TM 5-623
(2) Step 2.
Two-axle trucks ............
200
12
The percentage of deducts
Trucks with three or more
attributable to load, climate/durability, and other factors
axles .......................
50
3
can be computed as described below; the following is
based on the example in (1) above:
Table 4-3. Design Index for Flexible Pavements for Roads
Load =
6%s X 100 = 80 percent
and
Streets, Traffic Categories I Through IVa
Climate/durability =
17/8s x 100 = 20 percent
Total = 100 percent
Class road
Category I
Category Category
(3) Step 3.
The percent deduct values
Category
attributable to each cause are the basis for determining
or street
II
III
IV
the primary cause(s) of pavement deterioration. In the
A
3
4
5
6
B
3
4
5
6
example given in (1) and (2) above, distresses caused
C
3
4
4
6
primarily by load have resulted in 80 percent of the total
D
2
3
4
5
deducts, whereas all other causes have produced only 20
E
1
2
3
4
percent. Thus, traffic load is by far the major cause of
F
1
1
2
3
deterioration for this pavement section.
These
Category I. Traffic essentially free of trucks (99 percent group 1,
percentages are indicated on figure 4-1, an example of a
plus 1 percent group 2).
completed DA Form 5147-R (Section Evaluation
Category II. Traffic including only small trucks (90 percent group
Summary).
1, plus 10 percent group 2).
Category III. Traffic including small trucks and a few heavy
(4) Step 4. The drainage situation of each
trucks (85 percent group 1, plus 14 percent group 2, plus 1
pavement section should also be investigated. If moisture
percent group 3).
is causing accelerated pavement deterioration, it must be
Category IV. Traffic including heavy trucks (75 percent group 1,
determined how it is happening and why (groundwater
plus 15 percent group 2, plus 10 percent group 3).
table, infiltration of surface water, ponding water on the
Group 1. Passenger cars and panel and pickup trucks.
pavement, etc.). If moisture is contributing significantly to
Group 2. Two-axle trucks.
the rate of pavement condition deterioration, ways must be
Group 3. Three-, four-, and five-axle trucks.
found to prevent or minimize this problem. For example, if
*From TM 5-822-5.
pumping occurs in concrete joints or cracks, drainage
(3) According
to
the
information
in
conditions should be examined and foundation support
subparagraph (1) above and table 4-3, the design index
evaluated. Any drainage and foundation defects should be
for this pavement section is 5. Based on the information in
corrected and the joints or cracks filled or sealed. The
figure 4-8, the pavement thickness required over a CBR of
appropriate effect should be circled on the form. In our
10 is 12Y inches; over a CBR of 40, the required thickness
example, figure 4-1, circle "MINOR" in line 4b.
is 4.0 inches.
Therefore, this pavement section is
structurally strong enough for the load it is carrying, and
e. Deficiency of load-carrying capacity.
load-carrying capacity deficiency is circled "No" in our
(1) Before it can be determined whether an
example, figure 4-1, line 5.
existing pavement section is strong enough to support a
particular traffic condition, it is necessary to determine the
f. Surface roughness.
pavement's load-carrying capacity.
Methods for
(1) Surface roughness is an important
determining load-carrying capacity are given in TM 5-822-
operational condition. Although a rough pavement will
5 (AFM 88-7) and TM 5-822-6 for roads, and TM 5-827-2
usually have a low PCI, the reverse is not necessarily true.
(AFM 88-24) and TM 5-827-3 for airfield pavements.
For example, a pavement section may have a high
(2) For example, assume an asphalt pavement
percentage of medium-severity alligator cracking (a
section has the following structural composition:
serious structural distress) and, thus, a low PCI. However,
California
Layer
Thickness
bearing ratio
if this is the only distress present, the pavement surface
(CBR)
may not be rough.
Subgrade ..........................
........................
10
(2) Minor, moderate, or major surface
Base..................................
10 inches .........
40
roughness can be determined by riding over the pavement
Surface .............................
4 inches ...........
-
section at its speed limit and observing its relative riding
Further assume that this pavement section is a Class A
quality. In our example, figure 4-1, surface roughness was
road (see table 4-3) subjected to the following traffic load:
moderate; so "Moderate" was circled at line 6.
Traffic type
Vehicles/day
Percent of total
traffic
Passenger cars .............
1400
85
4-10
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