCM-clay. This indicates that the low initial water content, relatively large porosity, thermal hysteresis, frost contraction, hydrophobicity, and high viscosity of PPCMs are the main reasons for the improvement in PPCM-clay freeze-thaw resistance. These findings provide a theoretical basis for the potential application of PPCM-clay as a dam or embankment material for weakening soil frost damage in winter construction in cold regions.

Landfill mined soil-like fraction (LMSF) is the material obtained from mining of old waste. Utilization of LMSF in infrastructure applications is limited due to several challenges including possible presence of organic content, heavy metals, heterogeneous composition, etc., and require stabilization prior to usage. In light of this, LMSF was stabilized with alkali activated slag at different curing temperatures including freeze curing (- 21 degree celsius), ambient curing (25 degree celsius), thermal curing (60 degree celsius) and their combinations. Further, the performance of stabilized LMSF was evaluated on cyclic exposure to different climatic conditions, viz., - 21 degree celsius, 0 degree celsius, 10 degree celsius, 25 degree celsius and 45 degree celsius in both closed (without water exposure) and open system (water inundated) conditions. The performance of stabilized LMSF under these climatic conditions was evaluated through unconfined compressive strength (UCS), indirect tensile strength, cyclic loading tests, and microstructural aspects. Based on initial trials, ambient curing (25 degree celsius) and 2 days thermal curing at 60 degree celsius yielded better performance of stabilized LMSF. The 28 days stabilized LMSF has shown stable performance against cyclic exposure to different climatic conditions by satisfying the maximum allowable mass loss criteria after 12 cycles as per IRC-37, except for exposure to subfreezing temperature of - 21 degree celsius in open system. Further, not much reduction in UCS and indirect tensile (except for - 21 degree celsius in open system) strength was observed on cyclic exposure to different climatic conditions, inferring the stability of cementitious compounds and resistance against degradation. 2 days of thermal curing at 60 degrees C notably enhanced the performance of stabilized LMSF in different exposure conditions under both static and cyclic loading conditions, suggesting it as favourable curing condition for sustainable and low-cost stabilization of LMSF in different climatic conditions ranging from sub-freezing to arid regions.

Block stone structural layers are commonly utilized in roadbed projects within permafrost areas. However, due to significant temperature fluctuations and frequent freeze-thaw cycles, some of these rock layers have weathered and fractured. Continuous weathering of these rocks results in the block stone embankment gaps becoming clogged, reducing macropore and porous media areas. Consequently, the convective heat transfer function of the block stone roadbed diminishes, failing to adequately protect the frozen soil. This study aims to assess whether recycled weathered rock materials, modified with cement, can match the mechanical properties and damage expansion characteristics of unweathered rocks. Weathered sandstone was selected for modification into rock-like materials. Detailed investigations were conducted into their physical and mechanical properties, alongside damage propagation characteristics following freeze-thaw cycles. Compared to red sandstone, weathered sandstone rock materials exhibit significantly enhanced compressive strength, aligning freeze-thaw damage models with red sandstone rock characteristics, thereby affirming the feasibility of reusing weathered sandstone rocks.

The soil freezing and thawing process affects soil physical properties, such as heat conductivity, heat capacity, and hydraulic conductivity in frozen ground regions, and further affects the processes of soil energy, hydrology, and carbon and nitrogen cycles. In this study, the calculation of freezing and thawing front parameterization was implemented into the earth system model of the Chinese Academy of Sciences (CAS-ESM) and its land component, the Common Land Model (CoLM), to investigate the dynamic change of freezing and thawing fronts and their effects. Our results showed that the developed models could reproduce the soil freezing and thawing process and the dynamic change of freezing and thawing fronts. The regionally averaged value of active layer thickness in the permafrost regions was 1.92 m, and the regionally averaged trend value was 0.35 cm yr(-1). The regionally averaged value of maximum freezing depth in the seasonally frozen ground regions was 2.15 m, and the regionally averaged trend value was -0.48 cm yr(-1). The active layer thickness increased while the maximum freezing depth decreased year by year. These results contribute to a better understanding of the freezing and thawing cycle process.

Antarctic soils are heavily affected by climate change in terms of properties and ecosystem functions. With increasing global temperatures, the frequency of freeze and thaw cycles of Antarctic soils will increase, thus affecting their mechanical behavior, with varying responses in erosion. This study quantitatively evaluated the effect of increasing frequency of freezing-thawing (F-T) cycles on rheological properties of four soils from the maritime Antarctica. Using an amplitude sweep test, the effects of 1, 5 and 9F-T cycles on soil micromechanics were evaluated and compared to a reference soil without F-T. These rheological parameters were determined: (i) the linear viscoelastic strain interval (LVR) (gamma LVR), (ii) the shear stress at the end of the LVR (rLVR), (iii) the maximum shear stress (rmax), (iv) the strain at the yield point (gamma YP), and (v) the storage and loss modulus at the yield point (G'YP). F-T cycles influenced soil rheological properties. Higher F-T frequency either increased or decreased gamma LVR and gamma YP, depending on the soil material. A 35% increase in rLVE occurred after one F-T cycle; however, at the fifth cycle a decrease of approximately 27% occurred, when compared to one cycle treatment, reaching similar values of no F-T. But after nine cycles, rLVE increased again by approximately 29% compared to previous treatment. The resistance and elasticity of the Antarctic soil microstructure showed great variation among the different soils, while soils with different textures behaved similarly for some rheological properties. Rheometry was confirmed as a method with little soil material consumption, however, soil rheology of Antarctic soils requires further studies to disentangle its interactions with soil chemical properties.

The soil freeze-thaw phenomenon is one of the most outstanding characteristics of the soil in Heilongjiang Province. Quantitative analysis of the characteristics of changes in key variables of the soil freeze-thaw processes is of great scientific importance for understanding climate change, as well as ecological and hydrological processes. Based on the daily surface temperature and air temperature data in Heilongjiang Province for the past 50 years, the spatial-temporal distribution characteristics of key variables and their correlations with air temperature and latitude in the freeze-thaw process of soil were analyzed using linear regression, the Mann-Kendall test, the local thin disk smooth spline function interpolation method, and correlation analysis; additionally, the spatial-temporal distribution of key variables and the changes in the surface temperature during the freeze-thaw process are discussed under different vegetation types. The results show that there is a trend of delayed freezing and early melting of key variables of the soil freeze-thaw process from north to south. From 1971 to 2019 a, the freezing start date (FSD) was delayed at a rate of 1.66 d/10 a, the freezing end date (FED) advanced at a rate of 3.17 d/10 a, and the freezing days (FD) were shortened at a rate of 4.79 d/10 a; with each 1 degrees C increase in temperature, the FSD was delayed by about 1.6 d, the FED was advanced by about 3 d, and the FD was shortened by about 4.6 d; with each 1 degrees increase in latitude, the FSD was delayed by about 2.6 d, the FED was advanced by about 2.8 d, and the FD was shortened by about 5.6 d. The spatial variation in key variables of the soil freeze-thaw process under the same vegetation cover was closely related to latitude and altitude, where the lower the latitude and altitude, the more obvious the variation trend; among them, the interannual variation trend of key variables of soil freeze-thaw under meadow cover was the most obvious, which varied by 9.65, 16.86, and 26.51 d, respectively. In addition, the trends of ground temperature under different vegetation types were generally consistent, with the longest period of unstable freeze-thaw and the shortest period of stable freeze in coniferous forests, compared to the shortest period of unstable freeze-thaw and the longest period of stable freeze in meadows. The results of the study are important for our understanding of soil freeze-thaw processes and changes in Heilongjiang Province, as well as the evolution of high-latitude permafrost; they also promote further exploration of the impact of soil freeze-thaw on agricultural production and climate change.

The Mongolian Plateau is located in the permafrost transitional zone between high-altitudinal and high-latitudinal permafrost regions in the Northern Hemisphere. Current knowledge of the thermal state and changes in the permafrost on the Mongolian Plateau is limited. This study adopted an improved calculation method of the Mongolian Plateau air freezing and thawing index using the monthly air temperature reanalysis dataset from the Climate Research Unit (CRU). The spatial and temporal variation characteristics from 1901 to 2019 were further assessed by the Mann-Kendall (M-K) test and spatial interpolation methods. The results indicate that the spatial distributions of the freezing and thawing index show clear latitudinal zonality. Over the study period, the air freezing index decreased by 4.1 degrees C center dot d/yr, and the air thawing index increased by 2.3 degrees C center dot d/yr. The change point in the air thawing index appeared in 1995 (p < 0.05) based on the M-K method, in contrast to the so-called hiatus in global warming. Our results reveal rapid warming on the Mongolian Plateau, especially in the permafrost region, and are useful for studying permafrost changes on the Mongolian 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 degrees 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.