e) Over the liner, provide a minimum of 6 inches
(150 mm) of compacted clean sand or similar material as
described above. Securely attach and seal the liner to the
inside of the concrete foundation ring wall beneath the tank
f) Install pipe or pipes through the concrete
foundation ring wall as a telltale for tank bottom leaks.
These pipes will also permit water beneath the tank to escape
by gravity. In addition, provide a leak detection system for
the tank bottom.
g) Perform subsurface investigation in sufficient
detail to determine if any compressible, weak, organic, or
otherwise objectionable soils exist within a distance of two
h) Estimate the magnitudes and rates of settlement
(uniform, differential, and seismic induced) as part of the
design. Provide adequate flexibility in piping,
appurtenances, and other systems to accommodate anticipated
settlements. Accomplish flexibility by using pipe offsets or
ball joints. Do not use corrugated or bellows type expansion
compensators. Do not exceed differential settlement values
given in NAVFAC DM-7.01.
i) Where objectionable materials exist or magnitudes
of anticipated settlement are sufficient to cause damage or
unacceptable distortion, consider subsurface improvement.
Potential improvement techniques may include removal of
objectionable materials and replacement with clean compacted
granular fill, preloading or surcharging in conjunction with
drainage wicks, deep dynamic compaction, vibrocompaction,
stone columns, compaction grouting, or similar techniques.
j) Where justified by subsurface conditions and
economics, consider using deep foundations such as driven
piling or drilled shafts. Design foundation in accordance
with NAVFAC DM-7.02.
UNDERGROUND HORIZONTAL STORAGE TANKS
General Design Considerations. Where underground
storage tanks of 1,200 barrels (191 m3) or less capacity are
required, use factory-built horizontal cylindrical double-wall