Water migration behavior is the main cause of engineering disasters in cold regions, making it essential to understand its mechanisms and the resulting mechanical characteristics for engineering protection. This study examined the water migration process during soil freezing through both experimental and numerical simulations, focusing on the key mechanical outcomes such as deformation and pore water pressure. Initially, a series of controlled unidirectional freezing experiments were performed on artificial kaolin soil under various freezing conditions to observe the water migration process. Subsequently, a numerical model of water migration was formulated by integrating the partial differential equations of heat and mass transfer. The model's boundary conditions and relevant parameters were derived from both the experimental processes and existing literature. The findings indicate that at lower clay water content, the experimental results align closely with those of the model. Conversely, at higher water content, the modeled results of frost heaving were less pronounced than the experimental outcomes, and the freezing front advanced more slowly. This discrepancy is attributed to the inability of unfrozen water to penetrate once ice lenses form, causing migrating water to accumulate and freeze at the warmest ice lens front. This results in a higher ice content in the freezing zone than predicted by the model, leading to more significant freezing expansion. Additionally, the experimental observations of pore water pressure under freeze-thaw conditions corresponded well with the trends and peaks projected by the simulation results.

Long-term freeze-thaw cycles have a significant impact on the safety and durability of tunnels located in cold regions. In this study, a hydro-thermal-mechanical coupling model and calculation method were developed based on the Guanjiaoshan Tunnel. The model's precision and rationality underwent comprehensive validation. The study aimed to discuss the temporal and spatial distributions of temperature, water, and mechanical fields under long-term freeze-thaw cycles. The findings revealed that the water migration influence zones can be classified into three distinct zones. The ice-water phase change and stress exhibit periodic fluctuations following an annual cycle. Significantly, the lining's stress, or danger level, exhibited two peaks during the autumn and spring seasons. The magnitude of the autumn peak exceeded that of the spring peak. Throughout the initial 12year period, the tunnel's danger level consistently remained below the threshold value of 1.0, affirming its adherence to safety standards during its early service period. Furthermore, the construction of tunnels has the potential to contribute to frozen soils expansion in specific zones due to prolonged freeze-thaw cycles. These study results not only enhance our understanding of hydro-thermal variations but also provide valuable insights for predicting the long-term security performance of tunnels in cold regions.

Alpine permafrost environments are highly vulnerable and sensitive to changes in regional and global climate trends. Thawing and degradation of permafrost has numerous adverse environmental, economic, and societal impacts. Mathematical modeling and numerical simulations provide powerful tools for predicting the degree of degradation and evolution of subsurface permafrost as a result of global warming. A particularly significant characteristic of alpine environments is the high variability in their surface geometry which drives large lateral thermal and fluid fluxes along topographic gradients. The combination of these topography-driven fluxes and unsaturated ground makes alpine systems markedly different from Arctic permafrost environments and general geotechnical ground freezing applications, and therefore, alpine permafrost demands its own specialized modeling approaches. In this work, we present a multi-physics permafrost model tailored to subsurface processes of alpine regions. In particular, we resolve the ice-water phase transitions, unsaturated conditions, and capillary actions, and account for the impact of the evolving pore space through freezing and thawing processes. Moreover, the approach is multi-dimensional, and therefore, inherently resolves the topography-driven horizontal fluxes. Through numerical case studies based on the elevation profiles of the Zugspitze (DE) and the Matterhorn (CH), we show the strong influence of lateral fluxes in 2D on active layer dynamics and the distribution of permafrost.

This article presents experimental results and analysis of change in freezing characteristics of clays and silts with change in pH and moisture content in the pore structures. The plastic and non-plastic silts and clays in the cold regions undergo significant changes in thermal properties causing non-equilibrium thermal conditions which can lead to frost-heave, thaw-weakening, thawing-induced landslides, and mass wasting events. In geotechnical engineering, particularly in cold regions, a soil's thermal properties play a large role in the design, functionality, and longevity of an earthen structure. The thermal properties of the soil will also govern the porous media phase changes influencing thermal hysteresis and heat capacity in soils. These variables will change with seasonal freeze-thaw cycles, which can lead to changes in a soil's structure, fabric, density, moisture content, and strength over time. With global warming causing the temperatures to gradually rise over time, the rapidly varying seasonal freeze-thaw cycles are now becoming an issue in areas where the designs have relied heavily on the permafrost. This research study investigates the fundamental changes to freezing and thawing characteristics of plastic and non-plastic silts with changes in frost penetration rates (cooling rate); moisture content (liquid limit, plastic limit, and optimum moisture content); pH (2-7); and soil type with different percentages of fines content and specific surface area.