1. Permafrost what is permafrost where does it occur what problems exist

2. Understanding Permafrost important to civil engineering and architecture crucial part of studying global change protecting the environment in cold regions

3. 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 84°N in northernmost Greenland, and as far south as 26°N in the Himalayas

4. occurrence

5. 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.

6. 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.

7. 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

8. 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)Williams and Smith 1989

9. Thickness varies

10. Geothermal gradient Depth of permafrost is a function of air temperature and geothermal gradient

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

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

13. Active layer Melting each summer causes constructions to sink into the ground The soil becomes saturated and looses all strength

14. Active layer

15. Problems with permfrost Permafrost restricts use of the ground surface, and limits the locations of roads, buildings, communities, pipelines, airfields, and bridges.

16. Problems with permfrost Where the ground is frozen and there is little water in the soil, there are no difficulties in building new structures.

17. 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.

18. 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

19. Suggestions Small homes Roads and major highways Large constructions Pipe line Sewage Drinking water