30 June 2001
feed into the base course. This detail is also undesirable because the filter is a poor surface and is
subject to clogging, and the drain is located too close to the pavement to permit easy repair.
Recommended practice is shown in the "correct" column in Figure 20-9.
b. Frost Protection and Transitions for Inlets, Hydrants, and Lights. Experience has shown
that drain inlets, fueling hydrants, and pavement lighting systems, which have different thermal
properties that the pavements in which they are inserted, are likely to be locations of abrupt
differential heave. Usually, the roughness results from progressive movement of the inserted
items. To prevent these damaging movements, the pavement section beneath the inserts and
extending at least 1.5 meters (5 feet) radially from them should be designed to prevent freezing of
frost-susceptible materials by sue of an adequate thickness of nonfrost-susceptible base course,
and by use of insulation. Consideration should also be given to anchoring footings with spread
bases at appropriate depths. Gradual transitions are required to surrounding pavements that are
subject to frost heave.
12. PAVEMENT THICKNESS TRANSITIONS.
a. Longitudinal Transitions. Where interruptions in pavement uniformity cannot be avoided,
differential frost heaving should be controlled by use of gradual transitions. Length of longitudinal
transitions should vary directly with the speed of traffic and the amount of heave differential.
Transition sections should begin and end directly under the pavement joints, and should in no case
be shorter than one slab length. As an example, at an airfield where differentials of heave of
25 millimeters (1 inch) may be expected at changes from one subgrade soil condition to another,
gradual changes in base thicknesses should be effected over distances of 61 meters (200 feet) for
the runway area, 30.5 meters (100 feet) for taxiways, and 15.25 meters (50 feet) for aprons. The
transition in each case should be located in the section having the lesser total thickness of
pavement and base. Pavements designed to lower standards of frost heave control, such as
shoulders and overruns, have less stringent requirements, but may nevertheless need transition
b. Transverse Transitions. A need for transitions in the transverse direction arises at changes
in total thickness of pavement and base, and at longitudinal drains and culverts. Any transverse
transition beneath pavements that carry the principal wheel assemblies of aircraft traveling at
moderate to high speed should meet the same requirements applicable to longitudinal transitions.
Transverse transitions between the traffic areas C and D should be located entirely within the limits
of traffic area D and should be sloped no steeper than 10 horizontal to 1 vertical. Transverse
transitions between pavements carrying aircraft traffic and adjacent shoulder pavements should be
located in the shoulder and should not be sloped steeper than 4 horizontal to 1 vertical.
13. OTHER MEASURES TO REDUCE FROST HEAVE. Another measure to reduce the effects of
heave is the use of insulation to control depth of frost penetration. Insulation can only be used in
shoulders and overruns. The use of synthetic insulating materials within a pavement cross section
must have the approval of HQUSACE (CEMP-ET) or the appropriate Air Force Major Command.
When synthetic insulating materials are used, transitions between cut and fill, changes in character
and stratification of subgrade soils, subgrade preparation, and boulder removal should also receive
special attention in field construction control.
14. REPLACEMENT OR RECONSTRUCTION OF EXISTING PAVEMENTS. Objectionable differential
heave has been noticed where existing airfield pavements have been partially reconstructed or new
segments added. These discontinuities in elevation can result in problems of snow removal,