TM 5-822-5/AFM 88-7, Chap. 1
stabilized base or subbase course, the thickness of
conditions are a factor. Where paving of shoulders
conventional base or subbase is divided by the
is deemed necessary, the shoulders will be designed
equivalency factor for the applicable stabilized soil.
as a class F road or street.
Examples for the application of the equivalency
factors are as follows--
8-9. Bituminous Sidewalks.
a. Example 1. Assume a conventional flexible
Permanent bituminous sidewalks will consist of a 4-
pavement has been designed which requires a total
inch-thick base with a 1-inch-thick bituminous
thickness of 16 inches above the subgrade. The
surfacing. Material used locally in base construction
minimum thickness of AC and base is 2 and 4
for roads will normally be suitable as sidewalk base
inches, respectively, and the thickness of subbase is
material. Bases may also be constructed of soils
10 inches. It is desired to replace the base and
stabilized or modified in place with portland
subbase with a cement-stabilized gravelly soil
cement, lime, bituminous materials, or other
having an unconfined compressive strength of 890
acceptable stabilizers. In frost and permafrost areas,
psi. From figure 8-2 the equivalency factor for a
bases of sidewalks should be nonfrost-susceptible.
subbase having an unconfined compressive strength
The bituminous surfacing may consist of hot- or
of 890 is 2.0. Therefore, the thickness of stabilized
cold-mix bituminous concrete, sand-asphalt or sand-
subbase is 10 inches 2.0=5.0 inches. To calculate
tar mixes, or sheet asphalt; in locations where the
the thickness of stabilized base course, divide the
surface texture is not of prime importance,
subbase equivalency factor by 2 and then divide the
bituminous surface treatments may be used.
unbound base course thickness by the result.
Temporary walks or walks that are seldom used will
Therefore, 4 inches 1.0 = 4.0 inches of stabilized
be constructed of stable or stabilized soils or rock
base course. The final section would be 2 inches of
screenings containing granular and colloidal
AC and 9 inches of cement-stabilized gravelly soil.
The base course thickness of 4.0 inches would also
ensure maximum density and stability under varied
have been required due to the minimum thickness of
weather conditions, including frost action. Where
necessary, the life of these walks may be prolonged
b. Example 2. Assume a conventional flexible
by the application of bituminous surface treatments
pavement has been designed which requires 2 inches
or by the addition of suitable stabilizing agents. The
of AC surface, 4 inches of crushed stone base, and
use of soil sterilants may be considered to prevent
6 inches of subbase. It is desired to construct an all-
vegetation growth through bituminous sidewalks.
bituminous pavement (ABC). The equivalency
factor from table 8-1 for a base course is 1.15 and
8-10. Bituminous Driveways.
for a subbase is 2.30. The thickness of AC required
Base course materials in residence driveway areas
to replace the base is 4 inches 1.15=3.5 inches,
will be compacted to not less than 100 percent, and
and the thickness of AC required to replace the
the top 6 inches of the subgrade to not less than 90
subbase is 6 inches 2.30 = 2.6 inches. Therefore,
percent (95 percent for cohesionless sands and
the total thickness of the ABC pavement is
gravels) of the maximum density from ASTM D
2+3.5+2.6 or 8.1 inches, which would be rounded
1557. Minimum base course thicknesses for resi-
to 8.0 inches.
dence driveways are as follows:
8-8. Shoulders and Similar Areas.
These areas are provided only for the purpose of
minimizing damage to vehicles which use them ac-
cidentally or in emergencies; therefore, they are not
considered normal vehicular traffic areas. Normally,
only shoulders for class A roads will be paved.
Others will be surfaced with soils selected for their
stability in wet weather and will be compacted as
required. Dust and erosion control will be provided
The minimum paving requirements for residence
by means of vegetative cover, anchored mulch,
driveways are a multiple bituminous surface treat-
coarse-graded aggregate, or liquid palliatives (TM
ment for base course CBR values less than 80 and
5-830-3/AFM 88-17, Chap 3). Shoulders will not
a single-bituminous surface treatment for CBR
block base-course drainage, particularly where frost
values of 80 or above.