Vented Cell Structure for Confinement and Interlock of Earth Materials

Abstract

A vented cell structure for confinement and interlock of earth materials comprising polymeric strips bonded together on their faces in a side by side relationship at bonding areas 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 a layer of cells. The strips form walls of the cells, and each of the cells has an open interior. At least some of the strips having openings through the strips providing communication with the open interior of the cells. The strips have improved coefficients of friction and interaction over the prior art. In some examples, at least one of the openings has an open area of greater than 804 mm.sup.2.

Claims

1. A vented cell structure for confinement and interlock of earth materials comprising: (a) a plurality of polymeric strips bonded together on their faces in a side by side relationship at bonding areas 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 a layer of cells; (i) the strips forming walls of the cells; (ii) each of the cells having an open interior; (b) at least some of the strips having openings through the strips providing communication with the open interior of the cells; (c) at least one of the strips having a coefficient of friction greater than 1.37 under a normal stress of 30 psf; (d) at least one of the strips having a coefficient of friction greater than 1.75 under a normal stress of 50 psf; (e) at least one of the strips having a coefficient of friction greater than 1.88 under a normal stress of 60 psf; (f) at least one of the strips having a coefficient of interaction greater than 0.92 under a normal stress of 30 psf; (g) at least one of the strips having a coefficient of interaction greater than 1.18 under normal a stress of 50 psf; (h) at least one of the strips having a coefficient of interaction greater than 1.26 under a normal stress of 60 psf.

2. The vented cell structure of claim 1, wherein at least one strip has at least one opening with an open area of greater than 804 mm.sup.2.

3. The vented cell structure of claim 1, wherein more than 75% of the openings have an open area of greater than 804 mm.sup.2.

4. The vented cell structure of claim 1, wherein more than 90% of the openings have an open area of greater than 804 mm.sup.2.

5. The vented cell structure of claim 1, wherein each cell has a same number of openings communicating with each adjacent cell.

6. The vented cell structure of claim 1, wherein each cell has a different number of openings communicating with each adjacent cell.

7. The vented cell structure of claim 1 wherein each opening has a same geometric shape.

8. The vented cell structure of claim 1, wherein each opening has a different geometric shape.

9. The vented cell structure of claim 1, wherein the openings are non-circular.

10. The vented cell structure of claim 1, wherein the openings are polygon shaped.

11. The vented cell structure of claim 1, wherein the openings are triangular.

12. The vented cell structure of claim 1, wherein each strip has a width between about 3 inches to 12 inches.

13. A reinforced earth material structure comprising: (a) the vented cell structure of claim 1; and (b) a fill material within the cells; said fill material in adjacent cells communicating through said openings to form a continuous interlocking material network.

14. The reinforced earth material structure of claim 13, wherein the fill material comprises earthen materials such as sand, gravel, crushed concrete, recycled asphalt, engineered fill, foamed glass aggregate, including any combination thereof.

15. The reinforced earth material structure of claim 13, wherein the fill material consists essentially of gravel.

16. A vented cell structure for confinement and interlock of earth materials comprising: (a) a plurality of polymeric strips bonded together on their faces in a side by side relationship at bonding areas 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 a layer of cells; (i) the strips forming walls of the cells; (ii) each of the cells having an open interior; (b) at least some of the strips having openings through the strips providing communication with the open interior of the cells; (i) at least one of the openings has an open area of greater than 804 mm.sup.2.

17. The vented cell structure of claim 16, wherein a majority of the openings have an open area of greater than 804 mm.sup.2.

18. The vented cell structure of claim 16, wherein more than 75% of the openings have an open area of greater than 804 mm.sup.2.

19. The vented cell structure of claim 16, wherein more than 90% of the openings have an open area of greater than 804 mm.sup.2.

20. The vented cell structure of claim 16, wherein each cell has a same number of openings communicating with each adjacent cell.

21. The vented cell structure of claim 16, wherein each opening has a same geometric shape.

22. The vented cell structure of claim 16, wherein the openings are non-circular.

23. The vented cell structure of claim 16, wherein each cell has at least 1 opening communicating with each adjacent cell.

24. The vented cell structure of claim 16, wherein the strips have a coefficient of friction under a stress of 30 psf at greater than 1.37.

25. The vented cell structure of claim 16, wherein the strips have a coefficient of interaction under a stress of 30 psf at greater than 0.92.

26. A reinforced earth material structure comprising: (a) the vented cell structure of claim 16; and (b) a fill material within the cells; said fill material in adjacent cells communicating through said openings to form a continuous interlocking material network.

27. The reinforced earth material structure of claim 26, wherein the fill material comprises sand, gravel, crushed concrete, recycled asphalt, engineered fill, foamed glass aggregate, including any combination thereof.

28. The reinforced earth material structure of claim 26, wherein the fill material consists essentially of gravel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 is a perspective view of a prior art vented cell structure;

[0040] FIG. 2 is a perspective view of the prior art vented cell structure of FIG. 1 filled with soil;

[0041] FIG. 3 is a side view of prior art vented cell structure, prior to expansion and fill;

[0042] FIG. 4 is one use of the improved vented cell structure of this disclosure, to reinforce a gravel road on the side of a mountain;

[0043] FIG. 5 is a side view of one embodiment of vented cell structure made in accordance with principles of this disclosure, prior to expansion and fill;

[0044] FIG. 6 is a side view of another embodiment of vented cell structure made in accordance with principles of this disclosure, prior to expansion and fill; and

[0045] FIG. 7 is a side view of another embodiment of vented cell structure made in accordance with principles of this disclosure, prior to expansion and fill.

[0046] The present technology may be more completely understood and appreciated in consideration of the following detailed description of various embodiments in connection with the accompanying drawings.

[0047] The figures are rendered primarily for clarity and, as a result, are not necessarily drawn to scale. Moreover, various structure/components, including but not limited to fasteners, and the like, may be shown diagrammatically or removed from some or all of the views to better illustrate aspects of the depicted embodiments, or where inclusion of such structure/components is not necessary to an understanding of the various exemplary embodiments described herein. The lack of illustration or description of such structure/components in a particular figure is, however, not to be interpreted as limiting the scope of the various embodiments in any way.

DETAILED DESCRIPTION

[0048] Referring to FIG. 1, a prior art cell structure 10 is shown having vent openings 32 communicating between adjacent cells 20. The cells 20 are preferably formed by first bonding a plurality of plastic or polymeric strips 14 in side by side relationship, using ultrasonic welding as discussed in U.S. Pat. Nos. 4,572,753 and 4,647,325, each of which is incorporated herein by reference. The strips 14 can include a blend (usually as a compatibilized alloy) of (i) a high performance polymer and (ii) a polyethylene or polypropylene polymer. The blend is generally an immiscible blend (an alloy), wherein the high performance polymer is dispersed in a matrix formed by the polyethylene or polypropylene polymer. By the term polymeric strips, it is meant that the strips may be plastic, polymeric, polymeric alloys, or a combination.

[0049] The bonding between strips may best be described by thinking of the strips 14 as being paired, starting with an outside strip 18 paired to an outermost inside strip 24, a pair of the next two inside strips 24, etc. The two strips 14 of each pair are preferably bonded together at bonding areas 16 located at substantially equal intervals along the length of the strips. Each pair of strips 14 is bonded to each adjacent pair at bonding areas 26 located about halfway between the bonding areas 16. The cell structure 10 can be formed by pulling the plurality of bonded polymeric strips 14 in a direction perpendicular to the faces of the strips 14, causing the polymeric strips to bend in a sinusoidal fashion. Examples of typical widths are 3-12 inches, often about 6 inches.

[0050] The vented openings 32 may be formed by any suitable method either before or after the polymeric strips 14 are bonded together. In a preferred method, the vents are formed by drilling holes through several adjacent strips after the strips have been bonded together. In the prior art embodiment shown in FIG. 1, the vent openings are present in pairs in a repeating pattern such that each cell 20 has eight openings communicating with each adjacent cell 20 and/or with the outside. In the prior art embodiment which forms the basis for FIG. 1, each strip is about eight inches high and the welds 16 are formed at lengthwise intervals of about thirteen inches. Each weld 16 is about 6? inches from a weld 16 in the embodiment shown. The openings 32 are circular, having diameters of about one-half of an inch and are formed in pairs.

[0051] FIG. 2 illustrates the use of the prior art vented cell structure filled with carthen material 34. Earthen material 34, generally confined within the individual cells 20, is connected between adjacent cells at the vent openings 32 to form a continuous interlocking network throughout the cell structure. Under an applied load, interlocking between adjacent cells causes the filled structure to have reduced long-term settling and greater load bearing capacity than filled cell structures which do not have communication between adjacent cells. Load bearing capacity is a measure of the ability of the filled cell structure to withstand vertical pressures including, for instance, localized uplift pressures caused by freezing temperatures and water pressure from underground springs, or common downward pressures from traffic, equipment, or structure foundations. Applied loads may be intermittent or variable, and the degree of interlock between adjacent cells will fluctuate accordingly. This disclosure is related to improvements for the degree of interlock, as discussed in connection with FIGS. 5-7 and the Experimental Section, below.

[0052] FIG. 3 is a side view of the prior art vented cell structure 10, prior to expansion and fill. This embodiment shows perforated vent openings 32, with each being circular in shape and being staggered. There are greater than 50 perforated vent openings 32, per wall of each cell 20, often greater than 70 perforated vent openings 32.

[0053] FIG. 4 illustrates the use of vented cell structure 100 of this disclosure in one application. In the example shown, the vented cell structure 100 reinforces and confines a gravel road 50 located on the side of a mountain 60, thereby preventing erosion and possible washout of the road. The in-fill can include sand, gravel, crushed concrete, recycled asphalt, engineered fill, foamed glass aggregate, or any combination thereof. Often, AASHTO #57 stone gravel is used. In some cases, the in-fill consists essentially of gravel.

[0054] The vented cell structure 100, constructed according to principles of this disclosure, is shown in various embodiments of FIGS. 5-7. The inventors have discovered that the ability of in-fill material (aggregate) to maintain interlock with the cell structure is helpful in increasing friction and interaction, even at low pressures. This has significance because the aggregate is able to maintain engagement with the cell wall under at rest (very low pressure) conditions even when no load is applied, and therefore the infill will not settle out of the cell or drift downward over time. In other words, the vented cell structure 100 will remain engaged with the infill under ambient conditions, whether a load is present or not, and addresses a common issue associated with loss of interlock in situations where the load is intermittent or dynamic. In the prior art, when a sufficiently high enough load is not present to develop adequate lateral earth pressures to fully engage with the cell wall, the infill can slowly migrate downward over time, eventually leaving the tops of the cells exposed at ground surface. Trafficking over the exposed material in turn results in damage to the geocells which negatively impacts the long term performance and design life of the road base, for example, in applications such as the gravel road 50 shown in FIG. 4. In the case of the prior art, the remedy for addressing the exposed material requires placing an additional 2-3 inches of gravel to re-establish a protective wearing course over the vented cell structure 10. In the case of the improved vented cell structure 100, discussed below, the need for this type of remedy is eliminated or substantially reduced, thereby reducing overall long term maintenance and repair costs associated with projects such as the gravel road 50 shown in FIG. 4.

[0055] In general, it has been found that there is a relationship between the size of the vent openings and the advantageous results discussed above. In FIG. 5, the vented cell structure 100 has a plurality of openings 110, which can be non-circular openings. For example, the openings can be polygons, such as regular polygons. In the example of FIG. 5, each opening 110 is triangular in shape. The openings 110 are arranged on the structure 100 in a pattern to help maximize the amount of open area, while still maintaining good structural integrity. In FIG. 5, there are 3 rows of triangular openings 110, each row having a middle triangle opening 112 in between two triangle openings 114, 116 pointed in an opposite direction to that of the middle triangle opening 112.

[0056] In FIG. 6, the vented cell structure 100 has triangular openings 120 and diamond openings 122. In this example, there are two rows, and each row has the diamond opening 122 in between two triangle openings 120. One row includes the triangle openings 120 pointed up, while the other row includes the triangle openings 120 pointed down.

[0057] In FIG. 7, the vented cell structure 100 has hexagonal openings 130. In this example, there are 4 rows of hexagonal openings 130.

[0058] It should be understood that many different shapes and patterns of openings can be used. Also, each cell can have either a same number of openings communicating with each adjacent cell, or a different number. In addition, each opening can have a same geometric shape or a different geometric shape.

EXPERIMENTAL

[0059] Pullout testing was conducted comparing the prior art cell structure to the cell structure made in accordance with principles of this disclosure. The testing was done using gravel, specifically AASHTO #57 stone gravel in accordance with ASTM D 6706.

[0060] The cell structure 100, according to this disclosure (referred to in the table below as prototype strips) and the cell structure of the prior art as shown in FIG. 3 (referred to below as standard Geoweb), were subjected to pullout tests under identical test conditions at normal stresses of 30, 50, and 60 psf. The results indicate that the prototype strips achieved a higher Coefficient of Friction (F*) and higher Coefficient of Interaction (Ci) in all test runs.

TABLE-US-00001 Normal Coefficient of Friction, F* Coefficient of Interaction, Ci Stress Standard Standard (psf) Geoweb Prototype Geoweb Prototype 30 1.37 1.78 0.92 1.20 50 1.75 2.00 1.18 1.35 60 1.88 2.08 1.26 1.41

[0061] This finding is informative, as cell structure performance is very much dependent upon the frictional interaction between the infill material and the cell wall.

[0062] The prototypes used in the study used large noncircular perforations (i.e., triangular openings 110, as shown in the pattern of FIG. 5), such to facilitate the effects of interlock, and the perforations had an open area equal to a circle having a diameter greater than 30 millimeters (i.e., greater than about 707 mm.sup.2).

[0063] In general, it has been found advantageous to use noncircular openings, including triangular, diamond, or polygonal (including regular polygons such as pentagon, hexagon, octagon, etc.) having an open area equal to a circle having a diameter greater than 32 millimeters (i.e., greater than about 804 mm.sup.2).

[0064] There can be variations used. For example, in one example, only a majority of the openings have an open area of greater than 804 mm.sup.2. In some cases, more than 75% of the openings have an open area of greater than 804 mm.sup.2. In some cases, more than 90% of the openings have an open area of greater than 804 mm.sup.2. In some cases, 99% or more of the openings have an open area of greater than 804 mm.sup.2.

[0065] The above describes example principles. Many embodiments can be made using these principles.