WO 2007/104083 PCT/AU2007/000278 MODULAR RAINTANK WITH PANELS HAVING STRUTS AND NODES CLAIM OF PRIORITY This application claims priority to Australian provisional application No. 2006901293, filed March 12, 2006. FIELD OF THE INVENTION The present invention relates to underground raintanks, and in particularly to modular plates which form underground raintanks. BACKGROUND OF THE INVENTION Underground infiltration and raintanks are formed from plastic perforated tank modules, which are butted or stacked together to form the required tank size, wrapped in geotextile and surrounded in good draining medium such as sand. The geotextile material allows water to pass therethrough but prevents any sand from passing. Thus, water flows into the infiltration tank via a connecting pipe and percolates into the surrounding strata through the geotextile-covered perforated walls of the tank. Similarly, water percolating through the soil above the tank enters the tank through the geotextile-covered top perforated wall of the tank. To form a reuse or water-harvesting tank, the above tank system is typically fully surrounded by a water impervious sheet. There are many existing underground water tank products in the market place, and each of these suffers from various disadvantages. Some existing products comprise two perforated half-box modules with a plurality of columns located in the box and parallel to the sidewalls of the box. To assemble the tank, the two half-box modules are pushed together such that the columns of one half-box module interlock with the columns of the other module. Although the tank is strong, it uses a large amount of plastic material. Additionally, the tank contains only approximately 50% void volume and water flow through the sidewalls is quite restricted. Other products are made from perforated plastic wall panels or plates which interlock together to assemble individual tank modules. These plastic wall panels comprise a skeletal grid framework to support the geotextiles. The skeletal framework of plastic members contains numerous apertures through WO 2007/104083 PCT/AU2007/000278 2 which water is able to flow. Thus assembled tank modules, while having a large void volume and better flow through the walls, are considerably weaker than the tanks assembled from two half-box modules. In addition, such tank modules still use a large amount of plastic materials and are expensive to make. 5 In the existing prior art infiltration wall panels, the strut members are arranged in parallel arrays which are all of the same cross section, and the arrays intersect each other with no reinforced loading points. Such an arrangement of arrays does not distribute the loading across the panel equally, and can concentrate forces onto particular points of the array causing failure. As a result, 10 the prior art wall panels are inherently weak because all the synergistic effects of parallel vectors have no reservoir for absorbing forces on the plate. Accordingly, a need exists for a modular raintank which would provide adequate void space and water flow through as well as a strong geotextile supporting skeleton, thereby avoiding the above-mentioned deficiencies of the 15 prior art. SUMMARY OF THE INVENTION The present invention satisfies this need. The invention is an underground water infiltration system assembled from a plurality of modular panels which have perforated surfaces to allow water flow. 20 In one embodiment, the present invention is a modular wall panel for an underground infiltration/storage raintank, comprising: a rectilinear periphery formed of four edge members; a plurality of longitudinally running strut members extending between the edge members and intersecting the periphery edge members at a plurality of 25 junctions; a plurality of transversely running strut members extending between the edge members and intersecting the longitudinally running strut members and the periphery edge members at a plurality of junctions; at least one first reinforcing node formed at a plurality of junctions of the 30 longitudinally running strut members and the transversely running strut members and their junctions with the periphery edge members; WO 2007/104083 PCT/AU2007/000278 3 at least one second reinforcing node formed at a plurality of junctions, the second reinforcing node being larger in diameter than the first reinforcing node; and a plurality of diagonally extending non-parallel strut members extending 5 between adjacent nodes. In one embodiment of the invention, the second reinforcing nodes are located closer to their adjacent transversely running strut members than to the adjacent peripheral members. In another embodiment, the longitudinally extending strut members 10 adjacent the periphery are closer to the periphery than they are to the adjacent longitudinally extending strut members. In another embodiment, the longitudinally extending strut members adjacent the central longitudinally extending strut member are closer to the central longitudinally extending strut member than they are to their adjacent other 15 longitudinally extending strut members. In another embodiment, the present invention is a modular wall panel for an underground infiltration/storage tank, comprising: a rectilinear periphery formed of four edge members; a plurality of longitudinally running strut members extending between the 20 edge members and intersecting the periphery edge members at a plurality of junctions; a plurality of transversely running strut members extending between the edge members and intersecting the longitudinally running strut members and the periphery edge members at a plurality of junctions; 25 at least one first reinforcing node formed at a plurality of junctions of the longitudinally running strut members and the transversely running strut members and their junctions with the periphery edge members; at least one second reinforcing node formed on the longitudinally rutting strut members, the second reinforcing nodes being larger than the first reinforcing 30 nodes; at least one third reinforcing node located on a plurality of junctions, the third reinforcing nodes being larger than the first reinforcing nodes and the second reinforcing nodes; WO 2007/104083 PCT/AU2007/000278 4 a plurality of diagonally extending non-parallel strut members extending between adjacent nodes. In yet another embodiment, the present invention is a modular wall panel for an underground infiltration/storage raintank, comprising: 5 a rectilinear periphery formed of four edge members; a plurality of longitudinally running strut members extending between the edge members and intersecting the periphery edge members at a plurality of junctions; a plurality of transversely running strut members extending between the 10 edge members and intersecting the longitudinally running strut members and the periphery edge members at a plurality of junctions; at least one first reinforcing node formed at a plurality of junctions of the longitudinally running strut members and the transversely running strut members and their junctions with the periphery edge members; 15 at least one second reinforcing node formed at a plurality of junctions, the second reinforcing node being larger in diameter than the first reinforcing node; and a plurality of diagonally extending non-parallel strut members extending between adjacent nodes, 20 wherein the first reinforcing and the second reinforcing nodes are surrounded by a plurality of supporting web members, the supporting web members interconnecting the strut members which abut said first and second reinforcing nodes. In yet another embodiment, the junctions and the reinforcing nodes which 25 extend along periphery edge members are also surrounded by supporting web members which interconnect the strut members which abut the nodes and the periphery edge members. In yet another embodiment, the wall panels have studs extending from the periphery to mate with respective holes in other wall panels to assemble a tank 30 module. In yet a further embodiment of the present invention, the wall panel is of substantially constant thickness. In another embodiment of the present invention, the strut members are thinner in width than in thickness. In yet a further WO 2007/104083 PCT/AU2007/000278 5 embodiment, the strut members have a reinforcing web running along their side surfaces. The present invention as shown in the accompanying drawings overcomes the problems presented by the devices of the prior art. Because the modular wall 5 panel of the present invention contains reinforcing nodes, the thickness of the struts is reduced. Such a construction not only saves plastic material and increases the surface opening area of the wall panel as compared to prior art products, but provides an increase in the strength of wall panel and the assembled tank module as well. 10 BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described by way of example with reference to the accompanying drawings in which: FIG. 1 is a front view of a wall panel according to one embodiment of the present invention. 15 FIG. 2 is a front view of a wall panel according to another embodiment of the present invention. FIG. 3 is a close up view of one corner of the wall panel according to the embodiment shown in FIG. 1. FIG. 4 is a close up view of the middle portion of the wall panel according 20 to the embodiment shown in FIG. 1. FIG. 5 is a front view of a wall panel according to another embodiment of the present invention. FIG. 5A is a close up view of a portion of the wall panel of the embodiment shown in FIG. 5. 25 FIG. 6 is a front view of a wall panel according to yet another embodiment of the present invention. FIG. 6A is a close up view of a portion of the wall panel of the embodiment shown in FIG. 6. DESCRIPTION OF PREFERRED EMBODIMENT 30 The following discussion describes in detail several embodiments of the invention and multiple variations of those embodiments. This discussion should not be construed, however, as limiting the invention to those particular WO 2007/104083 PCT/AU2007/000278 6 embodiments. Practitioners skilled in the art will recognize numerous other embodiments as well. Referring to FIG. 1, one embodiment of the present invention is modular wall panel 1. The shape of wall panel 1 is defined by four periphery frame 5 members 2. In the illustrated embodiment, the wall panel includes a top periphery frame member 2a, a bottom periphery frame member 2b, and two side periphery frame members 2c. Internal strut members 3 extend between the periphery frame members 2. Stud members 4 extend outwardly from periphery frame members 2. 10 As seen in FIG. 1, the stud members 4 can be of different sizes, with shorter studs 4a being located on the top periphery frame member 2a and the bottom periphery frame member 2b, and the longer studs 4b being located on the two side periphery frame members 2c. The smaller studs 4a and the longer studs 4b on wall panel 1 allow wall panel 1 to be connected with complementary holes 15 6 of wall panel 5 (shown in FIG. 2), when assembling an individual tank module. To assemble an individual tank module (not shown), two wall panels 1 are taken and four wall panels 5 are connected to and between wall panels 1, using studs 4a and 4b on wall panels 1 and corresponding holes 6 on wall panels 5. When four wall panels 5 are connected to two wall panels 1, a box-like individual 20 tank module is assembled. During assembly of individual tank modules (not shown), shorter stud members 4a of wall panels 1 are mated with holes 6 in wall panels 5. Holes 6 of wall plate 5 are deep enough to accommodate two of the shorter stud members 4a - one from below and one from above. Thus, assembled tank modules can be 25 stacked upon each other so as to build connected multi height tank modules to create deeper rainwater tanks for the same footprint. The infiltration system (not shown) is typically assembled by stacking individual tank modules on top of each other, and by placing individual tank modules in abutment with each other. The infiltration system is wrapped with a 30 geotextile material which allows water flow-through. The geotextile materials used to wrap infiltration systems are well known in the art and commercially available. The assembled infiltration system presents improved water flow, increased tank module strength and increased void space.
WO 2007/104083 PCT/AU2007/000278 7 Referring back to FIG. 1, this embodiment of the present invention comprises an interconnecting combination of transverse struts 10, longitudinal struts 11, and diagonal struts 12. The arrangement of the struts insures that the vector forces are distributed asymmetrically along the reinforced struts. 5 In the illustrated embodiments of the present invention, the wall panels are provided with load bearing reinforcing structures or nodes 7, 8, and 9, located in at least one junction of the strut members to direct and dissipate the induced forces. These reinforcing nodes 7, 8, and 9 strengthen the interconnecting combinations of struts and absorb the transmitted loading through the strut 10 members, thereby increasing the strength of the wall panel of the invention. Referring to FIG. 3, a closer view of a corner of wall panel 1 is shown. The periphery frame members 2 of the wall panel 1 are deep in thickness and thin in cross section - this increases the strength of wall panel 1. A web member 13 is positioned along the struts 10, 11 & 12 and along the periphery frame members 15 2. The web member 13 is for bracing the struts and periphery frame members and increases their structural strength. The web member 13 could be positioned on one or both sides of the struts, but is preferably positioned on the inner surface of the periphery frame members 2. Still referring to FIG. 3, the wall panel 1 for an underground 20 infiltration/storage tank has a plurality of longitudinally running strut members 11. The longitudinally running strut members are preferably parallel to each other. A plurality of transversely running strut members 10 intersect the longitudinal running strut members 11. Preferably, the transversely running strut members are parallel to each other. 25 Referring to FIG. 4, which illustrates another close-up view of portion of the wall panel 1, reinforcing nodes 7 are formed at the junctions of the longitudinally 11 and transversely 10 running strut members and their junctions with periphery edge members 2. Additionally, some transversely running strut members 11 contain reinforcing nodes 8, which are stronger than reinforcing nodes 7. 30 Still referring to FIG. 4, reinforcing nodes 9 are located on one of the longitudinally running strut members 11 adjacent each end thereof. Although wall panel 1 preferably contains two reinforcing nodes 9 and they are preferably on the central longitudinally running strut member, one of ordinary skill will recognize WO 2007/104083 PCT/AU2007/000278 8 that the number of the nodes and their location is variable. As compared to the other reinforcing nodes 7 and 8, the reinforcing nodes 9 are relatively large cylinders with an intermediate planar web. A plurality of diagonally extending strut members 12 extend between adjacent nodes 7, 8 & 9. 5 In the illustrated embodiment, as seen for example in FIG. 3, the outermost longitudinally running strut members 11 are closer to the periphery edge members 2 than to their adjacent longitudinally running strut members 11. This arrangement assists in distributing the load the over wall panel 1. Thus, the outermost diagonal strut members 12, along with the outermost longitudinally 10 running strut members 11, provide a reinforced edge at the corners of the wall panel 1, with the four outermost diagonal strut members 12 being angled more acutely than the rest of the diagonal strut members 12 of the wall panel 1. Thus, the vectors generated by a force on top of the wall panel 1 are absorbed by the reinforced edge and the reinforced nodes (7, 8 & 9). 15 As the internal diagonal strut members 12 and the outer diagonal strut members 12 are of different orientations to each other, the plate can resist a greater loading than if the diagonal strut members were all similarly aligned. Hence, the combinations of the non-parallel diagonal struts and the reinforced nodes absorb and direct the loading on the plate to strengthen the plate against 20 compressive forces and to resist buckling and twisting. In another embodiment, the present invention is a wall panel 5 that connects to wall panel 1 when assembling a tank module. Referring to FIG. 2, wall panel 5 is rectangular in shape and comprises four periphery edge members 2. Similar to the embodiment of the invention shown in FIG. 1, wall panel 5 25 contains multiple internal strut members which extend between the periphery edge members 2. Specifically, the wall panel 5 contains longitudinally running strut members 11, transversely running strut members 10 and diagonally running strut members 12. Wall panel 5 includes holes 6 positioned along two opposing periphery 30 edge members at their junctions with the longitudinally running strut members 11. In addition, there is a plurality of additional holes 6 positioned along those longitudinally running strut members 11. The holes 6 are positioned on the WO 2007/104083 PCT/AU2007/000278 9 longitudinally running strut members 11 such that they are along the same horizontal line. Stud members 4a and 4b of wall panels 1 mate with corresponding holes 6 of wall panels 5 when a wall panel 1 and a wall panel 5 are joined together to 5 assemble a raintank module. It can be seen that, aside from having holes 6 and not having any stud members 4a and 4b, wall panel 5 is otherwise similar in construction to wall panel 1. Unlike wall panel 1, wall panel 5 includes not two but four large reinforcing nodes 9 at the junctions between the longitudinally running strut members 11 and transversely running strut members 10. 10 FIG. 5 illustrates another preferred embodiment of the wall panel of the invention. Similarly to the embodiment shown in FIG. 1, wall panel 21 shown in FIG. 5 also contains peripheral edge members 2, studs 4a and 4b, longitudinally running strut members 11, transversely running strut members 10, and diagonally running strut members 12. However, in wall panel 1, only the diagonally running 15 strut members 12 are non-parallel to each other. Referring to FIG. 5 (and similarly to wall panel 1), the diagonally running strut members 12 of wall panel 21 are zigzag-shaped and non-parallel to each other. In contrast to wall panel 1, the longitudinally running strut members 11 of wall panel 21 have forked end portions, with the two branches 11a being non 20 parallel to each other and to strut member 11. In addition, transversely running strut members 10 also have a forked end portion, with the two branches 10a being non-parallel to each other and to strut member 10. As a result, in wall panel 5, the longitudinally running strut members 11 are non-parallel to each other, the transversely running strut members 10 are non-parallel to each other, 25 and the diagonally running strut members 12 are non-parallel to each other. Still referring to FIG. 5, wall plate 21 is similar to wall plate 1 in that it also contains reinforcing nodes 7, 8 and 9. However, each of nodes 7 and 8 in wall plate 21 is surrounded by a supporting web member 22. As shown in FIG. 5, a supporting web member 22 surrounds its corresponding node and interconnects 30 all of the strut members which pass through that node. Thus, the use of supporting web members 22 provides enhanced structural strength to the strut members of wall panel 5.
WO 2007/104083 PCT/AU2007/000278 10 As shown in more detail in FIG. 5A, supporting web members 22 also surround the holes 6 and interconnect the diagonally running strut members 12 and the periphery edge member 2 which adjoin the holes 6. By reinforcing the connections between the periphery edge members and the internal strut 5 members, the supporting web members 22 provide additional strength to wall panel 5. FIG. 6 illustrates another embodiment of the present invention. Referring to FIG. 6, wall panel 31 is similar in size and shape to wall panel 5 of FIG. 4. Yet, the configuration of internal struts in wall panel 31 is similar to wall panel 21 of 10 FIG. 5. In wall panel 31, as in wall panel 21, the longitudinally running strut members 11 are non-parallel, the transversely running strut members 10 are non parallel, and the diagonally running strut members 12 are non-parallel. As seen in more detail in FIG. 6A, wall panel 31, just like wall panel 21, includes reinforcing nodes 7, 8 and 9, which are surrounded by supporting web 15 members 22. In the illustrated embodiment, wall plate 31 contains four large nodes 9. Like wall plate 5 of FIG. 4, wall panel 31 includes holes 6 positioned along two opposing periphery edge members at their junctions with the longitudinally running strut members 11. Also, there is a plurality of additional holes 6 positioned along those longitudinally running strut members 11. The 20 holes 6 are positioned on the longitudinally running strut members 11 such that they are along the same horizontal line. To assemble an individual tank module using wall panels 21 and 31, two wall panels 21 and four wall panels 31 are interconnected using longer and shorter studs of wall panels 21 and the corresponding holes 6 of wall panels 31. 25 A box-like individual tank module (not shown) is thus formed. The present invention has developed a method of distributing the loading on the wall plate with reduced plastics, increasing the void capacity, and the wall perforation capacity providing better lateral flow, ease of manufacture, use of less plastics, increased strength, and in some embodiments a more aesthetic look. 30 Thus, there is provided modular wall panels which, when connected together, provide an extremely strong tank module that has superb void percentage and flow rates through the walls of the tank.
WO 2007/104083 PCT/AU2007/000278 11 It should be obvious to people skilled in the art that modifications and alterations can be made to the above embodiments without departing from the spirit of the present invention. 5