Page 239 - Geotechnical Engineering Soil and Foundation Principles and Practice

Pore Water Pressure, Capillary Water, and Frost Action
234 Geotechnical Engineering

Table 11.1 k t k u
Thermal conductivity Dry density (frozen soil) (unfrozen soil)
Moisture
(from charts of 3 3 2 2
kN/m lb/ft content, % W/m K Btu/ft -hr/8 F/ft W/m K Btu/ft -hr/8F/ft
Kersten, 1952)
Sandy soils:
20.4 130 5 2.3 1.3 2.6 1.5
10 4.2 2.4 3.1 1.8
18.9 120 5 1.7 1.0 2.0 1.2
15 4.0 2.3 2.8 1.6
Soils with 450% silt and clay:
18.9 120 10 1.7 1.0 1.6 0.9
17.3 110 10 1.3 0.8 1.3 0.7
18 2.1 1.2 1.7 1.0
15.7 100 10 1.0 0.6 1.0 0.6
20 1.8 1.0 1.4 0.8
14.1 90 10 0.8 0.5 0.8 0.5
30 2.1 1.2 1.3 0.7
Selected thermial conversion factors:
1 Btu ¼ 1.055 kJ
2
1 Btu/ft -hr-8F/ft ¼ 1.730 W/m K (watts per meter-kelvin)
1 cal/cm s K ¼ 418.4 W/m K
3
1 Btu/ft 2 ¼ 37.26 kJ/m (kilojoules per cubic meter)
1 cal/cm 3 ¼ 4187 kJ/m 3
1 Btu/lb ¼ 2.326 kJ/kg ¼ 22.81 kJ/kN
1 cal/g ¼ 4.1868 kJ/kg
1 W (watt) ¼ 1 J/s
1J ¼ 1N m

Some representative values for k t are given in Table 11.1. Calculations for depth
of thawing use k u , which is lower than k t because the heat conductivity of liquid
water is less than that of ice.

Example 11.7
The average temperature for a 10-day period is 58C. Calculate the depth of freezing in a
3
3
sandy soil with
d ¼ 18.9 kN/m (120 lb/ft ) and a moisture content of 12%.
Answer: Interpolating in Table l1.1 gives k t ¼ 3.3 W/mK. L ¼ 340 12 18.9 ¼ 77,000 kJ/
3
m . From eq. (11.15),
s ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
13:1 3:3 10 5
Z ¼ ¼ 0:6m ð24 in:Þ
77,000

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