In cold regions, the performance, safety, and serviceability of engineering facilities overlying on freeze- thaw susceptible soils are being compromised to varying degrees due to the alternate seasonal freezing and thawing cycles (FTCs). FTCs induce temporary and permanent microstructural deterioration of the underlying soils, especially fine-grained soils. In this study, we investigate the shear strength and stiffness behavior of low-compressibility silt subjected to alternate FTCs. Four series (S1 to S4) of unconsolidated undrained triaxial compression tests were performed on moist tamped solid cylindrical soil specimens. The specimens were prepared at four compaction states by changing dry unit weight and moisture content. At each compaction state, unfrozen (normal) specimens and specimens subjected to different number of FTCs were tested at total confining pressures ( 63 ) of 100 kPa, 200 kPa, and 300 kPa. At lower moisture content and increased 63, strain-hardening behavior was more obvious in the stress- strain response. The strain-hardening behavior was subdued with the number of FTCs. Higher moisture content and lower dry unit weight make the silt susceptible to frost action and thaw weakening. Percentage reduction in peak shear strength ranged from 20 to 32% for specimens subjected to 16 FTCs in S1 and S2, 8 FTCs in S3, and 04 FTCs in S4. The reduction in resilient modulus ( MR) with the number of FTCs ranged from 2 to 48% for the four compaction states. The reduction in apparent cohesion value was in the range of 23-64%. After an initial decrease in the range of 16-59%, the angle of internal friction showed a net increase in the range of 8-142%. The current study reveals that low- compressibility silt is susceptible to frost action and thaw weakening. The results show that the S4 with the highest moisture content and void ratio (lowest dry unit weight) aggravates the frost action in the soil.

In Interior Alaska, a slope underlying the Trans Alaska Pipeline System has recently experienced downslope movement, which is attributed to a buried frozen, ice-rich peat layer. We performed a field investigation of the site, including coring and sampling, and conducted a suite of laboratory tests, including mechanical tests at temperatures between -0.56 and -5 degrees C to quantify the secondary creep behavior and to estimate the impact of soil cooling on the creep deformation. We tested a variety of soils, including ice-rich silt, silty peat, and peat with the majority having an organic content of 10% or greater. The results indicated that temperature has a strong control on the resulting time-dependent mechanical properties. Here we provide secondary creep power law relationships for these soils. The analysis indicates that cooling the soils can be effective in reducing creep movement; for example, cooling by 1.1 degrees C from -0.56 to -1.67 degrees C results in an order of magnitude reduction in the shear deformation rates. These results are significant as they add to the limited amount of work done on the time-dependent mechanical behavior of ice-rich peat and organic soils at warm sub-freezing temperatures.

Relevance. Engineering-geological surveys are an integral part of mining operations for various purposes. The quality of soil core sampling has an important impact on the results of engineering geological surveys. At the same time, obtaining a frozen rock core is complicated by an increase in the bottomhole zone temperature, which arises as a result of drilling. As the temperature rises, the physical and mechanical properties of frozen soils change, which leads to a transformation of the mechanism of their destruction and an increase in the likelihood of drilling emergencies. A core obtained under conditions of rising temperature does not allow for a reliably accurate assessment of the properties and structure of soils in their natural conditions. Therefore, there is a need to develop technological and technical means that help maintain the temperature regime of a rock mass under mechanical effect on it. The analysis of the conditions of core drilling in frozen rocks showed that, along with technological reasons, the design of the rock-cutting tool affects the increase in bottom-hole temperature. The article reveals the dependence of the temperature change at well bottom when drilling on the design features of the core rock-cutting tool. Aim. To study the impact of the design features of a drilling core tool on the nature of destruction of frozen soils, represented by loose sedimentary rocks as the most susceptible to changes in physical and mechanical properties with increasing temperature. The study was based on frozen soils that make up the of Yakutia, a large industrial region that requires frequent geotechnical surveys for its development. Objects. Core drilling tool design, mechanism of frozen rocks destruction, conditions for core sampling in frozen soils. Methods. Analytical method, experimental method, production test method. Results. The authors have determined the main directions for the development of core tools for high-quality core sampling in frozen soils. They derived the dependence of the magnitude of the temperature increase at well bottom on the orientation and size of the cutters reinforcing the rock-cutting tool.

Extensive experimental studies have demonstrated the time-dependent mechanical behaviors of frozen soil. Nonetheless, limited studies are focusing on the constitutive modeling of the time-dependent stress-strain behaviors of frozen clay soils at different subzero temperatures. The objective of this study is to numerically investigate the time-dependent behavior of frozen clay soils at a temperature range of 0 degrees C to - 15 degrees C. The Drucker-Prager model is adopted along with the Singh-Mitchell creep model to simulate time-dependent uniaxial compression and stress relaxation behaviors of frozen sandy clay soil. The numerical modeling is implemented through the finite element method based on the platform of Abaqus. The constitutive modeling is calibrated by a series of experimental results on laboratory-prepared frozen sandy clay soils, where the strain hardening, the post-peak softening, and stress relaxation behaviors are captured. Our results show that both the rate-dependent model and creep model should be adopted to characterize a comprehensive time-dependent behavior of frozen soils. The rate-dependent stress-strain behaviors heavily rely on the rate- and temperature-dependent hardening functions, where the creep strain provides a very limited contribution. Nevertheless, the creep strain should also be adopted when a long-term analysis or stress relaxation behavior is involved.

A modified plastic Burgers model considering cohesion decay is proposed for frozen soils. A series of triaxial compression and creep tests were conducted on a kind of frozen silty clay for obtaining the model parameters. According to typical triaxial creep strain curves with only a decaying creep stage, a deformation parameter calibration method for a plastic Burgers model is proposed, and the validity of the method was further verified. When the original plastic Burgers model was incorporated with a cohesion decay function, it was shown that the successive development process of frozen soil creep strain from the decaying to non-decaying stage could be described reasonably. The modified model is applicable to frozen ground engineering cases with non-decaying creep involved.

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.

In the context of climate change, research on frozen soils has attracted much attention in recent years, and numerous research papers have been published on these topics in the last decade. However, the present status and developmental trends in frozen soils research have not been reported systematically. Herein, a bibliometric analysis was conducted using 7,108 research papers on frozen soils published between 2010 and 2019. The results indicate that: (a) although the number of articles published increased from 432 in 2010 to 1,066 in 2019, the average number of citations per paper reached a maximum of 5.40 in 2014, and subsequently decreased to 2.99 in 2019; (b) China, the USA, and Canada ranked first to third in terms of total papers; (c) the most popular author keywords were boreal, tundra, Landsat, lakes, decomposition, dissolved organic carbon, permafrost thaw, and carbon cycle; and (d) the five most popular research topics in 2010-2019 were the characteristics and factors influencing frozen soils, the Arctic carbon cycle under the background of its complex environment, permafrost changes on the Qinghai-Tibet Plateau in the context of climate change, ancient frozen soils in various historical periods, and frozen soils in the Arctic.

Recently, very active studies have been undertaken on the response and stability of permafrost carbon pool and key biogeochemical processes in permafrost regions to climate warming. By observing the significant differences in microbial community structure in regions of seasonal frost and permafrost, it is evident that microbes play key roles in the conversion of permafrost carbon. This paper reviews research progress at the cutting edges on the conversion and decomposition of permafrost carbon to climate warming and subsequent changes in microbial activities over the past decade. Findings indicated that: (1) Freezethaw cycles of soils in the active layer in permafrost regions showed an increasing annual trend and the existing survival patterns of permafrost microbes may be altered by the increasing freeze-thaw frequency; and (2) Soil microbes are an essential part of the cold-regions ecosystem and they play vital roles in soil carbon and nitrogen cycling, the mineralization and decomposition of soil organic matter. Thus, climate warming and subsequent permafrost degradation affect the conversion and decomposition of permafrost carbon, resulting in changes in CO2 and CH4 emissions, soil environmental factors, and soil microbial community structures. The laws for governing permafrost carbon conversion and the self-regulation mechanisms of soil microbes are important for natural ecosystems and environments in cold regions, and affect the strengths of greenhouse gas sources and sinks in permafrost regions.

The influence of seasonally frozen ground (SFG) on water, energy, and solute fluxes is important in cold climate regions. The hydrological role of permafrost is now being actively researched, but the influence of SFG has received less attention. Intuitively, SFG restricts (snowmelt) infiltration, thereby enhancing surface runoff and decreasing soil water replenishment and groundwater recharge. However, the reported hydrological effects of SFG remain contradictory and appear to be highly site- and event-specific. There is a clear knowledge gap concerning under what physiographical and climate conditions SFG is more likely to influence hydrological fluxes. We addressed this knowledge gap by systematically reviewing published work examining the role of SFG in hydrological partitioning. We collected data on environmental variables influencing the SFG regime across different climates, land covers, and measurement scales, along with the main conclusion about the SFG influence on the studied hydrological flux. The compiled dataset allowed us to draw conclusions that extended beyond individual site investigations. Our key findings were: (a) an obvious hydrological influence of SFG at small-scale, but a more variable hydrological response with increasing scale of measurement, and (b) indication that cold climate with deep snow and forest land cover may be related to reduced importance of SFG in hydrological partitioning. It is thus increasingly important to understand the hydrological repercussions of SFG in a warming climate, where permafrost is transitioning to seasonally frozen conditions.

While the composition and diversity of soil microbial communities play a central and essential role in biogeochemical cycling of nutrients, they are known to be shaped by the physical and chemical properties of soils and various environmental factors. This study investigated the composition and diversity of microbial communities in 48 samples of seasonally frozen soils collected from 16 sites in an alpine wetland region (Lhasa River basin) and an alpine forest region (Nyang River basin) on the Tibetan Plateau using high-throughput sequencing that targeted the V3-V4 region of 16S rRNA gene. The dominant soil microbial phyla included Proteobacteria, Acidobacteria, and Actinobacteria in the alpine wetland and alpine forest ecosystems, and no significant difference was observed for their microbial composition. Linear discriminant analysis Effect Size (LEfSe) analysis showed that significant enrichment of Hymenobacteraceae and Cytophagales (belonging to Bacteroidetes) existed in the alpine wetland soils, while the alpine forest soils were enriched with Alphaproteobacteria (belonging to Proteobacteria), suggesting that these species could be potential biomarkers for alpine wetland and alpine forest ecosystems. Results of redundancy analysis (RDA) suggest that the microbial community diversity and abundance in the seasonally frozen soils on the Tibetan Plateau were mainly related to the total potassium in the alpine wetland ecosystem, and available potassium and soil moisture in the alpine forest ecosystem, respectively. In addition, function prediction analysis by Tax4Fun revealed the existence of potential functional pathways involved in human diseases in all soil samples. These results provide insights on the structure and function of soil microbial communities in the alpine wetland and alpine forest ecosystems on the Tibetan Plateau, while the potential risk to human health from the pathogenic microbes in the seasonally frozen soils deserves attention. (C) 2020 Elsevier B.V. All rights reserved.