STACKABLE GRID MATERIAL

Abstract: A stackable grid material (109 for soil confinement comprises a repeating pattern of cell structures (40) with cell walls and open cell tops and bottoms. The cell wall material of the grid is notched such that the top edges of the cell wall material (28) on the perimeter of a lower layer of grid material overlaps with the bottom edges of cell wall material (24) on the perimeter of an upper layer of grid material. The internal cell walls (20) are able to rest on top one another in spite of the overlap at the perimeter walls due to the positioning and shape of the notches (42, 48).

Description: The present invention relates to a grid structure which can be stacked up and filled with soil to create free standing walls and similar structures. A grid structure comprising a repeating pattern of cells which are open at the top and bottom and used for soil confinement to provide a road base made from soils (sand, rounded rock, poorly graded aggregate, concrete, and the like) has been known and used for some time. A prime example is "Geoweb" (Trade Mark) plastic grid soil confinement system sold by Presto Products, Incorporated, P.O. Box 2399, Appleton, Wisconsin 54913 and disclosed in a booklet entitled "Geoweb Grid Confinement System" available from Presto Products, Incorporated. "Geoweb" grid cells are made from plastic strips which are joined on their faces in a side by side relationship at alternating spacings so that when the strips are stretched out in a direction perpendicular to the faces of the strips, the resulting grid section is honeycomb-like in appearance, with sinusoidal or undulent shaped cells. Voluminous reports have praised the ability of "Geoweb" grid cell material to support roadways. "Geoweb" grid cells have also been used in applications where one grid layer is stacked on another, such as a stepped back design for hill slope retention. Even free standing walls have been built with "Geoweb" grid cells. However, because the cells are open at the top and bottom, there is a tendency for fill material to leak out of the cells if the cell below is not properly positioned. Also, the exposed soil in a cell not adequately covered is subject to being blown away by the wind. In an effort to overcome these problems, free standing structures have been built with alternating layers of grid confinement cells and sheet material, such as water permeable fabric. While this approach has helped to cover the exposed open tops and bottoms of the cells, it has not been completely successful, and, more importantly, requires the additional use of the separate sheet material. The present invention is characterised in that the cell walls of the grid structure have regions of differing height such that at least a part of the top edge of the cell wall on the perimeter of a lower layer of a grid structure overlaps at least a part of the bottom edge of the cell wall of the perimeter of an upper layer of a grid structure on top of the lower layer when the internal cell walls of the upper layer rest on top of the internal cell walls of the lower layer. The grid structure can be used in repeated layers without the need for intermediate sheet material, and significantly reduces exposure to or leakage from material in the perimeter cells. The grid structure makes it simple to build a wall or other free standing structure without exposed tops and bottoms of cells on the perimeter faces of the structure. In the accompanying drawings: Figure 1 is a perspective view depicting the construction of a wall using grid structures; Figure 2 is an enlarged perspective view of a corner portion of a grid structure like the structures used in the wall shown in Figure 1 before it is filled with soil; Figure 3 is a plan view of one of the inside strips of the grid structure used on upper layers of the wall of Figure 1; Figure 4 is a plan view of one of the outside strips of the grid structure used on upper layers of the wall of Figure 1; Figure 5 is a plan view of one of the inside strips of the grid structure used on the lowermost layer of the wall of Figure 1; Figure 6 is a plan view of one of the outside strips of the grid structure used on the lowermost layer of the wall of Figure 1; Figure 7 is a side elevational view taken along line 7-7 of Figure 1; Figure 8 is a sectional view (excluding the soil) taken along line 8-8 of Figure 1; and Figure 9 is a sectional view taken along line 9-9 of Figure 7. Figure 1 depicts a wall being constructed with stackable soil confinement grid structures 10. The grid structure 10 is comprised of a plurality of strips of plastic 20 which are bonded together, one strip to the next, at alternating and equally spaced bonding areas. In Figure 2, each layer of grid structure 10 is made of an even number of uniformly thick plastic strips 20 in side by side relationship, bonded by ultrasonic welding. The regions of differing height of the inside strips 22 differ in their pattern from the outside strips 24, as more fully described hereafter. The bonding between strips may best be described by thinking of the strips as being paired, starting with an outside strip 24 paired to an outermost inside strip 22, a pair of the next two inside strips 22, and so on. Each such pair is bonded at a bonding area constituting an end weld 32 adjacent to the end 34 of each strip 20. A short tail 36 between the end 34 of the strip 20 and the end weld 32 is provided to stabilize segments of the strip 20 adjacent to the outside weld 32. Each pair of strips is welded together at additional bonding areas 14, creating equal length strip segments between the end welds 32. In addition to these welds, one strip 20 from each adjacent pair of strips is also welded together at positions intermediate each of the welds in the pairs of strips, referred to hereafter as non-pair bonding areas 16. As a result, when the plurality of strips 20 are stretched in a direction perpendicular to the faces of the strips, the plastic strips bend in a sinusoidal manner and form a grid of cells 40 in a repeating cell pattern. Each cell 40 has a cell wall made from one strip 20 and a cell wall made from a different strip 20. In this configuration, the end section of each strip 20 forms one wall of a cell on the perimeter of the grid structure 10. In addition, there are outside strips 24 which form cell walls all lying on the perimeter of the grid structure. When several layers of grid structures 10 are stacked on top of one another, it is the open tops and bottoms of these perimeter cells which are exposed if each cell above and below is not directly aligned. The lowermost or base grid structure 12 of a stack is designed to rest on a flat surface (Figure 1). Since it has no grid structure layer 10 below it with which it needs to align, the bottom edge of each strip 20 in the base structure layer 12 is uniformly even. However, in many instances a grid structure layer 10 would be suitable as the bottom layer of a stack. The base structure layer 12 has inside strips 26 and outside strips 28 which differ from each other just as the inside strips 22 and outside strips 24 of the layer 10 differ from each other. Figures 3 to 6 respectively are plan views of the inside and outside strips 22, 24, 26 and 28, showing the shapes of these strips. The inside strip 22 (Figure 3) used for grid structure layers 10 has a central cut-out section 42 which is a predetermined distance below the upstanding edge section 44 adjacent to the ends 34 of the strip 22. The central section 42 extends just beyond the region of the outermost non-pair bonding area 16. The bonding areas 14 are about 33 cm (13 inches) apart on each strip, as are the non-pair bonding areas 16. Since the non-pair bonding areas 16 are intermediate the bonding areas 14, each cell wall comprises a section of the plastic strip about 16.5 cm (6.5 inches) in length, between the alternating bonding areas 14 and non-pair bonding areas 16. The tail 36 is about 2.54 cm (1 inch) in length. The central section 42 begins about 14 cm (5.5 inches) from one end weld 32 of the strip 22 and runs to a point about 14 cm (5.5 inches) from the other end weld 32. Since the outermost non-pair bonding area 16 is about 16.5 cm (6.5 inches) from the end weld 32, this central section 42 extends about 2.54 cm (1 inch) past the outermost non-pair bonding area 16 on each half of the strip 22. The bottom edge of each strip 22 also has inwardly cut-out or notched corner areas 48 at each end section adjacent to each end weld 32 (at each bottom corner). This results in a central section 46 descending below the level of the corner areas 48. The distance between the levels of section 46 and corner areas 48 is approximately equal to the predetermined distance between the height of the top central section 42 and upstanding section 44. This predetermined distance is about 1.3 cm (0.5 inch). The length of the notch in the corner areas 48 is about 6.4 cm (2.5 inches), which is slightly longer than the tail 36, extending about 3.8 cm (1.5 inches) outside of the end weld 32. As seen in Figure 4, the outside strip 24 has a uniformly even straight top edge with no cut-outs but includes notches or cut-outs in its bottom corner areas 48 which are identical to the notches in the corner areas 48 of the inside strip 22. As shown in Figures 5 and 6, strips 26 and 28 are respectively identical to strips 22 and 24 except that (as mentioned previously) the bottom edges of strips 26 and 28 are uniformly even and straight with no cut-outs over the length of each strip. After being welded together, the plastic strips 20 tend to retain a recti-linear shape. This allows the grid structure 10 to be easily shipped, stored and handled until it is used to make a wall or other structure. A method of constructing walls (as shown in Figure 1) is to anchor guiding posts 18 into the ground at the corner positions where the wall is to be built. The base layer grid structure 12 is next stretched out and the corner cells are slid down over the posts 18. Soil (such as sand or any other readily accessible and suitable fill material) is next filled into the cells 40 of the base layer grid structure 12 and compacted (if desired). A grid structure layer 10 is then stretched out and slid down over the posts 18. In this position, and as shown in Figures 7 and 8, the notches 48 in the bottom of this second layer 10 and the cut outs 42 in the top of the base layer 12 cooperate so that in the central section of the grid structures, the cell walls of the top layer rest on the cell walls of the bottom layer. In these internal areas, alignment of the cells is not critical. On the perimeters of the grid structures, however, the downwardly extending central sections 46 of the strips 24 of the grid structure layer 10 contact the top edges of the outside strips 28 of the base layer 12 along its entire length, and the central sections 46 of the strips 22 will contact the upstanding edge sections 44 of the inside strips 26 for a distance of about 10.2 cm (4 inches). In order to get the second layer 10 to nest properly, the flexible plastic strips must be slightly deformed so that the interfering areas become overlapping areas, the portions of the cell wall on the base layer 12 being outside the portions from the second layer of the grid structure 10 (See Figure 9). Because of the notches 48 in the bottom edges, the perimeter corners of the perimeter cells cross over the upstanding sections 44 of the lower layer grid structure. After placement, the second layer 10 is then filled with soil, and the process is repeated, stacking as many layers of the grid structure 10 as necessary to build the wall to the desired height. Each plastic strip 20 is 20.3 cm (8 inches) wide. The grid structures may be manufactured to result in grids of any dimension, but are typically 91.4 to 244 cm (3 to 8 feet) wide and 2.44 to 6.1 m (8 to 20 feet) in length when stretched out for use. The preferred plastic is sheet extruded polyethylene, 1.27 mm (50 mil) thick. Carbon black may be included to help prevent ultraviolet degradation of the grid material exposed to sunlight. The bonding may be accomplished by a number of methods known in the art. A method of ultrasonic welding is accomplished using the process and apparatus disclosed in US-A-4,647,325. The bond is formed by groups of welding tips simultaneously contacting the strips 20, the weld thus substantially traversing the entire width of the strips 20. The design provides two features which help to keep soil or other fill material in perimeter cells from escaping from stacked grid structures. First, the overlap on the cell walls on the perimeter of the grid structure is useful to align the cells during stacking. By nesting the walls of the top cells into the bottom cells, the perimeter cells are easily aligned and stay in alignment during the process of filling the cells with soil. Second, the overlap creates a barrier against soil particles leaking out between layers of aligned cell walls. The grid structure can be used to form walls using locally available fill, such as soil, in a simple, quick and inexpensive fashion, but which have minimal loss of soil material from the perimeter cell walls. This is especially useful in situations where very dry, fine granular soil such as sand is used. It is conceivable to build "sand houses" in desert terrain, like the sod houses of early prairie pioneer days in the United States of America. Of course it should be understood that a wide range of changes and modifications can be made to the construction described above. For example, if overlapping and alignment is needed on only one surface of a wall, no distinct outside strips 24 and 28 would be needed. Likewise, no special base layer 12 is needed if the surface on which the wall is built is soft enough so that downwardly extending bottom edge sections 46 of the strips 22 and 24 would sink into the soft surface. Further, instead of having cut-out central sections 42 on top of the strips 20 and downwardly extending central sections 46 on the bottom, the two could be reversed. If the central section of strips 22 extended above the end sections, then the outside strips 24 and 28 would not need a cut-out or notch in their bottom corners, but would need a notch in the bottom edge at each bonding area.

Claims: 1. A grid structure (10, 12) comprising a repeating pattern of cells (40) which are open at the top and bottom; characterised in that the cell walls (20) of the grid structure have regions of differing height (42, 44, 46, 48) such that at least a part of the top edge of the cell wall (28) on the perimeter of a lower layer of a grid structure (12) overlaps at least a part of the bottom edge (46) of the cell wall (24) on the perimeter of an upper layer of a grid structure (10) on top of the lower layer when the internal cell walls (22) of the upper layer (10) rest on top the internal cell walls (26) of the lower layer (12). 2. A grid structure as claimed in Claim 1, wherein the overlap comprises side by side cell walls, the cell wall perimeter of the lower grid fitting on the outside of the cell wall perimeter of the upper grid. 3. A grid structure as claimed in Claim 1 or 2, wherein the cell walls comprise long strips (22) of flexible material bonded together, one strip to the next, at alternating and equally spaced bonding areas (14). 4. A grid structure as claimed in Claim 3, wherein the strips are plastic and the bonding areas comprise ultrasonic welds substantially traversing the width of the strip. 5. A grid structure as claimed in any preceding Claim, wherein the cell walls (22) on the perimeter of the top of the grid structure have upstanding sections (44), and the bottom of the grid structure has cut-outs at the perimeter corners (48) of perimeter cells which cross over the upstanding sections (44) of a lower layer of grid material. 6. A grid structure as claimed in Claim 1 and comprising: an even number of uniformly-wide, plastic strips (20) in side by side relationship comprising a plurality of inside strips (22) and two outside strips (24) flanking the sides of the two outermost inside strips; the strips being ultrasonically welded together at positions along the strips such that each pair of adjacent strips is welded together at end welds (32) adjacent to the ends (34) of the strips, leaving a short tail (36) between the end of the strip and each end weld (32), and also being welded at bonding areas (14) between the end welds (32) to create equal length segments between all welds; and one strip from each of two adjacent pairs of strips also being welded together at non-pair bonding areas (16) intermediate each of the welds at the bonding areas (14); the top edge of each inside strip (22) having a cut-out central section (42) of a predetermined distance below the height of the upstanding edge (44) of the strip adjacent to the end weld (32); the top edge of each outside strip (24) being of uniform height; and the bottom edge of each strip having inwardly cut-out areas (48) adjacent to the end welds (32), the bottom edge cut-outs being of a depth approximately equal to the said predetermined distance. 7. A grid structure as claimed in Claim 6, wherein the length of the bottom edge cut-out (48) is longer than the length of the tail (36), and the central cut-out section (42) of the top edge extends beyond the outermost non-pair bonding area (16). 8. A grid structure as claimed in Claim 6 or 7, wherein the strips comprise polyethylene. 9. A grid structure as claimed in Claim 6, 7 or 8, wherein the strips are about 1.27 mm (50 mil) in thickness. 10. A grid structure as claimed in Claim 6, 7, 8 or 9, wherein the predetermined distance is about 1.27 cm (0.5 inch). 11. A grid structure as claimed in Claims 6, 7, 8, 9, 10, wherein the strips are about 20.3 cm (8 inches) thick and the equal length segments between welds each measure about 33 cm (13 inches). 12. A grid structure as claimed in any one of Claims 6 to 13, wherein the bottom cut-outs (48) extend about 3.8 cm (1.5 inches) inside of the end welds (32), and the central cut-out section (42) extends about 2.54 cm (1 inch) beyond the end non-pair bonding area (16). 13. A grid structure as claimed in Claim 1 and comprising a plurality of plastic strips (22) bonded together on their faces in a side by side relationship at bonding areas (14, 16) which are staggered from strip to strip such that the plurality of strips may be stretched in a direction perpendicular to the face of the strips to form the cells (40), the strips forming the cell walls, the strips comprising two outside strips (24) and one or more inside strips (22); and the inside strips (22) having at least one cut-out (42, 48) in the top and bottom edge. 14. A grid structure as claimed in Claim 13, wherein the outside strips (24) have edges such that the cell walls formed by the outside strips overlap at each cell wall formed by the outside strips. 15. A grid structure as claimed in Claim 13 or 14, wherein the inside strips (22) have a top edge with a cut-out central section (42) and a bottom edge with cut-out end sections (48). 16. A grid structure as claimed in Claim 13, 14 or 15, wherein the outside strips (24) have an even top edge and a bottom edge with cut-out end sections (48). 17. A grid structure as claimed in Claims 13, 14, 15 or 16, wherein each strip includes two tail sections (36) each of about 2.54 cm (1 inch) in length between an end weld (32) and the end of the strip; the length of the section of plastic strip between bonding areas (14, 16) is approximately 16.5 cm (6.5 inches); and the cut-out (42) on the top edges of the inside strips (22) begins at about 14 cm (5.5 inches) from each end weld (32) and the cut-outs (48) on the bottom edges of both the inside and outside strips (22, 24) extend about 3.8 cm (1.5 inches) past the end welds (32), resulting in the overlapping portions of the cell walls on a perimeter of the grid being approximately 10.2 cm (4 inches) in length. 18. A grid structure as claimed in any one of Claims 13 to 17, wherein the strips (20) are approximately 20.3 cm (8 inches) in width and both cut-outs on the top and bottom edges are approximately 1.27 cm (0.5 inch) deep.

Inventors: BACH, GARY, KETTNER, TIMOTHY
Applicants: REYNOLDS CONSUMER PRODUCTS, INC.
Application year: 1988
Main classification: E02D29
IPC codes: E02D29, E04C1