TM 5-822-5/AFM 88-7, Chap. 1
they cannot be determined by a plate-bearing test.
without frost melting, is numerically smaller than
If the modulus of reaction, k, determined from tests
the index of reaction obtained from figure 18-5, the
on the equivalent base course and subgrade, but
test value shall govern the design.
Major Command. Also, and unbound course will
18-8. Use of State Highway Requirements.
not be placed between two relatively impervious
To provide further flexibility in design options, and
bound layers. If the combined thickness, in inches,
to exploit economical local materials and related
of pavement and contiguous bound base courses is
experience, state highway requirements may be used
less than 0.09 multiplied by the design air freezing
for pavements with a design index less than 4. The
index (this calculation limits the design freezing
decision to use local state highway requirements
index at the bottom of the bound base to about 20
will be based on demonstrated satisfactory
degree-days), not less than 4 inches of free-draining
performance of pavements in that state as de-
material shall be placed directly beneath the lower
termined by observation and experience. This
layer of bound base or, if there is no bound base,
should give reasonable assurance that the life cycle
directly beneath the pavement slab or surface
cost resulting from use of state highway re-
course. The free-draining material shall contain 2.0
quirements is comparable to that from use of Army
percent or less, by weight, of grains that can pass
and Air Force criteria and procedures. If state
the no. 200 sieve, and to meet this requirement, it
requirements are used, the entire pavement should
probably will have to be screened and washed. If
conform in every detail to the applicable state
the structural criteria for design of the pavement do
criteria.
not require granular unbound base other than the 4
inches of free-draining material, then the material in
18-9. Free-Draining Material Directly Beneath
the 4-inch layer must be checked for conformance
Bound Base or Surfacing Layer.
with the filter requirements below. If it fails the test
Base courses may consist of either granular un-
for conformance, an additional layer meeting those
bound materials or bound base materials or a com-
requirements must be provided. When using a
bination of the two. However, a cement- or lime-
drainage layer, the drainage layer must extend to an
bound base should not be placed directly beneath
open ditch or subdrains must be used. Pavement
bituminous pavement unless approved by HQU-
drainage is discussed in TM 5-820-2.
SACE (CEMP-ET) or the appropriate Air Force
18-15
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