Global warming is profoundly altering soil freeze -thaw cycle (FTC) patterns, and the formation of different thicknesses and durations of snow cover by snowfall results in heterogeneity of environmental and biological factors, which can have complex effects on soil water and carbon cycle processes. In order to better develop rational regulation strategies to increase the potential of soil carbon sequestration and emission reductions under climate change conditions, a three-year in situ control trial of field snow was set up to simulate climate scenarios using two treatments: snow removal and natural snow. The effects of FTCs and biochar on soil CO 2 emission flux (CO 2 Flux) were analyzed by constructing a driven coupling model between soil hydrothermal environmental factors, unstable organic carbon components and stable organic carbon components. The results showed that CO 2 Flux decreased by 9.36% to 11.34% for 1% biochar treatment, while CO 2 Flux increased by 15.41% to 18.32% for 2% biochar treatment. Moreover, the snow removal treatment increased CO 2 Flux by 9.86% to 13.99% compared to the natural snow treatment. The snow during freezing and thawing has a dual effect on soil hydrothermal dynamics, with snow removal making the freeze -thaw action more intense in perturbing the soil carbon matrix, while the interfacial behavior of biochar with soil minerals protects the stability of the soil structure. Biochar reduces soil carbon emissions thanks to its highly stabilized components and unique surface structure, which enhances the carbon sequestration and emission reduction effect by increasing the proportion of inert organic carbon, promoting the formation of organic -inorganic complexes, and encapsulating and adsorbing soil organic matter. The results of the study can provide important theoretical support and practical models for the assessment of the environmental effects of biochar and the reduction of carbon sequestration in agriculture under climate change conditions.

A universal testing machine and a 50 mm split Hopkinson pressure bar (SHPB) were used to conduct salt erosion and freeze -thaw (F -T) cycle coupling tests on cement soil specimens with 0.5% polyvinyl alcohol (PVA) fiber and without fiber in order to study the effects of salt solution and F -T cycles on the dynamic and static mechanical properties of cement soil. In four distinct solution settings (clear water, 9 g/L sodium sulphate solution, 9 g/L sodium chloride solution, and 9 g/L sodium sulphate and sodium chloride mixed solution). After F -T cycles, the cement soil specimens underwent the unconfined compressive strength (UCS) test, SHPB test, and SEM test. The findings indicate that as the number of F -T cycles increases, the dynamic and static mechanical properties of cement soil specimens decrease, and the rate of decline is rapid followed by slow. After five F -T cycles, the combined solution ' s unconfined compressive strength dropped to 15.91% (without fiber) and 29.41% (with fiber), respectively. After five F -T cycles, the dynamic compressive strength in sodium sulphate solution fell by 95.17% (without fiber) and 93.86% (with fiber). Fibers help to some degree by preventing salt erosion and F -T cycles. With more F -T cycles, the absorbed energy declines exponentially, and the order of the solutions ' effects on the absorbed energy is: mixed sodium chloride and sodium sulphate solution > sodium chloride solution > sodium sulphate solution > clear water.

In this study, the mechanical and durability performance of clay soils reinforced with different proportions of Cherry Marble Powder (CMP) and non-woven geotextile configurations, both independently and in combination, is investigated in detail at both the macro and micro levels. The effectiveness of reinforcement in the stabilization of clay soils in cold climates has been evaluated by means of Gray Correlation Analysis (GCA). The results show that as the CMP ratio and the number of geotextiles increase, the peak strength of the soil increases, with higher CMP levels showing perfect plastic behavior and more geotextiles showing linear strain hardening, particularly in combination. Substantial strength reductions post-7th cycle ranged between 91.09 % and 103.38 % for 12 % CMP and 219.83 % and 270.42 % for three-layered geotextile groups. Cohesion increased by 59.76 % and 179.41 %, while the internal friction angles remained stable and decreased after F-T cycles, except with additives. Failure modes shifted with CMP content, F-T cycles and confining pressure. The transition was from strain hardening to strain softening, with increased shear fracture planes and brittleness. The energy absorption capacity (EAC) increased with the CMP ratio, with the geosynthetic reinforcement increasing the EAC by a factor of 1.5 before and after the F-T cycles. The combined use of CMP and geotextiles in soil stabilization improved the engineering properties in areas of frost, with the optimum gradation being three layers of geotextile and a CMP ratio of 12 %, which effectively mitigated the effects of the maximum F-T cycle.

Rapidly growing urbanization and industrialization drive the continued development of soil stabilization and ground improvement techniques. Rice husk ash (RHA) is widely regarded as a highly promising construction material in civil engineering due to its excellent pozzolanic properties and has garnered significant attention from researchers. This paper presents an experimental study and a micro-mechanical discussion on the role of RHA in the mechanical improvement of soil. RHA was mixed with the native soil in varying proportions, ranging from 0% to 12%. Several laboratory tests were conducted, including standard proctor compaction tests, Atterberg limit tests, freeze-thaw tests, unconfined compression tests, X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM). The results indicated that the optimal moisture content (OMC) of the soil mixture increased while the maximum dry density (MDD) decreased with higher RHA dosage. The Atterberg limits of the soil mixture exhibited a positive correlation with the RHA content. A substantial enhancement in the soil's strength, stiffness, and ductility was observed upon the incorporation of RHA. It was noted that the strength loss of the untreated samples and those with 12% RHA was 34.91% and 12.89%, respectively, following 12 freeze-thaw cycles. Furthermore, XRD test results revealed that the treated specimen had an identical mineral composition to the control specimen, with no generation of hydration products. SEM analysis also highlighted that the filling effect of RHA significantly reduced pore content and pore connectivity within the soil, accompanied by a shift in the specimen's pores from mesopores to small and micropores. The excellent thermal insulation and heat retention properties of RHA, along with its pore-refining effect, make a positive contribution to enhancing the frost resistance of the specimens. These findings contribute to guiding the effective application of RHA in civil engineering, offering eco-friendly solutions for biomass waste management, and promoting the sustainable development of construction materials.

In view of the specialized climatic conditions in high-cold and high-altitude regions, the direct, repeated freezethaw and freezing processes resulting from diurnal and seasonal temperature changes pose a significant threat to the integrity of the roadbed stones in these areas. Weathering and fragmentation constitute a form of rock damage. Rock damage negatively impacts the air convection within the rock subgrade, rendering it incapable of safeguarding frozen soil. The objective of this study is to investigate the mechanical properties and the constitutive model for freeze-thaw damage of three recycled weathered rock materials subjected to varying freeze-thaw cycles. Additionally, it aims to examine the damage and degradation mechanism of recycled weathered rock materials under the combined influence of freeze-thaw and load. The model is then employed to validate the experimental data. Research indicates that with an increase in the number of freeze-thaw cycles, the quality of the three types of recycled weathered rock samples exhibits a gradual decrease, accompanied by a corresponding reduction in P-wave speed. The elastic modulus and compressive strength of the three recycled weathered rock materials show an increase with rising confining pressure and a decrease with a growing number of freeze-thaw cycles. The types of damage include splitting and shear damage. The presented damage model can elucidate the pattern of damage evolution in the specimen under varying confining pressures and freeze-thaw cycles. The expansion of internal micro-cracks is influenced differently by freeze-thaw cycles and loads; moreover, the coupling effect of damage exhibits pronounced nonlinear characteristics. Substantiated by experimental results, the damage constitutive model demonstrates both reasonability and feasibility.

Changing precipitation patterns and global warming have greatly changed winter snow cover, which can affect litter decomposition process by altering soil microenvironment or microbial biomass and activity. However, it remains unknown how and to what extent snow cover affects litter decomposition during winter and over longer periods of time. Here, we conducted a meta-analysis to synthesize litter decomposition studies under different levels of snow cover. Overall, deepened snow significantly enhanced litter decomposition rate and mass loss by 17% and 3%, respectively. Deepened snow enhanced litter carbon loss by 7% but did not impact the loss of litter nitrogen or phosphorus. Deepened snow increased soil temperature, decreased the frequency of freeze-thaw cycles, and stimulated microbial biomass carbon and bacterial biomass during winter, but had no effect on these parameters in summer. The promoting effect of deepened snow cover on litter decomposition in winter is mainly due to its positive effect on microbial decomposition by increasing soil temperature and reducing freezethaw cycles exceeded its negative effect on physical fragmentation of litter by reducing freeze-thaw cycles. Our findings indicate that the changes in winter snow cover under global change scenarios can greatly impact winter litter decomposition and the associated carbon cycling, which should be taken into consideration when assessing the global carbon budget in modeling.

In cold regions, freeze-thaw cycles (FTCs) can alter the properties of soil used as a foundation filler, leading to failures in foundation engineering. The increase in biomass power plants has resulted in a significant amount of waste biomass ash, causing negative environmental impacts. To address these issues, waste wheat straw biomass ash (WSBA) is harnessed to enhance the properties of silty clays. This study examines how WSBA affects the mechanical properties and microstructure of silty clay after FTCs through FTCs tests, Triaxial tests, and Scanning Electron Microscopy (SEM) tests. The findings reveal that incorporating WSBA significantly enhances the mechanical properties and microstructure of the soil by filling internal pores and strengthening its structure. The mechanical properties of all soil samples exhibit significant deterioration after 1 FTC, with gradual stabilization ensuing after 6 FTCs. Notably, WSBA-modified samples show better resistance to freeze-thaw weathering compared to unmodified samples, particularly at a WSBA content of 10%. Furthermore, the study establishes empirical formulas linking mechanical parameters, freeze-thaw cycles, and WSBA content using binary quadratic equations. The investigation results could serve as a valuable reference for projects involving roadway subgrade backfill materials in regions with seasonal frozen soil.

In the context of global warming, increasingly widespread and frequent freezing and thawing cycles (FTCs) will have profound effects on the biogeochemical cycling of soil carbon and nitrogen. FTCs can increase soil greenhouse gas (GHG) emissions by reducing the stability of soil aggregates, promoting the release of dissolved organic carbon, decreasing the number of microorganisms, inducing cell rupture, and releasing carbon and nitrogen nutrients for use by surviving microorganisms. However, the similarity and disparity of the mechanisms potentially contributing to changes in GHGs have not been systematically evaluated. The present study consolidates the most recent findings on the dynamics of soil carbon and nitrogen, as well as GHGs, in relation to FTCs. Additionally, it analyzes the impact of FTCs on soil GHGs in a systematic manner. In this study, particular emphasis is given to the following: (i) the reaction mechanism involved; (ii) variations in soil composition in different types of land (e.g., forest, peatland, farmland, and grassland); (iii) changes in soil structure in response to cycles of freezing temperatures; (iv) alterations in microbial biomass and community structure that may provide further insight into the fluctuations in GHGs after FTCs. The challenges identified included the extension of laboratory-scale research to ecosystem scales, the performance of in-depth investigation of the coupled effects of carbon, nitrogen, and water in the freeze-thaw process, and analysis of the effects of FTCs through the use of integrated research tools. The results of this study can provide a valuable point of reference for future experimental designs and scientific investigations and can also assist in the analysis of the attributes of GHG emissions from soil and the ecological consequences of the factors that influence these emissions in the context of global permafrost warming.

The complicated heterogeneity and discontinuity of soil-rock mixture (SRM) usually cause high variability in SRM's creep characteristics, which can easily cause geological disasters (e.g., landslides) under harsh environment such as freeze-thaw (F-T) cycles. However, the nonlinear creep behaviors of SRM material, under varying internal structures induced by F-T cycles, skeleton changes and stress states, have not been reported and it is still challenging to describe these complicated creep behaviors using current existing creep models. Therefore, direct shear creep tests were carried out to study the creep evolutions of SRM under various F-T cycles (0 to 15 cycles) and rock contents (15% to 55%). A new element combination creep model was then proposed to describe SRM's nonlinear creep behaviors involving the instantaneous elastoplastic and viscoelastic-plastic deformations. Results showed that the creep deformation tended to decrease as the rock content increased. The initial 3 to 5 F-T cycles significantly affected the creep behaviour of SRM. The proposed new creep model could well describe the nonlinear creep behaviors of SRM material under different stress states.

Freeze-thaw (F-T) weathering can alter the geometry of soils and rocks, imposing severe damage to the Earth's surface. However, it has the potential to favor the beneficiation of mineral resources. In this study, we simulated F-T weathering cycles on the graphite ore from Luobei, a seasonally frozen region in China. The deterioration of the graphite ore caused by F-T weathering was characterized by various means, including the P-wave velocity test, uniaxial compression test, optical microscope, and micro X-ray CT. The results showed that the emergence and propagation of surface defects and cracks in the graphite samples under F-T weathering resulted in weakened mechanical properties of the samples. Moreover, comminution and flotation tests indicated that F-T weathering also amplified the selective liberation between graphite and gangue minerals during crushing and grinding, which contributed to improved separation efficiency and flotation recovery of graphite with significantly reduced chemical usage and energy input. Our study offers a promising strategy for improved and more costefficient beneficiation of graphite ores in cold regions where natural F-T weathering occurs.