Remember, thawing of permafrost can take place if the ground cover is removed or disturbed. In the context of global change, large-scale thawing of permafrost in the Fairbanks area is a predictable response to global warming. The permanently frozen gravels exposed in the tunnel present quite another picture of a material in a permafrost condition. There is only interstitial ice present, and the gravels appear to have grain to grain contact. No ice wedges or other bodies of ice occur in the gravels.
Ice wedges seem to truncate when they reach the gravels.
Thawing of clean gravels like those found in the tunnel would then cause little or no settlement of the surface, no engineering problems upon thawing so to speak. But remember, excavation of ice-cemented permafrost gravel is a real engineering problem. The muck is reworked silt with intermixed organic material. The muck was deposited unfrozen, and decay of the organic material was free to take place. It is believed that the muck may have gone through several cycles of freezing and thawing, decay taking place in the thawed stage.