TM 5-822-5/AFM 88-7, Chap. 1
rials that will result in detrimental frost action. The
susceptible subgrade soils should be avoided by
contract plans and specifications should require the
making certain that the subgrade is
subgrade preparation work established for nonfrost
properly graded and compacted prior to placement
areas in this manual in frost areas. They also should
of base course, by ensuring that the first layer of
provide for special treatments such as removal of
base course filters out subgrade fines under traffic,
unsuitable materials encountered with sufficient
and by eliminating the kneading caused by over-
information included to identify those materials and
compaction or insufficient thickness of the first
specify necessary corrective measures. However,
layer of base course. Excessive rutting tends to
construction operations quite frequently expose
cause mixing of subgrade and base materials. This
frost-susceptible conditions at isolated locations of
can be greatly minimized by frequent rerouting of
a degree and character not revealed by even the
material-hauling equipment.
b. Visual inspection. After completion of each
most thorough subsurface exploration program. It
is essential, therefore, that personnel assigned to
layer of base course, a careful visual inspection
field construction control be alert to recognize
should be made before permitting additional mate-
situations that require special treatment, whether or
rial placement to ensure that areas with high per-
not anticipated by the de- signing agency. They
centages of fines are not present. In many instances
must also be aware of their responsibility for such
these areas may be recognized both by examination
recognition.
of the materials and by observation of their action
under compaction equipment, particularly when the
materials are wet. The materials in any areas that do
18-21. Base Course Construction.
not meet the requirements of the specifications,
Where the available base course materials are well
which will reflect the requirements of this manual,
within the limiting percentages of fine material set
should be removed and replaced with suitable
forth above, the base course construction control
material. A leveling course of fine-grained material
should be in accordance with normal practice. In
should not be used as a construction expedient to
instances where the material selected for use in the
choke open-graded base courses, to establish fine
top 50 percent of the total thickness of granular
grade, or to prevent overrun of concrete. Since the
unbound base is borderline with respect to per-
base course receives high stresses from traffic, this
centage of fine material passing the no. 200 sieve,
prohibition is essential to minimize weakening
or is of borderline frost susceptibility (usually ma-
during the frost-melting period. Action should be
terials having 11/2 to 3 percent of grains finer than
taken to vary the base course thickness so as to
0.02 millimeters by weight), frequent gradation
provide transition, when this is necessary, to avoid
checks should be made to ensure that the materials
abrupt changes in pavement supporting conditions.
meet the design criteria. If it is necessary for the
contractor to be selective in the pit in order to
18-22. Compaction.
obtain suitable materials, his operations should be
inspected at the pit. It is more feasible to reject
Subgrade, subbase, and base course materials must
unsuitable materials at the source when large vol-
meet the applicable compaction requirements for
umes of base course are being placed. It may be
nonfrost materials.
desirable to stipulate thorough mixing at the pit and,
if necessary, stockpiling, mixing in windrows, and
18-23. Use of Insulation Materials in Pavements.
spreading the material in compacted thin lifts in
The use of synthetic insulating material within a
order to ensure uniformity. Complete surface
pavement cross section must have the written ap-
stripping of pits should be enforced to prevent
proval of HQUSACE (CEMP-ET) or the appropri-
mixing of detrimental fine soil particles or lumps in
ate Air Force Major Command, which can also
the base material.
provide advice and assistance in regard to the
a. Gradation of base course materials. The
structural analysis. Criteria for design of pavements
gradation of base course materials after compaction
containing insulating layers are contained in
should be determined frequently, particularly at the
appendix D.
start of the job, to learn whether or not fines are
being manufactured in the base under the passage of
18-24. Design Example-Heavily Trafficked Road.
the compaction equipment. For base course
Design flexible and rigid pavement for the following
materials exhibiting serious degradation charac-
conditions-
teristics, a test embankment may be needed to study
a. Class B (rolling terrain within the "built-up
the formation of fines by the proposed compaction
area")
process. Mixing of base course materials with frost-
b. Category III
18-19
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