•We propose a method to calculate the microcrack propagation length under frost heaving pressure.•The variation law of rock elastic modulus with freezing-thawing cycles is established.•We propose the ...theoretical model for frost heaving pressure in circular rock tunnel.
The failure of rock tunnel lining in cold region involves the evaluation of frost heaving pressure in surrounding rock. Although many theoretical models of frost heaving pressure have been proposed, the combination effect of reduction in rock elastic modulus and increase of rock void ratio due to freezing-thawing cycles has not been considered. For this issue, on basis of the elastic model for frost heaving pressure in the circular tunnel surrounding rock, this study establishes the relationship between the rock elastic modulus and the number of freezing-thawing cycles based on fracture mechanics and mesodamage theory. Thereafter, we propose the damage model for frost heaving pressure by considering the combination of rock elastic modulus and void ratio. It is assumed that frost heaving pressure mainly occurs when water in microcracks is frozen into ice. The calculation example shows that frost heaving pressure gradually increases and tends to be a constant with increasing the number of freezing-thawing cycles. It indicates that the proposed model is capable of calculating the variation of frost heaving pressure with the number of freezing-thawing cycles.
Climate change, with both warmer spring temperatures and greater temperature fluctuations, has altered phenologies, possibly leading to greater risk of spring frost damage to temperate deciduous ...woody plants. Phenological observations of 20 woody species from 1993 to 2012 in Trelease Woods, Champaign County, Illinois, USA, were used to identify years with frost damage to vegetative and reproductive phases. Local temperature records were used in combination with the phenological observations to determine what combinations of the two were associated with damage. Finally, a long-term temperature record (1889-1992) was evaluated to determine if the frequency of frost damage has risen in recent decades.
Frost ≤−1.7°C occurred after bud-break in 14 of the 20 years of observation. Frost damage occurred in five years in the interior and in three additional years at only the forest edge. The degree of damage varied with species, life stage, tissue (vegetative or reproductive), and phenological phase. Common features associated with the occurrence of damage to interior plants were (1) a period of unusual warm temperatures in March, followed by (2) a frost event in April with a minimum temperature ≤−6.1°C with (3) a period of 16-33 days between the extremes.
In the long-term record, 10 of 124 years met these conditions, but the yearly probability of frost damage increased significantly, from 0.03 during 1889-1979 to 0.21 during 1980-2012. When the criteria were "softened" to ≤−1.7°C in April and an interval of 16-37 days, 31 of 124 years met the conditions, and the yearly damage probability increased significantly to 0.19 for 1889-1979 and 0.42 for 1980-2012.
In this forest, the combination of warming trends and temperature variability (extremes) associated with climate change is having ecologically important effects, making previously rare frost damage events more common.
There is an increasing trend of tunnel infrastructure construction in cold regions due to the advance of a western development strategy. To reduce the frost damage sustained by a tunnel, it is ...important to consider the mechanical properties of frost heave in the surrounding rock by analyzing the anisotropic frost heave of a cold-region tunnel. This paper elaborates on the behavior of anisotropic frost heave in the rock surrounding a cold-region tunnel, and the coefficient of displacement relief is adopted to indirectly quantify the influence of the tunnel construction process. The analytical elasto-plastic solutions of the stress and deformation in the surrounding rock are derived with Drucker-Prager criteria (hereinafter referred to as the D-P criteria) by modifying the constitutive equation for the frozen surrounding rock. Finally, an example is given to obtain the influence law of the distribution of stress and deformation in the surrounding rock. The results indicate that the plastic radius and frost force calculated by considering isotropic frost heave are greater than those obtained by considering anisotropic frost heave. The influence of the related parameters also analyzed. Some useful insights are provided for future numerical simulations and the design and construction of cold-region tunnels.
One-dimensional frost growth and densification in laminar flow over flat surfaces has been theoretically investigated. Improved representations of frost density and effective thermal conductivity ...applicable to a wide range of frost circumstances have been incorporated. The validity of the proposed model considering heat and mass diffusion in the frost layer is tested by a comparison of the predictions with data from various investigators for frost parameters including frost thickness, frost surface temperature, frost density and heat flux. The test conditions cover a range of wall temperature, air humidity ratio, air velocity, and air temperature, and the effect of these variables on the frost parameters has been exemplified. Satisfactory agreement is achieved between the model predictions and the various test data considered. The prevailing uncertainties concerning the role of air velocity and air temperature on frost development have been elucidated. It is concluded that that for flat surfaces increases in air velocity have no appreciable effect on frost thickness but contribute to significant frost densification, while increase in air temperatures results in a slight increase the frost thickness and appreciable frost densification.
•Frosting tests were done on a flat plate under various environmental conditions.•A 3D photogrammetric method was used for frost roughness measurement.•Frost growth were analyzed from the perspective ...of frost crystal structure.•The effects of environmental conditions on frost roughness were characterized.
Laboratory experiments were conducted to characterize frost thickness and roughness on a horizontal cold flat surface with respect to the type of frost crystal. Air velocities, free stream temperatures, wall temperatures, and relative humidities were varied from 0.5 to 1.5 m s−1, 16 to 6 °C, and -25 to −15 °C, and 50 to 75%, respectively. Three-dimensional photogrammetry was employed for evaluating frost roughness characteristics. The results showed that the frost growth corresponded with changes of frost crystal formation. Feather and needle crystals created a thick and porous layer with a rough surface, while flake and irregular crystals formed a thin and dense frost layer with a relatively smooth surface. Frost root-mean-square height began to decrease sooner under higher air velocities, higher air temperatures, and higher wall temperatures. The maximum value of frost root-mean-square height was largest under lower air velocities, lower air temperatures, lower wall temperatures, and higher relative humidities. Larger frost surface skewness occurred under lower air velocities, lower air temperatures, higher wall temperatures, and higher relative humidities. The impacts of increasing relative humidity on the frost roughness parameters plateaued at higher relative humidities.
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•This paper introduces the frost phenomenon on the cold plane and evaporator surface.•This paper gives a potential research and development interests in frost field.•Hydrophobicity is ...a preferable frosting retardation method, which are summarised in detail.
Frosting begins when the surface temperature falls below both the water freezing temperature and the moist air dew point temperature. Frost formation is a widespread phenomenon, but in essence, it is a nonlinear and complex physical change involving heat and mass transfer. People’s understanding of frost is still mainly in the initial experimental observation and empirical calculation stage. Therefore, this paper presents a panoramic view of frost research status in concise language, including the frost generation and propagation mechanism, the measurement and calculation of frost physical properties, the arrangement of frost experiment, and the simulation of frost. Then we summarize the methods of surface frosting retardation, among which surface hydrophobicity treatment is considered the most effective. The mechanism of hydrophobicity on frosting retardation and the preparation of the hydrophobic surface are summarised detailedly. Several defrosting methods are introduced later. Finally, the potential directions for further research are listed.
Based on the actual twin-tunnel freezing project of the Shanghai Metro in China, this study aims to establish a model test system that can simulate horizontal ground freezing, and the temperature ...distribution and frost heave ‘displacement are investigated. The model test results show that the frost heaving displacement of the soil was closely related to the closure time of the frozen wall. When the sequential freezing mode was adopted in the model test, the frost heaving displacement during the freezing period of the downlink tunnel was smaller than that during the freezing period of the uplink tunnel under the influence of water migration. Considering two different freezing modes, namely, sequential freezing and simultaneous freezing of uplink and downlink tunnels, we conducted a numerical simulation of the horizontal ground freezing of the twin tunnels. Compared with simultaneous freezing, sequential freezing can reduce frost heave displacement to a larger extent. This study can provide a reference for the design and construction of twin tunnels using artificial ground-freezing technique.
Combined mechanical and environmental actions reduce service life of reinforced concrete structures more than each of the participating actions alone. In this contribution, the influence of ...freeze-thaw cycles on capillary water absorption and chloride penetration into ordinary concrete with two different water-cement ratios and air-entrained concrete was investigated. Water profiles in concrete were quantified by neutron radiography. Capillary water absorption and chloride penetration are both slowed down considerably by air entrainment. Chloride ions dissolved in water are filtered out of the penetrating salt solution and remain concentrated near the surface. Capillary water absorption and chloride penetration into ordinary concrete are accelerated considerably by frost damage. After exposure to freeze-thaw cycles a damage gradient from the surface to the center of the samples was observed. Transport mechanisms were studied in some detail and the data obtained can serve as a basis for more realistic prediction of service life of reinforced concrete structures under the influence of combined freeze-thaw cycles and chloride penetration.
Due to the rigid deformation limit of high-speed railways, the anti-frost heave design has become a critical concern in seasonally frozen regions. In this study, the authors explained the frost heave ...mitigation techniques adopted for the high-speed railway between Harbin and Dalian in northeast China and then presented the thermal, deformation, and water content data monitored on the Gongzhuling test site. According to these data, the authors proposed the possible frost heave mechanisms of the high-speed railway foundation. The foundation is composed of well-graded gravel with cement and A/B group fill, which are treated as non-frost-susceptible materials in general. Based on the monitored data, the authors found that the surface layer (0–0.5 m) contributed most to the total frost heave and this might be caused by local water accumulation inside the foundation (0.6–1.2 m). In order to demonstrate the frost heave ability of these “non-frost-susceptible” materials, the authors conducted an indoor frost heave test with a mixture of gravel and 3% Kaolinite clay. Through this experiment, it was demonstrated that, with sufficient water supply, gravel with a limited amount of fine material can produce significant frost heave. Accordingly, we can conclude that the accumulated water inside high-speed railway foundation causes the frost heave deformation. Therefore, the treatment of the water accumulation within the fills needs to be considered for frost heave elimination or prevention.
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