AU2005203085C1 - Improved Storage Tank and Method of Installation - Google Patents

Abstract

Abstract A water storage tank 10 has exterior walls 12, 14, 16 and an interior space defining a storage volume. The tank 10 has passageways 30, 32, 34, 36 5 extending from an upper part of the tank to a lower part of the tank. The passageways have an opening at an upper end thereof such that a reinforcing or strengthening material, particularly concrete, can be inserted into the one or more passageways to strengthen the tank. The tank can be installed underground or even under driveways. The tank is also suitable as a transport tank because the passageways act as baffles. 10 (Figure 1)

Description

1 IMPROVED STORAGE TANK AND METHOD OF INSTALLATION Field of the Invention The present invention relates to a tank, such as a storage tank for storing liquids. The tank, in some embodiments, is particularly suitable for use as an 5 underground storage tank. Other aspects of the present invention relate to a method for installing a tank and to a method for making a driveway or other trafficable area. Background to the Invention Recent drought conditions across much of Australia have lead to the widespread introduction of water restrictions for many urban or metropolitan areas. 10 Partly as a result of this, but also in response to increased demand in urban areas due to population growth and constraints arising from dam capacity limits, local councils in Australia have, in the past decade or so, have reevaluated their philosophy on water storage tanks. For example, in Sydney, until the late 1990s, local council regulations prohibited the installation of rainwater storage tanks. This prohibition has now largely is been removed across the greater Sydney area. Indeed, the New South Wales State Government is now offering rebates to householders who install rainwater storage tanks in Sydney. This change in mindset towards rainwater storage tanks has also been taken up by householders. Water restrictions in a number of metropolitan areas in 20 Australia mean that watering of gardens and washing of motor cars at home is now banned. As a result, a number of householders are installing rainwater storage tanks to catch rainwater falling on the roofs of their houses so that the householders may continue to water their gardens and wash their cars at home using the stored rainwater. To obtain a reasonable supply of rainwater to hopefully carry a 25 householder through periods of drought and/or water restrictions, the rainwater storage tank should suitably be of a large volume. Unfortunately, many urban housing blocks are now quite small in area. Further, current trends are for householders to build houses of ever increasing size on their blocks of land. As a result, householders are experiencing difficulty in finding suitable locations for positioning water storage 30 tanks. In many instances, there is simply not enough space available to install the tank at an above-ground location.

2 Similarly, underground installation of rainwater storage tanks on urban properties is also complicated by the small size of the urban blocks of land and, frequently, by the installation of in-ground swimming pools in the backyard providing further restrictions on the positioning of underground storage tanks. 5 Most modern housing developments in Australia result in the construction of houses having a driveway extending from a footpath, across the front yard and to the garage of the house. The ground underneath the driveway represents an unused area that potentially offers a suitable location for an underground rainwater storage tank. However, it has not been possible to install underground rainwater 10 storage tanks under driveways because the weight of the concrete in the driveway, especially when combined with the weight of vehicles driving on the driveway, would frequently exceed the maximum strength of the tank, leading to potentially dangerous breakage or collapse of the tank. Brief Description of the Invention 15 In a first aspect, the present invention provides an installed underground tank for storing liquids, said tank having exterior walls and an interior space defining a storage volume, and one or more passageways extending from an upper part of the tank to a lower part of the tank, said one or more passageways having an opening at an upper end thereof, wherein a reinforcing or strengthening 20 material fills the one or more passageways to thereby strengthen said tank. As used throughout this specification the expression "to strengthen said tank" and its contextual variants should be taken to include using the reinforcing or strengthening material to increase the resistance of the tank against structural failure resulting from externally applied loads, particularly externally applied loads that apply 25 a downwardly directed force. Suitably, the one or more passageways extend through the storage volume of the tank. Even more suitably, the one or more passageways extend from an upper wall of the tank, through the storage volume of the tank and down to a lower wall of the internal volume of the tank. 30 In some embodiments, the one or more passageways extend in a generally vertical direction when the tank is in an installed position.

3 In some instances, the one or more passageways may have an opening at their lower end. In these instances, a pourable or flowable reinforcing material, such as concrete, may be poured into the passageways such that it passes out the opening at the lower end of the passageway and forms a pool or slab around and at 5 least partly underneath the tank. This also assists in bearing loads applied to the upper part of the tank, as well as more securely fixing the tank in position. Further, the reinforcing material can come into direct contact with the ground or a support surface underneath the tank, such that the loads transmitted by the reinforcing material are borne by the ground or supporting surface underneath the tank. 10 In a second aspect, the present invention provides a tank for storing liquids, said tank having exterior walls and an interior space defining a storage volume, and one or more passageways extending from an upper part of the tank to a lower part of the tank, said one or more passageways having an opening at an upper end thereof such that a reinforcing or strengthening material can be inserted into the 15 one or more passageways to thereby strengthen said tank, wherein the one or more passageways extend through a storage volume of the tank. The tank in accordance with the present invention may have an opening in an upper part therof, which opening is facing in a generally upwards direction. The opening may, for example, be a manhole type opening. 20 The tank in accordance with the present invention is particularly suitable for underground installation. Accordingly, in a third aspect, the present invention provides a method for installing an underground storage tank comprising providing a tank having exterior walls and an interior space defining a storage volume, and one or more passageways extending from an upper part of the tank to a 25 lower part of the tank, said one or more passageways having an opening at an upper end thereof such that a reinforcing or strengthening material can be inserted into the one or more passageways to thereby strengthen said tank, preparing a suitable hole in the ground, placing the tank in the hole, and pouring a flowable material into the one or more passageways to thereby fill the passageways and form a reinforcing or 30 strengthening material in the one or more passageways. Preferably, the flowable material is a settable material and the method 4 includes the step of allowing the flowable material to set to form a reinforcing or strengthening material in the one or more passageways. In one embodiment of the method of the present invention, the one or more passageways in the tank have openings at their lower ends and the flowable 5 material is poured into the one or more passageways such that the flowable material flows out through the openings in the lower end of the one or more passageways and fills a space between the bottom of the hole and a lower part of the tank, whereafter continued pouring of the material causes the flowable material to fill the one or more passageways. 10 In an especially suitable embodiment of the present invention, the flowable material is used to cover the upper part of the tank as well as fill the one or more passageways of the tank. This is especially suitable in instances where the tank is to be positioned underneath a driveway or other trafficable area. The strengthening material is suitably concrete. The concrete may be a 15 reinforced concrete, in which case appropriate reinforcement, such as steel reinforcing bars, are inserted into the one or more passageways prior to pouring the concrete therein. Although concrete is especially suitable for use in the present invention, it will appreciated that other strengthening or reinforcing materials may be 20 used. These may include polymerisable or settable resins, reinforcing structures made of metal, which structures include arms or legs that can be inserted into the one or more passageways, other similar reinforcing structures made of different materials other than metal, and the like. In a fourth aspect, the present invention provides a method for forming 25 a driveway, said method comprising the steps of providing a tank having exterior walls and an interior space defining a storage volume, and one or more passageways extending from an upper part of the tank to a lower part of the tank, said one or more passageways having an opening at an upper end thereof such that a reinforcing or strengthening material can be inserted into the one or more passageways to thereby 30 strengthen said tank, preparing a hole in the ground, placing the tank in the hole, pouring a flowable material into the one or more passageways to fill the one or more 5 passageways and continuing pouring such that the flowable material also forms a driveway above the tank. Preferably, the flowable material comprises a settable material and the method further includes allowing the flowable material to set to form a reinforcing or 5 strengthening material in the one or more passageways and to form a driveway capable of carrying vehicular traffic. The method of the fourth aspect of the present invention may further comprise the steps of laying appropriate reinforcing means, such as steel reinforcing bars, in the driveway prior to pouring the flowable material to form the driveway. The 10 flowable material is suitably concrete. Brief Description of the Drawings Preferred embodiments of the present invention will now be described with reference to the following drawings in which: Figure 1 shows a perspective view of a tank in accordance with an 15 embodiment of the present invention; Figure 2 shows a top view of the tank shown in Figure 1; Figure 3 shows a bottom view of the tank shown in Figure 1 (Figure 3 is shown a larger scale than Figure 2); Figure 4 is a cross sectional perspective view taken along the 20 longitudinal axis of the tank shown in Figure 1; Figure 5 is a side view of a cross section taken along line A-A shown in Figure 2; Figure 6 is a cross sectional view taken along line C-C shown in Figure 2; 25 Figure 7 is a cross sectional end view taken along line D-D shown in Figure 2; Figure 8 is a perspective view of a tank in accordance with another embodiment of the present invention. The tank shown in Figure 8 is generally similar to the tank shown in Figures 1 to 7, except that the tank shown in Figure 8 is a larger 6 capacity tank; Figures 9 to 11 show a sequence of steps used to install an underground tank and construct a driveway in accordance with aspects of the present invention; Figure 12 shows a perspective view of a tank in accordance with 5 another embodiment of the present invention; Figure 13 shows a plan view of the tank shown in Figure 12; Figure 14 shows a front view of the tank shown in Figure 12; Figure 15 shows a side view of the tank shown in Figure 12; Figure 16 shows a cross-sectional view taken along line A-A of the 10 tank shown in Figure 12; Figure 17 shows a sectional view taken along line B-B of the tank shown in Figure 12; Figure 18 shows a perspective view of a tank in accordance with a further embodiment of the present invention; and is Figure 19 shows a perspective view of a tank in accordance with a further embodiment of the present invention. Detailed Description of the Drawings It will be understood that the drawings are provided for the purposes of illustrating preferred embodiments of the present invention. Thus, the present 20 invention should not be considered to be limited solely to the features as shown in the drawings. Figures 1 to 7 show a tank 10 in accordance with an embodiment of the present invention. The tank 10 is particularly suitable for underground installation. However, it will be appreciated that the tank should not be considered to be limited 25 solely to use in underground installations. The tank 10 shown in Figures 1 to 7 is particularly useful for storing liquids, such as rainwater collected from the roofs of buildings. For convenience, the tank will be described hereinafter with reference to its use as tank for rainwater.

7 The tank 10 comprises end walls 12 and 14 and a generally cylindrical side wall 16. As per shown in Figures 2 and 3, end walls 12 and 14 are convex walls to assist in improving the strength of the generally cylindrical tank 10. The tank 10 is suitably made from a polyethylene or other plastics 5 material. However, it will be appreciated that the tank 10 may be made from other suitable tank structure materials, such as fiberglass or sheet metal. As mentioned above, the tank 10 is suitably made from polyethylene. The tank 10 may be made by a rotomolding process, as will be know to person as skilled in the art. In manufacturing the tank 10 an upper mould part and a lower 10 mould part are joined together and the tank is formed as a single piece tank by rotamoulding. The mould parts are then separated and the tank removed. Centre flange 18 represents the line where the two mould parts abut each other. This is conventional in the art and need not be described further. The end walls 12 and 14 include a plurality of reinforcing ribs 20, only 15 some of which are numbered in the figures. Reinforcing ribs 20 are used to enhance the strength of the tank. Similarly, the generally cylindrical side wall 16 includes a plurality of reinforcing ribs 22. A tank opening 24 is located in the upper part of the side wall 16. As 20 can be seen, opening 24 faces in an upwards direction when the tank is installed. Opening 24 is suitably positioned such that it is above the full storage water level in the tank. The tank opening 24 allows appropriate inlet and outlet pipes to respectively enter and exit the tank 10. When the tank 10 is used in an underground installation, the opening 24 may be closed with a lid (not shown) which has apertures allowing the 25 inlet and outlet pipes to pass therethrough. The inlet pipe transfers rainwater collected from the roof of a building into the tank, whilst the outlet pipe allows water stored in the tank to be selectively removed therefrom. In order to facilitate selective removal of water from the tank 10 the tank is suitably fitted with a submerged pump (not shown). The fitment and operation of the inlet and outlet pipes and the submerged 30 pump will be readily understood by person skilled in the art and need not be discussed further.

8 The tank 10 also includes rectangular projections 26, 28 extending downwardly from the central flange 18 and laterally from the centre of the bottom of the tank. As best shown in Figure 7, the generally rectangular projections 26, 28 are positioned on either side of the tank. These projections act as a stand and allow the 5 tank to be easily oriented in its upright orientation. The tank 10 also includes 4 passageways 30, 32, 34, 36 that extend through the inner volume of the tank. Each of the passageways 30, 32, 34, 36 has respective upper openings 38, 40, 42, 44. These are shown in Figure 2. Similarly, each of the passageways 30, 32, 34, 36 has respective lower openings 46, 48, 50, 52, 10 which are shown in Figure 3. Each of the passageways 30, 32, 34, 36 have a wall extending from its upper opening to its lower opening. The wall extends through the inner volume of the tank and acts to define the passageway between the upper and lower openings. The wall of the passageway also acts to isolate the interior of each passageway from the 15 interior of the tank. Thus, reinforcing or strengthening material can be inserted into each passageway without that material coming into contact with and contaminating the contents stored in the inner volume of the tank. Figure 4 shows the wall 54 of passageway 30 and the wall 56 of passageway 36. Figure 5 also shows these features. Figure 6 is a cross sectional side view taken through a section line that 20 passes through the passageways 30 and 36. Figure 7 is an end view cross sectional view taken along a sectional plane passing through the passageways 30, 32 again, Figures 4, 5, 6 and 7 show the passageways as extending through the interior volume of the tank whilst ensuring that the interior of the passageways remains isolated from the interior volume of the tank. 25 Figures 9 to 11 show schematic diagrams illustrating one possible installation for a tank in accordance with the present invention. In Figure 9, the tank 10 is placed into a hole 70 dug into the ground. Hole 70 has side walls 72 and 74. Formwork 76 is appropriately positioned on the ground above the hole 70 holding the tank 10. The normal ground level is shown by reference numeral 78 in Figure 9. As 30 can be seen from Figure 9, the upper part of tank 10 is positioned such that it is below the normal ground level 78.

9 Once the tank has been positioned in the hole 70, an aggregate material 80, such as gravel is used to largely fill the space between the side of the tank 10 and the side walls 72, 74 of the hole 70. The aggregate 80 packs out the space between the outer walls of the tank 10 and the walls of the hole 70 to (a) assist in maintaining 5 the tank in its proper position and (b) minimise the amount of concrete that sits above the tank 10. After positioning the aggregate, steel reinforcing bars 82 are positioned within the form work 76 and concrete 84 is poured into the form work. Reinforcing bars may also be positioned in the passageways 30 and 32, if desired or required. The 10 concrete 84 passes through the openings 38, 40 of respective passageways 30 and 32. The concrete fills passageways 30 and 32 and extends underneath the tank 10, as shown schematically at reference numeral 84. When the passageways 30 and 32 are full of concrete, the concrete then fills the space 86 above the tank and the space defined by the form work 76 to thereby form a driveway positioned above the tank. 15 As can be seen from Figure 11, when the concrete 84 sets, the passageways 30 and 32 (and indeed all other passageways formed in the tank) are filled with a set, hardened concrete that acts as a pier supporting the driveway 88 formed above the tank 10. Thus, the concrete piers that are formed in the passageways of the tank strengthen the tank, bear the load of the driveway and any 20 vehicular traffic on the driveway and enable the underground storage tank to be positioned underneath the driveway with minimal risk of collapse of the upper walls or roof parts of the tank. In order to complete installation of the tank and construction of the driveway, the formwork 76 shown in Figure 11 is removed once the concrete has 25 cured. Figure 8 shows an alternative embodiment for tank in accordance with the present invention. The tank 100 shown in Figure 8 is essentially similar to the tank 10 shown in Figure 1, except that tank 100 shown in Figure 8 is of significantly larger volume. For convenience, like features on Figure 8 have been denoted by like 30 reference numerals to that used in Figure 1, but with a prime attached thereto. In another embodiment of the present invention, the passageways do 10 not pass through the interior volume of the tank but rather pass through the exterior walls of the tank, are formed as part of the exterior walls of the tank or are attached to the exterior walls of the tank. In a further alternative embodiment, rather than having hollowed passageways passing through the interior volume of the tank, solid members 5 pass through the interior member of the tank. These solid members constitute reinforcing members passing through the interior volume of the tank and act to support or bear loads applied to the upper part of the tank, for example loads applied by a driveway located above the tank. Further embodiments of a tank in accordance with the present 10 invention are shown in Figures 12 to 19. Figures 12 to 17 show various views of a tank in accordance with a further embodiment of the present invention. The tank 100 shown in Figure 12 is of generally rectangular outer configuration. The tank 100 has an exterior surface 102 that has an upper part 104 and a lower part 106. Parts 104 and 106 are more clearly 15 shown in Figures 14 and 15. The tank 100 includes a plurality of passageways 108, 110, 112, 114, 116 and 118. The passageways are most clearly shown in Figure 13. As can be seen from Figure 1, the passageways are defined by the upper surface 102 generally curving downwardly towards the central parts of each of the passageways. The lower part of 20 the passageways is formed with a similar shape. Thus, the passageways have a middle portion that is of generally smaller width or diameter than the upper openings and lower openings of the passageways. The tank 100 further includes a tank opening 120. Tank opening 120 is positioned on the upper surface 102 of tank 100. Suitably, the tank 100 includes an 25 upwardly projecting duct 122 that has the opening 120 formed at an upper end thereof (see Figure 14). The lower end of duct 122 is suitably in fluid communication with the internal volume of the tank 100. The tank also includes a plurality of recessed reinforcing ribs 124. For clarity, only some of the recessed reinforcing ribs have been numbered in Figures 12 30 to 17. The recessed reinforcing ribs 124 provide increased strength to the tank. It will be appreciated that outwardly projecting reinforcing ribs may alternatively or also be 11 provided for the same purpose. As best shown in Figures 16 and 17, the interior volume of the tank includes generally circular shaped cross sectional regions 126, 128, 130, 132. The shape of these regions assists in providing strength to the tank. Similar shaped cross 5 sectional regions are formed in the interior of the tank, when viewed in cross section in a direction transverse to the view shown in Figure 16. Figure 18 shows a perspective view of the tank in accordance with another embodiment of the present invention. The tank 150 shown in Figure 18 is of generally similar construction to the tank 100 shown in Figures 12 to 17. However, 10 the tank shown in Figure 18 only has four passageways extending therethrough. The passageways are designated by reference numerals 152, 154, 156 and 158. In contrast, the tank 100 shown in Figures 12 to 17 has six passageways. Other features of the tank shown in Figure 18 that are in common with the features of the tank 100 shown in Figures 12 to 17 are denoted by the same 15 reference numerals as used in Figures 12 to 17, but with the addition of a prime. Figure 19 shows a tank 160 that is generally similar to that shown in Figures 12 and 18, but with only a single passageway therein. The tanks shown in Figures 12 to 19 have generally straight side edges. However, it will be appreciated that similar tanks having one or more curved edges 20 may also be provided. For example, the tank shown in Figure 19 may be provided with a generally circular outermost edge (when viewed in plan). Similarly, the tank shown in Figures 12 and 18 may also have one or more curved outermost edges. For example, such tanks may have two curved opposed edges (for example, along the shortest sides of the tank shown in Figure 12), with the opposed curved edges being 25 interconnected by sides having two generally straight outermost edges. Similarly the tank 160 shown in Figure 19 may be lengthened in one dimension such that the passageway therein is longer than it is wide. The tanks shown in Figures 12 to 19 may be installed underground or under drive ways or other areas that receive vehicular traffic. Installation may be 30 carried out in a generally similar manner as described with reference to Figures 9 to 11. In broad terms, a hole is excavated, the tank placed in position, concrete poured 12 and allowed to set. As a further advantage of the present invention, where passageways or reinforcement means pass through the interior volume of the tank, the passageways or reinforcement means act as baffles. Thus, the tank could also be used as a mobile S storage tank, for example, mounted onto the back of a truck. It will be appreciated that mobile storage tanks must be baffled for safety purposes. The present invention provides a tank for storage of liquids that is particularly suitable for underground installation with minimal risk of collapse of the upper part or roof of the tank. The tank can be installed underneath driveways of 10 houses, thereby taking advantage of what would be otherwise unusable space. When used as a rainwater tank, the tank allows storage of collected rainwater in urban environments without adversely impacting on the outdoor areas of a suburban housing block. The method for installing the tank, as described with reference to 15 Figures 9 to 11, also results in the production of concrete piers that form part of the driveway. Not only do the concrete piers strengthen the tank and act to bear loads applied to the driveway, the piers also strengthen the driveway. When used in underground installations, the tank will need to be provided with a submerged pump. This is particularly useful in urban environments 20 because the pump is contained within the tank and thus there is little or no noise pollution caused by operation of the pump. In some embodiments of the present invention, the tank may be installed such that access to the opening 24 is possible after installation. For example, where the tank is installed in a driveway, an appropriate blank may be included in the 25 driveway formwork such that the concrete of the driveway does not cover the opening of the tank. An appropriate manhole cover or grate may then be positioned over that opening for safety purposes. This is advantageous as access to the tank can be obtained for the purposes of maintenance or repair. Those skilled in the art will appreciate that the present invention may 30 be susceptible to variations modifications other than those specifically described. It is to be understood that the present invention encompasses all such variations and 13 modifications that fall within its spirit and scope.

Claims (21)

1. A method for installing an underground storage tank comprising providing a tank having exterior walls and an interior space defining a storage volume, and one or more passageways extending from an upper part of the tank to a lower part of the tank, said one or more passageways having an opening at an upper end thereof such that a reinforcing or strengthening material can be inserted into the one or more passageways to thereby strengthen said tank, preparing a suitable hole in the ground, placing the tank in the hole, and pouring a flowable, settable material into the one or more passageways to thereby fill the passageways and allowing the flowable material to set to form a reinforcing or strengthening material in the one or more passageways.

2. A method as claimed in claim I wherein the one or more passageways in the tank have openings at their lower ends and the flowable material is poured into the one or more passageways such that the flowable material flows out through the openings in the lower end of the one or more passageways and fills a space between the bottom of the hole and a lower part of the tank, whereafter continued pouring of the material causes the flowable material to fill the one or more passageways and allowing the flowable material to set.

3. A method as claimed in claim I or claim 2 wherein the flowable material also covers the upper part of the tank.

4. A method as claimed in claim 3 wherein the flowable material forms a driveway or other trafficable area.

5. A method as claimed in any one of claims I to 4 wherein the flowable material is concrete.

6. A method as claimed in claim 5 wherein the concrete is a reinforced concrete and the method further includes placing appropriate reinforcement, such as steel reinforcing bars, into the one or more passageways prior to pouring the concrete therein.

7. A method for forming a driveway, said method comprising the steps of providing a tank having exterior walls and an interior space defining a storage volume, and one or 15 more passageways extending from an upper part of the tank to a lower part of the tank, said one or more passageways having an opening at an upper end thereof such that a reinforcing or strengthening material can be inserted into the one or more passageways to thereby strengthen said tank, preparing a hole in the ground, placing the tank in the hole, pouring a flowable and settable material into the one or more passageways to fill the one or more passageways and continuing pouring such that the flowable material also forms a driveway above the tank and allowing the flowable and settable material to set to thereby form a reinforcing or strengthening material in the one or more passageways and to form the driveway.

8. A method as claimed in claim 7 wherein the flowable material is concrete.

9. An installed underground storage tank for storing liquids, said tank having exterior walls and an interior space defining a storage volume, and one or more passageways extending from an upper part of the tank to a lower part of the tank, said one or more passageways having an opening at an upper end thereof, wherein a reinforcing or strengthening material fills the one or more passageways to thereby strengthen said tank, said reinforcing or strengthening comprising a flowable and settable material that is poured into the one or more passageways and allowed to set.

10. An installed underground storage tank as claimed in claim 9 wherein the reinforcing or strengthening material comprises concrete.

11. An installed underground storage tank as claimed in claimed in claim 9 or claim 10 wherein the one or more passageways extend through a storage volume of the tank.

12. An installed underground storage tank as claimed in claim 11 wherein the one or more passageways extend from an upper wall of the tank, through the storage volume of the tank and down to a lower wall of the tank.

13. An installed underground storage tank as claimed in any one of claims 9 to 13 wherein the one or more passageways have an opening at their lower end.

14. An installed underground storage tank as claimed in any one of claims 9 to 13 wherein at least one of the one or more passageways has an upper opening that tapers inwardly from an upper part thereof to a lower part thereof. 16

15. An installed underground storage tank as claimed in claim 14 wherein the at least one passageway tapers to a generally mid region of smallest dimension and tapers outwardly from the region of smallest dimension to a lower opening.

16. An installed underground storage tank as claimed in any one of claims 9 to 15 wherein the tank has straight outermost edges.

17. An installed underground storage tank as claimed in any one of claims 9 to 16 wherein the tank has a least one curved outermost edge.

18. An installed underground storage tank as claimed in claim 17 wherein the tank has two opposed curved outermost edges connected by respective straight outermost edges, when viewed from above.

19. An installed underground storage tank substantially as hereinbefore described with reference to the accompanying drawings.

20. A method for installing an underground tank substantially as hereinbefore described with reference to the accompanying drawings.

21. A method for forming a driveway substantially as hereinbefore described with reference to the accompanying drawings.