Engineering geology


Subsidence, flow and heave occur on poorly drained silts and clays when ground ice is melted; sands and gravels are generally thaw-stable.

Conservation of the permafrost is generally the best means of ensuring ground stability for built structures.
Any disturbance of the natural insulation (provided by the soil and vegetation) increases summer thaw, and depresses permafrost beneath buildings and roads.

Block supports for heated buildings, with clear airspace beneath, can be stable on gravel active layer over preserved permafrost.

Piles into stable frozen ground generally need to reach depths around 10 m.
Utilidors are pile-supported conduits built in streets for heated services pipelines and cables.
Trans-Alaska oil pipeline rests on piled trestles, each with internal circulating coolant and heat fins on top to dissipate stray heat from the oil; it is a giant utilidor.

Gravel pads or embankments, a few metres thick, can be enough to provide insulation and let the permafrost expand into them, stabilizing the compacted old active layer. Internal cold air ducting or insulation layers of peat or wood chips further improve conservation of the permafrost and protection of the structure.

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