Technical data

13
Underground tanks
A typical underground fuel oil storage tank installation
No vehicles in this area
Location of tank
All underground tanks MUST be buried in concrete.
Superimposed loads, such as vehicles, should NOT be allowed
within the protection area shown in the following illustration
(minimum 2m from the outer edge of the tank). The area
should be fenced or clearly marked to restrict access.
If this cannot be followed a reinforced concrete slab must be
designed/installed by a qualified civil/structural engineer so
that no loads are transmitted directly on to the tank.
The standard installation depth of 500mm, to the top of the
tank body, MUST NOT be exceeded.
Installation
It is recommended that a full risk assessment be completed on
the site, installation process and all parts prior to installation.
None of these tanks can be installed in wet ground conditions
(where at any time the ground water may rise above the base
of the tank).
Q The excavation should allow for a minimum of 250mm all
round the tank and approximately 500mm below the tank for
hard core and concrete
Q Allow for suitable pumps to keep the excavation dry until
the installation is complete
Q Fit suitable planking and strutting as necessary
Q Lay: A) 200mm thick hard core (or as necessary
for site conditions)
B) 50mm sand blinding
C) 500 gauge polythene sheet over the base of the
excavation
Q If necessary set temporary shuttering to contain the
concrete surround
No vehicles in this area
Gravel
Concrete backfill
45º
300mm concrete
150mm concrete
500 gauge polythene sheet on 50mm sand blinding
200mm hardcore depending on site conditions
Q Lay a wet bed of concrete 150mm thick (strength 20N/mm
2
,
slump test 50mm)
Q Lower tank carefully onto the concrete. Check that the tank
is true and level
Q Haunch concrete 300mm up around base of tank
Q Back filling;
A) Back fill evenly all around the tank with concrete
(minimum 15 N/mm
2
) proceeding in 150mm layers. It is
vital to ensure that the tank is filled with water 300-
500mm ahead of the concrete back fill, then emptied
of all water and refilled with the intended liquid to
be stored
B) Alternatively the concrete can be placed around an
empty tank in four progressive lifts with a 12 hour
delay between each lift to limit the concrete pressure.
The tank will have to be carefully restrained by
temporary strutting to prevent any chance of flotation
during this process
Ensure that there are no voids or areas of differing
pressure around the tank
Q Do not use a vibrating poker
Q Complete concrete backfill to 200mm below tank lid
Q Finish to ground level with 12-15mm gravel or earth
Q Ensure that the tank lid is a minimum of 150mm above
ground and is situated in an area where ground water will
not lie
Q Ensure that the tank lid has the ability to hinge open to 90°
Q Ensure that all holes placed in the tank neck for fuel outlet
pipes are sealed (eg with a suitable flexible grommet) to
prevent ingress of water