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"Frost"
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Experimental and Theoretical Study on Frost Deformation and Damage of Red Sandstones with Different Water Contents
Volumetric expansion of water by 9% in saturated pores and cracks causes substantial frost deformation in rock masses. Frost deformation is an important index reflecting the frost resistance of rocks; however, water saturation has a great influence on the frost deformation characteristics. In this research, the frost strains and acoustic emission activities of red sandstone with different water saturations are monitored under freeze–thaw conditions. The experimental results show that both the peak and the residual frost heaving strains greatly increase for sandstone beyond 85% water saturation. However, there is no significant frost heaving strain that occurs in low-saturation red sandstone (less than 85% water saturation). The acoustic emission activities show the same change trend and further confirm the existence of this critical saturation. In addition, the pore size distribution also has a great influence on the frost heaving strain and freeze–thaw damage. All the liquid pore water in this red sandstone is frozen at − 20 °C because the pores are larger than the critical freezing radius (2.58 nm at − 20 °C) according to the measured pore size distribution. Based on the pore micromechanics and Gibbs–Thomson equation, a developed frost heaving model is proposed considering the effects of water saturation and the pore size distribution. The proposed model can be used to predict the frost heaving strain at any freezing temperature for unsaturated red sandstone. This study thus provides the frost deformation characteristics of red sandstone and contributes to a better understanding of the freeze–thaw damage mechanism of unsaturated sandstone.
Journal Article
How Robert Frost made realism matter
Robert Frost stood at the intersection of nineteenth-century romanticism and twentieth-century modernism and made both his own. Frost adapted the genteel values and techniques of nineteenth-century poetry, but Barron argues that it was his commitment to realism that gave him popular as well as scholarly appeal and created his enduring legacy. This highly researched consideration of Frost investigates early innovative poetry that was published in popular magazines from 1894 to 1915 and reveals a voice of dissent that anticipated \"The New Poetry\" -- a voice that would come to dominate American poetry as few others have.
BOOK
Rare frost events reinforce tropical savanna-forest boundaries
1. The ability of vegetation to ameliorate or exacerbate environmental extremes can generate feedbacks that mediate the distribution of biomes. It has been suggested that feedbacks between vegetation and frost damage may be important for maintaining savanna, particularly at the edge of the tropics. 2. We quantified frost damage and air temperature across a network of 30 permanent plots distributed across tropical savanna-forest boundaries in Brazil during an uncommonly hard frost. 3. Tree cover strongly buffered temperatures during frost events, such that forest sites were up to 5°C warmer than nearby sites occupied by open shrub savanna. Consequently, in forest, woody plants were not damaged, but in savanna, there was extensive dieback of trees and shrubs. Within savanna, frost had disproportionately large effects on small individuals, likely due to colder temperatures near the ground and the lower thermal mass of thin stems. Across species, frost tolerance was strongly correlated with latitudinal range limit, revealing the importance of minimum temperature as a species filter at the regional scale. Counterintuitively, savanna species, which are adapted to open habitats where frost is more likely, were more vulnerable to cold than were forest species and experienced more than twice the amount of leaf damage as co-occurring forest species. 4. Synthesis. Frost reinforces the effects of fire on vegetation structure by preferentially damaging trees in open environments and generating high loads of dead, flammable fuels. However, frost does not currently occur with sufficient frequency in the region to maintain open savanna by itself. Nevertheless, it occurs with sufficient frequency and severity that it likely acts as an environmental filter and evolutionary selective factor for some of the most frost-sensitive species.
Journal Article
Late-spring frost risk between 1959 and 2017 decreased in North America but increased in Europe and Asia
Late-spring frosts (LSFs) affect the performance of plants and animals across the world’s temperate and boreal zones, but despite their ecological and economic impact on agriculture and forestry, the geographic distribution and evolutionary impact of these frost events are poorly understood. Here, we analyze LSFs between 1959 and 2017 and the resistance strategies of Northern Hemisphere woody species to infer trees’ adaptations for minimizing frost damage to their leaves and to forecast forest vulnerability under the ongoing changes in frost frequencies. Trait values on leaf-out and leaf-freezing resistance come from up to 1,500 temperate and boreal woody species cultivated in common gardens. We find that areas in which LSFs are common, such as eastern North America, harbor tree species with cautious (late-leafing) leaf-out strategies. Areas in which LSFs used to be unlikely, such as broad-leaved forests and shrublands in Europe and Asia, instead harbor opportunistic tree species (quickly reacting to warming air temperatures). LSFs in the latter regions are currently increasing, and given species’ innate resistance strategies, we estimate that ~35% of the European and ~26% of the Asian temperate forest area, but only ~10% of the North American, will experience increasing late-frost damage in the future. Our findings reveal region-specific changes in the spring-frost risk that can inform decision-making in land management, forestry, agriculture, and insurance policy.
Journal Article
Frost Mitigation Techniques for Tunnels in Cold Regions: The State of the Art and Perspectives
Tunnels located in cold regions are vulnerable to frost damage resulting from the special atmosphere, which directly threatens the safety of the tunnel structure and operation. Frost problems of tunnels in cold regions have not been fundamentally resolved. This paper reviews design theory and the frost mitigation techniques currently used in the design, construction and maintenance of cold region tunnels. The depths of freezing and thawing and frost heaving force are the key indexes of design theory. Insulation is the main design technology used to prevent frost heaving and thawing, and the active heating technology has also been applied in practice. In construction, reducing the heat of hydration and blasting by specific winter construction techniques can prevent tunnel freeze–thaw damages. In operation, the restoration of drainage systems, the reinforcement of structures and the reinstallation of freezing-prevention systems are effective measures to treat frost problems. Finally, some constructive suggestions and opinions are put forward to improve the service performance of tunnels.
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Reading and interpreting the works of Robert Frost
\"Describes the life and work of poet Robert Frost\"-- Provided by publisher.
BOOK
Study on water–heat coupling migration law and frost heave effect of soil slope in seasonal frozen regions during groundwater recharge
To study the law of water–heat coupling migration and the frost heave deformation characteristics of soil slopes in seasonal areas under groundwater recharge conditions, this paper constructs a water–heat–stress coupling model considering moisture migration, ice–water phase change, ice resistance, and frost heave effects based on COMSOL modelling software. Then, numerical simulation results are compared with the experimental results to verify the effectiveness of the multi-field coupling model. The results show that the slope temperature change has an evident lag compared with the ambient temperature change. The shallow soil of slopes changes dramatically under external ambient temperature, while the deep soil gradually tends to the ground temperature under the geothermal influence. The slope temperature distribution rules are basically the same in different groundwater recharge levels. The maximum freezing depth of the slope is deeper at a high groundwater level. When the groundwater level is high, the total moisture content of the slope is larger, and the thawing area may be saturated or oversaturated in the spring thawing period. For unsaturated soil slopes in seasonal freezing for a long time, the total moisture content of slopes tends to increase slightly after each freeze–thaw cycle due to groundwater recharge. The problems of slopes in seasonal frozen areas are manifested by the frost heave of the soil at the top of slopes, which may cause frost heave damage. When the groundwater level is high, the maximum horizontal displacement of the slope surface and the frost heave deformation at the top of slopes increase greatly.
Journal Article