Multilayer integral geogrids having cellular layer structure, and methods of making and using the same

Abstract

To provide integral geogrids having a multilayer construction, including one or more layers having a porous structure, that provides enhanced vertical compressibility and enhanced frictional characteristics of the integral geogrids.SOLUTION: A multilayer integral geogrid 200, including one or more porous layers, has a plurality of oriented multilayer strands 205 interconnected by partially oriented multilayer junctions 235 with an array of openings therein. The multilayer integral geogrid having one or more porous layers is produced from a coextruded or laminated multilayer polymer starting sheet. The integral geogrid has a multilayer construction, with at least one outer layer thereof having the porous structure. By virtue of the porous layer structure, the multilayer integral geogrid provides for increased layer vertical compressibility under load, resulting in enhanced material properties that provide performance benefits to use of the multilayer integral geogrid to stabilize and strengthen soil, aggregates, or other particulate materials.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application is related to and claims the benefit of priority to U.S. Patent Application No. 17 / 355,843, filed June 23, 2021, entitled "Multi-Axial Integral Geogrid and Methods of Making and Using Same," and International Patent Application No. PCT / US2021 / 038863, filed June 24, 2021, entitled "Multi-Axial Integral Geogrid and Methods of Making and Using Same," both of which are hereby incorporated by reference in their entirety; both applications are hereby incorporated by reference in their entirety ... No. 63 / 154,209, filed on Feb. 26, 2021, entitled "Horizontal Mechanically Stabilizing Geogrid with Improved Geotechnical Interaction," and claims priority to U.S. Provisional Patent Application No. 63 / 154,588, filed on Feb. 26, 2021, entitled "Horizontal Mechanically Stabilizing Geogrid with Improved Geotechnical Interaction." This application is also related to a concurrently filed patent application entitled "Horizontal Mechanically Stabilizing Geogrid with Improved Geotechnical Interaction," the disclosures of which are incorporated herein by reference in their entireties.

[0002] 1. Field of the invention The present invention relates generally to monolithic geogrids and other oriented grids used for strengthening and stabilizing structures or buildings, and other geotechnical engineering purposes. More specifically, the present invention relates to monolithic geogrids having a multi-layer structure, including one or more layers having a porous structure that improves the vertical compressibility and frictional properties of the monolithic geogrid. The present invention also relates to such monolithic geogrids having the ability to interlock and stabilize a greater variety and range of aggregate qualities, as well as other desirable properties disclosed herein. The present invention also relates to soil structures incorporating the monolithic geogrids of the present invention, characterized by enhanced engineering behavior and properties, such as density, stiffness, strength, and ductility.

[0003] The invention also relates to a method for producing such a multi-layer monolithic geogrid having one or more porous layers.Finally, the invention relates to the use of such a multi-layer monolithic geogrid for consolidation and stabilization of soils and particles, and to a method of such consolidation and stabilization.

[0004] For purposes of this invention, the term "integral geogrid" is intended to include integral geogrids and other integral grid structures that are made by orienting (i.e., stretching) a polymeric starting material in a sheet or sheet-like shape having the required thickness and having holes or recesses made or formed therein. [Background technology]

[0005] 2. Description of Related Technology Polymer integral grid structures, such as integral geogrids, having mesh openings defined by various geometric patterns of substantially parallel oriented strands and joints between them, have been manufactured and sold for over 35 years. Such grids are manufactured by extruding an integrally cast starting sheet with a specific pattern of holes or recesses, followed by controlled uniaxial or biaxial stretching and orientation of the sheet and the partially oriented joints that define the mesh openings formed by the holes or recesses into highly oriented strands (hereinafter also referred to as ribs). Such uniaxial or biaxial stretching and orientation of the sheet changes the tensile strength and modulus of elasticity of the strands. These integrally oriented polymer grid structures can be used to hold or stabilize particulate material of any suitable shape, such as soil, earth, sand, clay, gravel, etc., in any suitable location, such as beside a road or other cut or fill, under a road surface, on the surface of a runway, etc.

[0006] Various hole shapes and patterns have been experimented with to achieve higher levels of strength to weight ratio or to achieve faster processing speeds in the manufacturing process. Orientation is performed under controlled temperature and strain rate. Process variables include draw ratio, molecular weight, molecular weight distribution, and the degree of branching or crosslinking of the polymer.

[0007] The manufacture and use of such integral geogrids and other integral grid structures can be accomplished by well known techniques. As described in detail in U.S. Patents 4,374,798 to Mercer, 4,590,029 to Mercer, 4,743,486 to Mercer and 4,756,946 to Mercer, and 5,419,659 to Mercer, a starting polymeric sheet material is first extruded and then punched to form the required defined pattern of holes or recesses. The punched sheet material is then stretched and oriented as necessary to form the integral geogrid.

[0008] Such integral geogrids, namely uniaxial integral geogrids and biaxial integral geogrids (collectively "integral geogrids" or individually "uniaxial integral geogrids" or "biaxial integral geogrids"), were both invented by Mercer, supra, in the late 1970s and have enjoyed tremendous commercial success over the past 35 years, revolutionizing the overall technology for strengthening soils, road subpavements, and other civil engineering structures made from granular or particulate materials.

[0009] Mercer has discovered that an entirely new substantially uniplanar monolithic geogrid can be formed by starting with a relatively thick substantially uniplanar polymer starting sheet, preferably on the order of 1.5 mm (0.059055 in) to 4.0 mm (0.15748 in) thick, having a pattern of holes or recesses centered in the rows and columns of a notional substantially square or rectangular grid, and stretching the starting sheet uniaxially or biaxially to extend the orientation of the strands out to the joints. As explained by Mercer, "uniplanar" means that all sections of the sheet material are symmetrical about the median plane of the sheet material.

[0010] In U.S. Patents 3,252,181 to Hureau, 3,317,951 to Hureau, 3,496,965 to Hureau, 4,470,942 to Beretta, 4,808,358 to Beretta, and 5,053,264 to Beretta, a starting material having a desired pattern of holes or recesses is formed in combination with a cylindrical polymer extrusion, and a substantially uniplanar surface is achieved by passing the extrudate over an expanding mandrel. The expanded cylinder is then cut longitudinally to produce a flat, substantially uniplanar starting sheet.

[0011] Another monolithic geogrid is described in U.S. Patent No. 7,001,112 to Walsh (hereinafter "Walsh '112 patent"), assigned to Tensar International Limited, an affiliate of Tensar International Corporation, Inc. (hereinafter "Tensar"), the assignee of this patent application, of Atlanta, Georgia. Walsh '112 patent discloses oriented polymer monolithic geogrids, including biaxially oriented monolithic geogrids, in which oriented strands form triangular mesh openings with partially oriented junctions at each corner, where six highly oriented strands meet at each junction (hereinafter sometimes referred to as "triaxial monolithic geogrids"). The triaxial monolithic geogrids of Walsh '112 patent have been commercialized by Tensar with great success.

[0012] Further integral geogrids are disclosed in U.S. Patent Nos. 9,556,580 to Walsh, 10,024,002 to Walsh, and 10,501,896 to Walsh, all of which are assigned to Tensar Technologies Limited, another affiliate of the assignee of the present patent application. Walsh U.S. Patent Nos. 9,556,580, 10,024,002, and 10,501,896, cited above, disclose integral geogrids having what is known to those skilled in the art as a high aspect ratio, i.e., the ratio of the thickness or height of the cross-sectional strand to the width of the cross-sectional strand is greater than 1.0. It has been shown that the performance of multiaxial integral geogrids can be improved by using geogrid structures with ribs having an aspect ratio greater than 1.0, but increasing the aspect ratio increases the total amount of polymer required, thereby increasing the weight and cost of the geogrid.

[0013] Traditionally, the polymeric materials used in the manufacture of monolithic geogrids have been high molecular weight homopolymer or copolymer polypropylene and high density, high molecular weight polyethylene. Various additives, such as ultraviolet light inhibitors, carbon black, processing aids, etc., are added to these polymers to achieve desired effects in the final product and / or manufacturing efficiency.

[0014] Also, traditionally, the starting material for the manufacture of such monolithic geogrids has typically been a monolithic construction, i.e., a substantially monoplanar sheet having a single layer of homogeneous polymeric material.

[0015] While monolithic geogrids produced from the conventional starting materials described above generally exhibit satisfactory properties, it would be structurally and economically advantageous to produce monolithic geogrids that, when incorporated into soil structures, provide a relatively high degree of stiffness suited to the requirements of particular applications, such as geosynthetic reinforcement, or have other properties desirable for a particular geosynthetic application.

[0016] Thus, a need exists for a starting material that is not only suited to the process constraints associated with the manufacture of integral geogrids, but also, when the integral geogrid is manufactured and used, provides a higher degree of soil structural stiffness than that associated with conventional geogrid starting materials, or provides other properties, such as density, strength and ductility, not available in conventional single layer integral geogrids.

[0017] Additionally, while monolithic geogrids manufactured in conventional configurations from the conventional starting materials described above may generally exhibit sufficient properties, it would be structurally and economically advantageous to produce monolithic geogrids with structures and geometries capable of bonding and stabilizing a wider variety and range of aggregate qualities suited to the requirements of a particular service application, such as geosynthetic reinforcement, or with other properties desirable for a particular geosynthetic application.

[0018] It is contemplated that the present invention may be applied to all integral grids, regardless of the method of initiating sheet formation or orienting the starting materials into an integral geogrid or grid structure. The subject matter of the above-mentioned U.S. Patent Nos. 3,252,181, 3,317,951, 3,496,965, 4,470,942, 4,808,358, 5,053,264, 7,001,112, 9,556,580, 10,024,002, and 10,501,896 is expressly incorporated by reference into this application as if set forth in its entirety herein. These patents are cited by way of example and are not to be construed as being comprehensive or exclusive of other techniques known in the art for the manufacture of integral polymer grid materials.

[0019] Despite the functional properties available in current single-layer integral geogrids, performance improvements over prior art integral geogrids have yet to be achieved. One such enhancement is disclosed in U.S. Patent Application Serial No. 15 / 766,960 (hereinafter "the '960 Application"; published as U.S. Patent Application Publication No. 2018 / 0298582A1), also assigned to Tensar International Limited. The '960 Application discloses various embodiments of coextruded multi-layer polymer sheets as starting materials for the manufacture of integral geogrids. By virtue of the coextruded multi-layer starting material structure, the components of the coextruded multi-layer sheet, after extrusion and stretching, produce a monolithic geogrid with enhanced material properties that provide performance advantages in soil geosynthetic reinforcement.

[0020] One embodiment disclosed in the '960 application is a three-ply integral geogrid manufactured from a co-extruded three-ply starting sheet in which the middle layer of the oriented integral geogrid has an expanded or "foamed" structure. According to the '960 application, the only advantages of the expanded or foamed multi-layer structure are reduced raw material costs and reduced geogrid weight, "which may include desirable physical and chemical properties of the foam layer itself." No other advantages associated with the expanded or foamed multi-layer structure are disclosed. The subject matter of the '960 application is expressly incorporated by reference into this application as if set forth in its entirety herein.

[0021] To date, current monolithic geogrid products produced with current production / processing techniques are capable of producing multiaxial geogrid products with desirable properties and characteristics; however, current processing / production techniques do not allow for the material type to be varied within the cross section of the entire geogrid. As a result, the amount of polymer must be significantly increased to enhance the desired physical, mechanical and geometric properties that will improve performance.

[0022] Additionally, current processing / production techniques limit the ability to increase or enhance certain parameters that improve performance while simultaneously controlling or not changing other parameters whose alteration reduces performance.

[0023] Additionally, current processing / production techniques do not allow for the use of different polymeric materials in different portions of a geogrid structure as a means of maximizing performance.

[0024] Thus, there is a need for a monolithic geogrid that provides a good "initial fit" between the aggregate and the geogrid and maximizes aggregate density after compaction is complete, thereby minimizing any potential shifting or relocation of the remaining aggregate that may normally occur after compaction and during the initial stages of "in service" loading. More specifically, there is a need for a monolithic geogrid that provides the above-mentioned properties by improving the compressibility of the layer under loading. The term "initial fit" as used herein means maximizing aggregate density after compaction is complete, thereby minimizing any potential shifting or relocation of the aggregate that may normally occur after compaction and during the initial stages of "in service" loading. Summary of the Invention

[0025] It is therefore an object of the present invention to provide improved functional performance from multiaxial integral geogrids by enhancing certain physical, mechanical and geometric properties of the multiaxial integral geogrid structure that improve functional performance, for example, by modifying and / or incorporating other new physical, mechanical and geometric properties. By carefully physically placing and manipulating the amounts of various polymeric materials with desired mechanical and physical properties in specific locations of the integral geogrid structure, as well as optimizing all other physical parameters of the geogrid structure, significant performance improvements can be achieved.

[0026] It is another object of the present invention to provide a multi-layer integral geogrid in which the layers have been modified such that the amount of polymer required is reduced by converting the polymer in those layers from a solid, i.e., continuous structure, to a porous structure, i.e., a structure distributed with a plurality of voids, cavities, pores, cracks, bubbles, holes or other types of openings, i.e., porous-like openings, created by the methods described herein.

[0027] More specifically, after the filing of the '960 application, it was surprisingly discovered that improved initial compatibility between the aggregates and layers of a multi-layer integral geogrid having a porous structure can be achieved when certain parameters for the layers having a porous structure are included in the geogrid as described herein. These parameters include: 1. The minimum thickness or height of the ribs of a multi-layer integrated geogrid having one or more porous layers according to the present invention is preferably from about 0.5 mm to about 6 mm, more preferably from about 1.15 mm to about 4 mm. 2. The aspect ratio of the ribs of the multi-layer integrated geogrid having one or more porous layers according to the present invention is preferably about 0.75 to about 3.0, more preferably about 1 to about 2. 3. The initial height or thickness of one or more of the porous layers after stretching at its thinnest height (perhaps the midpoint of a strand or rib) is from about 0.1 mm to about 4 mm, more preferably from about 0.5 to about 3 mm. 4. The porous openings of the one or more porous layers comprise at least 20% by volume of the one or more porous layers, preferably about 30% to about 50%. 5. One or more porous layers have minimal "crushability" or loss in height under load of at least 20%, preferably about 30% to about 50%. 6. The one or more porous layers have a height or thickness that is at least 10% of the total height of the final monolithic geogrid, and preferably from about 20% to about 35%.

[0028] The inclusion of the above mentioned physical properties in the multi-layer monolithic geogrid having one or more porous layers according to the present invention improves the initial compatibility between the aggregate and the geogrid after compaction is completed. This improved initial compatibility in turn reduces the movement or relocation of the remaining aggregate that may normally occur during and after compaction during the initial stages of "in service" loading. Thus, roads and other transportation surfaces, or aggregate and soil layers, are improved in construction with more stability and reduced deformation and movement during use or loading.

[0029] More specifically, the present invention provides improved microscopic interaction by using a multi-layered monolithic geogrid having one or more porous layers, as the layers of compressible polymer act to nest the aggregate particles, promoting and maintaining maximum aggregate properties.

[0030] Additionally, by judiciously modifying the polymer to reduce the density and / or volume of polymer used in one or more layers of the extruded sheets used to manufacture the multi-layer integral geogrid, one can create a monolithic geogrid structure having similar physical dimensions to traditional monolithic geogrids, but using reduced amounts of polymer material, and therefore reduced costs.

[0031] Thus, to achieve the above-mentioned objectives, the present invention is directed to monolithic geogrids having a multi-layer structure, at least one layer of which has a porous structure. These multi-layer geogrids are often referred to herein as monolithic geogrids having at least one layer with a porous structure, or more simply as "multi-layer monolithic geogrids having one or more porous layers" or "multi-layer monolithic geogrids having one or more porous layers." By virtue of the multi-layer monolithic geogrids having one or more porous layers, the multi-layer monolithic geogrids of the present invention provide enhanced compressibility of the layers under load, as well as other desirable properties.

[0032] More specifically, a layer having a porous structure includes a plurality of distributed porous openings, i.e. voids, cavities, pores, cracks, bubbles, holes or other types of openings. The porous structure may be associated with a foamed structure of the layer, with a particulate filler distributed throughout the layer, or any other method of forming porous openings in a porous layer.

[0033] And for embodiments of the invention having three or more layers, the compressible layers having a porous structure are preferably placed as at least two outer (or exterior or "cap") layers of the multi-layered integral geogrid. Having the two outer layers compressible has unique geomechanical advantages. One important advantage is that the compressible outer layers allow the aggregates to not only penetrate through the openings and be trapped within the openings, but also embed themselves in the outer layers of the integral geogrid surface, resulting in what is sometimes referred to herein as the "crush-fit" phenomenon. Because the aggregates are "crush-fit" to the surface of the porous outer layer of the integral geogrid, the integral geogrid can enhance the lateral restraint of the aggregates under load by resisting aggregate movement through the enhanced frictional properties of the surface of the porous outer layer, and by the bonding action caused by the aggregate particles being partially crushed against the surface of the porous outer layer.

[0034] The crushable nature of the porous outer layer results in plastic and elastic deformation, which causes the aggregates to be forced into the outer layer and bond to its surface. At the same time, the surface of the outer layer is forced back, enhancing the bond and "crash fit" between the aggregates and the multi-layer integral geogrid. And, according to certain embodiments of the present invention, the crushable nature of the porous outer layer may have the potential to form chemical bonds with the surrounding soil. By combining the improved surface morphology and enhanced engineered outer layer structure described herein, the multi-layer integral geogrid according to the present invention provides improved performance due to improved aggregate containment and lateral restraint.

[0035] A key characteristic of the multi-layered integral geogrid according to the present invention is the compressibility or crushability of the porous layers. For example, in the three-layered embodiment described above, the compressibility of the two outer porous layers is important to anchor the aggregates to the surface of the integral geogrid. Ideally, each compacted layer is durable enough to withstand the process of embedding in the particulate material (i.e., in terms of resisting delamination or shredding from the other layers) and compresses at least about 20% under load. Additionally, the compacted layers rebound at least about 85%. The basic concept of the present invention is that the porous layers are not only compressible enough to contain the aggregates during embedding, but can also "rebound" as the compressible porous layers push back against the aggregates to "bond" the multi-layered integral geogrid in place. It is believed that crushing and rebounding improve performance due to friction and bonding properties that improve the lateral confinement of the aggregates.

[0036] Additionally, the structure of the multi-layered integral geogrid with one or more porous layers may include co-extruded or laminated layers. The creation of porous openings in the layer with the porous structure may occur during extrusion / lamination or during stretching / orientation or both.

[0037] The resulting multi-layer integrated geogrid, having layers with a porous structure, having a plurality of oriented multi-layer strands interconnected by partially oriented multi-layer joints, and having a series of openings therebetween, can be configured in any of a variety of repeating geometric patterns as described herein.

[0038] According to the present invention, the starting material for making a multi-layered monolithic geogrid with one or more porous layers includes a multi-layered polymeric starting sheet having holes or recesses therein that provide a series of openings that are formed when the starting material is biaxially stretched. The multi-layered polymeric starting sheet includes one or more layers capable of forming a porous structure. Two preferred embodiments are described in detail herein. In a first preferred embodiment according to the present invention, the layer capable of forming a porous structure includes a foaming agent that forms a porous layer as part of the final multi-layered geogrid upon extrusion of the layer and / or stretching / orientation of the starting sheet (hereinafter sometimes referred to as the "foaming embodiment").

[0039] In a second preferred embodiment according to the present invention, the layer capable of forming a porous structure includes a particulate filler distributed within the layer that upon stretching / orientation of the starting sheet produces a porous structure within the layer as part of the final multilayer geogrid (hereinafter sometimes referred to as the "filler embodiment"). According to a preferred embodiment, the layers of the multilayer polymer starting sheet may be coextruded or laminated together.

[0040] In addition to the two preferred embodiments detailed herein, the present invention also contemplates other methods of creating porous openings in one or more porous layers that may be devised by one skilled in the art, such as gas injection, so long as the porous openings in the porous layer comply with the parameters described herein.

[0041] According to certain embodiments of the present invention, a multi-layer integral geogrid having one or more porous layers comprises a plurality of oriented multi-layer strands interconnected by partially oriented multi-layer oriented joints and having a series of openings therebetween. According to one embodiment, a three-layer integral geogrid has a non-porous layer interposed between two outer layers having a porous structure. According to another embodiment, a multi-layer integral geogrid has a repeating pattern of a non-porous layer interposed between two layers having a porous structure. According to yet another embodiment, a multi-layer integral geogrid has a non-porous layer associated with an adjacent layer having a porous structure.

[0042] According to one embodiment, the multi-layered integrated geogrid with one or more porous layers is a rectangular geogrid having a repeating geometric pattern of partially oriented joints interconnecting oriented strands that define rectangular openings. According to another embodiment, the multi-layered integrated geogrid with one or more porous layers is a triaxial geogrid having a repeating hexagonal geometric pattern of partially oriented joints interconnecting oriented strands that define triangular openings. According to yet another embodiment, the multi-layered integrated geogrid with one or more porous layers is a geogrid having a repeating geometric pattern of partially oriented joints interconnecting oriented strands that form exterior hexagons, each of which is formed in the shape of an interior hexagon that surrounds and supports six interior interconnected structures that define smaller hexagonal openings, referred to herein as "repeating flow hexagons within a hexagonal pattern." This embodiment of the invention having "repeating flow hexagons within a hexagonal pattern" may also be referred to herein as the "hexagonal" embodiment.

[0043] According to yet another embodiment of the invention, a soil structure comprises a mass of granular material having one or more porous layers and reinforced and stabilized by embedding a multi-layer integral geogrid having a repeating geometric pattern of the type described in the previous paragraph.

[0044] According to yet another embodiment of the present invention, a method of making a starting material for a multilayer integral geogrid having one or more porous layers includes the steps of providing a multilayer polymer starting sheet having one or more layers capable of forming a layer having a porous structure as part of the final multilayer geogrid, and providing holes or recesses that interconnect the oriented multilayer strands and provide a repeating geometric pattern of partially oriented multilayer joints that define openings when the starting material is biaxially stretched.

[0045] In accordance with another embodiment of the present invention, a method of making a multilayer integral geogrid having one or more porous layers includes the steps of providing a multilayer polymer starting sheet having one or more layers capable of forming a layer having a porous structure as part of the final multilayer geogrid, providing holes or recesses therein, and biaxially stretching the multilayer polymer sheet having holes or recesses therein to provide a repeating geometric pattern of partially oriented multilayer joints interconnecting the oriented multilayer strands to define openings therein.

[0046] Also, in accordance with yet another embodiment of the present invention, a method for stretching a mass of particulate material includes embedding in the mass of particulate material a multi-layered integral geogrid having one or more porous layers and having a repeating geometric pattern of partially oriented joints interconnecting oriented multi-layer strands that define openings.

[0047] It is therefore an object of the present invention to provide a multi-layer integral geogrid having one or more porous layers, the integral geogrid having increased compressibility of the layers under load. The multi-layer integral geogrid having one or more porous layers may have a non-porous layer interposed between two layers having a porous structure, may have a repeating pattern of a non-porous layer interposed between two layers having a porous structure, or may have a non-porous layer bonded to an adjacent layer having a porous structure.

[0048] Therefore, another object of the present invention is to provide a starting material for making a multi-layered integral geogrid having one or more porous layers. The multi-layered polymeric starting sheet comprises one or more layers capable of forming a porous structure. In a first embodiment according to the present invention, i.e., the foaming embodiment, the layer capable of forming a porous structure comprises a foaming agent that upon extrusion of the layer and / or stretching / orientation of the starting sheet forms a porous layer as part of the final multi-layered geogrid. In a second embodiment according to the present invention, i.e., the filler embodiment, the layer capable of forming a porous structure comprises a particulate filler distributed within the layer that upon stretching / orientation of the starting sheet forms a porous structure within the layer as part of the final multi-layered geogrid.

[0049] Another object of the present invention is to provide a multi-layer integral geogrid having one or more porous layers and a plurality of oriented multi-layer strands interconnected by partially oriented multi-layer joints with a series of openings therebetween produced from a multi-layer polymer starting sheet. The multi-layer integral geogrid having one or more porous layers may be a rectangular geogrid having a repeating geometric pattern of partially oriented multi-layer joints interconnecting oriented multi-layer strands that define rectangular openings, a triaxial geogrid having a repeating geometric pattern of partially oriented multi-layer joints interconnecting oriented multi-layer strands that define triangular openings, or a geogrid having a repeating geometric pattern of partially oriented multi-layer joints interconnecting oriented multi-layer strands that define exterior hexagons, each of which surrounds and supports an interior oriented hexagon, i.e., a "repeating flow hexagon within a hexagonal pattern."

[0050] A related object of the present invention is to provide a shape that can bind and stabilize a wider variety and range of qualities of aggregate than shapes associated with conventional geogrid structures, while providing enhanced compressibility and other desirable properties.

[0051] It is yet another object of the present invention to provide an earth structure comprising a mass of granular material having one or more porous layers and reinforced and stabilized by embedding a multi-layer integral geogrid having a repeating geometric pattern as described herein.

[0052] It is yet another object of the present invention to provide a method of producing a starting material for a multi-layer monolithic geogrid having one or more porous layers, the method comprising the steps of providing a multi-layer polymer starting sheet having one or more layers capable of forming a layer having a porous structure as part of the final multi-layer geogrid, and providing holes or recesses that interconnect the oriented multi-layer strands and provide a repeating geometric pattern of partially oriented multi-layer connections that define openings when the starting material is biaxially stretched.

[0053] The multilayer polymer starting sheet may be produced by coextrusion of multiple layers or by laminating multiple layers together.

[0054] Another object of the present invention is to provide a method for making a multi-layer integral geogrid having one or more porous layers, comprising the steps of providing a multi-layer polymer starting sheet having one or more layers capable of forming a layer having a porous structure as part of the final multi-layer geogrid, providing holes or recesses therein, and biaxially stretching the multi-layer polymer starting sheet to provide a repeating geometric pattern of partially oriented multi-layer joints and openings interconnecting the oriented multi-layer strands. The method for making the rectangular or triangular opening integral geogrids described above can use known geogrid manufacturing methods such as those described in the above-mentioned U.S. Patents 4,374,798, 4,590,029, 4,743,486, 5,419,659, 7,001,112, 9,556,580, 10,024,002 and 10,501,896, and other patents. The method of making the above-described integral geogrid having a repeating geometric pattern of partially oriented multi-layer joints interconnecting oriented multi-layer strands, each of which defines an outer hexagon that surrounds and supports an inner oriented hexagon, can use a manufacturing method such as that described below.

[0055] More specifically, it is an object of the present invention to provide a method for producing a multi-layer integrated geogrid having one or more porous layers, in which the layers having a porous structure are formed by first providing a foam structure in a layer of a multi-layer polymer starting sheet from which the layers can be formed, and then orienting the multi-layer polymer starting sheet to stretch the foam material and form the porous structure.

[0056] Similarly, another object of the present invention is to provide a method for producing a multi-layer monolithic geogrid having one or more porous layers, in which the layers having a porous structure are formed by first distributing a particulate filler in a layer of a multi-layer polymer starting sheet from which a layer can be formed, and then orienting the multi-layer polymer starting sheet to expand the distribution of the particulate filler, forming a porous structure when the particulate filler partially separates from the polymer layer material.

[0057] It is yet another object of the present invention to provide a method of strengthening a mass of particulate material comprising embedding in the mass of particulate material a multi-layer integral geogrid having one or more porous layers and having a repeating geometric pattern of partially oriented multi-layer joints and openings interconnecting oriented multi-layer strands.

[0058] The many advantages associated with the multi-layer monolithic geogrid having one or more porous layers according to the present invention are numerous in nature.

[0059] The multi-layer integrated geogrid having one or more porous layers of the present invention not only has a multi-layer structure, but also at least one of the layers has a porous structure, which allows the integrated geogrid to increase the compressibility of the multi-layer integrated geogrid under load.

[0060] Also, the multi-layered nature of the multi-layered integral geogrids having one or more porous layers of the present invention results in greater overall aggregate bonding with the integral geogrid compared to conventional single layer integral geogrids. Furthermore, by virtue of the one or more porous layers, the multi-layered integral geogrids of the present invention are characterized by structural compliance, i.e., initial resilience or flexibility, which results in better compaction and higher density, yet as a result of the initial resilience of the multi-layered integral geogrid, has a greater composite stiffness of the final integral geogrid when incorporated into a soil structure.

[0061] Additionally, certain embodiments of the multi-layer monolithic geogrids having one or more porous layers of the present invention provide higher aspect ratios in all strands as compared to conventional monolithic geogrids, and the multi-layer monolithic geogrids having one or more porous layers of the present invention can better accommodate a variety of aggregate aspect ratios since the higher aspect ratios associated with certain embodiments of the monolithic geogrids of the present invention increase aggregate interlocking.

[0062] In summary, the porous layers of the multi-layer integral geogrids of the present invention create unique physical and mechanical properties and behaviors in the integral geogrid product. It is believed that when aggregate is placed and compressed in the multi-layer integral geogrid, the compressible porous outer layer nature of the ribs and nodes, along with other scientifically designed aspects of the geogrid, improves the initial fit between the aggregate and the geogrid, improves the density of the aggregate after compression is complete, and reduces the movement or relocation of residual aggregate that may normally occur after compression and during the initial stages of loading during use. While not intending to be binding, it is currently believed that the above-mentioned initial fit of the multi-layer integral geogrids of the present invention is a key factor in reducing the amount of deformation that occurs during use of the geogrid. The benefits of initial fit associated with the present invention are evidenced, for example, by test results in a laboratory transport device where significantly fewer passes are required to achieve a steady state for the multi-layer integral geogrids of the present invention. Additionally, various embodiments of the multi-layer integral geogrids of the present invention are characterized by the fact that the increased rib height is achieved with less material than prior art geogrids, and the increased aspect ratio is achieved with less material than prior art geogrids. Due to the increased flexibility and pliability of the in-plane ribs and increased out-of-plane stiffness, the multi-layer integral geogrid of the present invention provides improved geogrid / aggregate interaction and therefore improved bonding.

[0063] Thus, by virtue of one or more porous layers, the multi-layer integral geogrid of the present invention provides not only increased layer compressibility under load, but also increased aggregate bonding and restraint as an aggregate stabilized product.

[0064] These, together with other objects and advantages which will become apparent hereinafter, are contained in the details of construction and operation as more fully described below, and reference is made to the accompanying drawings which form a part hereof and in which like reference numerals refer to like parts throughout, and which are intended to illustrate the invention, but are not necessarily drawn to scale, and in which: [Brief description of the drawings]

[0065] [Figure 1] FIG. 1 is a perspective view of a cross section of a triaxial three-layer integrated geogrid with two outer layers with porous structure according to one embodiment of the present invention, with the cross section highlighted in the foreground. [Diagram 2] FIG. 2 shows a single planar tri-layer polymer starting sheet for the triaxial multi-layer integral geogrid shown in FIG. 1 before any holes or recesses are formed. [Diagram 3] FIG. 3 is a top perspective plan view of the starting sheet shown in FIG. 2 with holes formed therein for forming the triaxial three-layer integrated geogrid shown in FIG. [Figure 4] FIG. 4 is a perspective cross-sectional view of a portion of the starting sheet shown in FIG. [Diagram 5] FIG. 5 shows a single planar five-layer polymer starting sheet for a triaxial five-layer monolithic geogrid having two outer layers and an innermost layer having a porous structure, prior to the formation of holes or recesses, in accordance with another embodiment of the present invention. [Figure 6] FIG. 6 is a perspective cross-sectional view of a portion of a triaxial five-layer monolithic geogrid having two outer layers and an innermost layer having a porous structure associated with the starting sheet shown in FIG. [Figure 7] FIG. 7 is a plan view of a rectangular three-layer integrated geogrid having two outer layers with porous structure according to yet another embodiment of the present invention. [Figure 8] FIG. 8 is a perspective view of a rectangular three-layer integrated geogrid having two outer layers with the porous structure shown in FIG. [Figure 9] FIG. 9 is a top perspective plan view of a starting sheet with holes formed therein to form a rectangular three-layer integrated geogrid having two outer layers with the porous structure shown in FIG. [Figure 10] FIG. 10 is a plan view of a hexagonal three-layer integrated geogrid having two outer layers with porous structure in accordance with yet another embodiment of the present invention. [Figure 11] FIG. 11 is a perspective view of a hexagonal three-layer integrated geogrid having two outer layers with the porous structure shown in FIG. [Figure 12]FIG. 12 is a top perspective view of a starting sheet with holes formed therein to form a hexagonal three-layer integrated geogrid having two outer layers with the porous structure shown in FIG. [Figure 13] FIG. 13 is a perspective view of a hexagonal two-layer integrated geogrid having one porous and one non-porous layer. [Figure 14] FIG. 14 shows a monoplanar bi-layer polymer starting sheet for the hexagonal bi-layer integral geogrid shown in FIG. 13 before any holes or recesses are formed. [Figure 15] FIG. 15 is a top perspective plan view of a starting sheet with holes formed therein for forming the hexagonal two-layer integrated geogrid shown in FIG. [Figure 16] FIG. 16 is a plan view of possible sizes and spacing of holes shown in the starting sheet of FIG. [Figure 17] 17A-17E show the hypothetical compression mechanism of a three-layer integrated geogrid having two outer layers with porous structure according to the present invention under load. [Figure 18] 18A-18C show the hypothetical flexible rib mechanism of the two outer layers of a three-layer integrated geogrid having two outer layers with a porous structure according to the present invention under load, demonstrating both vertical and horizontal flexibility of the integrated geogrid. [Figure 19] FIG. 19 is a graph showing a comparison of the behavior of inelastic ribs in a starting sheet of a conventional single layer integrated geogrid to the behavior of elastic ribs in a starting sheet of a multi-layer integrated geogrid having two outer layers with a porous structure of the present invention. [Figure 20] FIG. 20 illustrates the isotropic properties associated with the triangular geometric features of the triaxial multi-layer integral geogrids as shown in FIGS. [Figure 21] FIG. 21 illustrates the isotropic properties associated with continuous ribs in three directions, which is the structural geometry characteristic of hexagonal multi-layer integral geogrids such as those shown in FIGS. [Figure 22]FIG. 22 shows an overlay of hollow hexagons associated with a hexagonal multi-layer integral geogrid as shown in FIGS. 10, 11 and 13 on a triaxial geogrid. [Figure 23] FIG. 23 shows hollow hexagonal and six rib elements associated with a hexagonal multi-layer integral geogrid as shown in FIGS. [Figure 24] FIG. 24 is a partial plan view showing various strand lengths of a hexagonal multi-layer integral geogrid as shown in FIGS. [Diagram 25] FIG. 25 shows the effect of increasing rib height on surface deformation for a hexagonal three-layer integrated geogrid according to the present invention similar to that shown in FIGS. [Figure 26] FIG. 26 is a plot of the effect of increasing rib height on surface deformation related to the test results shown in FIG. [Figure 27] FIG. 27 is a table summarizing the effect of increasing rib height on surface deformation related to the test results shown in FIGS. [Figure 28] FIG. 28 is a plot of the increased rib height achievable with a hexagonal three layer integral geogrid according to the present invention versus the rib height achievable with a solid single layer geogrid. [Figure 29] FIG. 29 is a plot of the mass reduction per unit area achievable with a hexagonal three layer integral geogrid according to the present invention versus the mass per unit area achievable with a solid single layer geogrid. [Diagram 30] FIG. 30 is a plot of the improved performance achievable with a hexagonal three layer integral geogrid having a compressible porous outer layer according to the present invention versus the performance achievable with a hexagonal solid single layer geogrid. [Diagram 31] FIG. 31 is a table summarizing structural data related to the hexagonal three-layer integral geogrid with compressible porous outer layer and the hexagonal solid single layer geogrid used in the test results shown in FIG. 30. [Diagram 32]FIG. 32 is another plot of the improved performance achievable with a hexagonal three layer integral geogrid with a compressible porous outer layer according to the present invention versus the performance achievable with a hexagonal solid single layer geogrid. [Diagram 33] FIG. 33 is a table summarizing structural data related to the hexagonal three layer integral geogrid with compressible porous outer layer and the hexagonal solid single layer geogrid used in the test results shown in FIG. [Diagram 34] FIG. 34 is a plot of the improved compressibility achievable with a hexagonal three layer integral geogrid having a compressible porous outer layer according to the present invention versus the compressibility achievable with a hexagonal solid single layer geogrid. [Diagram 35] FIG. 35 is a table summarizing the force required to produce a certain compressibility associated with the hexagonal three layer integral geogrid with compressible porous outer layer according to the present invention and the hexagonal solid single layer geogrid used in the test results shown in FIG. [Diagram 36] FIG. 36 is a plot of the stiffness achievable with a hexagonal three layer integral geogrid with a compressible porous outer layer according to the present invention versus a hexagonal solid single layer geogrid. [Figure 37] FIG. 37 is a table summarizing the stresses and strains associated with the hexagonal three-layer integral geogrid with compressible porous outer layer and the hexagonal solid single layer geogrid used in the test results shown in FIG. [Figure 38] FIG. 38 is a partial plan view showing various strand lengths of a hexagonal three layer integrated geogrid as shown in FIGS. 10 and 11, and continuous ribs associated with the left machine direction, right machine direction and cross directions, similar to that shown in FIG. [Figure 39] FIG. 39 is a plan view of possible hole sizes and spacing associated with the starting sheets used to manufacture the hexagonal three layer integrated geogrid shown in FIG. [Diagram 40]FIG. 40 is a side cross-sectional view of a partial cross section of a hexagonal three-layer integrated geogrid having two outer layers with a porous structure according to the embodiment of the invention shown in FIG. [Diagram 41] FIG. 41 shows the experimental setup used to measure the compressibility of monolithic geogrids according to various embodiments of the present invention. [Diagram 42] FIG. 42 shows a graph illustrating the compressibility of various embodiments of a monolithic geogrid according to the present invention compared to a monolithic geogrid without a layer having a porous structure using the apparatus shown in FIG. [Diagram 43] FIG. 43 shows a graph illustrating the compressibility of various embodiments of a monolithic geogrid according to the present invention compared to other monolithic geogrids that do not have a layer having a porous structure, using the apparatus shown in FIG. [Diagram 44] FIG. 44 shows another experimental apparatus, the Plate Load Test Rig ("PLTR"), used to measure the displacement of integral geogrids according to various embodiments of the present invention. [Diagram 45] FIG. 45 shows a graph illustrating a comparison of the displacement of various embodiments of a monolithic geogrid according to the present invention to other monolithic geogrids that do not have a layer with a porous structure using the apparatus shown in FIG. [Diagram 46] FIG. 46 shows another graph comparing the displacement of various embodiments of a monolithic geogrid according to the present invention with other monolithic geogrids that do not have a layer with a porous structure using the apparatus shown in FIG. [Figure 47] FIG. 47 shows a graph comparing the effect of compressibility on the relationship between rib aspect ratio and surface deformation for two monolithic geogrids having layers with porous structure. [Figure 48] FIG. 48 shows a graph comparing the effect of compressibility on the relationship between rib aspect ratio and surface deformation for two other monolithic geogrids having layers with porous structure. [Figure 49]FIG. 49 shows a graph illustrating a comparison of the base geometry on the ability of the rib aspect ratio to affect surface deformation for two monolithic geogrids that do not have a layer with a porous structure. [Figure 50] FIG. 50 shows a table showing a comparison of the advantages of base shapes in similarly compressible monolithic geogrids. [Figure 51] FIG. 51 shows a graph illustrating a comparison of the effect of base geometry on the relationship between rib aspect ratio and surface deformation in a similarly compressible monolithic geogrid. [Figure 52] FIG. 52 shows a table showing a comparison of the effect on surface deformation of the location of a layer having a porous structure in a multi-layer integral geogrid for a single base shape. [Figure 53] FIG. 53 shows a graph illustrating a comparison of the effect of the position of the layer having a porous structure on the relationship between the aspect ratio of the ribs and the surface deformation for a single base shape related to FIG. [Figure 54] FIG. 54 shows another table showing a comparison of the effect of the location of a layer having a porous structure in a multi-layer integral geogrid on the surface deformation for a single base shape related to FIG. [Figure 55] FIG. 55 shows another graph illustrating a comparison of the effect of the position of the layer having a porous structure on the relationship between the aspect ratio of the ribs and the surface deformation for a single base shape related to FIG. [Figure 56] FIG. 56 shows a table showing a comparison of the effect on the surface deformation of a layer having a porous structure for a monolithic geogrid according to the invention with a single base shape related to FIG. 52 and a prior art geogrid without a layer having a porous structure. [Figure 57] FIG. 57 shows a graph illustrating a comparison of the effect of the compressibility of the layer with a porous structure on the relationship between the aspect ratio of the ribs and the surface deformation for a monolithic geogrid according to the invention with a single base shape related to FIG. 52 and a prior art geogrid without a layer with a porous structure. [Figure 58]FIG. 58 shows a graph illustrating compression force versus displacement data for a flexible foam embodiment of the present invention. [Figure 59] FIG. 59 shows a graph illustrating compression force versus displacement data for rigid foam embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] Only the preferred embodiment of the invention will be described in detail, it being understood that the scope of the invention is not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. As will be explained below, the invention is capable of other embodiments and of being practiced or carried out in various ways.

[0067] Moreover, in describing the preferred embodiments, technical terminology is used for the sake of clarity, and each term is intended to have the broadest meaning as understood by one of ordinary skill in the art and is intended to encompass all technical equivalents that operate in a similar manner to accomplish a similar purpose.

[0068] As used herein, the term "porous" is used according to the generally accepted definition, i.e., to a material having a plurality of voids, cavities, pores, cracks, bubbles, holes, or other types of openings distributed therein, produced by the methods described herein. Similarly, the term "non-porous" refers to a material produced by the methods described herein that does not contain voids, cavities, pores, bubbles, holes, or other types of openings, i.e., a material that has a structure that is generally continuous or substantially solid. The above-mentioned voids, cavities, pores, cracks, bubbles, holes, or other types of openings produced by the methods described herein that provide a porous structure may be referred to herein as "porous openings".

[0069] Also, as used herein, the terms "coextruded," "coextrusion," and "coextrusion" are used according to their generally accepted definitions, i.e., in reference to a process beginning with two or more polymeric materials that are extruded together and formed into a single die to form a multilayer sheet.

[0070] Also, as used herein, the terms "laminated," "laminating," and "lamination" are used according to their generally accepted definitions, i.e., in reference to a process beginning with two or more sheets of polymeric material that are manufactured separately in one manufacturing process and then bonded or adhered together in another manufacturing process to produce a multilayer sheet of two or more layers.

[0071] Also, as used herein, the term "crash fit" is used to describe a material that is sufficiently compressible such that, when sufficient force is applied, it will conform, physically adapt, and reshape to match the shape and texture of any stronger and / or harder material above or on top of it.

[0072] According to one preferred embodiment of the invention, the multi-layer integral geogrid with one or more porous layers has a non-porous layer interposed between two outer layers having a porous structure to form a three-layer integral geogrid. According to another embodiment of the invention, the multi-layer integral geogrid with one or more porous layers has a repeating pattern of a non-porous layer interposed between two layers having a porous structure. According to yet another embodiment of the invention, the multi-layer integral geogrid with one or more porous layers has a non-porous layer associated with an adjacent single layer having a porous structure.

[0073] More specifically, a multi-layer integral geogrid having one or more porous layers includes a plurality of oriented multi-layer strands interconnected by partially oriented multi-layer joints and having a series of openings therebetween, each oriented multi-layer strand and each partially oriented multi-layer joint having a plurality of layers including one or more porous layers, and the plurality of layers are in contact along each oriented multi-layer strand and each partially oriented multi-layer joint.

[0074] Even more specifically, one or more of the porous layers includes a distribution of a plurality of voids, cavities, pores, bubbles, holes or other types of openings therein. This porous structure may be associated with a foamed structure of the layer or may be associated with particulate fillers distributed throughout the layer to generate expansion of the porous layer in the final multi-layer integrated geogrid.

[0075] Also, as used herein, the term "expanded" used to describe one or more of the porous layers described above refers to the ability of the porous layer to expand during the various stages of forming a multi-layer integral geogrid according to the present invention. The term "expanded" used to describe one or more of the porous layers described above refers to the structure of the porous layer, including associated deformation (including expansion in size) of the porous layer, i.e., a plurality of voids, cavities, pores, cracks, bubbles, holes or other types of openings present in the porous openings, after formation of the multi-layer integral geogrid by stretching to orient the geogrid.

[0076] Additionally, the multi-layer structure may include co-extruded or laminated layers. Expansion of the porous layer may occur during extrusion / lamination, stretching / orientation, or both. The resulting multi-layer integral geogrid may have one or more porous layers, a plurality of oriented multi-layer strands interconnected by partially oriented multi-layer joints, and a series of openings therebetween, and may be configured in any of a variety of repeating geometric patterns, as described herein.

[0077] As shown in FIG. 1, a tri-layer integrated geogrid 200 (here a triaxial integrated geogrid) according to one embodiment of the present invention includes a third layer, i.e., a non-porous inner layer 220, disposed between a first porous outer layer 210 and a second porous outer layer 230.

[0078] As indicated above, the first and second porous outer layers 210, 230 include a distribution of porous openings 250 therein. The porous openings 250 may be associated with the foamed structure of the first and second porous outer layers 210, 230, or may be associated with porous openings that are initially formed during co-extrusion of the starting sheets and then deformed during formation, i.e., expanded in size by stretching the starting sheets with holes during formation of the integral geogrid. Alternatively, the porous openings 250 may be associated with particulate filler distributed within the first and second porous outer layers 210, 230, or may be associated with porous openings that are formed adjacent to the particulate filler by stretching the starting sheets with holes during formation of the integral geogrid.

[0079] According to the foaming embodiment of the first porous outer layer 210 and the second porous outer layer 230, the invention may include using a foaming agent to provide the expanded first porous outer layer 210 and the expanded second porous outer layer 230, i.e., each having a porous foam structure. That is, according to one embodiment of the invention for producing layers of a monolithic geogrid by co-extrusion (described below), one possible process is to mix a chemical foaming agent with the polymer to be extruded to form the expanded first porous outer layer 210 and the expanded second porous outer layer 230. The heat generated to melt the polymer causes the chemical foaming agent to decompose, resulting in the release of gas. The gas then distributes in the polymer melt and expands as it exits the die. As a result, the first outer layer 210 and the second outer layer 230 foam to form a porous layer, i.e., a layer having a plurality of porous openings. Similar to chemical foaming, the injection of gas resulting in the formation of the first porous outer layer 210 and the second porous outer layer 230 is also considered a foaming process according to this embodiment of the invention.

[0080] In accordance with the particulate filler embodiment of the first and second porous outer layers 210, 230, the present invention uses a dispersion of particulate filler to provide an expanded first and second porous outer layers 210, 230, i.e., each having a porous structure. The inclusion of such particulate filler in the first and second porous outer layers 210, 230 creates a product with a thicker or bulkier profile, which may lead to improved performance of the monolithic geogrid in certain applications. Depending on the application for which the multi-layered monolithic geogrid is to be used, such particulate fillers may include, for example, CaCO3 (calcium carbonate), hydrous magnesium silicate (talc), CaSiO3 (wollastonite), calcium sulfate (gypsum), diatomaceous earth, titanium dioxide, nanofillers (such as nanoclays), multi-walled carbon nanotubes ("MWCNTs"), single-walled carbon nanotubes ("SWCNTs"), natural or synthetic fibers, metal fibers, glass fibers, dolomite, silica, mica, and aluminum hydrate.

[0081] According to both the foam and filler embodiments, the materials of construction of the first porous outer layer 210 and the second porous outer layer 230 may be the same or different from each other, but are preferably the same material. Generally, the materials of construction of the non-porous inner layer 220 are different from the materials of construction of the first porous outer layer 210 and the second porous outer layer 230.

[0082] Contemplated embodiments of the present invention include those in which one or more foam layers are used in combination with one or more solid layers, those in which one or more filled layers are used in combination with one or more solid layers, and those in which one or more foam layers and one or more filled layers are used in combination with one or more solid layers.

[0083] FIG. 2 shows a single planar three layer polymer starting sheet 100 for a three layer integral geogrid having one or more porous layers 200 as shown in FIG. 1 before any holes or recesses are formed.

[0084] As shown in FIG. 2, the multilayer polymer starting sheet 100 is an embodiment of a three-layer sheet of the present invention. That is, preferably, the sheet 100 includes a first extended outer layer 110, a second extended outer layer 130, and a non-porous inner layer 120. The first extended outer layer 110 and the second extended outer layer 130 are arranged on opposite planar surfaces of the non-porous inner layer 120, preferably in a monoplanar or substantially monoplanar configuration. Additionally, while a three-layer configuration of the sheet 100 is shown for illustrative purposes, the present invention contemplates the use of sheets having multiple layers arranged in various configurations, multiple layers having various thickness combinations, and multiple layers having various construction materials, all as determined by the particular application in which the integral geogrid is to be used. For example, while a three-layer configuration of the sheet 100 is shown for illustrative purposes, the present invention contemplates the use of sheets having more than three layers. In general, the layer configurations, layer thicknesses, and construction materials of the layers are selected to facilitate the manufacture of the integral geogrid as well as to provide the integral geogrid with the desired degree of compressibility, stiffness, and other performance characteristics.

[0085] Further, according to another embodiment of the present invention, a multi-layered integral geogrid may have two layers, i.e., a non-porous layer associated with a single adjacent layer having a porous structure. The geogrid is typically installed on top of a soil layer such as clay, silt or sand. All of the above-mentioned materials are "fine-grained" materials, i.e., materials characterized by very small particle size in size of the geogrid openings. And typically, a granular aggregate of "large" (i.e., 0.25" to 3" diameter) particles is installed on top of the geogrid. It is assumed that the compressible layer, i.e., the porous layer, is optimally positioned such that the granular aggregate is positioned on top of the compressible layer. It is believed that it is not critical that the compressible layer be in contact with the fine-grained soil. Thus, such a two-layered integral geogrid will have a solid layer at the bottom and a compressible layer on top when installed.

[0086] As shown in Figure 13 (discussed in more detail below), a multi-layer integral geogrid 1500 of the present invention has the above-mentioned non-porous layers associated with a single adjacent layer having a porous structure. That is, instead of disposing a non-porous layer between two porous layers, a two-layer integral geogrid 1500 of the present invention has one porous layer 1510 and one non-porous layer 1520. As shown in Figure 14, a two-layer polymer starting sheet 1700 associated with an embodiment of a two-layer integral geogrid of the present invention includes an extended outer layer 1710 and a non-porous layer 1720.

[0087] As mentioned above, the three layer polymer starting sheet 100 used as the starting material for the three layer integrated geogrid of the present invention is preferably punched through, although formed recesses can be used instead. According to embodiments in which the sheet is formed with recesses, the recesses are provided on both sides of the sheet 100, i.e., on both the front and back of the sheet. Furthermore, the recesses extend through each layer of the multi-layer sheet.

[0088] According to a preferred embodiment of the present invention, the three-layer polymer starting sheet 100 has a total thickness of from about 2 mm to about 12 mm, and according to a more preferred embodiment of the present invention, the sheet 100 has a total thickness of from about 4 mm to about 10 mm.

[0089] With regard to the individual thicknesses of the sheet layers, it should be noted that, according to a preferred embodiment of the present invention, the first expanding outer layer 110 has a thickness of about 0.5 mm to about 4 mm, the non-expanding inner layer 120 has a thickness of about 0.5 mm to about 4 mm, and the second expanding outer layer 130 has a thickness of about 0.5 mm to about 4 mm, resulting in a total thickness of about 2 mm to about 12 mm for the starting sheet 100. Also, according to a more preferred embodiment of the present invention, the first expanding outer layer 110 has a thickness of about 1 mm to about 3 mm, the non-expanding inner layer 120 has a thickness of about 1 mm to about 3 mm, and the second expanding outer layer 130 has a thickness of about 1 mm to about 3 mm.

[0090] Generally, the layers of the starting sheet are polymeric in nature. The polymeric materials of the first expanding outer layer 110, the non-porous inner layer 120 and the second expanding outer layer 130 may be the same as each other or different from each other. Preferably, the material of the first expanding outer layer 110 and the material of the second expanding outer layer 130 are the same as each other. More preferably, the material of the non-porous inner layer 120 is different from both the material of the first expanding outer layer 110 and the material of the second expanding outer layer 130.

[0091] For example, the materials of construction may include high molecular weight polyolefins and broad molecular weight distribution polymers. As known to those skilled in the art of polymer science, the term "high molecular weight" polyolefins refers to resins having a melt flow rate ("MFR"; also known as melt flow index ("MFI")) less than 1 as determined by ASTM D 1238-20. As also known, the term "broad molecular weight distribution" polymers refers to resins having molecular chains that vary in size and are represented by a broad binomial distribution curve on a molecular weight distribution graph. Furthermore, the polymeric materials may be virgin stock or may be recycled materials, such as, for example, post-industrial or post-consumer recycled polymeric materials. Also contemplated is the use of one or more polymeric layers that are less expensive than the high molecular weight polyolefins and broad specification polymers described above.

[0092] According to a preferred embodiment of the present invention, the constituent material of the first extended outer layer 110 and the constituent material of the second extended outer layer 130 are broad specification polymers, such as virgin polypropylene ("PP") or recycled polypropylene, such as post-industrial PP or other recycled PP. As used herein, the term broad specification polymer refers to a polymer having an MFR (or MFI) of 1-6 as measured by ASTM D 1238-20 and an ash content of less than 6% as measured by ASTM D 4218-20. Also according to a similar preferred embodiment, the constituent material of the non-porous inner layer 120 is a high molecular weight polyolefin, such as PP. However, polymeric components having constituent materials other than polypropylene may be included in the multilayer polymer starting sheet 100 depending on the particular application of the integrated geogrid.

[0093] In accordance with the present invention, the multilayer polymer starting sheet 100 can be produced by coextrusion of the layers as disclosed in the above-mentioned '960 application, or by lamination of separately produced layers. For example, lamination of separately produced layers can be accomplished by reheating and softening one surface of each separately produced layer, laying one over the other so that the reheated and softened surfaces are adjacent to one another, and then applying pressure to fuse the separately produced sheets together.

[0094] Figure 3 is a top perspective plan view of the multi-layer polymer starting sheet 100 shown in Figure 2 with holes 140 provided to form the triaxial three-layer integrated geogrid 200 shown in Figure 1. Figure 4 is a perspective cross-sectional view of a portion of the three-layer polymer starting sheet 100 shown in Figure 3.

[0095] The size and spacing of the holes 140 shown in Figure 4 are as disclosed in the Walsh '112 patent. According to Figure 1, a triaxial three-layer integral geogrid 200 having one or more porous layers includes highly oriented strands 205 and partially oriented joints 235, also as disclosed in the Walsh '112 patent. The second expanded outer layer 130 of the three-layer polymer starting sheet 100 (shown in Figure 3) is stretched and oriented into the second porous outer layer 230 of the strands 205 and joints 235. Similarly, the first expanded outer layer 110 of the three-layer polymer starting sheet 100 is stretched and oriented into the second porous outer layer 210 of the strands 205 and joints 235. As the second expanding outer layer 130 and the first expanding outer layer 110 are stretched and oriented, the non-porous inner layer 120 is also stretched and oriented into the middle layer 220 of both the strands 205 and the joints 235 .

[0096] As indicated above, while a three-layer structure of the multilayer polymer starting sheet 100 is shown for illustrative purposes, the present invention also contemplates multilayer integral geogrids having one or more porous layers having more than two layers, and the use of starting sheets 100 with more than three layers.

[0097] For example, the starting sheet can be a five-layer configuration, such as the multilayer polymer starting sheet 400 shown in Figure 5. The starting sheet 400 includes an intermediate expansion layer 420, a first non-porous inner layer 410, a second non-porous inner layer 430, a first expansion outer layer 440, and a second expansion outer layer 450. The first non-porous inner layer 410 and the second non-porous inner layer 430 are disposed on opposite planes of the intermediate expansion layer 420, preferably in a single plane or substantially in a single plane. The first expansion outer layer 440 and the second expansion outer layer 450 are disposed on opposite planes of the first non-porous inner layer 410 and the second non-porous inner layer 430, respectively, preferably in a single plane or substantially in a single plane.

[0098] In a particular embodiment of the invention shown in FIG. 5, a multilayer polymer starting sheet 400 is made by coextrusion or lamination of a first material forming an intermediate extension layer 420, a second material forming a first non-porous inner layer 410, a third material forming a second non-porous inner layer 430, a fourth material forming a first extension layer 440, and a fifth material forming a second extension outer layer 450.

[0099] In general, the polymeric materials of the intermediate expansion layer 420, the first non-porous inner layer 410, the second non-porous inner layer 430, the first expansion outer layer 440, and the second expansion outer layer 450 may be the same as each other or may be different from each other. For example, the intermediate expansion layer 420 may have a first constituent material, the first non-porous inner layer 410 and the second non-porous inner layer 430 may have a second constituent material, and the first expansion outer layer 440 and the second expansion outer layer 450 may have a third constituent material. In summary, various combinations of constituent materials of the five layers mentioned above may be employed depending on the specific application in which the five-layer integrated geogrid having layers with a porous structure made from the sheet 400 is used.

[0100] FIG. 6 is a perspective view of a cross section of a triaxial five-layer integral geogrid 500 having three or more porous layers associated with the five-layer polymer starting sheet 400 shown in FIG. 5. The triaxial five-layer integral geogrid 500 having three or more porous layers includes highly oriented multi-layer strands 505 and partially oriented multi-layer joints 535. After holes are provided in the sheet 400, the first and second expanded outer layers 440 and 450 of the sheet 400 are stretched and oriented to the first and second porous outer layers 540 and 550 of the multi-layer strands 505 and multi-layer joints 535, respectively. Similarly, the first and second non-porous inner layers 410 and 430 of the sheet 400 are stretched and oriented to the first and second non-porous inner layers 510 and 530 of the strands 505 and joints 535, respectively. Additionally, as the first and second expanded outer layers 440, 450, and the first and second non-porous inner layers 410, 430 are stretched and oriented, the intermediate expanded layer 420 is simultaneously stretched and oriented in the intermediate porous layer 520 of both the multi-layer strands 505 and the multi-layer joints 535.

[0101] Also, similar to the multilayer polymer starting sheet 100 (i.e., the three-layer embodiment), the multilayer polymer starting sheet 400 having five layers may have expansion layers that are foamed or have a filler, and may be formed by coextrusion or lamination.

[0102] According to a preferred embodiment of the present invention, the five-layer integrated geogrid 500 has a total thickness of about 1 mm to about 6 mm, and according to a more preferred embodiment of the present invention, the five-layer integrated geogrid 500 has a total thickness of about 1.5 mm to about 3.5 mm.

[0103] With regard to the individual thicknesses of the layers of the five-layer integrated geogrid 500, according to a preferred embodiment of the present invention, the first porous outer layer 540 has a thickness of about 0.1 mm to about 2 mm, the second porous outer layer 550 has a thickness of about 0.1 mm to about 2 mm, the first non-porous outer layer 510 has a thickness of about 0.1 mm to about 2 mm, the second non-porous inner layer 530 has a thickness of about 0.1 mm to about 2 mm, and the middle non-porous layer 520 has a thickness of about 0.1 mm to about 2 mm.

[0104] Turning now to the geometric shapes of multi-layer integral geogrids having one or more porous layers, the present invention contemplates at least three general categories: triangular (e.g., "triaxial"), rectangular, and hexagonal.

[0105] The geometry of the triaxially expanded multi-layer integral geogrid 200 is as shown in FIG. 1 (three layers) and FIG. 6 (five layers).

[0106] The geometry of a rectangular multi-layer integral geogrid 700 with one or more porous layers is shown in FIG. 7. The rectangular multi-layer integral geogrid 700 with one or more porous layers includes highly oriented multi-layer strands 705 and partially oriented multi-layer joints 710. As shown in FIG. 8, the rectangular three-layer integral geogrid 700 with two or more porous layers includes a third layer, i.e., a non-porous inner layer 720, disposed between a first porous outer layer 710 and a second porous outer layer 730. As in the triangular geometry described herein, the first porous outer layer 710 and the second porous outer layer 730 include a distribution of porous openings 750 therein. The porous openings 750 may be associated with the foam structure of the first porous outer layer 710 and the second porous outer layer 730, or may be associated with a particulate filler distributed in the first porous outer layer 710 and the second porous outer layer 730.

[0107] The second extended outer layer 630 of the three-layer polymer starting sheet 600 (described below) is stretched and oriented into the second porous outer layer 730 of the multilayer strands 705 and the multilayer junctions 740. Similarly, the first extended outer layer 610 of the multilayer polymer starting sheet 600 is stretched and oriented into the first porous outer layer 710 of the multilayer strands 705 and the multilayer junctions 740. As the second porous outer layer 730 and the first porous outer layer 710 are stretched and oriented, the non-porous inner layer 620 is simultaneously stretched and oriented into the non-porous inner layer 720 of both the multilayer strands 705 and the multilayer junctions 740.

[0108] Figure 9 is a top perspective plan view of a three layer polymeric starting sheet section 600 with holes 640 provided to form the rectangular three layer integral geogrid 700 shown in Figures 7 and 8. The multi-layer polymeric starting sheet 600 includes a third layer, or non-porous inner layer 620, provided between a first expanding outer layer 610 and a second expanding outer layer 630. As with the triangular geometry described herein, the first expanding outer layer 610 and the second expanding outer layer 630 form a distribution of porous openings 650 in the final integral geogrid 700 shown in Figures 7 and 8.

[0109] Also, like the triangular geometric embodiment of the multi-layer integral geogrid having one or more porous layers, the rectangular embodiment of the multi-layer integral geogrid having one or more porous layers may have a foamed porous layer or a porous layer that includes a particulate filler. Also, the starting sheets for the rectangular embodiment of the multi-layer integral geogrid having one or more porous layers are the same as those described herein above for the triangular embodiment and may be formed by coextrusion or lamination.

[0110] And finally, the geometry of a hexagonal multi-layer (here, three-layer) monolithic geogrid 1100 with one or more porous layers is shown in Figures 10 and 11. The impetus for the development of a hexagonal multi-layer monolithic geogrid with one or more porous layers is that it would be structurally and economically advantageous to produce a monolithic geogrid with a structure and geometry capable of bonding and stabilizing a wider variety and range of aggregate qualities suited to the requirements of the application, such as geosynthetic reinforcement, or with other properties desired for the particular geosynthetic application.

[0111] Hexagonal multi-layer integral geogrids with one or more porous layers are designed to improve upon triaxial integral geogrids by substantially enhancing aggregate support and interaction while retaining the isotropic properties of the triaxial geometry. The significant improvements of the hexagonal multi-layer integral geogrid over the triaxial geometry and other prior art geometries relate to at least two key design features. First, with respect to the geometry, the hexagonal multi-layer integral geogrid retains the 360 ​​degree properties of the triaxial geometry by retaining every other rib in each of the three rib directions as a continuous rib. However, the hexagonal multi-layer integral geogrid converts every other node along the non-continuous rib from a non-functional element (node) to a functional feature (a new open hexagon with six new rib elements). These six new rib elements become a functional feature rather than a single non-functional node. The open hexagon and six rib elements significantly enhance the extent to which the hexagonal multi-layer integral geogrid can interact with and support the aggregate. Additionally, the hexagonal multi-layered integral geogrid shape provides continuous ribs in three directions, providing 360-degree strength and stability. This is done in a variety of ways, including converting non-functional nodes into functional elements and improving macro interactions by incorporating taller ribs, as explained above.

[0112] Second, in accordance with one embodiment of the present invention, a coextruded hexagonal multi-layer monolithic geogrid utilizes the multi-layer structure and foam or filler reinforcement described herein. That is, with a coextruded multi-layer structure and two outer layers of porous structure, the present invention provides a micro-interaction associated with top and bottom layers of compressible polymer designed to nest aggregate particles and promote and maintain maximum aggregate properties. This advanced coextrusion process technology also provides other production and manufacturing advantages, such as improved adhesion between layers due to coextrusion, controlled creation of porous structure while maintaining proper relative velocity and shear rate between layers, and cost savings due to a single-step process to create multi-layer sheets. That is, the combination of these design features in a hexagonal multi-layer monolithic geogrid provides various production and manufacturing advantages that allow this new and novel geogrid to be manufactured with significantly better performance than triaxial geogrids, and with only a small increase in cost.

[0113] To achieve the above-mentioned ability to bind and stabilize a wider variety and range of aggregate qualities than geometries associated with conventional geogrid structures, while at the same time providing varying degrees of localized out-of-plane and in-plane stiffness, the hexagonal multi-layer integral geogrid with one or more porous layers of the present invention has a repeating pattern of interconnected oriented multi-layer strands and partially oriented multi-layer joints that form a repeating pattern of outer layer hexagons, each supporting and surrounding an oriented multi-layer inner hexagon to define three different shaped openings in the multiaxial integral geogrid. To provide additional strength and stability, the outer hexagonal geometry forms straight strands that run continuously in three different directions throughout the multiaxial integral geogrid.

[0114] When so formed, the inner multi-layer hexagon includes six oriented multi-layer strands, supported by six oriented multi-layer connecting strands extending from the partially oriented multi-layer junctions of the outer hexagon to each corner of the inner hexagon to form an oriented multi-layer triple node. The multi-layer triple node has a much higher level of orientation than the multi-layer junctions, which tend to be fully oriented. This configuration creates an inner multi-layer hexagon that is floating, i.e., suspended, relative to the outer multi-layer hexagon structure. This structure allows the inner multi-layer hexagon to move up or down and "float" or bend (i.e., deform) relative to the main plane of the integral geogrid during placement and compaction of the aggregate, enhancing the ability of the integral geogrid to bond and stabilize to the aggregate. As noted above, the above-described integral geogrid structure is referred to herein as a multi-layer integral geogrid "with repeated suspended hexagons in a hexagonal pattern," or simply a "hexagonal" multi-layer integral geogrid.

[0115] 10 and 11, the hexagonal three-layer integrated geogrid 1100 with one or more porous layers includes a plurality of interconnected oriented multi-layer strands with a series of openings therein, repeating floating hexagons within the hexagonal pattern of the interconnected oriented multi-layer strands, and linear multi-layer strands that include openings and extend continuously throughout the multi-axial integrated geogrid. These linear multi-layer strands that extend continuously throughout the multi-axial integrated geogrid constitute the strong axis strands. More specifically, the hexagonal three-layer integrated geogrid 1100 with one or more porous layers includes a repeating pattern of floating inner hexagons 1130 within each outer hexagon 1110. The outer hexagon 1110 includes a plurality of outer oriented multi-layer strands or ribs 1120 interconnected by partially oriented multi-layer connectors 1115. The inner hexagon 1130 includes a plurality of oriented multi-layer connector strands 1145 and 1150 interconnected by multi-layer triple nodes 1135, defining a hexagonal central opening 1170. The outer hexagon 1110 is connected to the smaller inner hexagon 1130 by a plurality of multi-layer support strands 1140 and 1160, defining a plurality of trapezoidal openings 1180. At the center of each of the patterns of three adjacent outer hexagons 1110 is a triangular opening 1190. As shown, the joints 1115 are much larger than the triple nodes 1135.

[0116] In another aspect of the hexagonal geometry embodiment of the present invention, support strands 1140 and 1160 extend inward from the partially oriented junction 1115 and connect with triple nodes 1135 of the floating inner hexagon 1130 (or other such internal geometric configuration described herein) and are supported by such support strands, constituting an "artificial discontinuity" or "floating artificial discontinuity."

[0117] As is evident from FIG. 10, another feature of the hexagonal three-layer integral geogrid 1100 with one or more porous layers of the present invention is the linearly continuous nature of the outer multilayer strands 1120 of the repeating outer hexagonal pattern. That is, the oriented multilayer strands 1120 are linearly continuous through the partially oriented multilayer joints 1115 as they extend continuously throughout the multiaxial integral geogrid in three different directions approximately 120° apart from each other, as indicated by arrows 120A, 120B, and 120C in FIG. 10 and FIG. 11. These linear multilayer strands that extend continuously throughout the multiaxial integral constitute the strong axis strands. Those skilled in the art will appreciate that different orientations of the same basic geometry are possible after stretching, provided that appropriate corresponding rotations of the geometry of the starting sheet with holes are performed. The linearly continuous nature of the multilayer strands 1120 provide both enhanced strength and in-plane stiffness to the hexagonal multilayer integral geogrid with one or more porous layers of the present invention.

[0118] Preferably, the thickness of a hexagonal three-layer integrated geogrid 1100 having two outer porous layers at its thickest dimension (at the joints 1115) is about 0.5 to 100 μm, and more preferably, the thickness of such a multiaxially expanded three-layer integrated geogrid 1100 is about 4 to about 8 mm.

[0119] With respect to the geometry of the integral geogrid, FIG. 20 illustrates the isotropic properties associated with the triangular geometry of the triaxial multi-layer integral geogrid as shown in FIGS. 1 and 6. Also, FIG. 21 illustrates the isotropic properties associated with continuous ribs in three directions, which is the structural geometry of the hexagonal multi-layer integral geogrid as shown in FIGS. 10, 11 and 13.

[0120] Additionally, Figure 22 shows an overlay of hollow hexagons associated with a hexagonal multi-layer integral geogrid as shown in Figures 10, 11 and 13 on a triaxial geogrid, and Figure 23 shows hollow hexagons and six rib elements associated with a hexagonal multi-layer integral geogrid as shown in Figures 10, 11 and 13.

[0121] FIG. 24 is a partial plan view showing various strand lengths of a hexagonal multi-layer integral geogrid such as those shown in FIGS.

[0122] Additionally, Figure 38 is a partial plan view showing various strand lengths for a hexagonal three layer integrated geogrid as shown in Figures 10 and 11, as well as continuous ribs associated with the left machine direction, right machine direction and cross direction, similar to that shown in Figure 21. Figure 39 is a plan view of possible hole sizes and spacing associated with the starting sheets used to manufacture the hexagonal three layer integrated geogrid shown in Figure 38. Figure 40 is a side cross-sectional view of a partial section of a hexagonal three layer integrated geogrid having two outer layers with a porous structure according to an embodiment of the invention shown in Figure 11.

[0123] Now, more specifically, returning to FIG. 24, in one embodiment of a hexagonal three layer integrated geogrid according to the present invention shown in FIG. 24, the multi-layer integrated geogrid has a height of rib A having a wide range of 1-4 mm, preferably in the range of 2-3 mm, preferably a dimension of 1.97 mm. The width of rib A has a wide range of 0.75-3 mm, preferably in the range of 1-2 mm, preferably a dimension of 1.6 mm. The length of rib A has a wide range of 30-45 mm, preferably in the range of 35-40 mm, preferably a dimension of 37 mm. The aspect ratio of rib A has a wide range of 1:1-3:1, preferably in the range of 1.5:1-1.8:1, with a preferred value of 1.7:1.

[0124] The height of the rib B has a wide range of 1-3 mm, preferably in the range of 1.5-2.5 mm, preferably a dimension of 1.6 mm. The width of the rib B has a wide range of 0.75-3.5 mm, preferably in the range of 1-3 mm, preferably a dimension of 1.8 mm. The length of the rib B has a wide range of 15-25 mm, preferably in the range of 18-22 mm, preferably a dimension of 21 mm. The aspect ratio of the rib B has a wide range of 0.75:1-2:1, preferably in the range of 1.2:1-1.4:1, with a preferred value of 1.3:1.

[0125] The height of the rib C has a wide range of 1-4 mm, preferably in the range of 2-3 mm, preferably a dimension of 2.7 mm. The width of the rib C has a wide range of 0.75-3.5 mm, preferably in the range of 1-2.5 mm, preferably a dimension of 1.6 mm. The length of the rib C has a wide range of 15-30 mm, preferably in the range of 20-25 mm, preferably a dimension of 23 mm. The aspect ratio of the rib C has a wide range of 1:1-3:1, preferably in the range of 1.5:1-2.5:1, preferably a preferred value of 1.7:1.

[0126] The height of the rib D has a wide range of 1.5-4 mm, preferably in the range of 2-3.5 mm, preferably a dimension of 2.3 mm. The width of the rib D has a wide range of 1-4 mm, preferably in the range of 1.5-2.5 mm, preferably a dimension of 1.5 mm. The length of the rib D has a wide range of 10-30 mm, preferably in the range of 15-25 mm, preferably a dimension of 18 mm. The aspect ratio of the rib D has a wide range of 1:1-3:1, preferably in the range of 1.4:1-1.7:1, preferably a value of 1.6:1.

[0127] The height of the rib E has a wide range of 1-4 mm, preferably in the range of 1.5-3.0 mm, preferably a dimension of 1.9 mm. The width of the rib E has a wide range of 0.75-3.5 mm, preferably in the range of 1-3 mm, preferably a dimension of 1.7 mm. The length of the rib E has a wide range of 15-30 mm, preferably in the range of 20-25 mm, preferably a dimension of 22 mm. The aspect ratio of the rib E has a wide range of 0.75:1-2:1, preferably in the range of 1:1-1.5:1, preferably a preferred value of 1.3:1. The thickness of the main nodes has a wide range of 1.5-10 mm, preferably in the range of 3-8 mm, preferably a dimension of 5.1 mm.

[0128] Also, in one embodiment of a hexagonal three layer integral geogrid according to the present invention having first and second compressible porous outer layers disposed on opposite surfaces of an inner non-porous layer as shown in FIG. 40, the multi-layer integral geogrid has a cap thickness (dimension "A") of the lower joint (i.e., joint 1115; see FIG. 11) having a dimension in the broad range of 1 to 3 mm, preferably in the range of 1.5 to 2.5 mm, preferably 1.7 mm; a cap thickness (dimension "B") of the upper joint having a dimension in the broad range of 1 to 3 mm, preferably in the range of 1.5 to 2.5 mm, preferably 1.7 mm; or a central joint core thickness (dimension "C") having a dimension in the range of 1.5-2.5 mm, preferably 1.7 mm; a lower cap thickness (dimension "D") of Rib A (see FIG. 24) having a dimension in the broad range of 0.4-1 mm, preferably 0.5-0.8 mm, preferably 0.7 mm; an upper cap thickness (dimension "F") of Rib A having a dimension in the broad range of 0.4-1 mm, preferably 0.5-0.8 mm, preferably 0.7 mm; and a central core thickness (dimension "E") of Rib A having a dimension in the broad range of 0.4-1 mm, preferably 0.5-0.8 mm, preferably 0.6 mm.

[0129] Figure 12 is a top perspective view of a three layer polymer starting sheet 1300 with holes formed therein to form the hexagonal three layer integral geogrid 1100 having two outer porous layers as shown in Figures 10 and 11. It includes a third layer, or inner non-porous layer 1320, disposed between a first expanding outer layer 1310 and a second expanding outer layer 1330.

[0130] Also, like the triangular and rectangular geometric embodiments of the multi-layer integral geogrid having one or more porous layers, the hexagonal embodiment of the multi-layer integral geogrid 1100 having one or more porous layers has a foamed porous layer or a porous layer that includes a particulate filler. Also, the starting sheets for the hexagonal embodiment of the multi-layer integral geogrid having one or more porous layers are the same as those disclosed herein above for the triangular and rectangular geometric embodiments, and can be formed by co-extrusion or lamination.

[0131] The multi-layer polymer starting sheet 1300 used as starting material for the multi-layer hexagonal monolithic geogrid 1100 having one or more porous layers according to the present invention is preferably provided with holes therethrough, although it is possible to use recesses formed therein instead. According to an embodiment of the starting material having recesses formed in the sheet, the recesses are provided on both sides of the sheet, i.e., on both the front and back sides of the sheet.

[0132] As shown in FIG. 12, the three layer polymer starting sheet 1300 includes a repeating pattern 1310 of holes 1320 and spaces 1330 that, when oriented, provide suspended hexagons within the hexagonal pattern of the hexagonally expanded three layer integrated geogrid 1100 shown in FIGS. 10 and 11.

[0133] More specifically, a preferred hexagonal three layer integral geogrid according to the invention is as shown in Figure 38, which also shows the continuous strands (or "ribs") associated with the left machine direction ("MD Left"), right machine direction ("MD Right"), and cross direction ("TD"). As shown in Figure 38, the "Across the Plane" (sometimes referred to herein as "A / F") dimension of the outer hexagonal repeat unit of a hexagonal embodiment of a integral geogrid according to the invention is the distance between the parallel strong axis strands of the outer hexagon, i.e., the strong axis strands that run parallel to each other in each of the left machine direction, right machine direction, and cross direction. Even more specifically, according to the depictions of the hexagonal embodiments of the invention shown in Figures 10, 11, and 38, the A / F dimension is the distance between any of the parallel strands 1120, i.e., in each of the left machine direction, right machine direction, and cross direction. According to one preferred embodiment of a hexagonal triple layer integrated geogrid shown in Figure 38, the A / F dimension, i.e. the distance from one multi-layer joint 1115 associated with a strand 1120 of the outer hexagon (see also Figures 10 and 11) to the opposite multi-layer joint 1115 associated with a parallel strand 1120 of the outer hexagon, is about 80 mm. Also, for the same embodiment, the plan dimension, i.e. the distance from one multi-layer triple node 1135 of the inner hexagon (see Figure 11) to the opposite multi-layer triple node 1135 of the inner hexagon, is about 33 mm. In this preferred embodiment of a multi-layer integrated geogrid according to the invention, the total thickness of the starting sheets has a wide range of 2-12 mm, preferably in the range of 4-8 mm, preferably a dimension of 5.5 μm. The size / diameter of the holes has a wide range of 2-7 mm, preferably in the range of 3-5 mm, preferably a dimension of 3.68 mm. The main pitch in the first stretch direction has a wide range of 5-9 mm, preferably in the range of 6-8 mm, preferably a dimension of 6.7088 mm. The minor pitch in the first stretch direction has a wide range of 1-4 mm, preferably in the range of 2-3 mm, preferably a dimension of 2.58 mm. The second main / minor pitch in the first stretch direction has a wide range of 4-8 mm, preferably in the range of 5-7 mm, preferably a dimension of 5.934 mm. The main pitch in the second stretch direction has a wide range of 4-8 mm, preferably in the range of 5-7 mm, preferably a dimension of 6.192 mm.

[0134] Also, in general, the tri-layer polymer starting sheet 1300 is polymeric in nature. For example, the materials of construction may include high molecular weight polyolefins and broad specification polymers. Furthermore, the polymeric materials may be virgin stock or recycled materials, such as, for example, post-industrial or post-consumer recycled polymeric materials. Also contemplated is the use of one or more polymeric layers that are less expensive than the high molecular weight polyolefins and broad specification polymers described above. According to a preferred embodiment of the present invention, the high molecular weight polyolefin is polypropylene.

[0135] According to a preferred embodiment of the present invention, the multi-layer strands 1120, 1140, 1145, 1150 and 1160 of the hexagonal three-layer integral geogrid 1100 have what is known to those skilled in the art as high aspect ratio, i.e., the ratio of the thickness or height of the multi-layer strand cross section to the width of the multi-layer strand cross section is greater than 1.0, according to the above-mentioned Walsh patents, i.e., U.S. Pat. Nos. 9,556,580, 10,024,002 and 10,501,896. Although not essential to the present invention, a high aspect ratio of the strands or ribs is preferred. Thus, the multiaxial integral geogrid of the present invention provides increased compatibility between the geogrid and the aggregate, resulting in improved interlocking, lateral restraint and containment of the aggregate.

[0136] As described herein, instead of having the above-described embodiments having three or more layers, a multi-layer integral geogrid having one or more porous layers according to the present invention may have a non-porous layer associated with a single adjacent porous layer. That is, as shown in Figure 13, a hexagonal two-layer integral geogrid 1500 according to the present invention has one porous layer 1510 and one non-porous layer 1520. The remaining elements of the hexagonal two-layer integral geogrid 1500 are as described above, except that the multi-layer structure has only two layers, namely the porous layer 1510 and the non-porous layer 1520.

[0137] As shown in Figure 14, a bi-layer polymeric starting sheet 1700 associated with a bi-layer integrated geogrid embodiment of the present invention includes an expansion layer 1710 and a non-porous layer 1720. The expansion layer 1710 and the non-porous layer 1720 are preferably arranged in a monoplanar or substantially monoplanar configuration. Figure 15 is a top perspective plan view of a bi-layer polymeric starting sheet 1900 having a pattern of holes 1940 provided to form the hexagonal bi-layer integrated geogrid 1500 shown in Figure 13.

[0138] More specifically, referring to FIG. 13, a hexagonal two-layer integral geogrid 1500 with one porous layer includes a repeating pattern of floating inner hexagons 1530 within each outer hexagon 1510. The outer hexagons 1510 include a plurality of outer oriented multi-layer strands or ribs 1520 interconnected by partially oriented multi-layer connectors 1515. The inner hexagons 1530 include a plurality of oriented multi-layer connector strands 1545 and 1550 interconnected by multi-layer triple nodes 1535 and define a hexagonal central opening 1570. The outer hexagons 1510 are connected to smaller inner hexagons 1530 by a plurality of multi-layer support strands 1540 and 1560 that define a plurality of trapezoidal openings 1580. The center of each of the patterns of three adjacent outer hexagons 1510 is a triangular opening 1590. As shown, the junction 1515 is much larger than the triple node 1535 .

[0139] The present invention also relates to methods of making the various above-described embodiments of a multi-layer monolithic geogrid having one or more porous layers.

[0140] More specifically, it is an object of the present invention to provide a method for manufacturing a multi-layer integrated geogrid having one or more porous layers, where the layer having the porous structure is made by first providing a foam structure, i.e., a plurality of porous openings, in a layer of a multi-layer polymer starting sheet, and then biaxially orienting the multi-layer polymer starting sheet to expand the foam material and create a distorted distribution of porous openings in the foam material.

[0141] Similarly, another object of the present invention is to provide a method for manufacturing a multi-layer monolithic geogrid having one or more porous layers, where each layer having a porous structure is created by first distributing a particulate filler in a layer of a multi-layer polymer starting sheet, and then biaxially stretching the multi-layer polymer starting sheet to expand the distribution of the particulate filler and create a distribution of porous openings as the particulate filler partially separates from the polymer layer material.

[0142] For example, a method of making the above-described triaxial multi-layer integral geogrid 200 having one or more porous layers includes the steps of: providing a multi-layer polymer starting sheet 100; forming a plurality of holes or recesses in the multi-layer polymer starting sheet 100 in a selected pattern, for example, according to the disclosure of the Walsh '112 patent; and biaxially stretching and orienting the multi-layer polymer starting sheet having the patterned plurality of holes or recesses therein to form a multi-layer integral geogrid having one or more porous layers and having a plurality of oriented multi-layer strands interconnected between partially oriented multi-layer joints to create the holes or recesses as grid openings.

[0143] Generally, once the multi-layer polymer starting sheet 100 has been prepared with holes or recesses, a triaxial multi-layer integral geogrid 200 having one or more porous layers can be manufactured from the sheet 100 according to the methods described in the patents identified above and methods known to those of skill in the art.

[0144] Also, with respect to a method of making a multiaxial "repeating suspended hexagons within a hexagonal pattern" embodiment of a multilayer integral geogrid having one or more porous layers, the method includes the steps of providing a polymer sheet 1300; providing a patterned plurality of holes or depressions 1310 in the polymer sheet 1300; and orienting the polymer sheet 1300 having the patterned plurality of holes or depressions 1310 therein to provide a series of openings 1170, 1180, and 1190 therein, a plurality of interconnected oriented multilayer strands 1120, 1140, 1145, 1150, and 1160 including repeating suspended hexagons 1130 within an outer hexagon 1110 pattern of interconnected oriented multilayer strands, and three straight multilayer strands having openings and extending continuously throughout the multiaxial multilayer integral geogrid having a layer having a porous structure 1100.

[0145] Generally, once the starting sheet 1300 has been prepared with holes or recesses, a multiaxial multi-layer integral geogrid 1100 having one or more porous layers can be manufactured from the starting sheet 1300 according to the methods described in the patents identified above and methods known to those skilled in the art.

[0146] With regard to laminating layers of a multi-layer integral geogrid instead of using co-extrusion, an approximation to co-extrusion can be obtained by one of the following methods, although the resulting product will likely not have all the advantages associated with the preferred co-extrusion embodiment. First, separate layers of separate shaped starting sheets can be extruded as separate monolayers, each layer having the necessary extrusion material recipe. Then, in a post-extrusion process, the layers can be joined by any of the processes described below to approximate an integrally shaped co-extruded material. For example, a gluing / bonding process can be used, whereby a suitable adhesive is applied to the surfaces of the sheets to be joined, for example by a padding roller process, and the sheets are then forced together under suitable pressure and / or heat to produce a bond. In another approach, a heating / laminating process can be used, whereby a suitable heat source is applied to the surfaces of the sheets to be joined, for example by an induction heating roller or gas, and the sheets are then forced together under suitable pressure and / or heat to produce a bond. In yet another approach, a mechanical welding / joining process can be used, whereby a continuous local weld is performed, for example by ultrasonic welding or friction welding. And in yet another approach, a chemical welding / bonding process can be used whereby a suitable solvent is introduced to the surfaces of the sheets to be bonded, for example by a padding roller process, and the sheets are then forced together under suitable pressure and / or heat to produce the bond.

[0147] As indicated above, the hexagonal geometry of the outer hexagon 1110 and the smaller inner hexagon 1130 is a preferred embodiment for providing the floating geometric configuration of the present invention. However, other geometries are possible within the scope of the present invention. For example, the geometric shape may be a rectangle or square with four support or connecting strands connecting each inner corner of the outer rectangle or square to the corresponding outer corner of the smaller inner rectangle or square. Alternatively, the geometric shape may be a triangle with only three support or connecting strands between adjacent inner corners of the outer triangle and the outer corner of the smaller inner triangle.

[0148] In the rectangular or square embodiments of the invention described in the previous paragraph, there are preferably two straight strands that extend continuously across the geogrid for each outer rectangle or square, with such continuous strands extending at an angle of about 90° from each other. In triangular embodiments, there may be three straight strands that extend about 120° from each other for each outer triangle, similar to the straight strands 1120 of the preferred hexagonal embodiment described in detail herein.

[0149] Also, different geometries are possible without departing from the invention. For example, the inner geometry may be a circular ring supported within a preferred outer hexagon with six supporting strands similar to the preferred embodiment disclosed herein. Thus, it is not intended that the geometries of the outer repeating structure and the inner or internal floating structure be limited to the same geometry.

[0150] 17A-17E show a hypothesized compression mechanism of a three-layer integral geogrid having one or more porous layers according to the present invention, associated with the porous openings of the first porous outer layer 1710 and the second porous outer layer 1730 upon loading. As shown in FIG. 17A, before loading is applied, the porous openings 1750 and the polymer 1740 around them are undisturbed. As loading begins (FIG. 17B), the polymer 1740 around the porous openings 1750 begins to compress. As loading continues (FIG. 17C), the polymer 1740 around the porous openings 1750 stops yielding and the porous openings 1750 begin to compress. As loading continues further (FIG. 17D), the porous openings 1750 compress further and the polymer 1740 around the porous openings begins to deform again. And finally, as shown in FIG. 17E, when the load is removed, the ribs of the expanded multi-layer integrated geogrid are decompressed while the permanent deformation of the porous openings 1750 remains, due to some collapse of the porous openings 1750, along with the permanent deformation of the polymer 1740 around the porous openings.

[0151] Figures 18A-18C show the flexible rib mechanism hypothesis of an extended porous layer of a three-layer integral geogrid with one or more porous layers. The flexible rib mechanism hypothesis is also associated with the presence of porous openings in the first porous outer layer 1810 and the second porous outer layer 1830, demonstrating both vertical and horizontal flexibility of the integral geogrid under load. As shown in Figure 18A, before load is applied, the porous openings 1850 and the polymer 1840 around the porous openings 1850 are undisturbed. When load is applied (Figure 18B), the system begins to undergo elastic compression as the porous openings 1850 begin to deform. Finally, the system stops yielding as the porous openings 1850 begin to compress and densify, as shown in Figure 18C. Thus, both vertical and horizontal flexibility of the integral geogrid under load is achieved by the porous openings 1850 present in the first 1810 and second 1830 porous outer layers of the three layer integral geogrid.

[0152] Figure 19 is a graph comparing the behavior of inelastic ribs in a starting sheet of a conventional monolithic geogrid with the behavior of elastic ribs in a starting sheet of a multi-layer monolithic geogrid of the present invention having one or more porous layers. As can be seen, the ribs of the multi-layer monolithic geogrid having one or more porous layers that are vertically and horizontally flexible facilitate more optimal aggregate positioning and densification. This feature of the extended multi-layer monolithic geogrid allows for the use of "larger" ribs without the ribs becoming "breakers" of the aggregate system.

[0153] Turning now to additional experimental results demonstrating the performance advantages of the present invention, reference is made to Figures 25, 26 and 27. Figure 25 shows a hexagonal three-layer integral geogrid according to the present invention, similar to that shown in Figures 10 and 11, and illustrates the effect of increasing rib height on surface deformation during tracking testing. The only difference in each of the three specimens associated with Figure 25 is the thickness of the starting sheet, which of course determines the resulting rib height of the integral geogrid. Figure 26 is a plot of the effect of increasing rib height on surface deformation associated with the test results shown in Figure 25. And Figure 27 is a table summarizing the effect of increasing rib height on surface deformation associated with the test results shown in Figures 25 and 26. As is evident from the traffic test results shown in Figures 25, 26 and 27, the surface deformation of the integral geogrid advantageously decreases as the rib height increases.

[0154] Additionally, the monolithic geogrids with layers having a porous structure according to the present invention have other advantageous features. Figure 28 is a plot of the increased rib height achievable with a hexagonal three-layer monolithic geogrid according to the present invention versus the increased rib height achievable with a solid single layer geogrid. And for the same monolithic geogrid to which the results of Figure 28 relate, Figure 29 is a plot of the reduced mass per unit area achievable with a hexagonal three-layer monolithic geogrid according to the present invention versus the reduced mass per unit area achievable with a solid single layer geogrid. As is evident from Figures 28 and 29, the monolithic geogrid with an outer "cap" layer having a porous structure according to the present invention has an average rib height that is more than 10% of the average rib height achievable with a solid single layer geogrid, while having a unit weight that is 11% lighter than the solid single layer geogrid.

[0155] Turning now to additional experimental traffic results demonstrating the performance advantages of the present invention, reference is made to Figures 30 and 31. Figure 30 is a plot of the performance improvement achievable with a hexagonal three-layer integral geogrid with a compressible porous outer layer in accordance with the present invention versus a hexagonal solid single layer geogrid. Figure 31 is a table summarizing the structural data associated with the hexagonal three-layer integral geogrid with a compressible porous outer layer and the hexagonal solid single layer geogrid used in the test results shown in Figure 30. The starting sheets associated with each specimen had a thickness of 6.2 mm for the three-layer integral geogrid with a compressible porous outer layer and 6.3 mm for the solid single layer geogrid. As is evident from the traffic test results shown in Figures 30 and 31, the three-layer integral geogrid with a compressible porous outer layer advantageously exhibited less surface deformation than the solid single layer geogrid. In fact, in terms of the number of traffic test passes to limit deformation, the three-layer integral geogrid of the present invention with a compressible porous outer layer is approximately 9 times better than the solid single layer geogrid.

[0156] Similarly, Figures 32 and 33 show experimental traffic results that demonstrate the performance advantages of the present invention. Figure 32 is another plot of the performance improvement achievable with a hexagonal three-layer integral geogrid with a compressible porous outer layer in accordance with the present invention versus a hexagonal solid single layer geogrid. Figure 33 is a table summarizing the structural data associated with the hexagonal three-layer integral geogrid with a compressible porous outer layer and the hexagonal solid single layer geogrid used in the test results shown in Figure 32. The starting sheets associated with each specimen in the results of Figures 32 and 33 were thicker, with the three-layer integral geogrid with a compressible porous outer layer being 7.5 mm thick and the solid single layer geogrid being 7.5 mm thick. As is evident from the traffic test results shown in Figures 32 and 33, the three-layer integral geogrid with a compressible porous outer layer advantageously exhibited less surface deformation than the solid single layer geogrid. In fact, in terms of the number of traffic test passes to limit deformation, the three-layer integral geogrid of the present invention with a compressible porous outer layer is approximately five times better than a solid single layer geogrid.

[0157] Turning now to the compressibility of the monolithic geogrids of the present invention, FIG. 34 is a plot of the improved compressibility achievable with a hexagonal three-layer monolithic geogrid with a compressible porous outer layer according to the present invention versus a hexagonal solid single layer geogrid. Also, FIG. 35 is a table summarizing the force required to produce a given compressibility associated with a hexagonal three-layer monolithic geogrid with a compressible porous outer layer according to the present invention and the hexagonal solid single layer geogrid used in the test results shown in FIG. 34. The results shown in FIGS. 34 and 35 show that the three-layer monolithic geogrid with a compressible porous outer layer according to the present invention requires significantly less force to compress than the solid single layer geogrid. More specifically, the three-layer monolithic geogrid with a compressible porous outer layer according to the present invention requires 12% to 54% more force to compress than the solid single layer geogrid.

[0158] Figures 36 and 37 also show experimental stress-strain results that demonstrate the performance advantages of the present invention. Figure 36 is a plot of the stiffness achievable with a hexagonal three-layer integral geogrid with a compressible porous outer layer in accordance with the present invention versus a hexagonal solid single layer geogrid. Figure 37 is a table summarizing the stress and strain associated with the hexagonal three-layer integral geogrid with a compressible porous outer layer and the hexagonal solid single layer geogrid used in the test results shown in Figure 36. Grids A and C are specimens with a three-layer compressible porous outer layer structure in accordance with the present invention. Grid E is a specimen with a solid single layer structure. As is evident from Figures 36 and 37, there was no loss in either stiffness or strength for the three-layer compressible porous outer layer structure in accordance with the present invention.

[0159] Turning now to further compression modulus comparisons, FIG. 41 shows the experimental setup used to measure the compression modulus of the integral geogrid 1100 specimens. The setup uses a 1.6 mm wide metal probe 1910 to apply a force of 125 N to compress the integral geogrid 1100 specimens. As shown in FIG. 42, the compression modulus of the integral geogrid specimens having a layer with a porous structure according to the present invention, i.e., NX750, NX850 and NX950, is substantially greater than the compression modulus of the specimens not having a layer with a porous structure, i.e., TX160 and Hexagonal Mono.

[0160] Also, as shown in FIG. 43, the compressibility and rebound capacity of the integral geogrid specimens having a layer with a porous structure according to the present invention, i.e., Hexagonal UK7.5mm, NX750, NX850, Hexagonal UK5.45mm, NGA4.5mm, and NGB5mm, are all substantially greater than those of the specimens not having a layer with a porous structure, i.e., TX5, TX7, BX1200MD, BX1100MD, BX1100TD, TX160, and BX1200TD.

[0161] Figure 44 shows another experimental setup related to compressibility determination, the Plate Load Test Rig ("PLTR"), which is used to measure the displacement of the monolithic geogrid specimens. For testing, the monolithic geogrid specimens are laminated between a 4 inch layer of aggregate and a foam layer, and a steel plate is placed below the foam layer. To determine the compressibility of the monolithic geogrid specimens, a force of 1,000 lbs is applied to the aggregate / monolithic geogrid / foam laminate for 10 cycles. The monolithic geogrid specimens are then removed from the setup and checked for compressibility and surface damage to the ribs.

[0162] From testing with the apparatus shown in FIG. 44, the average displacements of various integral geogrid specimens using soft and rigid foams are shown in FIG. 45 and FIG. 46, respectively. For the meaning of "soft foam" and "rigid foam" as used in the above tests, FIG. 58 and 59, respectively, show graphs showing the compression force vs. displacement data for such soft and rigid foam embodiments. To generate the data shown in FIG. 58 and 59, an apparatus with a 3 inch by 3 inch square metal plate is connected to a force measuring device (e.g., an Instron machine, etc.) via a swivel joint that can accommodate the angle of the sample, and is mounted so that the foam specimen can be compressed at a rate of 10 mm / min. The apparatus is positioned to support the specimen on a horizontal plate.

[0163] As is evident from Figures 45 and 46, the displacements of the integral geogrid specimens having a layer with a porous structure according to the present invention, i.e., NX750, NX850, NGA and NGB, are advantageously smaller than the displacements of the specimens without a porous structure, i.e., TX5, TX160 and TX7.

[0164] Turning also to traffic testing, Figures 47-57 present experimental data reflecting various integral geogrid construction features and parameters that may affect deformation of the integral geogrid construction during use. Figures 47-51 and their respective associated discussions are presented herein solely as background information, i.e., as a means of explaining how the inventors' research and development efforts culminated in the integral geogrid constructions described herein as embodiments of the present invention. Experimental data relevant to the above-described embodiments of the present invention are presented in Figures 52-57.

[0165] For background information, Figure 47 shows a comparison of the effect of compressibility on the relationship between rib aspect ratio and surface deformation for two monolithic geogrids, a single layer monolithic geogrid and a coextruded multi-layer monolithic geogrid with one layer having a porous structure. Figure 47 shows that during traffic, at least directionally, the monolithic geogrid with a coextruded multi-layer structure with some compressibility has some advantage in terms of the relationship between surface deformation and rib aspect ratio. That is, for a coextruded multi-layer structure with some compressibility, it may be beneficial to obtain lower surface deformation without resorting to a very high aspect ratio.

[0166] However, referring to FIG. 48, another comparison of the effect of compressibility on the relationship between rib aspect ratio and surface deformation for two monolithic geogrids, a single layer monolithic geogrid and a coextruded multi-layer monolithic geogrid with one layer having a porous structure, shows that the advantages shown in FIG. 47 may not be as pronounced depending on the monolithic geogrid geometry. The monolithic geogrid used in the test of FIG. 47 has a plan dimension of 66 mm, whereas the monolithic geogrid used in the test of FIG. 48 has a plan dimension of 80 mm. In essence, the data in FIG. 48 shows that some advantage can be gained by optimizing both the material properties and geometry, as the 80 mm geometry is generally more suitable than the 66 mm geometry for most granular materials found in typical geogrid applications.

[0167] Turning now to a comparison of shapes alone, FIG. 49 shows the effect of base shape on the ability of rib aspect ratio to affect surface deformation for two integral geogrids without a layer of porous structure, namely the triaxial integral geogrid and the hexagonal integral geogrid described herein. FIG. 49 shows that during traffic, at least directionally, an integral geogrid with a hexagonal geometry has some advantage in terms of the relationship between surface deformation and rib aspect ratio. That is, with a hexagonal geometry, it may be beneficial to obtain lower surface deformation without resorting to a very high aspect ratio. Finally, for background information, FIG. 50 shows a comparison of the advantages of base shapes in similarly compressible integral geogrid products. That is, FIG. 50 shows that during traffic, for a triaxial integral geogrid and a hexagonal integral geogrid, each having a single inner layer with a porous structure disposed between first and second outer layers of non-porous structure, the hexagonal geometry is advantageous in that it results in lower rib aspect ratios and less surface deformation. Similarly, FIG. 51 provides a graphical comparison of the effect of base geometry on the relationship between rib aspect ratio and surface deformation in similarly compressible monolithic geogrids, namely the triaxial monolith and the hexagonal monolith described above.

[0168] Turning now to traffic data relevant to various embodiments of the present invention, the experimental results shown in Figures 52-57 demonstrate the advantages achieved by the monolithic geogrid having first and second outer layers of porous structure and an inner layer of non-porous structure as described herein.

[0169] Figure 52 shows a comparison of the influence of the position of the layer with a porous structure on the surface deformation in a multi-layered integrated geogrid for a single base shape. Figure 53 provides a graph comparing the influence of the position of the layer with a porous structure on the relationship between the aspect ratio of the ribs and the surface deformation for a single base shape related to Figure 52. As is evident from Figures 52 and 53, the integrated geogrid according to the present invention having an outer layer of a porous structure and an inner layer of a non-porous structure has less surface deformation during traffic than the integrated geogrid having a porous structure layer as the inner layer.

[0170] Also, FIG. 54 provides yet another comparison of the effect of the location of the layer with a porous structure in a multi-layered integrated geogrid on the surface deformation for the single base shape associated with FIG. 52. Related FIG. 55 shows another graphical comparison of the effect of the location of the layer with a porous structure on the relationship between the aspect ratio of the ribs and the surface deformation for the single base shape associated with FIG. 52. In the experiments reported in FIGS. 54 and 55, the performance of a three-layered integrated geogrid with an outer porous structure layer is compared to both a five-layered integrated geogrid with two "sandwiched" inner porous structure layers, and an integrated geogrid with a single layer without a porous structure. As is evident from FIGS. 54 and 55, of the three integrated geogrid structures described above, the integrated geogrid according to the present invention with an outer layer of a porous structure and an inner layer of a non-porous structure has the least surface deformation during traffic.

[0171] Finally, Figures 56 and 57 show experimental data reflecting the combined beneficial effects of incorporating various features of the monolithic geogrid of the present invention into the monolithic geogrid. Figure 56 provides a comparison of the effect on surface deformation of the layer with porous structure for a monolithic geogrid of the present invention having a single base shape associated with Figure 52 and a prior art geogrid without a layer with porous structure. Also associated Figure 57 provides a graphical comparison of the effect of the compressibility of the layer with porous structure on the relationship between rib aspect ratio and surface deformation for a monolithic geogrid of the present invention having a single base shape associated with Figure 52 and a prior art geogrid without a layer with porous structure. Figures 56 and 57 show that by optimizing both the shape and material properties by co-extrusion and precisely placing the layer with compressed porous structure, the monolithic geogrid of the present invention provides approximately a 25% reduction in surface deformation of the aggregate. Moreover, the above-mentioned results are achieved with starting sheet thicknesses of 12-28% of the thickness of the prior art geogrids.

[0172] In summary, the multi-layer integral geogrid having one or more porous layers of the present invention not only has a multi-layer structure, but at least one of its layers has a porous structure as a result of the distribution of porous openings, thereby providing the integral geogrid with improved compressibility of the layers under load.

[0173] The multi-layered nature of the multi-layer integral geogrids having one or more porous layers of the present invention results in greater overall aggregate bonding by the integral geogrid compared to conventional single layer integral geogrids. Furthermore, by virtue of the one or more porous layers, the multi-layer integral geogrids of the present invention are characterized by structural compliance, i.e., initial resilience or flexibility, resulting in better compaction and high density, yet as a result of the initial resilience of the multi-layer integral geogrid, have a greater composite stiffness of the final integral geogrid when incorporated into a soil structure.

[0174] Additionally, certain embodiments of the multi-layer monolithic geogrids with one or more porous layers of the present invention provide higher aspect ratios in all strands as compared to conventional monolithic geogrids. Because the higher aspect ratios associated with certain embodiments of the monolithic geogrids of the present invention increase aggregate interlocking, the multi-layer monolithic geogrids with one or more porous layers of the present invention can better accommodate a variety of aggregate aspect ratios.

[0175] A first aspect of the invention is a multi-layer monolithic geogrid for interlocking, stabilizing and strengthening aggregates, comprising a plurality of oriented strands interconnected by partially oriented joints and having a series of openings therebetween, said monolithic geogrid having a plurality of layers of polymeric material each, at least a first outer layer and a second outer layer of said layers having a porous structure, which improves the initial interaction and compatibility between the soil or aggregate and the monolithic geogrid to maximize the density and / or post compaction additive properties of the soil or aggregate.

[0176] The first and second porous outer layers may have a void volume of about 20% to about 70%. The first and second porous outer layers may have a compressibility of about 20% to about 60%. The first and second porous outer layers may have a foamed structure. The foaming may involve a foaming agent or gas injection. The first and second porous outer layers may have a structure that includes a particulate filler. The particulate filler may be calcium carbonate. The multi-layer integral geogrid may be made from coextruded multi-layer polymer sheets. The multi-layer integral geogrid may be made from stacked multi-layer polymer sheets. The oriented strands may be biaxially stretched. The multi-layer integral geogrid may have a first porous outer layer, a non-porous inner layer, and a second porous outer layer, and the first and second porous outer layers may be disposed on opposite planes of the non-porous inner layer. The multi-layer integral geogrid may be a triaxially integral geogrid. The multi-layer integral geogrid can be a rectangular integral geogrid. The multi-layer integral geogrid can be a hexagonal integral geogrid.

[0177] A second aspect of the invention relates to a starting material for making a multi-layer integrated geogrid, said starting material comprising a multi-layer polymer sheet having multiple layers, each layer being a polymeric material, at least a first and second outer layer of said multiple layers being an extended structure capable of forming a porous structure in the first and second outer layers of said multi-layer integrated geogrid, said multi-layer polymer sheet having holes or recesses that provide openings when said sheet is biaxially stretched.

[0178] The multilayer polymer sheet may be coextruded. The multilayer polymer sheet may be laminated. The multilayer polymer sheet may include a first outer layer, an inner layer that does not have an expanded structure capable of forming a porous structure, and a second outer layer, and the first outer layer and the second outer layer may be disposed on a plane opposite to the inner layer. In an embodiment, the first outer layer has a thickness of about 0.5 mm to about 4 mm, the inner layer has a thickness of about 0.5 mm to about 4 mm, and the second outer layer has a thickness of about 0.5 mm to about 4 mm. The multilayer polymer sheet may have an initial thickness of about 2 mm to about 12 mm. The multilayer polymer sheet may have an initial thickness of about 4 mm to about 10 mm.

[0179] A third aspect of the present invention relates to an earth structure comprising a mass of particulate material reinforced by embedding a multi-layer integral geogrid according to the first aspect of the present invention.

[0180] A fourth aspect of the invention relates to a method of reinforcing a mass of granular material comprising embedding a multi-layer monolithic geogrid according to the first aspect of the invention in the mass of granular material.

[0181] A fifth aspect of the invention is a method of making a multi-layer integral geogrid comprising the steps of: providing a multi-layer polymer sheet having a plurality of layers, each of which has a polymeric material, wherein at least a first outer layer and a second outer layer of the plurality of layers have an extended structure capable of forming a porous structure in the first outer layer and the second outer layer of the multi-layer integral geogrid; providing a patterned plurality of holes or recesses in the multi-layer polymer sheet; and biaxially orienting the multi-layer polymer sheet having the patterned plurality of holes or recesses to provide a plurality of oriented strands interconnected by partially oriented joints, the holes or recesses being configured as grid openings. wherein the first and second outer layers have a porous structure.

[0182] The first and second porous outer layers of the multi-layer integral geogrid may have a foamed structure. The first and second porous outer layers of the multi-layer integral geogrid may include particulate fillers. The step of providing the multi-layer polymer sheet may be co-extrusion. The step of providing the multi-layer polymer sheet may be lamination. The multi-layer integral geogrid may include a first porous outer layer, a non-porous inner layer, and a second porous outer layer, the first and second porous outer layers being disposed on opposite planar surfaces of the non-porous inner layer. In an embodiment, the first porous outer layer may have a broad specification of polymeric components, the non-porous inner layer may have a high molecular weight polyolefin component, and the second porous outer layer may have a broad specification of polymeric components. The multi-layer polymer sheet may have an initial thickness of at least 2 mm. The multi-layer integral geogrid may be a rectangular integral geogrid. The multi-layer integral geogrid may be a rectangular integral geogrid. The multi-layer integral geogrid may be a hexagonal integral geogrid.

[0183] A sixth aspect of the invention is a method of making a multi-layer monolithic geogrid having one or more layers with a porous structure, comprising the steps of biaxially stretching a starting material, which is a multi-layer polymer sheet having one or more layers with a porous structure and a plurality of holes or recesses patterned therein, to provide a multi-layer monolithic geogrid having one or more layers with a porous structure, a plurality of oriented strands, a plurality of partially oriented joints, and a plurality of grid openings; and embedding the monolithic geogrid in a mass of particulate material. The present invention relates to a method comprising the steps of:

[0184] A seventh aspect of the invention relates to a multi-layer integral geogrid comprising a plurality of interconnected first oriented strands and a plurality of partially oriented joints forming a repeating pattern of exterior hexagons having a series of openings therein, each of the exterior hexagons supporting and surrounding a smaller interior hexagon having a second oriented strand, the first oriented strands and the plurality of partially oriented joints of the exterior hexagons forming a plurality of linear strands extending continuously throughout the multi-layer integral geogrid, the integral geogrid having a plurality of layers of polymeric material each extending throughout the geogrid, and at least one layer of the layers having a porous structure.

[0185] The foregoing is considered as illustrative only of the principles of the invention. Moreover, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation as described and illustrated.

Claims

1. A multi-layer integrated geogrid for interlocking, stabilizing, and strengthening aggregates, comprising: a plurality of oriented strands interconnected by partially oriented joints and having a series of openings therebetween; the monolithic geogrids each having a plurality of layers of polymeric material; At least a first outer layer and a second outer layer of the plurality of layers have a porous structure that improves initial interaction and compatibility between the soil or aggregate and the integral geogrid to maximize density and post-compression properties of the soil or aggregate. The multi-layer integrated geogrid.

2. 10. The multi-layer integral geogrid of claim 1, wherein said first and second porous outer layers have a void volume of about 20% to about 70%.

3. 3. The multi-layer integral geogrid of claim 1 or 2, wherein the first and second porous outer layers have a compressibility of about 20% to about 60%.

4. The multilayer integrated geogrid according to any one of claims 1 to 3, wherein the first porous outer layer and the second porous outer layer have a foamed structure.

5. 5. The multi-layer integrated geogrid of claim 4, wherein said foaming involves foaming agent or gas injection.

6. The multi-layer integrated geogrid of any one of claims 1 to 3, wherein the first and second porous outer layers have a structure including a particulate filler.

7. 7. The multi-layer monolithic geogrid of claim 6, wherein said particulate filler is calcium carbonate.

8. 8. The multi-layer integrated geogrid of any one of claims 1 to 7, wherein the multi-layer integrated geogrid is made from coextruded multi-layer polymer sheets.

9. 8. The multi-layer integrated geogrid of any one of claims 1 to 7, wherein the multi-layer integrated geogrid is made from laminated multi-layer polymer sheets.

10. The multilayer integrated geogrid according to any one of claims 1 to 9, wherein the oriented strands are biaxially oriented.

11. 11. The multi-layer integrated geogrid of any one of claims 1 to 10, wherein the multi-layer integrated geogrid has the first porous outer layer, a non-porous inner layer, and the second porous outer layer, the first porous outer layer and the second porous outer layer being disposed on opposite planar sides of the non-porous inner layer.

12. 12. The multilayer integrated geogrid of any one of claims 1 to 11, wherein the integrated geogrid is a triaxial integrated geogrid, a rectangular integrated geogrid or a hexagonal integrated geogrid.

13. 1. A starting material for producing a multi-layer integrated geogrid, comprising a multi-layer polymer sheet, each layer having multiple layers of a polymeric material, at least a first outer layer and a second outer layer of the multiple layers being an extended structure capable of forming a porous structure in the first outer layer and the second outer layer of the multi-layer integrated geogrid, the multi-layer polymer sheet having holes or recesses that provide openings when the sheet is biaxially stretched.

14. The starting material of claim 13 , wherein the multilayer polymer sheet is coextruded.

15. The starting material of claim 13 , wherein the multi-layer polymer sheet is laminated.

16. The starting material according to any one of claims 13 to 15, wherein the multilayer polymer sheet comprises the first outer layer, an inner layer that does not have an extended structure capable of forming a porous structure, and the second outer layer, and the first outer layer and the second outer layer are disposed on opposite planes to the inner layer.

17. 17. The starting material of claim 16, wherein the first outer layer has a thickness of about 0.5 mm to about 4 mm, the inner layer has a thickness of about 0.5 mm to about 4 mm, and the second outer layer has a thickness of about 0.5 mm to about 4 mm.

18. The starting material of any one of claims 13 to 17, wherein the multilayer polymer sheet has an initial thickness of from about 2 mm to about 12 mm.

19. 20. The starting material of claim 18, wherein the multilayer polymer sheet has an initial thickness of about 4 mm to about 10 mm.

20. 13. A soil structure comprising a mass of particulate material reinforced by embedding a multi-layer integral geogrid according to any one of claims 1 to 12.

21. 13. A method of reinforcing a mass of particulate material comprising embedding the multi-layer monolithic geogrid of any one of claims 1 to 12 in the mass of particulate material.

22. 1. A method for producing a multi-layer integrated geogrid, comprising: providing a multi-layer polymer sheet having a plurality of layers each of a polymeric material, wherein at least a first outer layer and a second outer layer of the plurality of layers have an extended structure capable of forming a porous structure in the first outer layer and the second outer layer of the multi-layer integrated geogrid; providing a pattern of a plurality of holes or recesses in the multilayer polymer sheet; and biaxially orienting the multilayer polymer sheet having the patterned plurality of holes or recesses to provide a plurality of oriented strands interconnected by partially oriented joints, the holes or recesses configured as grid openings. Including, The method, wherein the first outer layer and the second outer layer have a porous structure.

23. 23. The method of claim 22, wherein the first and second porous outer layers of the multi-layer integral geogrid have a foamed structure.

24. 23. The method of claim 22, wherein the first and second porous outer layers of the multi-layer integral geogrid comprise a particulate filler.

25. The method of any one of claims 22 to 24, wherein the step of providing the multilayer polymer sheet is coextrusion.

26. The method of any one of claims 22 to 24, wherein the step of providing the multilayer polymer sheet is lamination.

27. 27. The method of any one of claims 22-26, wherein the multi-layer integral geogrid comprises the first outer porous layer, a non-porous inner layer, and the second outer porous layer, the first outer porous layer and the second outer porous layer being disposed on opposite planar sides of the non-porous inner layer.

28. 28. The method of claim 27, wherein the first porous outer layer has a broad spectrum of polymeric components, the non-porous inner layer has a high molecular weight polyolefin component, and the second porous outer layer has a broad spectrum of polymeric components.

29. The method of any one of claims 22 to 28, wherein the multilayer polymer sheet has an initial thickness of at least 2 mm.

30. 30. The method of any one of claims 22-29, wherein the multi-layer integral geogrid is a triaxial integral geogrid, a rectangular integral geogrid or a hexagonal integral geogrid.

31. 1. A method for manufacturing a multi-layer integrated geogrid having one or more layers with a porous structure, comprising: biaxially stretching a starting material, which is a multilayer polymer sheet having one or more layers with a porous structure and a plurality of holes or recesses patterned therein, to provide a multilayer monolithic geogrid having one or more layers with a porous structure, a plurality of oriented strands, a plurality of partially oriented joints, and a plurality of grid openings; and embedding said monolithic geogrid into a mass of particulate material. The method comprising:

32. 1. A multi-layer integral geogrid comprising a plurality of interconnected first oriented strands and a plurality of partially oriented joints forming an exterior hexagonal repeating pattern having a series of openings therein, each of the exterior hexagons supports and surrounds a smaller interior hexagon having a second oriented strand; the first oriented strands of the exterior hexagons and the plurality of partially oriented joints form a plurality of linear strands that extend continuously throughout the multi-layer integral geogrid; the monolithic geogrid having multiple layers of polymeric material each extending throughout the geogrid; and At least one layer of the plurality of layers has a porous structure. The multi-layer integrated geogrid.

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