Thaw Weakening

The ice located in the frozen, frost-susceptible soils of cold regions is subjected to thawing when seasonal or diurnal temperatures rise. Thawing causes saturation of soil by excess water that is restricted from draining due to frozen underlayers. This saturation reduces soil strength due to generation of excess pore pressure and the saturated active layer becomes substantially weaker and tends to lose bearing capacity. This is called thaw weakening.

Occurrence of thaw weakening depends on frost-susceptible soil, its permeability, poor drainage conditions, and rate of thaw. Knutson (1993) categorized soil in high to low frost-susceptible soils. High frost-susceptible soils are typically coarse silts with less than 40% of particles smaller than 0.002 mm, more than 12% of particles smaller than 0.02 mm, and more than 50% of particles smaller than 0.2 mm.

Depending upon the surface temperature conditions, thawing can proceed downward from the top, or upward from the bottom, or in both...