Page 237 - Geotechnical Engineering Soil and Foundation Principles and Practice

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

Figure 11.15
Frost heave
causing muddy
conditions when
the ice melts.

11.9 DEPTH OF FREEZING

11.9.1 Locating Foundations below the Depth of Freezing

The most obvious way to prevent damage from frost heave is to found structures
below the maximum depth of freezing. A map showing maximum depths of
annual freezing that may be expected in the U.S. is shown in Fig. 11.16.

Freezing depths are determined not only by air temperatures but also by thermal
properties of soils and their cover. For example, a saturated soil will not freeze as
deeply under a given set of conditions as an unsaturated soil because of the heat
transfer required to freeze water. Also, soil under a thick layer of vegetation or
under a snow blanket will not freeze as deeply as if the soil were exposed to the
elements.

11.9.2 Weather Records
An evaluation of freezing conditions can be obtained from weather records.
Maximum and minimum daily temperatures are averaged and subtracted from the
nominal freezing temperature of water to obtain degree-days below freezing. The
same general procedure is used for furnace and air conditioner design, only the
reference temperature is the comfort zone for people and/or equipment. For
example, if the temperature range for a particular day is from 58Cto 158C,
the average is 108C, or 10 degree-days below freezing.

11.9.3 The Stefan Equation

Freezing and thawing depths during a single winter season can be used to estimate
the extent of freeze-thaw cycling, which is an important factor affecting

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2007 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.