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Freeze-thaw influence on the water retention capacity of silty sand subgrades
Published in Inge Hoff, Helge Mork, Rabbira Garba Saba, Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields, Volume 2, 2022
J.H.C. Everton, D. Saliko, S. Erlingsson
Another design method for cold region pavements accounts for a weakened subgrade when thawing during the spring (Andersland and Ladanyi, 2004). Thawing can occur even when no frost heaving occurs, which is related to the thawing speed and the material’s permeability. An example of such an issue is clay, which combines high matric suction with low permeability, making the conditions for ice segregation difficult and, therefore, frost heave less severe. However, the entrapped water in a clay subgrade layer will significantly reduce the bearing capacity during thawing (Christopher et al., 2006).
Acid Rock Drainage and Metal Migration
Published in Mritunjoy Sengupta, Environmental Impacts of Mining, 2021
For minimizing cost, a simple, single-layer soil cover is preferred. A fine-textured soil, such as clay or silt, is required to limit infiltration. To effectively limit oxygen transport, it is necessary to maintain the layer at a high moisture content. A single soil layer, however, is limited in its effectiveness for the following reasons:Without capillary barriers, a simple soil cover is prone to large seasonal variations in moisture content. This could result in desiccation cracking and an increase in permeability. In addition, decreasing the moisture content of the soil increases the rate of oxygen diffusion. These seasonal variations are greatest near the surface, and their effect is, therefore, greatest on thin covers. For single-layer soil covers to be effective, they need to be relatively thick to maintain a saturated zone during the dry season. The cover thickness required is probably a function of the climate.The fine-grained soils required to limit infiltration may be susceptible to frost. Ice segregation may result in degradation of the cover and increased permeability. Frost heave may also cause the surface of the cover to become irregular, allowing ponding and increased infiltration.A simple soil cover does not have the ability to prevent moisture from being sucked up from underlying tailings by capillary action. Likewise, it does not limit the migration of salts from the tailings to the surface due to surface evaporation and transpiration.A simple, single-layer fine-grained soil cover may not be able to adequately withstand wind and water erosion or burrowing and root action. Some form of erosion protection, such as vegetation or riprap, is normally required.
Acid Rock Drainage and Metal Migration
Published in M. Sengupta, Environmental Impacts of Mining, 2018
For minimizing cost, a simple, single-layer soil cover is preferred. A fine-textured soil, such as clay or silt, is required to limit infiltration. To effectively limit oxygen transport, it is necessary to maintain the layer at a high moisture content. A single soil layer, however, is limited in its effectiveness for the following reasons: Without capillary barriers, a simple soil cover is prone to large seasonal variations in moisture content. This could result in desiccation cracking and an increase in permeability. In addition, decreasing the moisture content of the soil increases the rate of oxygen diffusion. These seasonal variations are greatest near the surface and their effect is therefore greatest on thin covers. For single-layer soil covers to be effective, they need to be relatively thick to maintain a saturated zone during the dry season. The cover thickness required is probably a function of the climate.The fine-grained soils required to limit infiltration may be susceptible to frost. Ice segregation may result in degradation of the cover and increased permeability. Frost heave may also cause the surface of the cover to become irregular, allowing ponding and increased infiltration.A simple soil cover does not have the ability to prevent moisture from being sucked up from underlying tailings by capillary action. Likewise, it does not limit the migration of salts from the tailings to the surface due to surface evaporation and transpiration.A simple, single-layer fine-grained soil cover may not be able to adequately withstand wind and water erosion or burrowing and root action. Some form of erosion protection, such as vegetation or riprap, is normally required.
Frost susceptibility of sub-base gravel used in Pearl-Chain Bridges: an experimental investigation
Published in International Journal of Pavement Engineering, 2018
M. S. M. Lund, K. K. Hansen, I. B. Andersen
Frost heave is caused by the formation of ice lenses in soil. When the temperature of the surrounding air, typically above the soil, falls below zero, ice crystals form and coalesce into ice lenses, thereby initiating a freezing front that descends through the soil (Anderson et al.1984). The ice lenses grow because of water migration to the freezing front from a water supply below the soil. Eventually, the growth of ice lenses results in frost heaving, causing an upward displacement of the soil equal to the thickness of the ice (Taber 1929). For the ice lenses to grow, the ice has to be segregated from the soil particles. A pre-melted liquid water film around the soil particles caused by ice-particle interaction separates the ice from the soil particles, and the growth of the segregated ice increases due to these water films working as water supplying passages (Beskow 1935, Rempel 2007). Intermolecular forces across these thin water films create a fluid pressure gradient, causing the unfrozen water to be transported to the freezing zone (Rempel 2007, Rempel 2010). The theoretical understanding of the mechanisms driving frost heaving is complex, and many incorrect theories have been postulated throughout the last century. One of the most common misunderstandings is that capillary forces transport water from the water source to the freezing zone (Rempel 2010, Taber 1930). Because of ice segregation, bands of soil-free icelenses are formed between layers consisting of a mixture of ice, particles and water (Rempel, 2007). When the air temperature changes, the temperature gradient changes and the freezing front changes position, resulting in several bands of ice lenses at different soil depths (Anderson et al.1984).