Journal of Cold Regions Engineering

In this study, the thaw consolidation properties of fine-grained permafrost soils are investigated in terms of the characteristics of the relationships between the effective stress (${\sigma }_v^{\mathrm{\prime }}$), the void ratio (e), and the hydraulic conductivity (k_v). A total of 182 individual soil samples are included in the analysis covering a wide range of hydromechanical properties. The data are obtained from geotechnical studies undertaken for the Canadian Arctic Gas Pipeline project in the 1970s in the Mackenzie River Valley, Canada. The investigated characteristics are defined in agreement with the definition formulated by previous thaw consolidation models for fine-grained soils. Based on the general interpretation of the behavior of thawing soils, relationships are developed for the compression index of the thawed soil, the residual stress, the hydraulic conductivity change index of the thawed soil, and the initial hydraulic conductivity of the thawed soil. All properties are influenced by the ice content, which is characterized by the initial thawed void ratio for ice-rich soils and by the thawed void ratio for ice-poor soils. The liquid limit, the clay content, and the median grain size of the fine fraction are used as predictive parameters in combination with the initial ice content. The median grain size of the fine fraction yields the lowest error for the prediction of the characteristics of the ${\sigma }_v^{\mathrm{\prime }}-e-k_v$ relationships.

Abstract

We experimentally demonstrate the presence of a capillary bridge in the contact between an ice particle and a smooth aluminum surface at a relative humidity of approximately 50% and temperatures below the melting point. We conduct the experiments in a freezer with a controlled temperature and consider the mechanical instability of the bridge upon separation of the ice particle from the aluminum surface at a constant speed. We observe that a liquid bridge forms, and this formation becomes more pronounced as the temperature approaches the melting point. We also show that the separation distance is proportional to the cube root of the volume of the bridge. We hypothesize that the volume of the liquid bridge can be used to provide a rough estimate of the thickness of the liquid layer on the ice particle since in the absence of other driving mechanisms, some of the liquid on the surface must have been pulled to the bridge area. We show that the estimated value lies within the range previously reported in the literature. With these assumptions, the estimated thickness of the liquid layer decreases from nearly 56 nm at T = −1.7°C to 0.2 nm at T = −12.7°C. The dependence can be approximated with a power law, proportional to (T_M − T)^−β, where β < 2.6 and T_M is the melting temperature. We further observe that for a rough surface, the capillary bridge formation in the considered experimental conditions vanishes.

Practical Applications

Understanding the physics of ice and snow becomes vital as climate change accelerates. Ice exhibits exotic behavior since it is near its melting point. A liquid layer is present on ice surfaces, which is responsible for phenomena like the sticking of ice particles. Complex experiments using for example advanced laser-based methods or advanced molecular dynamics calculations have previously been used to estimate the thickness of this liquid layer. Here, we observe the formation of liquid bridges between ice and a smooth surface at temperatures well below the freezing point. We then estimate the thickness of the liquid layer on ice particles from the volume of the liquid bridge and show that it is within the range observed previously. This can help to understand this liquid layer and its relation to surface diffusion more intuitively.

Extreme cold weather conditions affect construction workers’ health and safety performance. Hence, the goal of this article is to identify and analyze these challenges so that effective measures can be developed and implemented to mitigate or eliminate them. To this end, a questionnaire was created and circulated through the online platform QuestionPro. The Kruskal–Walli’s test was used to examine the physical and mental health issues identified by the 111 responders, and quantitative analysis was performed by using physiological indicators such as heart rate and personal indicators, including degree of comfort and acclimation. The results showed that physical obstacles such as hypothermia and respiratory issues were perceived differently based on heart rate and garment comfort; and mental issues, such as poor concentration and frequent mood swings, varied with the workers’ heart rate and level of acclimatization. Some of the strategies developed for protecting the workers are ensuring that they wear sufficient layers of clothing and heated gloves and have access to technologies such as infrared heaters. Existing practices and legislation that control construction “workers” safety in extreme cold weather conditions are also addressed. The findings of this article will help construction industry professionals effectively manage projects while ensuring their workers’ safety in harsh cold weather conditions.

Frost heave, which is related to the variation in the hydrothermal interaction properties of soil, is the main factor causing the inhomogeneous deformation of structures in cold regions. The relevant requirement for describing frost heave is to obtain the soil freezing characteristic curve, which contains fundamental information for describing the hydrothermal behavior of frozen soil. In this study, the unknown parameters of the van Genuchten equation and the hydraulic conductivity of partially frozen soil were indirectly derived using the pulsed nuclear magnetic resonance (P-NMR) technique based on the soil freezing characteristic curve and Clapeyron equation. Based on continuum mechanics, a hydrothermal coupling model combined with the unknown parameters obtained from a P-NMR experiment was applied to quantify the hydrothermal performance of the frozen soil. The mathematical module of COMSOL Multiphysics was employed to solve the coupling equation numerically. To validate the proposed coupling model, water transfer experiments were conducted on silty clay in closed and open systems under freezing conditions in our laboratory. The measured experimental data were consistent with the prediction results, confirming the applicability of the coupling model of the frozen soil in predicting the hydraulic parameters based on the new soil freezing characteristic curve.

In the northern region of China, freeze–thaw cycles and chloride ion (Cl⁻) penetration are the primary factors affecting the durability of marine concrete. To investigate the influence of nanoparticles on the Cl⁻ penetration resistance of marine concrete under the action of freeze–thaw cycles, nano-SiO₂ and nano-Fe₃O₄ were added to plain concrete in different amounts. The Cl⁻ penetration resistance of concrete under the action of freeze–thaw cycles was measured in a 5% NaCl solution. The relative dynamic modulus, mass loss rate, and Cl⁻ content at different depths in concrete were measured to evaluate the salt-scaling resistance. The test results show that under salt freeze–thaw cycles, the relative dynamic modulus, bound Cl⁻ content, and Cl⁻ binding capacity of concrete with nanoparticles were higher than those of plain concrete. However, the mass loss, total Cl⁻ content, and free Cl⁻ content in concrete with nanoparticles were lower than those of plain concrete. With increasing nanoparticle content, the relative dynamic modulus, bound Cl⁻ content, and Cl⁻ binding capacity of the concrete first increased and subsequently decreased. However, the mass loss rate, total Cl⁻ content, and free Cl⁻ content first decreased and subsequently increased. The optimum amount of nano-SiO₂ and nano-Fe₃O₄ in the concrete was 2%. The improvement effect of nano-SiO₂ on the salt-scaling resistance of concrete was superior to that of concrete with the same amount of nano-Fe₃O₄. The addition of nanoparticles can accelerate the formation of hydrated products, enhance the chemical binding capacity and physical adsorption capacity of hydrated products to Cl⁻, and reduce the free Cl⁻ content in concrete. This can improve the Cl⁻ penetration resistance of marine concrete under the action of freeze–thaw cycles. This study provides a reference for the durable design of marine concrete in the northern region.

Abstract

This study investigates the bond behavior of glass aggregate–reinforced concrete (GARC) after freeze–thaw cycles, considering a number of freeze–thaw cycles (10, 20, and 30) and fine aggregate replacement rates (25%, 50%, and 75%) as variable parameters. Sixteen groups of specimens were designed to conduct central pullout tests after freeze–thaw cycles, and the bond–slip curves of each group were plotted. The bond performance of the GARC and its failure mechanism after freeze–thaw cycles were examined by analyzing the failure mode, ultimate bond strength, peak displacement, and bond stiffness. The results indicated that freeze–thaw cycles had a deteriorating effect on the bond performance of GARC. However, under the effect of the same number of freeze–thaw cycles, in comparison with the bonding performance of natural aggregate–reinforced concrete, GARC exhibited a higher resistance to the deterioration effect of freeze–thaw cycles, which was enhanced by increasing the replacement rate. In addition, the optimization effect of glass sand on the bonding properties became increasingly prominent as the freeze–thaw cycle deepened. Therefore, after freeze–thaw cycles, GARC exhibited excellent bonding behavior, and 75% GARC exhibited the best bonding performance. Based on the experimental data, considering the number of freeze–thaw cycles and aggregate replacement rate, the bond–slip constitutive equation of GARC after freeze–thaw conditions was established.

Practical Applications

Glass aggregate–reinforced concrete has excellent resistance to freeze–thaw cycle damage. After freeze–thaw cycles, glass aggregate concrete has better bonding performance with reinforcement than natural aggregate concrete, and the degree of improvement is related to the replacement rate of glass sand. The bond mechanism between the glass aggregate concrete and reinforcement was explained after freeze–thaw cycles. The research results proved the potential capacity and advantages of glass aggregate concrete under a complex environment and demonstrated the research potential of glass aggregate concrete. In addition, this study provided a new approach to improving the resistance of conventional concrete materials to complex environments. By replacing part of the river sand in concrete with glass sand, the resistance of concrete to freeze–thaw cyclic damage could be significantly improved without affecting the mechanical properties of reinforced concrete. This could also effectively address the problem of recycling waste glass and increasing shortage of river sand.

In cold regions, the flow of outside air into a tunnel often causes freeze–thaw damage to the surrounding rock, and insulation methods are usually adopted to avoid this damage. In this study, the heat transfer in a multilayer tunnel structure that includes a rock layer, an initial lining, an insulation layer, and a secondary lining was investigated, and convection between the tunnel air and the inner surface of the tunnel lining was considered. A mathematical model describing the heat transfer process was established, and an analytical solution for the temperature field was developed using Duhamel’s principle and the separation-of-variables method. The model and the solution were verified by comparing the computational results of the analytical solution with the computational results and in situ measurements available in the literature. By treating the minimum temperature of the inner surface of the surrounding rock as a function of the insulation thickness, a procedure to determine the minimum insulation thickness that ensures no freeze–thaw damage to the surrounding rock was developed based on the analytical solution using the bisection method. Computational examples were presented, and the effects of different factors on the minimum temperature of the inner surface of the surrounding rock and minimum insulation thickness were investigated.

Abstract

Maintaining frozen ground stability in the Arctic and sub-Arctic is a continuing challenge, particularly with climate warming. One engineering solution to tackle this problem is the use of thermosyphons, an artificial ground cooling apparatus, to stabilize the frozen ground. Passive thermosyphons function when the above-ground condenser section is colder than the subsurface evaporator section. This occurs when the ambient air temperature is colder than the subsurface ground temperature. Passive thermosyphons absorb thermal energy from subsurface ground layers and reject it into the atmosphere. Therefore, this passive technology augments natural ground cooling during the cold winter months. Hybrid thermosyphons operate in passive and active (powered refrigeration) modes. For remote locations, the electrical requirements for active thermosyphons limit their application. However, solar power is a promising method to provide an electrical source to operate active and hybrid thermosyphons. This technical note presents the results from an experimental study that tested the use of a solar array system that powered a refrigeration unit, which provided active cooling to a hybrid thermosyphon. The energy that was generated from the solar array successfully operated the refrigeration unit, provided active cooling to the hybrid thermosyphon, and lowered soil temperatures. This study showed the potential for the future development and application of a more energy-efficient off-grid hybrid thermosyphon system.

Practical Applications

Maintaining frozen ground stability in the Arctic and sub-Arctic is a constant challenge, especially as the climate is warming. Engineering solutions, such as artificial ground freezing techniques to stabilize the frozen ground, are commonly used in cold climates. Freezing the ground with artificial freezing systems is achieved without power when air temperatures are below freezing. When air temperatures are above freezing, the passive system seizes; however, freezing could continue if linked to a mechanical refrigeration unit. The electrical requirements of this cooling technique, when temperatures are above freezing, severely restrict their use in remote areas. This technical note presents an experimental study where a solar array system was tested for powering a refrigeration unit connected to an artificial freezing system. Freezing was extended at warmer air temperatures (above freezing) with a refrigeration unit that was operated by solar array-generated energy. The refrigeration unit successfully operated, and soil temperatures decreased. Supplying this ground cooling technique with a solar powered system could be possible for future applications.