28 February 2006
Figure 2-3 Example Change to UFC
CHAPTER 2 PRELIMINARY DESIGN DATA
The need for subsurface drainage and frost protection must
identified during the design stage to enable incorporation of appropriate features into the
pavement design./1/ Verification of design assumptions is important to obtain reliable
designs. If during construction any of the site conditions were found different than those
assumed in the design, the design may have to be modified. Some site-related factors
affect the need for frost protection and the need for subsurface drainage. In this section,
investigation of those site factors is discussed.
INVESTIGATION FOR FROST DESIGN. The key factors that determine the
need for frost protection include type and gradation of subgrade, climate, and depth of
groundwater table. Frost heaving will occur only if the following three conditions exist:
Presence of frost-susceptible material.
Penetration of freezing temperatures into the susceptible material.
Available supply of water.
The investigation for frost design involv
es evaluating site conditions for the
determination of the presence of these conditions./1/
Subsoil Investigations. Frost action is detrimental if it results in differential
heaving, which is caused by variations in subsurface conditions. Variability of subsurface
conditions, therefore, is an important consideration for frost design. Subsoil investigation
should include assessment of horizontal and vertical variations in subgrade soil type,
natural moisture content, and water table elevations. In various situations, variable
pavement sections may be needed for different parts of the project to accommodate the
differences in subsurface conditions along the project. These conditions must be
identified during the subsoil investigation. Consider removing isolated pockets or
sections of frost-susceptible soil to eliminate abrupt changes in subgrade conditions.
2-2.2 Classification of Soils for Frost Susceptibility. Frost susceptibility of a soil is
the potential for the formation of ice lenses in the soil under freezing conditions. Because
the water needed for formation and growth of ice lenses is supplied through capillary
action, severe frost heave occurs in soils with a high capillary rate. As the freezing
temperatures penetrate deeper into the ground, a heavy formation of ice lenses takes
place at each successive level, resulting in severe frost heave. All inorganic soils that
contain more than 3% by weight of particles finer than 0.02 mm in diameter are generally