TM 5-852-9/AFR 88-19, Vol. IX
consolidating the foundation material, or replacing it with more suitable material). In areas where permafrost
is stable, the passive approach is generally used. One common passive method is placing the structure on a
layer of gravel on top of rigid insulation. This layer of gravel and insulation must be designed to isolate the
frozen foundation from the building heat, keeping the ground permanently frozen. Ventilation ducts are often
placed in the gravel layer to control the temperature of the frozen ground by maintaining air movement.
Another common passive method is placing the structure on piling. The piling either extends into the
permanently frozen material, with an insulating layer under the building, or the structure is elevated,
permitting free passage of exterior air to dissipate the building heat. Where the permafrost is fragile, special
piling called thermal piling is sometimes used. There are several thermal pile designs, all intended to keep the
foundation material permanently frozen. In all cases, particular attention must be given to ensuring proper
surface and subsurface water drainage away from the structure. Poor drainage and ponding of water can
seriously affect the ground thermal regime and cause structural damage from permafrost degradation and
frost action. Building foundation design is discussed in TM 5-852-4/AFM 88-19, chapter 4. For structures
on spread or continuous wall footings, a soil investigation should be made at the site to determine the possible
presence of layers of silty soils that may be susceptible to frost heave during the freeze-thaw cycle.
Foundation designs should require removal of frost-susceptible soils under a building which will be affected
by freezing, and replacement of those soils with non-frost-susceptible gravelly backfill. Design should
consider the thaw bulb which will develop under the building upon completion; therefore all of the frost
susceptible materials may not require removal. The contract document should require the contractor to assure
these materials do not freeze and cause jacking during construction.