Horizontal frost heave disasters frequently occur in cold-region engineering projects, making it essential to understand water migration mechanisms along horizontal directions during freezing processes. Using a selfdeveloped one-dimensional visualization horizontal freezing apparatus, unidirectional horizontal freezing tests were conducted on soft clay under varying temperature gradients, and the development process of the cryostructures was continuously observed. The results indicate that the thermal-hydraulic processes, including temperature evolution, water content variation, pore-water pressure dynamics, and soil pressure changes, demonstrate similarities to vertical freezing patterns, with temperature gradients primarily influencing the magnitude of parameter variations. Under the influence of gravity, the freezing front forms an angle with the freezing direction, attributed to differential freezing rates within soil strata. Post-freezing analysis showed dualdirectional water redistribution (horizontal and vertical), with horizontal migration dominating. Maximum water content was observed 1-3 cm from the freezing front. Distinct cryostructures formed in frozen zones were identified as products of tensile stresses generated by low-temperature suction and crystallization forces. The study highlights the coupling of water transfer, thermal changes, mechanical stresses, and structural evolution during freezing and suggests that water migration and cryostructure formation are interrelated processes. This research provides robust experimental evidence for advancing the theoretical framework of horizontal water migration mechanisms in frozen soil systems.

There are many types of lenses in tailings ponds that have important influences on stability. Lens types of more than 150 tailings dams were analyzed in China's severely cold regions, cold regions, hot summers and cold winters (the civil building thermal design code (GB50176-2016)). The mechanism of lens formation is discussed in this paper. Triaxial tests of tailings were carried out with fine mud tailing lenses, notched lenses, ice lenses and soft plastic soil lenses. Moreover, a three-dimensional triaxial test model with a flexible boundary is constructed to study the influence of different lenses on the mechanical properties of the tailings. The lens can change the failure mode of the tailings. These faults can change the dilatancy failure of tailings to failure along the lens-tailings interface. With increasing confining pressure, the ability of the lens to weaken the strength of the tailings increases. At 500 kPa, the strengths of the samples with fine mud tailing lenses, notched lenses, ice lenses and soft plastic soil lenses are 95.28%, 88.79%, 76.99% and 5.49%, respectively, of those of the sample without lenses. In addition to soft plastic soil lenses, other lenses provide space to accommodate the deformation of tailings, thereby reducing the bulk strain of tailings. The conclusions of this study can provide theoretical support for studying the failure mode of tailings dams under the influence of lenses and improving the local stability of tailings ponds.

The criterion of ice lens initiation is a critical mechanical property that is essential for investigating the interactions between water and heat transport mechanisms in frost heave studies. Owing to the complexity of the ice lens initiation phenomenon, the criterion of ice lens initiation varies depending on different theoretical models, which makes uniform evaluation difficult. To investigate the intricate physical mechanism of the ice formation criterion, a unified theoretical model is proposed to simulate the ice formation process of four commonly used criteria (the neutral stress criterion, unfrozen water film criterion, pore ice pressure criterion and empirical water content criterion). The physical mechanisms of the different assessments are investigated by studying the frost heave, ice lens distribution and frost heave rate for four different soil properties. The results indicate that the neutral stress criterion is more accurate and stable for ice formation than the current wellestablished criterion for ice lens initiation. Furthermore, the study reveals significant similarities between the pore ice pressure and the unfrozen water film. The empirical water content is prone to significant errors because of the absence of a reliable physical basis.

Frost heaving in soils is a primary cause of engineering failures in cold regions. Although extensive experimental and numerical research has focused on the deformation caused by frost heaving, there is a notable lack of numerical investigations into the critical underlying factor: pore water pressure. This study aimed to experimentally determine changes in soil water content over time at various depths during unidirectional freezing and to model this process using a coupled hydrothermal approach. The agreement between experimental water content outcomes and numerical predictions validates the numerical method's applicability. Furthermore, by applying the Gibbs free energy equation, we derived a novel equation for calculating the pore water pressure in saturated frozen soil. Utilizing this equation, we developed a numerical model to simulate pore water pressure and water movement in frozen soil, accounting for scenarios with and without ice lens formation and quantifying unfrozen water migration from unfrozen to frozen zones over time. Our findings reveal that pore water pressure decreases as freezing depth increases, reaching near zero at the freezing front. Notably, the presence of an ice lens significantly amplifies pore water pressure-approximately tenfold-compared to scenarios without an ice lens, aligning with existing experimental data. The model also indicates that the cold-end temperature sets the maximum pore water pressure value in freezing soil, with superior performance to Konrad's model at lower temperatures in the absence of ice lenses. Additionally, as freezing progresses, the rate of water flow from the unfrozen region to the freezing fringe exhibits a fluctuating decline. This study successfully establishes a numerical model for pore water pressure and water flow in frozen soil, confirms its validity through experimental comparison, and introduces an improved formula for pore water pressure calculation, offering a more accurate reflection of the real-world phenomena than previous formulations.

A characteristic of frozen ground is a tendency to form banded sequences of particle-free ice lenses separated by layers of ice-infiltrated soil, which produce frost heave. In permafrost, the deformation of the ground surface caused by segregated ice harms engineering facilities and has considerable influences on regional hydrology, ecology, and climate changes. For predicting the impacts of permafrost degradation under global warming and segregated ice transformation on engineering and environmental, establishing appropriate mathematical models to describe water migration and ice behavior in frozen soil is necessary. This requires an essential understanding of water migration and segregated ice formation in frozen ground. This article reviewed mechanisms of water migration and ice formation in frozen soils and their model construction and introduced the effects of segregated ice on the permafrost environment included landforms, regional hydrological patterns, and ecosystems. Currently, the soil water potential has been widely accepted to characterize the energy state of liquid water, to further study the direction and water flux of water moisture migration. Models aimed to describe the dynamics of ice formation have successfully predicted the macroscopic processes of segregated ice, such as the rigid ice model and segregation potential model, which has been widely used and further developed. However, some difficulties to describe their theoretical basis of microscope physics still need further study. Besides, how to describe the ice lens in the landscape models is another interesting challenge that helps to understand the interaction between soil ice segregation and the permafrost environment. In the final of this review, some concerns overlooked by current research have been summarized which should be the central focus in future study.