ETL 1110-1-189
14 Feb 03
Table 8
Minimum Thickness of Pavement Layers (extracted from Table 6-1 of TM 5-822-5)1
Minimum Base Course CBR
502
100
80
Design Pavement Base
Total
Pavement Base
Total
Pavement Base
Total
Index (in.)
(in.)
(in.)
(in.)
(in.)
(in.)
(in.)
(in.)
(in.)
ST3
4.55
MST4
4.55
1
4
4
2
4
6
MST4
55
5.55
2
4
1.5
4
2.5
4
6.5
5.55
5.55
3
1.5
4
1.5
4
2.5
4
6.5
5.55
2
4
6
3
4
7
4
1.5
4
5
2
4
6
2.5
4
6.5
3.5
4
7.5
6
2.5
4
6.5
3
4
7
4
4
8
7
2.5
4
6.5
3
4
7
4
4
8
8
3
4
7
3.5
4
7.5
4.5
4
8.5
9
3
4
7
3.5
4
7.5
4.5
4
8.5
10
3.5
4
7.5
4
4
8
5
4
9
1
Table 6-1 extracted from TM 5-822-5, Chapter 6.
2
In general, 50 CBR Base Courses are only used for road classes E and F.
3
Bituminous surface treatment (spray application).
4
Multiple bituminous surface treatments.
5
Minimum total pavement thickness for road classes A through D is 6 inches.
geogrid can be used to cover roots, stumps, or stalks prior to geotextile installation to reduce the
potential for fabric puncture. Surface ruts in excess of 3 in. should be filled with select material.
The ability of nonwoven geotextiles to stretch makes them suitable for separation over uneven
subgrades. For very soft subgrades (CBR < 1), site mobility may be limited even for pedestrian
traffic. Stiff geogrids have been successfully used as retrievable walking platforms to facilitate
placement of the geosynthetic separation and reinforcement layers. In this application, the stiff
geogrid is unrolled along the outer edges of the traffic lane to provide construction personnel
with a temporary walkway to unroll and place the reinforcement materials.
The geotextile should be rolled out by hand, ahead of backfilling, directly on the subgrade.
For shallow-depth soft subgrades (CBR > 0.5), the geotextile is laid in the direction in which the
aggregate will be spread. For deep or very soft subgrades (CBR < 0.5), the geotextile is laid
transverse to the direction of the traffic lane. Table 9 should be used to determine the
appropriate overlap requirements, and the overlaps should be placed such that the spreading of
the aggregate base will not disturb the overlap distance. A minimum overlap distance of 1 ft is
required even if the geotextile intersections are sewn. The geotextile can be held in place using
staples, pins, or sandbags during windy conditions.
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