To paraquote a famous permafrost engineering pioneer (thanks again Eb, your memory lives on):
". . . when it comes to permafrost, there's bad permafrost and then there's really bad permafrost."
With regard to construction, syngenetic permafrost is usually really bad permafrost and if present at a building site, especially at shallow depth, it is critical to identify it before a foundation system for a given building is selected.
Heat introduced to the ground by construction activities (e.g. simply by ground clearing) and heat introduced into the ground by transfer from a warm building foundation will promote thaw of permafrost. If the permafrost is sufficiently rich in ground ice (syngenetic permafrost usually is), when it thaws the ground subsides. The subsidence results from the volume change (loss) as melting ice changes to water and drains away. The excess meltwater may also saturate the surrounding soil and reduce its strength, as water cannot resist shear forces imposed by a load (save for one or two instances reported in the New Testament). Such thawing permafrost is dubbed "non-thaw stable."
To cope with non-thaw stable frozen soils, specialized construction practices and foundation systems are required.
