Figure 2-3. Concrete foundation ring.
(2) Tanks on Cuts and Fills. Ordinarily, tanks
over the tank site, compacted in layers to the desired
should not be built on mixed cut-and-fill foundations.
f. Firewalls. All fuel storage tanks must have
The best practice is to erect the tank on an all-cut or an
all-fill foundation compacted to a minimum of 1800
dikes, constructed of impervious material, which serve
pounds per square foot.
as firewalls (fig. 2-4), with a reservoir capacity of at
(3) Foundation in Mixed Cut-and-Fill areas. If
least 100 percent of the tank volume plus one (1) foot of
a mixed cut-and-fill area must be used, the tank site
freeboard. These walls are intended to contain fuel
requires special grading and compaction, because the
spilled from burst or leaking tanks, and to help prevent
filled portion is likely to settle while the ground in place
the spread of fire to nearby tanks and other installations.
is not. When the fill section has proper bearing strength
Firewalls in forward areas, and wherever possible in rear
(1800 pounds per square foot), loosen the cut section to
areas, should be as high as possible to minimize
a depth of 24 inches. Compact it in layers of not over 9
damage from bombs, shrapnel, and explosion shock.
inches to the same density as the fill at optimum soil-
Refer to TM 5-302 and TM 5343 for detailed information
moisture content. When the fill section does not have
on the construction of firewalls.
proper bearing strength, put about 18 inches of backfill