Freeze-thaw cycles in seasonally frozen soil affect the boundary conditions of aqueducts with pile foundations, consequently impacting their seismic performance. To explore the damage characteristics and seismic behaviour of aqueduct bent frames in such regions, a custom testing apparatus with an integrated cooling system was developed. Two 1/15 scale models of reinforced concrete aqueduct bent frames with pile foundations were constructed and subjected to pseudo-static testing under both unfrozen and frozen soil conditions. The findings revealed that ground soil freezing has minimal impact on the ultimate bearing capacity and energy dissipation of the bent frame-pile-soil system, but significantly enhances its initial stiffness. Additionally, the frozen soil layer exerts a stronger embedding effect on the pile cap, ensuring the stability of the pile foundation during earthquakes. However, under large seismic loads, aqueduct bent frames experience greater damage and residual deformation in frozen soil compared to unfrozen soil conditions. Therefore, the presence of a seasonally frozen soil layer somewhat compromises the seismic performance of aqueduct bent frames. Subsequently, a finite element model considering pile-soil interaction (PSI) and frozen soil hydro-thermal effects was developed for aqueduct bent frames and validated against experimental results. This provides an effective method for predicting their seismic behaviors in seasonally frozen soil regions. Furthermore, based on the seismic damage characteristics of aqueduct bent frame with pile foundations observed in pseudo-static tests, a novel selfadaptive aqueduct bent frame system was designed to mitigate the adverse effects of seasonally frozen soil layer on seismic performance. This system is rooted in the principle of balancing resistance with adaptability, rather than solely depending on resistance. The seismic performance of this innovative system was then discussed, providing valuable insights for future seismic design of reinforced concrete aqueduct bent frames with pile foundations in seasonally frozen soil regions.

In seasonally frozen areas, freezing of topsoil is detrimental to the seismic response of bridge substructures and may cause bridge damage. In order to counter this problem, this paper proposes the use of a temperature-insensitive composite material (PolyBRuS) to replace the soil around the with the aim of preventing seismic damage brought about by the seasonally frozen soil, which is named as the replacement method. Firstly, a three-dimensional finite element model was built based on the model tests, and the results of the model tests were used for verification and calibration. Secondly, based on the finite element model, a time-history analysis of the seismic response of the bridge substructure was carried out to explore the nonlinear seismic response of the bridge foundation in different seasons and with or without replacement conditions. The result of numerical simulations showed that frozen soil significantly reduced the extent of the plastic zone of the soil under seismic loading and affected the seismic response of the bridge substructure, including an increase of foundation acceleration (19% increase), a decrease of foundation displacement (32% decrease), and an increase of foundation bending moment (10% increase). Notably, it can be found that the replacement method can reduce the seismic acceleration, increased column deformation (21% increase), and reduced column bending moment of the winter bridge foundations (9% decrease), consequently reducing the risk of seismic damage to the bridge substructure. Meanwhile, the compressive stress and compressive strain characteristics of the PolyBRuS material on the column side under seismic action are similar to those of unfrozen soil in summer. Above all, the adverse effects of surface freezing on bridge substructures can be effectively mitigated by the replacement method, and the bridge foundations will have similar seismic responses in winter and summer. This achievement has practical application prospects and is expected to provide a new seismic strategy for bridge engineering in seasonally frozen soil areas.

Frost damage on infrastructure in seasonally frozen regions is mainly caused by the coupled water-heat transfer during freeze-thaw processes. Because of complex geological deposition and weathering, the properties of seasonally frozen soil are spatially variable. In this study, based on random field theory, heat transfer process, and frozen soil physics, a water-heat coupling model is developed to explore the impact of non-uniform thermal parameters on soil water-heat behavior. The statistical characteristics of the water-heat behavior and frozen depth of a slope are analyzed. The simulation results show that the water-heat coupling process of the soil exhibits obvious seasonal differences. The uncertainty in thermal conductivity has a greater effect on soil waterheat state than the uncertainty in volumetric heat capacity. The maximum frozen depth (MFD) from the traditional deterministic analysis is slightly smaller than the mean value of analysis result considering the nonuniformity of thermal parameters; as such, the deterministic analysis is likely to underestimate the MFD, which may result in local frost damage to infrastructure in cold regions. To ensure the safety of infrastructure in cold regions, the most unfavorable conditions need to be considered, and the upper bound of the MFD based on the random analysis can serve as the guideline for frost protection design.

The presence of frozen soil layers leads to stratification in soil stiffness, thereby influencing the dynamic response of pile foundations in seasonally frozen soil regions. This study investigated the dynamic response of pile-soil interaction (PSI) systems in such regions. A reduced-scale (1/10) model of a pile group with an elevated cap in railway bridges was subjected to shake-table testing. During these tests, measurements were taken of soil and pile accelerations, displacement time histories, and pile strain. The acceleration amplification factor (AMF) and response spectrum of the soil and pile foundation were analyzed based on these data. Additionally, the pile-soil interaction and the dynamic shear stress-strain relationship of the soil were investigated. The experiment indicated that the presence of a frozen soil layer alters the energy dissipation order of the pile-soil interaction system. This leads to a weakened dynamic response of the pile foundation. Furthermore, the seasonally frozen soil layer acts as a filter for high-frequency ground motion, thereby mitigating resonance between ground motion and the pile foundation, ensuring the protection of the pile foundation. However, the significant stiffness contrast induced by the seasonally frozen soil can pose a threat to structural safety under increasing peak ground acceleration (PGA). As PGA increases, there is a transition from linear to nonlinear interaction between the pile and soil, initially affecting the unfrozen soil layer, then the frozen-unfrozen transition layer, and ultimately impacting the seasonally frozen soil layer.

Frost heave and thawing settlements of seasonally frozen soil have a direct impact on the stability of engineered ground in cold regions. On the basis of the theory of seepage and heat conduction of unsaturated soil, a coupled thermal-hydro-mechanical numerical model of frozen soil was established. The alignment of experimental testing outcomes with numerical simulation results confirms the model's precision. The research findings indicate that the duration of freezing emerges as the primary factor influencing seasonal frost heave, with the soil frost heave rate ranging from approximately 1.5% to 3.3%. Within a period of 45 to 60 days following the conclusion of the freezing period, the ground height will return to its pre-freezing level. Construction of foundations in Daqing between late May and mid-October can help mitigate the damage caused by frozen soil. The variation laws of hydrothermal migration and frost heave in seasonally frozen soil have been summarized. The obtained results offer guidance for predicting soil frost heave and designing frost-heaving-sensitive engineering projects in cold regions.

Seasonally frozen soil (SFS) is a critical component of the Cryosphere, and its heat-moisture-deformation characteristics during freeze-thaw processes greatly affect ecosystems, climate, and infrastructure stability. The influence of solar radiation and underlying surface colors on heat exchange between the atmosphere and soil, and SFS development, remains incompletely understood. A unidirectional freezing-thawing test system that considers solar radiation was developed. Subsequently, soil unidirectional freezing-thawing tests were conducted under varying solar radiation intensities and surface colors, and variations in heat flux, temperature, water content, and deformation were monitored. Finally, the effects of solar radiation and surface color on surface thermal response and soil heat-moisture-deformation behaviors were discussed. The results show that solar radiation and highabsorptivity surfaces can increase surface heat flux and convective heat flux, and linearly raise surface temperature. The small heat flux difference at night under different conditions indicates that soil ice-water phase change effectively stores solar energy, slowing down freezing depth development and delaying rapid and stable frost heave onset, ultimately reducing frost heave. Solar radiation causes a significant temperature increase during initial freezing and melting periods, yet its effect decreases notably in other freezing periods. Soil heatwater-deformation characteristics fluctuate due to solar radiation and diurnal soil freeze-thaw cycles exhibit cumulative water migration. Daily maximum solar radiation of 168 W/m(2) and 308 W/m(2) can cause heatmoisture fluctuations in SFS at depths of 6 cm and 11 cm, respectively. The research findings offer valuable insights into the formation, development, and use of solar radiation to mitigate frost heave in SFS.

Global warming has caused changes in the area and thickness of permafrost on the Qinghai-Tibet Plateau and prompted the transition from permafrost to seasonally frozen soil, which has affected the soil moisture, soil temperature, and distribution of plant roots. This, in turn, affects grassland vegetation productivity and aboveground/belowground biomass. In this study, we took Qinghai Province in the northeastern Qinghai-Tibet Plateau as the research area to model the spatial pattern of grassland biomass and then evaluated the potential influence of frozen soil type information on aboveground and belowground biomass. Our research shows that there are significantly more biomass observations in seasonally frozen soil regions than in permafrost regions. However, when we ignore the type of frozen soil, the model does not show more accurate simulation in seasonally frozen soil regions, mainly because the stronger correlation between permafrost biomass and environmental factors, such as precipitation, compensates for the lack of observational data. In addition, we found that the biomass estimation error can be reduced significantly by building different models for each type of frozen soil, which implies that the type of frozen soil has an important impact on grassland biomass. Therefore, in considering the effects of future climate warming, more attention should be given to the impact of changes in frozen soil type on regional vegetation productivity. In addition, our investigation contributes a benchmark dataset of above- and belowground vegetation carbon storage in different frozen soil types, which provides the research community with useful information for optimizing process-based carbon cycle models.

In recent years, with the global warming, the unfrozen water content of permafrost slope increases year by year. The decrease of slope stability is a great threat to the engineering construction in permafrost area. In this study, the south piedmont slope of Bayan Kara Mountain is taken as the research object. Through the field water and temperature monitoring of different positions and depths of the slope, the seasonal and interannual water change characteristics of the slope were analyzed. Combined with indoor shear strength test, numerical simulation and monitoring data, the moisture, temperature and stability of frozen soil slope in spring thawing period were analyzed. The analysis results show that: Water content and freeze-thaw cycles have great influence on the shear strength parameters at the interface. The slope moisture change in the region is divided into four stages, the water decline stage, the low water content stage, the water rise stage and the high water content stage. The freeze-thaw cycle and precipitation are the main reasons for the water change in each stage. From the middle of May to the middle of June is the high risk period of slope instability. The spring thaw landslide is dominated by shallow surface landslide, and the sliding surface is shallow.

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.