Amid global climate change, freeze-thaw cycles in cold regions have intensified, reducing the stability of infrastructures and significantly increasing the demand for grouting reinforcement. However, the deterioration in the durability of existing grouting materials under the combined effects of freeze-thaw cycles and low temperatures has become a major technical bottleneck restricting their application in cold regions. This paper focuses on polyurethane (PU) grouting materials with foaming and lifting characteristics, systematically reviewing the research progress and technical challenges associated with their engineering applications in cold regions. First, in terms of material composition and preparation, the core components and modified additives are detailed to establish a theoretical foundation for performance regulation. Second, addressing the application requirements in cold regions, standardized testing methods and comprehensive evaluation systems are summarized based on key indicators such as heat release temperature, impermeability, diffusion properties, mechanical strength, and expansion properties. Combined with microstructural characteristics, the deformation behavior and failure mechanisms of PU grouting materials under freeze-thaw cycles and salt-freezing environments are revealed. At the engineering application level, the challenges faced by PU grouting materials in cold regions-such as inhibited low-temperature reactivity and insufficient long-term durability-are highlighted. Finally, considering current research gaps, including the unclear mechanisms of microscopic dynamic evolution and the lack of studies on the combined effects of complex environments, future research directions are proposed. This paper aims to provide theoretical support for the development and application of PU grouting materials in cold-region geotechnical engineering.

As an innovative technology, transparent soil similar material can actively promote the development of soil model experiments by clarifying the structure, ratio, and strength characteristics. In order to study the factors affecting the mechanical properties of transparent soil materials, fused quartz is chosen as the aggregate material, nano-scale hydrophobic fumed silica is used as the binder, and a mixture of dodecane and No. 15 white oil is employed as the constituent material for transparent soils. In this study, indoor direct shear tests are conducted, and the range method is used to analyze the factors of quartz particle size, binder content and proportion, moisture content and dry density of the mixture solution. The relationship between the strength properties of transparent soil material and the above variables are quantitatively investigated. The results show that the transparent soil similar material can exhibit softening or hardening properties by changing the proportion of influencing factors, which can be suitable to most soils. Dry density has the most significant impact on cohesion while particle size of quartz has the greatest influence on the internal friction angle. The strength parameter of transparent soil has exponential distribution relationship with moisture content and linear distribution relationship with dry density. The cohesion and powder content are distributed exponentially while the internal friction angle and powder content are linearly distributed. As the particle size of quartz increases, the cohesion decreases overall and the internal friction angle increases. The strength parameters of transparent soil have a logarithmic distribution relationship with the unevenness coefficient of particle size and a linear relationship with the curvature coefficient of particle size. This study has established a quantitative control relationship between the key parameters of transparent soil materials and their mechanical properties. The revealed correlations between gradation of particles and strength parameters can serve as a guideline for simulation and visualization techniques based on transparent soils. It is of great significance for the visualization of the evolution mechanisms of geotechnical disasters.