What does Permafrost Mean?
Definition of Permafrost in Construction
Permafrost occurs in the northern climates, where there is consistent temperatures below freezing.
Permafrost starts at a certain elevation in the ground, below which the earth is constantly frozen. Permafrost is extremely difficult to build on. Above the permafrost, is what is referenced as the active layer. The active layer is that region of soil, earth, sand, etc. that freezes and thaws on a seasonal basis. The active layer varies in depth, dependent upon the climate.
If the climate allows a long period of above freezing temperatures, the active layer can be several meters thick. If the climate does not allow extended periods of above freezing temperatures, the active layer could be only a few feet thick.
The construction over permafrost, due to the insulating values of the active layer, must be carefully engineered. The use of artificial insulation is required to ensure, that if the active layer is removed, there is the same insulation over the permafrost that the active layer represented. Failure to properly engineer for the active layer and the permafrost can lead to structural failures, and erosion encroaching deep into the permafrost.