Lesson 3/Learning Event 3
Learning Event 3
Complete frost protection is provided when the thickness of non-frost susceptible base and pavement is
sufficient to protect the subgrade on even the coldest days. In other words, the maximum depth of frost
penetration (on the coldest day) is less than the depth of non-frost susceptible materials in the pavement.
Depth of Frost Penetration
The depth to which freezing temperature will penetrate below the surface of a pavement kept cleared of
snow and ice depends principally on the magnitude and duration of below-freezing air temperatures, on
the properties of the underlying materials, and on the amount of water which becomes frozen. The
curves in Figures 21 and 22 may be used to estimate values of frost penetration beneath paved areas kept
free of snow and ice. They have been computed for an assumed 12-in. thick rigid pavement, using the
modified Berggren formula and correction factors derived by comparison of theoretical results with field
measurements under different conditions. The curves yield maximum depths to which the 32,F
temperature will penetrate from the top of the pavement under total winter freezing index values in
indefinitely deep, homogeneous materials for the indicated density and moisture content properties.
Where individual analysis is desired or unusual conditions make special computation desirable, the
modified Berggren formula may be applied (see Notes, Figure 21). Neither this formula nor the curves
in Figures 21 and 22 are applicable for determining transient penetration depths under partial freezing
index values. Values obtained by use of Figures 21 and 22 should be verified whenever possible by
observations in the locality under consideration.
There are several means of dealing with frost action. In reality, some are more practical than others.
You should know the options and recognize which option is most likely to be the better alternative in
There are four preventive actions that can be taken:
Insulate the subgrade
Remove frost susceptible material
Prevent capillary movement into the freezing zone
Increase the distance from top of subgrade to ground water level.
The preventive action of increasing the distance from the top of the subgrade to ground water level is
accomplished by increasing the thickness of the flexible pavement. Determining what thickness is
needed to prevent or control the detrimental effects of frost action will be discussed in other parts of this