Note: Descriptions are shown in the official language in which they were submitted.
1- ` 2040435
40330-787
METHOD FOR ~NTOMBMENT
OF CONTAINER IN CONCRETE
There i8 a continuing interest in the safe
containment of liquids, particularly gasoline and other
fuels, because of the vast amount of fuel presently
stored throughout the country. It has become
increasingly apparent that underground storage tanks can
and do leak, thus causing serious short-term and long-
term problems. Therefore, many localities have chosen toexamine all underground tanks, mostly fuel storage tanks,
to determine if the tanks are leaking. It is an
expensive process to inspect the tanks and test the earth
surrounding the tanks for indications of leakage. Repair
or replacement of tanks which are shown to be leaking
increases the cost a great deal further.
Other liquids, in addition to fuels, create
containment problems as well. Many liquids used in
industry are hazardous from an environmental standpoint,
from a safety standpoint, or both. Often these liquids
are not suitable for storing in steel containers because
of their corrosive or reactive properties. Although
stainless steel can be used for certain chemicals, the
use of large stainless steel tanks can be very expensive.
Also, some chemicals are not suitable for storage in
stainless steel tanks as well.
Many chemicals are now being stored in plastic
and other non-metallic tanks. One such tank is made of
cross-linked polyethylene, an environmentally stable
material, by Poly Cal Plastics, Inc. of French Camp,
California as Zor~ Tanks. However, even if such non-
metallic tanks are chemically suitable for many types of
chemicals, they are still susceptible to damage from
extreme heat and fire, as well as physical damage which
could create leaks.
To aid the detection and prevention of leaks,
double wall (dual cont~;n~t) tanks have been used for
both underground and above ground storage. The space
. ~. ,;,
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between the two walls of the tanks is monitored for
leakage. When used underground, monitors can be used to
sense both water seepage in and stored liquid seepage
out. If a leak is detected, the tank can be drained and
S abandoned, dug up and removed, or repaired in place.
These options are all quite expensive. If the
contaminated soil surrounding the leaking tank must be
removed, the expense increases dramatically. However,
conventional double wall tanks are quite expensive and
are not presently able to meet fire code standards for
above-ground storage of flammable liquids. Therefore,
even when dual containment tanks are used, flammable
liquid is most often stored in below-ground tanks.
Creating a concrete encased hollow tank is not
without problems. One conventional method of doing so,
described in U.S. patent 4,826,644 mentioned above, is to
form an open-top hollow shell, place the tank within the
hollow shell and then pour the top. However, this
process creates cold joints which are possible sources of
leaks and weak points in the structure. Therefore, a
homogenous concrete shell, which would eliminate cold
joints, would be preferable. Entombing a hollow tank in
fluid concrete is hindered, if not prevented, by the fact
that the hollow tank has a tendency to bob up or float
within the fluid concrete. Although the tank could be
filled with water to give it neutral buoyancy, this
solution causes other problems, including difficulties
arising from trying to remove all the water from the tank
after the concrete has set.
The present invention is directed to a method
and apparatus for entombing a tank or other container
within a homogenous layer of concrete. The method is
carried out using wall forms combinable to create a
circumferential sidewall form which is mounted to a base
plate. The wall forms are secured to one another and are
laterally positioned on the base plate, preferably using
hydraulic jacks. The sidewall form and base plate define
2n40435
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an open-top enclosure within which the tank is
positioned. Concrete is poured within the enclosure to
surround the tank to create the concrete outer tank. One
or more hold-down members are mounted over the tank in
the enclosure. The hold-down members press on the top of
the tank to keep the tank from floating while the
concrete is fluid. The hold-down members keep the tank
properly horizontally and vertically positioned within
the form to ensure a proper concrete wall thickness is
maintained.
In one embodiment the invention a method for
entombing a container within a homogenous layer of
concrete comprising the following steps:
selecting an inner container;
enclosing the inner container within an
external framework;
selecting an intermediate container; housing
the inner container and external framework therewith
within the intermediate container to space the inner
container from the intermediate container;
selecting a concrete form sized to accept the
intermediate container;
placing the intermediate container within the
concrete form;
surrounding the intermediate container with
concrete within the concrete form;
maintaining the position of the intermediate
container within the concrete form during at least part
of and after the surrounding step, the maintaining step
including the steps of:
positioning a hold-down member above the
intermediate container, the hold-down member including a
container-engaging member;
engaging the intermediate container by the
container-engaging member; and
securing the hold-down member in place relative
to the form with the container-engaging member engaging
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J. ~.,
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the intermediate container to keep the intermediate
container properly vertically and horizontally positioned
within the form;
allowing the concrete to set to create a
homogenous layer of concrete entombing the intermediate
container; and
separating the form from the concrete entombed
container.
In a further embodiment the invention is a
method for entombing a container within a homogenous
layer of concrete comprising the following steps:
selecting a non-metallic inner container;
enclosing the inner container within an external
framework;
housing the inner container and external
framework therewith within an intermediate container to
create a container assembly;
the enclosing step being carried out using an
external framework sized to space the inner container
from the intermediate container;
selecting a concrete form sized to accept the
container assembly;
placing the container assembly within the
concrete form;
surrounding the container assembly with
concrete within the concrete form;
maintaining the position of the container
assembly within the concrete form during at least part of
and after the surrounding step, the maintaining step
including the steps of:
positioning a hold-down member above the
container assembly, the hold-down member including a
container-engaging member;
engaging the container assembly by the
container-engaging member; and
securing the hold-down member in place relative
to the form with the container-engaging member engaging
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- 2040435
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the container assembly to keep the container assembly
properly vertically and horizontally positioned within
the form;
allowing the concrete to set to create a
homogenous layer of concrete entombing the container
assembly; and
separating the form from the concrete entombed
container assembly.
In a further embodiment the invention is a
storage vault comprising:
an inner container assembly including:
an external framework; and
an inner, non-metallic container, having an
interior, mounted within the external framework;
an intermediate container housing the inner container
assembly, the external framework configured to keep at
least a part of the inner container spaced apart from the
intermediate container; and
a homogenous layer of concrete surrounding the
intermediate container.
The outer tank preferably includes bottom
supports. The bottom supports lift the tank a few inches
above the support surface on which the tank rests to
provide a visual inspection region between the bottom of
the outer tank and the support surface so the user can
visually monitor for leaks from the vault.
The spacer layer may be chosen so that if the
liquid stored within the inner tank contacts the spacer
layer, the spacer layer dissolves or "melts~ thus
permitting the leaked liquid to gather within a liquid
collection region between the inner tank and the liner.
A leak detection tube is used between the inner tank and
liner to permit monitoring of the liquid collection
region between the tube. This arrangement provides for
~ ~ thermal insulation without sacrificing the
ability to monitor for leaks. The spacer layer, being a
good thermal insulator, provides further protection for
~4
2040~35
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- 6 -
the contents of the inner tank during fires. The added
insulation also helps moderate the temperature swings of
the liquid within the inner tank which aids the control
of atmosphere pollution, as well as reducing safety
risks. Since no air space needs to be provided between
the inner and outer tanks for leak detection, pouring the
concrete around the combination of the inner tank, spacer
layer and liner is much simpler.
The use of reinforced concrete as the outer
tank provides several advantages. The concrete provides
a protective physical barrier for the inner tank, to
protect the inner tank from physical damage, at a
reasonable cost. The concrete outer tank also serves as
an effective thermal barrier. By using an Underwriters
Laboratories listed inner tank and the reinforced
concrete outer tank, an above-ground storage vault
suitable for use with flammable liquids is achieved.
The invention is transportable and can be used
above ground to store flammable liquids. This allows the
storage vault to be especially suited for temporary use
at construction sites. The costs associated with burying
tanks underground are also eliminated with the present
invention. If desired, multiple storage vaults can be
used and connected in parallel or in series according to
the use requirements. Also, two or more inner tanks can
be placed within a single outer tank.
Preferably the storage vault has a flat bottom.
Unlike many prior art storage containers, which are
spherical or cylindrical and must be supported on a
stand, the invention needs no separate support stand.
The invention is extremely stable and thus is quite
resistant to damage from earthquakes.
With the present invention a flammable liquid
can be stored safely above ground. This removes the tank
from local regulations and codes dealing with monitoring
below-ground storage tanks. The present invention still
permits the user to effectively monitor for leaks before
2040435
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any contamination to the surrounding earth occurs. The
ability to monitor the region between the primary and
secondary cont~;nr?nt vessels and the provision of skids
or supports on the bottom of the storage vault so that
the region beneath the outer tank can be visually
inspected, provides a double measure of protection
against damage to the environment.
The invention permits a user to store flammable
fuels above ground while meeting environmental and safety
requirements at a cost much less than comparable buried
storage tanks.
The invention also permits the concrete outer
tank to be made of a homogenous layer of concrete. This
eliminates cold joints, which are created when concrete
must be poured in several steps and allowed to harden
between the pours.
The non-metallic tanks may be made of plastic.
When the inner tank is not to be subjected to internal
pressurization during use, it may be desirable to entomb
the plastic tank directly in the concrete. To do so the
plastic tank is preferably pressurized, such as at 0.5 to
1.0 psi (0.034 to 0.069 bar), so the sides of the plastic
tank bow outwardly somewhat to resist the inward pressure
of the wet concrete. In such cases a greater number of
hold-down members, such as 12 instead of 4, are used to
distribute the load on the top of the plastic tank
created by the large buoyant forces from the wet
concrete.
In some cases non-metallic tanks, typically
plastic, are to be subjected to positive internal
pressures, such as 6 psi (0.41 bar), to eliminate the
- need to use pumps to remove the contents of the tank.
Since plastic tanks tend to bow outwardly under internal
pressurization, this would exert a pressure on the
concrete layer. To eliminate this problem, the plastic
tank can be mounted within an external framework which
generally holds the walls of the tank in place. The
"
20404 35
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framework enclosed plastic tank is then placed within an
intermediate barrier tank, which i8 preferably made of
steel. The intermediate barrier tank is then sealed shut
and is entombed as discussed above. The walls of the
plastic tank between the framework members may bow
outwardly when the tank is pressurized; however, the
framework members are sized so that the plastic tank
walls do not push against the walls of the intermediate
barrier tank so to keep from exerting forces directly on
the intermediate barrier tank. The external framework is
sufficiently rigid to minimize or substantially eliminate
exertion of pressurization forces from the plastic tank,
through the external framework and to the intermediate
barrier tank. This is expected to substantially
eliminate tension forces on the concrete outer tank when
the inner plastic tank is pressurized.
The inner plastic tank may be reinforced with
glass fiber or may be other resin impregnated structures.
Also, the region between the inner and intermediate tanks
can be monitored for leaks in addition to, or instead of,
monitoring for leaks between the intermediate barrier
tank and outer concrete tank.
Other features and advantages of the invention
will appear from the following description in which the
preferred embodiments have been set forth in detail in
conjunction with the accompanyinq drawings, in which:
Fig. 1 is a side cross-sectional view showing
a vault made according to the present invention.
Fig. 2 is an exploded cross-sectional view
taken along line 2-2 of Fig. 1.
Fig. 3 is a schematic illustration showing a
method for making the vault of Fig. 1.
Fig. 4 shows the inner tank of Figs. 1-3 within
the form assembly of Fig. 3.
Fig. 5 illustrates the internal reinforcing
members of the inner tank of Fig. 4 allowing the tank to
be used as a pressure vessel.
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_
g
Fig. 6 is an exploded isometric view of a
plastic tank assembly.
Fig. 7 is an isometric view of a further
alternative embodiment of a vault made according to the
invention with portions broken away to show the use of
the plastic tank assembly of Fig. 6 enclosed within a
steel tank which is entombed within a concrete tank.
Fig. 8 illustrates a hold-down assembly used
when entombing a non-metallic tank and using special
corner guides.
Fig. 9 is an enlarged view of the corner guide
of Fig. 8.
Referring now to Figs. 1 and 2, a vault 2 is
shown to include a steel inner tank 4 surrounded by a
spacer layer 6 of polystyrene. Inner tank 4 and spacer
layer 6 are entombed or encased within an outer tank 8.
Outer tank 8 includes a concrete layer 10 strengthened by
rebar 12, and a liquid impervious liner 14, preferably by
a sheet of polyurethane film. Conventional fill and vent
pipes 16 extend from inner tank 4. A leak detector tube
20 is positioned between inner tank 4 and liner 14 and
terminates at a liquid collection region 22. Tube 20
permits leaks from inner tank 4 to be monitored as the
leaking liquid collects within region 22.
Spacer layer 6 performs a dual function.
Spacer layer 6 is a good thermal insulator so to insulate
the contents of inner tank 4 from external heat sources,
such as forest fires. In addition, spacer layer 6 helps
keep the contents of inner tank 4 at a more uniform
temperature than would otherwise exist. This helps
reduce vapor pressures within inner tank 4 making the
storage of liquids safer and reducing the potential for
vapor leaks to the atmosphere. In addition, spacer layer
6 is chosen so that it melts or liquifies when the liquid
within inner tank 4 contacts the material of the spacer
layer. Typically, inner tank 4 will hold a liquid
hydrocarbon fuel, such as gasoline or diesel fuel. By
- lO- 2040435
choosing a spacer layer 6 made of polystyrene, if the
liquid within tank 4 leaks through and contacts spacer
layer 6, polystyrene spacer layer 6 melts or dissolves
thus creating an open region between inner tank 4 and
outer tank 8 permitting the leaked hydrocarbon to collect
at liquid collection region 22. This permits the leak to
be quickly noticed through leak detector tube 20 using
conventional methods.
As a further aid to detection of leaks, outer
tank 8 includes bottom supports 24 which raise the bottom
26 of vault 2 above the support surface 28 to create an
inspection region 30 between bottom 26 and support
surface 28.
Turning now also to Fig. 3, a simplified view
of the method for making vault 2 is shown. First, an
appropriate inner tank 4 is selected and has a number of
polystyrene panels 32 secured to the outer surface 34 of
inner tank 4, typically by an adhesive. A large sheet 36
of a liquid impervious material, such as polyethylene
film, is wrapped around the spacer layer encased inner
tank. The edges 38 of sheet 36 are gathered over the top
40 of inner tank 4 so to create a second liquid barrier.
A concrete form assembly 42 is used to entomb
the inner tank 4, spacer layer 6, liner 14 combination.
Form assembly 42 includes a base plate 44, having a pair
of openings 46, used to form bottom supports 24, and two
L-shaped wall forms 48, 50. Wall forms 48, 50 constitute
a sidewall form 51. After assembly of base plate 44 and
wall forms 48, 50, a rebar cage 52 is placed within an
enclosure 54 defined by wall forms 48, 50 and base plate
44. A layer 56 of concrete is then poured within
enclosure 54 to cover base plate 44. The combination 58
of inner tank 4, spacer layer 6 and sheet 36, which
creates liner 14, is then positioned within enclosure 54
on top of the still wet layer 56 of concrete. Additional
concrete is then placed within the region 60, see Fig. 4,
between combination 58 and wall forms 48, 50 sufficient
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to cover combination 50 and be generally level with top
edge 62 of sidewall form 51. The specific construction
of form assembly 42 will now be discussed with reference
to Fig. 4, in particular the structure for keeping
combination 58 from bobbing up out of the fluid concrete.
Form assembly 42, in addition to wall forms 48,
50 and base plate 44, includes a pair of form clamp
assemblies 64 at opposite corners 66, 68 of sidewall form
51, a lateral positioning assembly 70 adjacent base plate
44 and a pair of hold-down assemblies 72 which keep inner
tank 4 from floating within the concrete while it is
fluid.
Clamp assemblies 64 each include an L-bracket
73, welded to sidewall form 51, and a chain 74, secured
at one end to L-bracket 73 by an adjustment bolt 76.
Chain 74 has a hook 78 at the other end which engages the
corner of the adjacent wall form 48 or 50. Chain 74 is
tightened using a chain binder 80 which allows the user
to easily apply a strong clamping load on the two wall
forms 48, 50. Adjustment bolt 76 can be used to provide
any necessary fine adjustment to the tension in chain 74.
It has been found that use of two L-shaped wall forms 48,
50 and four form clamp assemblies 64 allow wall form 50
to be easily but securely fastened together while
ensuring the proper, in this rectangular, shape is
maintained.
Lateral positioning assemblies 70 each include
a jack block 82 welded to base plate 44 at a position
spaced apart from wall forms 48, 50. A hydraulic jack 84
is mounted between each jack block 82 and the opposing
side of wall forms 48, 50. Applying sufficient force on
wall forms 48, 50 through the use of jacks 84 positions
sidewall form 51 on base plate 44 and keeps the lower
ends of sidewall form 51 from moving laterally outwardly
due to the pressure of the concrete while it is still
fluid.
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Each hold-down assembly 72 includes an elongate
hold down bar 86 having chamfered endæ 88 guided between
vertical guide plates 90. Guide plates 90 are mounted to
wall forms 48, 50 and extend above top edge 62. Hold-
down bar 86 has a pair of downwardly extending hold-down
tubes 92 depending from its bottom surface 94 and a
strong back 96 mounted centrally above the top surface
102 of hold-down bar 86. Strong back 96 has an arcuate
guide surface 98 and a pair of vertical guide plates 100.
Hold-down assembly 72 includes a chain 104 having each
end 106 secured to an anchor point 108 on jack block 82.
Chain 104 passes from the jack block 82 on one side of
form assembly 42, between vertical guides 90, across
chamfered ends 88, over curved surface 98 of strong back
96 and down past the chamfered ends of hold-down bar 86
on the other side. Hold-down assembly 72, also includes
a chain ratchet 110. Chain ratchet 110 is used to
shorten the effective of length of chain 104 thus forcing
tubes 92 against the top 112 of inner tank 4.
Guide rings 114, each having an internal
diameter slightly larger than the external diameter of
tubes 92, are welded to top 112 at positions chosen to
engage the lower ends of tubes 92. Once so engaged,
lateral, as well as upward, movement of inner tank 4
within enclosure 54 is substantially eliminated.
Strong back 96 is used to strengthen hold-down
10 assembly 72. Strong back 96 keeps hold-down bar 86
from bowing upwardly due to the upward force on the hold-
down bar caused by tank 4 attempting to float when
surrounded by fluid concrete.
Turning now to Fig. 5, an inner tank 4' i9
shown to include U-channel reinforcing members 130 welded
to the inside surface 132 of inner tank 4' so that inner
tank 4' may be used as a pressure vessel. Reinforcing
members 130 form a number of hoops 134 circumscribing the
interior of tank 4'. The ends 136 of inner tank 4' have
vertically extending reinforcing members 130 mounted
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` 20~0435
- - 13 -
along their interior surfaces as well. Pairs of
reinforcing members 130 are placed back to back at
positions 138 along top 112 of inner tank 4' and at
positions 140 along the bottom 142 of inner tank 4'.
S This provides extra strength along the central portion of
tank 4'. A pair of lifting brackets 144 are welded to
top 112 of tank 4' adjacent positions 138 to facilitate
moving tank 4'.
A vault 2 made with an inner tank 4' can be
used as a vacuum storage vessel to safely handle waste
motor oil or crank case motor oil. The vault
incorporating reinforced inner tank 4' could have a
vacuum continuously applied to the inner interior of
inner tank 4'. A hose (not shown) would then be used to
connect inner tank 4' to the oil, or other liquid, to be
disposed of. The waste oil so collected could then
periodically be removed from the vault through the use
of, for example, a mobile vacuum tank truck which can
suck the waste oil directly out of the inner tank 4' and
into the mobile tank. This would permit gasoline service
stations, auto dealers, lube and oil change centres,
among others, to safely and conveniently store the waste
oil and grease in a safe, cost-effective manner. Even
without creating a vacuum in the interior of a vault 2,
vault 2 would still be useful for safely and
inexpensively storing such waste oil, waste grease and
other flowable materials, by pumping or pouring the waste
material directly into the vault.
To use form assembly 42, base plate 44 is
positioned on a, preferably, level support surface. Wall
forms 48, 50 are positioned on base plate 44 and are
fastened to one another by form clamp assemblies 64 at
each corner 66, 68. Hydraulic jacks 84 are then operated
to properly position sidewall form 51 on base plate 44
and keep the bottom of the sidewalls from kicking out due
to the pressure of the fluid concrete. Rebar cage 52 is
then placed within enclosure 54 and a layer 56 of
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concrete is poured into enclosure 54 to create bottom 26
of outer tank 8. Combination 58, see Fig. 3, is then
lowered into enclosure 54 until it rests on layer 56 of
concrete.
Hold-down bars 86 are then positioned over
enclosure 54 and lower ends of tubes 92 are positioned
within rings 114. Chains 104 are then placed over hold-
down bar 86 and fastened to jack blocks 82 at anchor
points 108. Chain ratchets 110 are used to tighten
chains 104 sufficiently to place an appropriate force on
hold-down bars 86. Concrete is then poured into
enclosure 54 to entomb combination 58, with the exception
of various fill and vent pipes 16 extending up through
concrete outer tank 8. Note that layer 56 of concrete is
still wet when the subsequent pour of concrete is made.
This ensures a homogenous concrete layer 10 with no cold
joints. Sidewall form 51 is then vibrated to settle the
aggregate in the concrete. The top surface 120 of outer
tank 8 is smoothed. Shear pins 122 can be used to keep
hold-down bars 86 from moving upwardly past upper holes
124 in vertical guides 90.
Once the concrete has set sufficiently, chain
ratchets 110 are actuated to loosen chains 104, shear
pins 122 are removed from holes 124 and hold-down bars 86
are lifted upwardly to remove tubes 92 from the layer of
concrete covering top 112 of inner tank 4. The holes
left by removal of tubes 92 are filled with fresh
concrete. After the concrete has cured sufficiently,
side-wall form 51 is removed from vault 2 and vault 2 is
separated from base plate 44.
The entombment of inner tank 4 could be
accomplished in other ways as well. For example, inner
tank 4 could be placed into form assembly 42 to rest on
base plate 44. Concrete could be pumped into form
assembly 42 through openings in base plate 44 to cause
inner tank 4 to lift above the base plate, with the
remaining procedure proceeding as above.
,.. .
-20qo43s
- 15 -
Some chemicals require specialized, expensive
.0 equipment to pump the chemicals from a holding tank
through a line. With a vault 2 made to withstand
pressurization, the air space above the free surface of
the liquid within the vault may be pressurized to force
the chemical from the vault without the chemical passing
through a pump. Similarly, the chemical could be sucked
into the vault 2 by placing the air space in the vault at
a partial vacuum as well.
Some materials are not suitable for storage in
a metal, typically steel, tank. Many chemicals are
therefore stored in plastic tanks. Although possessing
many advantages, plastic tanks are generally not nearly
as strong or rigid as steel tanks. The present invention
can be used with plastic (or other non-metallic) tanks if
appropriate modifications are made. At Fig. 6 a plastic
tank assembly 150 is shown to include a plastic tank 152
and an external framework 154. External framework 154
includes a set of upper and lower horizontal members 156,
158 formed from 3-inch or 4-inch U-channels welded
together along their lengths. Vertical members 160 are
welded to corresponding upper and lower horizontal
members 156, 158 to create a number of circumferential
rings 162. Rings 162 are secured together by horizontal
side members 164.
External framework 154 is substantially
completed as shown in Fig. 6 and then plastic tank 152 is
moved into the interior of framework 154. After in
position, the end-most horizontal member 166 is welded in
place. This is necessary due to the location of a
manhole protrusion 168 on tank 152. Manhole protrusion
168 may be plastic, metal or some other material. Also,
an end bar 170 is welded in place in a position similar
to the end bar 172 at the other end of external framework
154.
When assembled, plastic tank assembly 150 is
placed into a steel tank 174, see Fig. 7, which i8
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similar to steel tank 4. However, steel tank 174 has a
top 176 with an opening (not shown) sized and positioned
for receipt of manhole protrusion 168. Any gap between
manhole protrusion 168 and the opening is sealed, such as
using a silicone sealant, such as G.E. Silicone II, Stock
No. GE5090, which is apparently covered by U.S. Patent
Nos. 4,417,0421 and 4,843,973. Plastic tank assembly 150
and steel tank 174 combine to act as an inner tank
assembly 180 which can be entombed in the same manner as
inner tank 4 to create a vault 182.
When inner tank assembly 180 is used, the user
is 15 provided with what can be considered a triple-wall
tank structure with collection regions between plastic
tank 152 and steel tank 174 and also between steel tank
174 and the concrete outer tank 183. Leaks can be
monitored in either or both regions. If desired,
polystyrene panels 32 and sheet 36 (not shown in Fig. 7
for sake of clarity) may be eliminated, although at the
expense of additional protection.
The use of steel tank 174 provides several
functions. It keeps the wet concrete from pressing on
plastic tank 152, which could potentially collapse the
plastic tank. Steel tank 174 also acts as a protective
barrier for plastic tank 152. In addition, by separating
plastic tank 152 from steel tank 174, and thus from
concrete outer tank 183, vault 182 can be used in a
pressurized state. That is, providing a positive
pressure to plastic tank 152 of about 6 psi (about 0.41
bar) permits the contents of the plastic tank to be
forced out of the tank without the passage of the
contents through a pump. Since many chemicals are quite
damaging to pumps, making inner tank assembly 180
suitable for pressurization eliminates the need for using
a pump to draw the chemical from assembly 180. Although
it is expected that the walls of plastic tank 152 will
bow outwardly between circumferential rings 162, side
members 164 and end bars 170, 172, external framework 154
.. ,il ~
- 204 04 35
- 17 -
is configured so that plastic tank 152 will not touch
steel tank 174. In fact, it is preferred that the
maximum amount of deflection of the plastic tank be about
one-third the distance between plastic tank 152 and steel
tank 174. The use of external framework 154 thus
substantially eliminates any exertion of internal
pressure on steel tank 174 so that, in turn, steel tank
174 does not exert any pressure on concrete outer tank 8.
Tank 152 is preferably of the type made by Poly
Cal Plastics, Inc. of French Camp, California under the
trade-mark Zorb Tanks. This tank is made of a cross-
linked polyethylene to be environmentally stable and has
a wall thickness of about 1/2 inch (about 12.7 mm) for
sufficient strength. However, when exposed to sunlight,
elevated temperatures and oxygen, the stability of the
material is lessened. Of course, being a plastic, it is
sensitive to excessive heat and fire as well. Therefore,
the protection afforded by concrete outer tank 183,
polystyrene panels 32 and steel tank 176 eliminates many
of the shortcomings which otherwise exist with this or
other plastic tanks.
Turning now to Fig. 8, a hold-down assembly
184, similar to hold-down assembly 72, is shown with like
elements referred to by like reference numerals. Hold-
down assembly 184 includes 12 hold-down tubes 92 instead
of the four hold-down tubes shown in the embodiment of
Fig. 4. Hold-down assembly 184 is more rigid than
assembly 72 through the use of more hold-down bars 86,
cross-bars 185 and stiffener tubes 187 welded to bars 86.
This is so because hold-down assembly 184 is used when
plastic tank 152 is entombed directly within the concrete
without the use of external framework 154 or steel tank
174. Doing so helps distribute the forces exerted by
hold-down assembly 184 on the top of plastic tank 152 due
to the buoyant forces created by the fluid concrete.
Hold-down assembly 184 does not require the use
of any sort of guide rings 114 as used with the
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- 18 -
embodiment of Fig. 4. Rather, corner hold-down tube~
186, shown in more detail in Fig. 9, each include a
corner guide 188 extending downwardly therefrom, the
corner guides engaging the four corners of plastic tank
152. Since hold-down assembly 184 is properly positioned
with respect to the form assembly 42 with which it i8
used, plastic tank 152 is properly positioned by the
guidance given by corner guides 188. Using corner guides
appropriately configured to engage the corners or edges,
of tank 152, or of any other tank used with the
invention, eliminates the need for special guiding
structure such as used with the embodiment of Fig. 4.
It is preferred that plastic tank 152 be
pressurized above atmospheric pressure during direct
entombment within the concrete. Doing so at relatively
moderate pressures, for example about 1/2 to 2-~ psi
(about 0.035 bar to about 0.17 bar), causes tank 152 to
expand slightly. This pressurization has been found to
generally eliminate the need for internal bracing within
tank 152.
The elevated pressure within tank 152 is
preferably reduced after the concrete has set. This
permits tank 152 to shrink back to its original shape.
It is beiieved that a small space or gap is created
between tank 152 and concrete layer 10. This space or
gap forms an internal expansion region for tank 152 to
accommodate subsequent pressurization. This system of
pressurization is disclosed in more detail in U.S. Patent
Application Serial No. 07/319,598 filed March 6, 1989,
now U.S. Patent No. 4,931,235 issued June 5, 1990.
Modification and variation can be made to the 5
disclosed embodiments without departing from the subject
of the invention as defined by the following claims. If
desired, nonflammable liquids can be stored in vault 2.
Although it i5 preferred to include rebar cage 52 as a
part of outer tank 8, one need not necessarily do so.
Inner tank 4, although in the preferred embodiment made
2040435
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of steel, could be made of other suitable material
according to the particular li~uid being contained and
the environment. It is preferred that vault 2 have a
flat bottom for stability. However, other shapes are
also possible. Vertical force can be applied to inner
tank 4 during curing of the concrete in ways not shown.
For example, tubes 92 could be replaced by I-beams
permanently mounted to inner tank 4 and left within
concrete top 126. Also, by appropriately positioning
fill and vent pipes 16, the tops of these pipes may be
used to apply the necessary vertical force on inner tank
4 to keep the inner tank from floating before the
-- concrete has set. One or both of chain binders 80 and
chain ratchets 110 may be replaced by other suitable
tightening devices, such as hydraulic push-pull jacks.
Many different configurations of centering frame 154
could be used as well. Additional framework members
could be used with external framework 154, such as
between upper horizontal members 156 and between lower
horizontal members 158. Plastic tank 152 could be made
of other non-metallic materials.
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