Page 238 - Geotechnical Engineering Soil and Foundation Principles and Practice

Pore Water Pressure, Capillary Water, and Frost Action
Pore Water Pressure, Capillary Water, and Frost Action 233

Figure 11.16
Maximum frost
depths for design
purposes.

deterioration of pavement materials. The Stefan equation is a simplification as it is
based on the heat capacity of water in the soil and therefore overpredicts freezing
depths in dry soils. Also, it does not take into account additional water drawn into
the soil by frost heave, which can have a substantial effect on the rate of thawing.
The equation is
r ffiffiffiffiffiffiffi
L t F
Z ¼ C t ð11:15Þ
L
where Z ¼ depth of freezing, in meters (ft).
C t ¼ a constant. In SI, C t ¼ 13.1; in the English system, 6.93.
k t ¼ thermal conductivity coefficient of frozen soil, W/m K (watts per meter-
2
Kelvin) or Btu/ft -hr-8F per ft.
F ¼ degree days below 08Cor328F.
3
L ¼ latent heat of fusion of water in soil, kJ/m (kilojoules per cubic meter) or
3
Btu/ft .
L for water is 333.7 kJ/or 142.4 Btu/lb. L for soil water therefore is

L ¼ 340 w
d or
ð11:16Þ
L ¼ 1:43 w
d

where w is the percent moisture and
d is the dry unit weight of the soil, in kN/m 3
3
or lb/ft , respectively.
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