2-5 MINIMUM AND MAXIMUM COVER LIMITATIONS
Minimum Cover in Trafficked Applications
Pipe with diameters of 4" - 48" (100 - 1200mm) installed in
trafficked areas (AASHTO H-25 or HS-25 loads) must have at least one foot
(0.3m) of cover over the pipe crown, while 54" and 60" (1350
and 1500mm) pipes must have at least 18 inches (0.5m) of cover. In theory
the pipe can be buried with slightly less cover, but application variables
are such that 1' (0.3 m) or 18" (0.5m), depending on the diameter,
are the conservative limits. The backfill envelope should provide a minimum
E' value of 1000 psi (6,900 kPa). In Table 2-8, this condition is represented
by a Class III material compacted to 90% standard Proctor density, although
other material can provide similar strength at slightly lower levels of
compaction. Structural backfill material should extend six inches (0.15m)
over the crown of the pipe; the remaining cover should be appropriate
for the installation. If settlement or rutting is a concern, it may be
appropriate to extend the structural backfill to grade. Where pavement
is involved, subbase material can be used.
Additional information that may affect the cover requirements in certain
installations is included in Section 6. Some examples of what may need
to be considered are heavy equipment loads that the pipe might experience
only during the construction phase, paving equipment and similar loads
that are lighter than the design load, and the possibility of pipe flotation.
Table 2-8 – Minimum Cover
Requirements for Sure-Lok®, Hi-Q®, and AASHTO
Pipe with AASHTO H-25 or HS-25 Load
|
Inside Diameter, ID, in.(mm)
|
Minimum
Cover, H, ft. (m)
|
|
Inside Diameter,
ID, in.(mm)
|
Minimum
Cover, H, ft. (m)
|
|
3 (75)
|
1 (0.3)
|
|
24 (600)
|
1 (0.3)
|
|
4 (100)
|
1 (0.3)
|
|
30 (750)
|
1 (0.3)
|
|
6 (150)
|
1 (0.3)
|
|
36 (900)
|
1 (0.3)
|
|
8 (200)
|
1 (0.3)
|
|
42 (1050)
|
1 (0.3)
|
|
10 (250)
|
1 (0.3)
|
|
48 (1200)
|
1 (0.3)
|
|
12 (300)
|
1 (0.3)
|
|
54 (1350)
|
1.5 (0.5)
|
|
15 (375)
|
1 (0.3)
|
|
60 (1500)
|
1.5 (0.5)
|
|
18 (450)
|
1 (0.3)
|
|
|
|
Note: Minimum covers presented here were calculated assuming Class III
backfill material compacted to 90% standard Proctor density around the
pipe and a minimum of 6-inches (0.15 m) over the pipe crown, as recommended
in Section 6, with an additional layer of compacted native soil for a
total cover as shown. In shallow trafficked installations, especially
where pavement is involved, it may be best to use a good quality compacted
material to grade to prevent surface settlement and rutting.
MINIMUM AND MAXIMUM COVER LIMITATIONS
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