- Frost heaving
Frost heaving (or frost heave) occurs when
soil expands and contracts due to freezing and thawing. This process can damageplant root s through breaking ordesiccation , cause cracks in pavement, and damage the foundations of buildings, even below thefrost line . Moist, fine-grained soil at certaintemperature s is most susceptible to frost heaving.Cause
Originally, frost heaving was thought to occur due simply to the freezing of water in soil. However, the vertical displacement of soil in frost heaving can be significantly greater than the expansion that occurs when ice freezes. In the 1960s, frost heaving was demonstrated in soil saturated in
benzene andnitrobenzene , which contract when they freeze."Frost creep", an effect of frost heave, involves a freeze-thaw action allowing mass movement down
slope . Thesoil orsediment is frozen and in the process moved upwardperpendicular to the slope. Whenthaw occurs the sediment moves downwards thus mass movement occurs.The current understanding is that certain soil particles have a high affinity for liquid water. As the liquid water around them freezes, these soils draw in liquid water from the unfrozen soils around them. If the air temperature is below freezing but relatively stable, the
heat of fusion from the water that freezes can cause the temperature gradient in the soil to remain constant. The soil at the point where freezing is occurring continues to draw in liquid water from the soils below it, which then freezes and builds up into an "ice lens". Depending on the soil's affinity for moisture and amount of moisture available, a significant amount of soil displacement can result.The earliest known documentation of frost heaving came in the 1600s.
usceptible soil types
Three conditions are generally necessary for frost heaving to occur:
*freezing temperatures
*a supply of water
* asoil that has:
** the ability to conduct water
** a high affinity for water
** saturation (i.e. the pore spaces are filled with water)Silty and loamy
soil types are susceptible to frost heaving. The affinity of a soil for water is generally related to the surface area of the particles that it is composed of.Clay s have a high ratio of surface area to volume and have a high affinity for water. Larger particles likesand have a lower ratio of surface area to volume and therefore a low affinity for water.Conversely, the hydraulic conductivity of a soil is related to the pore size. Soils composed of very small particles like clay have small pores and therefore low hydraulic conductivity. Soils composed of larger particles like sand have larger pores and a higher hydraulic conductivity.
The offsetting nature of these two requirements mean that clayey and sandy soils are less conducive to frost heaving than
silt , which has a moderate pore size and moisture affinity.Frost creep: Soil locomotion due to frost heave
Frost creep, an effect of "frost heave", involves a freeze-thaw action allowing mass movement down
slope . Thesoil orsediment is frozen and in the process moved upwardperpendicular to the slope. Whenthaw occurs the sediment moves downwards thus mass movement, or locomotion, occurs.tructures created by frost heaving
In Arctic regions, frost heaving for hundreds of years can create structures, known as
pingo s, as high as 60metre s. Frost heaving is also responsible for creating stones in unique shapes such as circles, polygons and stripes. A notable example is the remarkably circular stones of the islands ofSpitsbergen .Polygonal forms caused by frost heave have been observed in near-polar regions of Mars by the high-resolution
HiRISE camera on theMars Reconnaissance Orbiter . In May 2008 theMars Phoenix lander touched down on such a polygonal frost-heave landscape and quickly discovered ice a few centimetres below the surface.See also
*
Frost law References
External links
* [http://www.pavement.com/Concrete_Pavement/Technical/Fundamentals/Frost.asp American Concrete Pavement Association] Frost Action and Frost Heave
* [http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd026_e.html "Canadian Building Digest" article]
* [http://irc.nrc-cnrc.gc.ca/pubs/ci/v5no2/v5no2_1_e.html National Research Council of Canada] Simple manhole innovation cuts frost heave in pavement
* [http://www.aip.org/png/html/frost.htm American Institute of Physics pictures of frost heaving]
* [http://www.ucsc.edu/currents/02-03/01-20/patterns.html Stone Circles Explained] , about stone structures created by frost heaving
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