Cold Regions Science and Technology最新文献

Frost heave poses a serious hazard to geotechnical engineering. However, conventional experimental and theoretical methods, which have limitations in accurately describing the deformation behavior of soils during frost heave, struggle due to the nonlinear and uncertain nature of the process. For this reason, the study leverages the advantages of the Generalized Regression Neural Network (GRNN) in handling nonlinear problems and small sample datasets. The structure of the GRNN model is further optimized using the Particle Swarm Optimization algorithm (PSO) and K-fold Cross Validation (K). The input variables for the model include water content (W), temperature (T), dry density (ρ), and plasticity index (I_p) under various working conditions. The frost heave rate (η) is considered as the output variable. Meanwhile, the model also considers the effects of both one-factor and two-factor interactions among the input variables on frost heave behaviors. Finally, a prediction model for η based on the K-PSO-GRNN is established. The results demonstrate that the K-PSO-GRNN model exhibits greater robustness and stability in predicting η compared to PSO-GRNN and GRNN (R² = 0.94, MAE = 0.14), and the prediction residuals for η range from 0 to 0.4. Among these variables, W has the most significant influence on η, followed by T, ρ, and I_p. Moreover, both ρ and I_p have significant interactions with T and have a notable impact on the soil's frost heave behavior. At high ρ, the soil shows reduced sensitivity to frost heave in response to changes in T, while at high I_p, the soil becomes more sensitive to frost heave with changes in T. η generally shows a positive correlation with W and ρ, and a negative correlation with T. The aforementioned K-PSO-GRNN model can be utilized for predicting η, which is valuable in forecasting non-uniform deformation hazards caused by frost heave and studying preventive measures.

The theoretical and experimental studies have been carried out on the water and salt migration and deformation characteristics of sulfate saline soil during freeze-thaw cycles. Based on the theory of unsaturated soil mechanics and the thermoelastic continuum and considering the influence of phase change within the pore on thermodynamic and hydrodynamic parameters, the multi-physical fields coupled model of hydro-thermal-salt-mechanical in unsaturated sulfate saline soil has been established. The variation processes of the temperature field, water field, salt field, and stress field of the soil during freeze-thaw cycles were analyzed, and the validity of the theoretical model was verified by indoor experiments. The results show that there are significant attenuation and hysteresis effects when heat is transferred in the soil during freeze-thaw cycles. The water content of migration in the soil increases with the height of the soil column, while the increment of migration water content decreases with the number of freeze-thaw cycles. The formation and dissolution of salt crystals from top to bottom and the sudden increase in the salt crystallization rate are mainly caused by variations in the solubility of the salt solutions due to temperature changes. The formation and dissolution of ice and salt crystals in the soil induce expansion and contraction, and the freeze-thaw cycle conditions have a significant effect on the expansion and residual deformation of the soil.

Ice shedding on conductors of transmission lines can induce severe vertical vibrations and abrupt tension changes, potentially causing structural damage and power outages. Prior experiments and numerical simulations assumed that ice sheds instantaneously from transmission lines, neglecting the practical delays in the ice shedding process, which resulted in unrealistic conductor dynamic responses. This study introduces a reduced-scale modeling system designed to simulate delayed ice shedding on conductors. The jump height and dynamic tension of an isolated-span transmission line following delayed ice shedding are analyzed, and various factors such as the two-dimensional delay duration, shedding sequence, and weight of ice accretion are examined through reduced-scale model tests. Based on the experimental data, simplified formulas are proposed to calculate the conductor's jump height and maximum tension after ice shedding by taking the time delay of the shedding process into account.

As the temperature decreases, when the freezing temperature is reached, the solution in the pores of saline soil undergoes ice crystallization and salt crystallization phenomena. Theoretical and experimental studies have been carried out in order to investigate the behaviour of water-salt phase transitions within the pores of saline soils. Firstly, the theoretical expression for the initial crystallization radius is given from the thermodynamic theory by considering the interphase chemical potential equilibrium and the Young-Laplace equation, and the relationship between the initial crystallization radius and temperature as well as the initial salt content is analyzed. Then, a theoretical model to predict the pore solution content and crystal content was developed in conjunction with the Van Genuchten soil-water characteristic curve model, and the water-salt phase transition behaviour of saline soils was analyzed by numerical calculations. Finally, the validity of the theoretical model was verified by a saline soil freezing test. The results show that the water-salt phase transition behaviour of the solution within the pores of saline soils is affected by temperature and initial salt content, and the water-salt phase transition behaviour mainly occurs at the early stage of freezing. Salt lowers the freezing temperature of the soil; the higher the salt content, the lower the freezing temperature, and the presence of salt inhibits the growth of ice crystals. As the temperature decreases, the precipitation of ice salt crystals during the phase transition of the soil pore solution reduces the soil porosity and decreases the channels for ion migration, resulting in a gradual increase in the soil pore volume ratio.

Maritime operations are impacted by ice accretion on decks, bulkheads, and offshore structures during the winter or in extremely frigid climates. In most cases, the traditional method of deicing maritime vessels is human labor, which requires enormous effort and lengthy hours for unsatisfactory results, particularly when the ice adhesion strength is high. This study experimentally examined combined effects of operational parameters, including operating pump pressure, nozzle geometry, water jet temperature, standoff distance, and time of cut, on the depth and width of a cut through an ice block. In comparison to other parameters, the influence of nozzle geometry on both the width and depth of cut was found to be more significant, with R-squared values of 85% and 62% respectively. Increasing the depth and width of the cut facilitated the delamination and disintegration of ice from an aluminum mold. This indicates that water jet deicing on maritime vessels could be effective, therefore achieving the objective of this study. The optimization of operational parameters is used to develop a cuttability chart for various thicknesses of accumulated ice on marine vessels.

Thaw settlement of soils is a comprehensive reflection of multiscale pore changes induced by freeze-thaw (F-T). In this study, three-dimensional (3D) X-ray computed tomography (CT) tests were utilized to investigate alterations in the macropore and mesopore structures, while mercury intrusion porosimetry (MIP) tests were used to examine the micropore structure in clay due to F-T influenced by different freezing temperatures without water supply. The maximum increase in CT transverse-sectional porosity after F-T can be used to identify where ice lenses formed most abundantly in the clay after thawing, and the diameter and horizontal orientation of the macropores exhibit the most significant increase after thawing. As the freezing temperature decreases, the location becomes farther from the cold end. Macropores are significantly more affected by F-T compared to mesopores, and changes in macropore porosity and diameter can be attributed to moisture migration and freezing shrinkage, with lower freezing temperatures amplifying the influence of freezing shrinkage and weakening the impact of moisture migration. Considering the small size of samples, the MIP porosity was defined to analyze the effects of F-T on the micropores. Compared to the CT volumeratic porosity, the influence of F-T on micropore porosity is less significant. As the freezing temperature decreases, the changes in micropore diameter become smaller. Overall, the lower the freezing temperature, the smaller the changes in macropores, mesopores and micropores. Lastly, a method is proposed for predicting the mass porosity based on the CT volumetric porosity and MIP porosity. This study demonstrates that changes in soil mass porosity reflect a comprehensive representation of multiscale pore variations and provides important theoretical support for thaw settlement control in artificial freezing engineering.

The geogrid-soil interface characteristic is a critical factor influencing the behavior of reinforced soil structures. In seasonal frozen regions, the shear strength of the geogrid-soil interface fluctuates periodically with temperature, necessitating consideration of freeze-thaw cycle effects during engineering design. In this study, a series of large-scale direct shear tests were conducted to investigate the geogrid-sand interface behavior under different freeze-thaw cycles. The mechanism of the evolution and variation of the geogrid-sand interaction was discussed based on test results and the associated mesoscopic analysis. The results indicate that freezing enhances the shear strength of the geogrid-sand interface, whereas freeze-thaw cycles reduce the geogrid-sand interface shear stress. The cohesion and friction angle of the geogrid-sand interface decreased as the number of freeze-thaw cycles increased, but tended to stabilize after several freeze-thaw cycles. The influence of freeze-thaw cycles on the tensile strength and elongation of the geogrid was insignificant. Internal changes in sand during freeze-thaw cycles were considered as the key issue that led to the deterioration of the geogrid-sand interface. Furthermore, considering the interface cohesion and normal stress, the influence of freeze-thaw cycles on the interaction coefficient k between geogrid and soil was analyzed, which is referable for the design and application of reinforced soil engineering in cold regions under similar conditions.

Despite substantial research on stabilizing sulfate saline soil, the behavior of post-stabilization pure salt expansion remains unclear. Understanding this behavior is essential because it can lead to soil degradation, potentially undermining the stability and lifespan of constructed infrastructure. To investigate the pure salt expansion and process of solidified and non-solidified sulfate saline soil under negative temperature, single-cycle cooling test, freeze-thaw cycles test were carried out. Various Na₂SO₄ content (i.e., 0.3%, 1%, 2%, 3.5%, and 5%) and c(NaCl) / c(Na₂SO₄) ratio (i.e., 0, 0.6, 1.2, and 2.0) were considered. Scanning electron microscope (SEM) observations and mercury intrusion porosimetry (MIP) were employ to analyze the pore structures and quantitatively characterize the multi-scale micropores. Results indicated that during a single-cycle cooling, the salt expansion of solidified saline soil was significantly smaller than that of non-solidified saline soil, with the difference reaching up to 36.4 times. After three freeze-thaw cycles at a Na₂SO₄ content of 2%, the final average salt expansion of solidified saline soil was only 41.8% of that in non-solidified saline soil. Under the same salt content, solidified saline soil had smaller and more evenly distributed pores. The proportion of small pores below 1 μm was 37.1%, 4.5 times higher than in non-solidified saline soil. Solidified saline soils with higher Na₂SO₄ content or chlorine-sulfate ion ratio had a greater proportion of large and small pores. Solidified saline soils with 3.5% Na₂SO₄ content had a proportion of pores above 100 μm as high as 23%. The research findings will serve as a reference for controlling salt expansion disease and facilitating engineering construction in sulfate saline soil areas.

Currently, there are very few investigations on the unfrozen water content of contaminated soil due to heavy metals. This will have an impact on the efficacy and use of freezing technology in the remediation of heavy metal-contaminated soil. Thus, the purpose of this research is to determine the unfrozen water content and contributing factors of heavy metal-contaminated loess. As a result, Lanzhou loess was employed as an experimental material to produce contaminated soil with varied initial water content and heavy metal concentrations. Additionally, Zn, Ni, Cu, Cr, Cd, and Pb were used as pollution elements. The findings indicate that: 1) Unfrozen water content of loess with heavy metal ions underwent three processes: severe phase transition, transition stage, and freezing stage; 2) Effects of different heavy metal ions on the amount of unfrozen water in loess are as follows: Cu > Cr > Pb > Cd > Ni > Zn when levels are low. Effects of different heavy metal ions on the amount of unfrozen water in loess are as follows: Cu > Zn > Cr > Ni > Pb > Cd when levels are high; 3) The prediction model of unfrozen water content in the loess polluted by heavy metals was established as follows: w_u = aT^–b. This will help the remediation and management of heavy metals in urban contaminated soil in the future by freezing technology.

Compacted snow runways for heavy wheeled aircraft are challenging in polar regions and possible extraterrestrial infrastructure constructions. A finite element method was successfully employed to simulate a wheel landing on layered snow using the ABAQUS software package based on the Phoenix runway in Antarctica. First, the method was validated with theoretical results of several layered systems. Thereafter, basic parameters of snow were chosen with reference to the Phoenix runway's pavement. Stress distributions under landing gear were calculated for the C17, A319, B757 and Il-76 aircraft. Furthermore, the effect of subgrades on stress distributions were discussed. This study explores current knowledge on snow pavements and provides technical support for the design and construction of compacted snow runways.