Permafrost

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Permafrost

• what is permafrost
• where does it occur
• what problems exist

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Understanding Permafrost

• important to civil engineering and architecture
• crucial part of studying global change
• protecting the environment in cold regions

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permafrost

• Permafrost underlies approximately 22.79 million
  square kilometers (about 24 percent of the
  exposed land surface) of the Northern Hemispher
• It occurs as far north 84N in northernmost
  Greenland, and as far south as 26N in the
  Himalayas

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occurrence
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Exactly what is permafrost?

• Permafrost is not defined by soil moisture
  content, overlying snow cover, or location
• Defined solely by temperature.
• Any rock or soil remaining at or below 0 C for
  two or more years is permafrost.

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Variable characteristics

• Permafrost can contain over 30 percent ice, or
  practically no ice at all.
• It can be overlain by several meters of snow, or
  little or no snow.

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Determining the location and extent of permafrost

• often difficult
• historical approach - assume that ground
  temperature equals the overlying air temperature
• ground and air temperatures usually differ, and
  by varying amounts

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Determining the location and extent of permafrost

• in areas where the mean annual air temperature is
  below freezing, permafrost may not exist
• land under glaciers, rivers, and streams is often
  free of permafrost despite freezing air
  temperatures at the surface
• (Williams and Smith 1989)

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Thickness varies
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Geothermal gradient

• Depth of permafrost is a function of air
  temperature and geothermal gradient

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Active layer

• The honeycomb polygonal shape is the result of
  the seasonal churning of the ground above the
  underlying layer of permafrost.
• Ice wedges

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Active layer

• The honeycomb polygonal shape is the result of
  the seasonal churning of the ground above the
  underlying layer of permafrost.
• Ice wedges

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Active layer

• Melting each summer causes constructions to sink
  into the ground
• The soil becomes saturated and looses all strength

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Active layer
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Problems with permfrost

• Permafrost restricts use of the ground surface,
  and limits the locations of roads, buildings,
  communities, pipelines, airfields, and bridges.

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Problems with permfrost

• Where the ground is frozen and there is little
  water in the soil, there are no difficulties in
  building new structures.

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Problems with permfrost

• However, if permafrost with lots of ice is
  allowed to thaw, major problems can develop,
  because the ground can lose most of its strength.
  

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Methods for building

• Keep frozen
• Build above the ground with a layer of cold air
  between the building and the subsurface
• Freeze the ground in cellars of large buildings
  freezers keep the building frozen to the
  suroundings
• Support down to solid ground

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Suggestions

• Small homes
• Roads and major highways
• Large constructions
• Pipe line
• Sewage
• Drinking water