Abstract:
A method of making a composite structure from a support structure or a plurality of support structures laid side-by-side on a base, is disclosed. The support structure is formed from frameworks each comprising a tube of a flexible material divided by dividing walls of a flexible material into an array of compartments. The frameworks are then filled with a suitable filler material. The frameworks have compartments with three different sizes which have advantages in the construction of certain composite structures.

Description:
BACKGROUND TO THE INVENTION 
     THIS invention relates to a method of forming a composite structure from a support structure or a plurality of support structures on a base, and to an article for use in forming such a support structure. 
     It is well known to form composite or support structures such as roadways, canal or river or bank linings, mine packs, sea walls or the like, from a material having a honeycomb structure, i.e having a plurality of compartments or cells divided by dividing walls, each compartment or cell being filled with a suitable filler material. Examples of such materials for use in the support structures are Hyson-Cells from M &amp; S Technical Consultants and Services (Pty) Limited, Geoweb from Presto Products Co, Tenweb from Tenax Corp, Armater from Crow Company, Terracell from Webtec Inc, Envirogrid from Akzo Nobel Geosynthetics Co and Geocells from Kaytech. 
     All these materials have a common feature that the size of the compartments or cells in the material is the same. In other words, in any sheet of the material, all the cells or compartments in that sheet have the same size. There are however applications where it would be useful to have a material of this type with compartments of different sizes. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention there is provided a method of making a composite structure from a support structure or a plurality of support structures laid side-by-side, on a base, each support structure being formed from a framework comprising a tube of a flexible material divided by dividing walls of a flexible material into an array of compartments or cells running the length of the tube, the compartments being arranged in rows and columns so that the tube divided by dividing walls has a honeycomb structure, which method includes the steps of: 
     (a) locating a framework or a plurality of frameworks side-by-side, on the base; 
     (b) filling some or all of the compartments with a filler material; 
     which is characterised in that either at least one framework includes compartments with two different sizes or in that at least two adjacent frameworks have compartments of different sizes, the size of a compartment being the cross-sectional area thereof at right angles to the axis of the compartment. 
     In one embodiment of the invention, a composite structure is formed from a single support structure or from a plurality of support structures, wherein each support structure is formed from a framework which includes compartments with two different sizes. 
     In this case, each framework preferably includes one or more rows of compartments with a first size and one or more rows of compartments with a second size. 
     There may also be a row of compartments with a transitional size between the last row of compartments with the first size and the first row of compartments with the second size. 
     Preferably, the compartments with the second size are a quarter of the size of the compartments with the first size. 
     Each framework may also include one or more rows of compartments with a third size, the compartments with the third size being a quarter of the size of the compartments with the second size, and so on, with each succeeding set of compartments with a lesser size being one quarter of the size of the preceding compartments. 
     In a further embodiment of the first aspect of the invention, the composite structure may be formed from a plurality of support structures, each support structure being formed from a framework, wherein at least two adjacent frameworks have compartments of different sizes. In other words, a first framework will have compartments of a first size and an adjacent framework will have compartments of a second size. 
     Preferably, the compartments of one framework are a quarter of the size of the compartments of the adjacent framework. 
     In this case, every second smaller compartment may be joined to a respective larger compartment, every other smaller compartment being joined by a brace to the adjacent framework at a point where two larger compartments are joined. 
     The framework, i.e the tube and the dividing walls, may be made from any suitable flexible material. Although the material must possess some degree of flexibility, the degree of flexibility may range from very flexible up to semi-rigid. The flexible material may be for example a plastics material such as for example a co-extruded or a biaxially extruded plastics material; a plastics laminate material such as for example a laminate of a plastics material and a metallic material or a textile material; a metallic material; a woven or non-woven textile material; a paper or cardboard material; and the like. The flexible material is preferably a suitable plastics material. 
     The framework may include a plurality of holes therethrough to permit drainage of any liquid substance through the holes and from the framework. 
     The framework may have any suitable height and any suitable compartment size, provided of course that in any support structure or composite structure formed, there is included compartments of at least two sizes. For example, the height of the framework may range from 2 mm to 10 m inclusive, and each compartment may have a wall length of from 5 mm up to 2 m. 
     In addition, within a particular framework or in adjacent frameworks, the heights of the compartment walls may vary, so that a first compartment adjacent a second compartment may extend beyond the second compartment, either at the top or at the bottom. 
     The compartments in the framework may have any suitable cross-section, such as square, hexagonal or octagonal, but preferably have a square cross-section, i.e each compartment is defined by four walls of substantially equal lengths. 
     The filler material may be any suitable filler material, depending on the nature of the composite structure to be formed. For example, when the composite structure to be formed is a roadway or a paved area, a lining for a canal, river, drain or spillway or the like, a support for an embankment, or a dam or harbour wall, then the filler material may be an inert filler material, .e.g sand or gravel or the like, or a composition comprising a filler material and a settable binder therefor. Examples of such compositions include: 
     (i) an inert filler material such as sand or gravel or the like, and a cementitious binder, for example ordinary Portland Cement; 
     (ii) an inert filler material such as sand or gravel or the like and a bituminous binder; 
     (iii) a filler material such as soil treated with a suitable chemical composition such as calcium chloride, a lignin sulphonate or an ionic liquid to cause the soil to bind or set; 
     (iv) a filler material such as sand or gravel or the like and a resin binder, for example (a) a thermosetting resin such as polyurethanes and polyesters, (b) a thermoplastic resin such as polyethylene, EVA, or PVC, and (c) a suitable wax. 
     The settable composition may include a conventional foam or foaming agent so that the final set composition is a foamed composition, to reduce the weight thereof. 
     Alternatively, when the composite structure is a purification pack or the like, for example for the purification of liquids such as water, or gasses, then the filler material may be any material suitable for purification, e.g diatomaceous earth, an ion exchange resin or the like. 
     In the method of the invention, the framework or frameworks may be supported in position by the use of flexible strings or rigid stays as is disclosed in a co-pending patent application. In addition, the wall or walls of each compartment in a framework may include one or more hollow protrusions or one or more hollow recesses so that the compartments protrude into or are protruded into by adjacent compartments to interlock adjacent compartments, as is disclosed in a further co-pending patent application. 
     According to a second aspect of the invention there is provided a framework comprising a tube of a flexible material divided by dividing walls of a flexible material into an array of compartments or cells running the length of the tube, the compartments being arranged in rows and columns so that the tube divided by dividing walls has a honeycomb structure, wherein the framework includes compartments with two different sizes, the size of a compartment being the cross-sectional area thereof at right angles to the axis of the compartment, the framework being for use in making a support structure on a base. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a first composite structure according to the invention; 
     FIG. 2 is a plan view of a second composite structure according to the invention; 
     FIG. 3 is a schematic view illustrating a method of making a framework for use in the method of the invention; and 
     FIG. 4 is a schematic side view of a further framework for use in the method of the invention. 
    
    
     DESCRIPTION OF EMBODIMENTS 
     The invention will now be described in more detail with reference to the accompanying drawings. 
     Referring to FIG. 1, a composite structure  10  consists of three frameworks  12 ,  14  and  16  laid side-by-side. The compartments  18  of framework  12  are a quarter of the size of the compartments  20  of the framework  14  which, in turn, are a quarter of the size of the compartments  22  of the framework  16 . 
     As indicated above, by size there is meant the cross-sectional area of the compartment at right angles to the axis of the compartment. This is illustrated in FIG. 1 where the area of the compartment  22 A is illustrated by cross-hatching, and the axis of the compartment  22 A is indicated by a dot marked  24 . 
     This composite structure  10  is believed to be more economical where equal performance is not required uniformly across the whole structure. For example, a first framework with smaller compartments may be stronger than a second framework with larger compartments, but also costs more. Thus the first framework should be used only where needed. 
     In order to join the respective frameworks  12 ,  14 , and  16  together, every second smaller compartment is joined to an opposed, respective larger compartment. The remaining smaller compartments are joined via respective bracing strips  26  of a flexible material to a point where two adjacent larger compartments are joined. 
     As indicated above, flexible strings or rigid stays (not shown) may be used to support the respective frameworks in position and to hold them down onto the base, prior to being filled with the filler material. 
     Once the frameworks  12 ,  14 ,  16  are in position on a base, the compartments  18 ,  20 ,  22  may be filled with a suitable filler material to form the composite structure  10 . 
     Referring to FIG. 2, a composite structure  30  consists of a single framework including compartments of various different sizes. The section of the composite structure  30  which is broken away is designed to illustrate the fact that the composite structure  30  may be of any desired width or length. The compartments  32  in the lines around the edge of the composite structure  30  have a first size a; the compartments  34  in the lines adjacent the lines of compartments  32  have a second size b which is four times the size a of the compartments  32 ; and the compartments  36  in the centre of the composite structure  30  have a size c which is four times the size b of the compartments  34 . 
     In addition, between the lines of compartments  32 ,  34  and  36 , there are compartments  38  with a transitional size, between the size of the compartments  32  and the compartments  34 , and the compartments  34  and the compartments  36  respectively. 
     Again the compartments  32 ,  34 ,  36 ,  38  are filled with a suitable filler material to form the composite structure  30 . 
     From FIG. 2 it can be seen that a single framework including compartments  32 ,  34  and  36  of three different sizes, can be utilised to form a composite structure  30 . 
     Referring to FIG. 3 a method of making a single framework  50  including compartments of three different sizes  52 ,  54 ,  56  is illustrated. The framework  50  is made from lengths of a suitable material such as a plastics material, with alternating lengths being indicated by solid lines or by dotted lines. 
     A first length  58  of material is joined to a second length  60  of material at join points  62 . Thereafter a third length  64  of material is joined to the second length  60  at join points  66 , thus creating the first two rows of compartments  52  having the largest size. A fourth length  68  is then attached to the third length  64  as follows. Firstly, the fourth length  68  is folded in half and is joined along the fold line to the third sheet  64  at a central join point  66 A. Thereafter, the fourth length  68  is attached to the third length  64  at join points  70  adjacent the join point  66 A. Then in a similar manner the fourth length  68  is attached to the third length  64  along a double fold at the join points  66  and then again to the third length  64  at join points  70 . Although FIG. 2 shows a gap between the folded portions of the fourth length  68 , in practice, the fourth length  68  will he attached to itself at points  72 , to form compartments  74  which are transitional compartments between the compartments  52  and the compartments  54 . 
     Thereafter a fifth length  76  is attached at join points  78  to the fourth length  68 , a sixth length  80  is attached to the fifth length  76  at join points  82 , and a seventh length  84  is attached to the sixth length  80  at join points  86 , to form the compartments  54 . 
     The eighth length  88  is attached to the seventh length  84  in the same way that the fourth length  68  is attached to the third length  64 , again to reduce the compartment size as is illustrated. 
     In this way, a single framework having compartments of varying sizes may be formed. 
     Referring to FIG. 4, there is shown a schematic side view of a framework  100  for use in the method of the invention, wherein adjacent compartments  102  have different heights and depths. This is useful where the framework  100  is intended to be used in a purification pack or the like. 
     As indicated above, the frameworks for use in the method of the invention may be made of any suitable material, and may include holes to permit the ingress or egress of liquids therethrough. 
     The method of the invention allows the utilization of a framework or frameworks with compartments of different sizes, so as to optimize the benefits afforded by the particular size of compartments. As indicated above smaller compartments are stronger but more expensive to manufacture and thus are used only where strength is required. These smaller compartments may abut larger compartments, which are not as strong, but which are used where great strength is not required. In addition, a framework with smaller compartments may be cut at a steeper angle than a framework with larger compartments which is useful in certain circumstances.