EP0989216A1

EP0989216A1 - Manufacturing method of geogrid

Info

Publication number: EP0989216A1
Application number: EP98118203A
Authority: EP
Inventors: Yen-Jung c/oIndustrial Technology Research Hu; Pung-Nien c/o Industrial Technolog Research Perng; Tien-Pao c/o Industrial Technolog Research Chiang; Shi-Chieh J. c/o Industrial Technolog Resea Cheng
Original assignee: Industrial Technology Research Institute ITRI
Current assignee: Industrial Technology Research Institute ITRI
Priority date: 1998-09-25
Filing date: 1998-09-25
Publication date: 2000-03-29
Anticipated expiration: 2018-09-25
Also published as: ATE283938T1; DE69827943T2; DE69827943D1; EP0989216B1

Abstract

An improved method for manufacturing polymeric geogrids is disclosed. The method includes the steps of: (a) co-spinning at least one high-melting point filament yarn with a plurality of low-melting point staple fibers to form a composite yarn, the low-melting point staple fiber has a melting point that is at least 10 ∼ 20 °C lower than the melting point of the high-melting point filament yarn; (b) weaving the composite yarn to form a net-structured fabrics; (c) heating the net-structured fabrics to cause the low-melting point staple fiber to melt and wrap about the high-melting point filament yarn; and (d) cooling the net-structured to form a geogrid. One of the main advantages of this process is that it does not require the coating step (with molten PVC or asphalt), as do the prior art processes. Thus, the geogrids can be manufactured in a more cost-effective and environmentally compatible manner. The geogrid of the present invention also exhibits substantially increased junction strength as well as retaining a greater portion of its ultimate strength at elongation.

Description

FIELD OF THE INVENTION

The present invention relates to an improved method for manufacturing geogrids with enhanced properties. More specifically, the present invention relates to an improved method for manufacturing woven geogrids, which can be used with foundations, soils, rock, earth, or other geomechanical materials to provide selective separation and reinforcement. The method disclosed in the present invention has many distinct advantages in that (1) it can be readily and easily implemented on-site; (2) it reduces manufacturing costs and minimizes or eliminates waste disposal problems that can cause environmentally pollution concerns; and (3) the geogrids so manufactured exhibit superior qualities, especially their ability to retain excellent strength after elongation.

BACKGROUND OF THE INVENTION

Geogrids have been used in various civil engineering and mining applications such as soil stabilization, reinforcement, and other applications. Geogrids, which as their names imply, are primarily two-dimensional in form, can be provided in soft or hard forms. Typically, the soft geogrids comprise intersecting (typically via weaving process) strands made from high tensile strength filaments so as to provide high load support characteristics. The grid openings formed from the intersecting stands typically are rectangular or square in shape, with the strands being placed at an angle of about 90 ° relative to each other. However, other shapes and/or relative angles may be used. Depending on the size of the grid, composition of the strands, and other factors, the commercially available geogrids may also be called geocells, geonets, or geocomposits. One of the companies that market these products is Tenax Company, located in Baltimore, Maryland.
The most common process in making geogrids involves the five main steps of: (1) spinning high-strength filament yarns; (2) warping; (3) weaving to form a two-dimensional net structure; (4) coating with polyvinyl chloride (PVC) or asphalt; and (5) drying/solidification to form the final geogrid. The purpose of the step of coating with PVC or asphalt is to cause the high-strength filament yarns to form filament bundles that are aggregated and covered by this matrix of binder material, which also serves as a protective material. The step of prepregging with PVC or asphalt also imparts many desired properties, such as UV-resistance and acid/base-resistances, to the grid structures.
It was observed by the co-inventors of the present invention that the geogrids made from the conventional process have several drawbacks. The most notable inadequacy with the conventional geogrids is that, because the only the fiber bundles (i.e., the so-called "ribs" of the geogrid) and the intersections thereof (i.e., the "nodal points") of the geogrids are covered by the PVC binder material, and no binder material is provided between the individual fibers, their junction strength is very poor. This severely limits the types of engineering projects that geogrids can be utilized with confidence. Furthermore, because the fiber bundles are prepregged with PVC or asphalt, the conventional process has raised serious environmental pollution concerns and causes clean-up problems.
In U.S. Pat. No. 5,091,247, it is disclosed a process for making woven geotextile grid (i.e., geogrid) for earth reinforcement applications. The grid is formed of woven fabric which is coated with a suitable polyvinylchloride or other plastic coating. The fabric is formed of a plurality of spaced-apart pick (i.e., transversal) yarn bundles which are interwoven with a plurality of spaced-apart warp (i.e., longitudinal) yarn bundles. The pick yarn bundles are held in place in the warp yarn bundles with locking yarns which run parallel to the pick yarns and which are positioned adjacent to the edges of the pick yarn bundles. The warp yarns extend between the pick yarn bundles and locking yarns to lock the pick yarn bundles into place. A plurality of pairs of leno yarns oriented parallel to the warp yarns additional strengthen the fabric by interlocking with one another in the spaces between the pick yarn bundles and locking yarns. After the fabric leaves the loom, it is dipped in a heated polyvinylchloride bath and dried using heating elements before being rolled for storage or shipment. The process disclosed in the '247 patent basically follows the convention process by dipping the woven fabric into a PVC bath, followed by drying/heating to form the geotextile grid. Again, because the PVC coating is only applied to the bundle surface and there is no adhesion force between the individual fibers, its junction strength is poor.
In U.S. Pat. No. 5,045,377, it is disclosed a process for making continuous fiber reinforced composite grid. The grid structures are formed by joining continuous fiber reinforced/resin matrix compound composite strands with similar compound composite strands, or with simple unreinforced plastic strands. The compound composite reinforced strands are formed by using prepreg, which comprises reinforcing fibers embedded in a plastic resin matrix. The prepreg tapes are fed from a supply roll into a die, and are continuously pulled through the die. In a separate route, a thermoplastic resin is supplied into the die and deposited onto the tapes to provide encapsulation of the prepreg in a second layer of plastic. Thereafter, thermoplastic resin is allowed to flow out to form transverse strands, thus resulting in a web or grid structure. The process discloses in the '377 patent differs from most of the conventional processes in that, among other things, first, it utilizes glass-fiber reinforced composites, thus its cost is substantially higher. Second, since the transverse direction stands are deposited onto the machine direction strands, the geogrids so produced are not woven geogrids; rather, they are non-woven geogrids. The geogrids produced from the '377 process provided several advantages while also suffer disadvantages. However, the '377 process still utilizes the same basic approach as the conventional process in that the thermoplastic resin is heated and melted to thereby provide a coating on the surface of the composite fiber.
In U.S. Pat. No. 5,199,825, it is disclosed a process for making a grid composite for protecting men and long well mining equipment during long well shield recovery. In this invention, a polymer grid is connected to a grid composite consisting of a polymer grid and a geotextile. The grid composite is formed by use of a polymer grid which is heat bonded to a continuous filament polyester, non-woven needle-punched engineering fabric. The engineering fabric or geotextile is bonded to the polymer grid using an open flame heat source or using a heated roll as a heat source. During the process, plastic pellets are melted and compressed by an extruder, and a gear pump and a melt mixer are used to provide a homogeneous melt. Since the process discloses in the '825 patent involves the step of bonding a polyester geotextile to a biaxial grid material formed by needle-punching, the geogrids so produced do not solve the lack of junction strength problem encountered in the conventional geogrids.
As discussed above, the conventional geogrids have a major limitation in that, because there is no binder material between the individual fibers within each fiber bundle, they lack the desired junction strength. While sever inventions have be disclosed to improve the properties of geogrids, they have not solved this problem. Therefore, it is desirable to develop an improved process so as to overcome this problem and enhance the applicability of geogrids. It is also equally desirable to develop an improved process which would make the manufacturing of geogrids environmentally compatible.
In order to improve the strength of the geogrid, U. S. Pat No. 5,669,796 discloses a heat bonded geogrid fabric having a woven or warp knit, weft inserted grid. It comprises a bicomponent fiber with filaments each having a sheath of an adhesive polyolefin material comprising a polyolefin and an adhesive and containing about 0.5 wt% to about 2 wt% carbon black and a core of polyethylene terephthalate having an intrinsic viscosity of at least 0.89 deciliters per gram as determined from a solvent base of orthochlorophenol at 25 °C. The bicomponent fiber having the sheath-core configuration is prepared by melt-extruding polymer from a spinneret. Before reaching the spinneret, the molten polymer, which contains polyolefin, adhesive and carbon black, is filtered. The sheath polymer and the core polymer are pumped separately into their respective channels in each spinneret and are extruded through the spinneret holes to form the bicomponent fibers. The method disclosed in the '796 improves the coverage of the core polymer by the sheath polymer; however, because it involves a relatively complicated procedure, it may be more expensive to manufacture.

SUMMARY OF THE INVENTION

The primary object of the present invention is to develop an improved process for making woven geogrids which can be advantageously used in various civil engineering projects to provide selective separation and reinforcement for foundations, soils, rock, earth, or other geomechanical materials. More specifically, the primary object of the present invention is develop an improved method for manufacturing geogrids, which can be used with various types of civil engineering projects with improved long-term mechanical strengths. The method disclosed in the present invention provides many distinct advantages in that: (1) the process can be readily and easily implemented on-site; (2) it reduces manufacturing costs and is highly environmentally compatible; and (3) the geogrids so manufactured exhibit superior qualities, including excellent mechanical strength and low rate of elongation. One of the main advantages of the method disclosed in the present invention is that it can greatly enhance the retention of mechanical strength of geogrids after elongation, without substantially increasing the manufacturing cost thereof. Most geogrids will be elongated after they are applied onto the intended objects such as earth, etc. Thus, ability to retain mechanical strength is a very important parameter gauging the characteristics of a geogrid.
Another main advantages of the process disclosed in the present invention is that it does not require the equipment and steps for receiving, containing and melting a thermoplastic (or asphalt) feed, and coating (i.e., dipping) the molten thermoplastic onto a geotextile fabric, as required by the prior art processes. Because the prior art processes involve the handling of a very hot (typically above 150 °C) molten polymer or asphalt mass, they require relatively expensive equipment and often result in a highly hazardous work environment. Furthermore, the unused thermoplastic resin or asphalt can cause serious disposal problems and often are environmental headaches.
Yet another distinct advantage of the process disclosed in the present invention is that, while most of the prior art processes can only achieve the purpose of applying a binder composition covering the yarn bundles and leaving the individual fibers uncovered, the present invention allows the coating composition to effectively penetrate into and intimately cover the individual fibers in an ubiquitous manner. The ubiquity of the coating composition down to the individual fiber level allows the geogrids made from the process disclosed in the present invention to exhibit superior qualities overthose made from the prior art processes, especially with regard to the junction strength. While the process disclosed in the '796 patent can achieve this purpose by using a sheath-core bicomponent fiber configuration, it involves a relatively complicated procedure and thus high manufacturing cost.
In a related research, the inventors of the present invention discovered that by combining one or more high-melting point filament yarns with one or more low-melting point filament yarns to form a hybrid bundle, and after warp beaming, weaving or twisting the hybrid bundle into a net structure with a predetermined grid pattern. Good coverage of the high-melting point filament yarns can be achieved. However, such coverage is only linear, and it may not provide complete coverage around the circumference of the high-melting point filament yarns.
In the process disclosed in the present invention to form a geogrid, unexpectedly superior results were observed when one or more high-melting point filament yarns and one or more low-melting point staple fibers are first co-spun into a composite yarn. The composite yarn is woven into fabrics with a net structure with a predetermined grid pattern. The grid pattern of the fabrics can be a rectangular or square shape with a predetermined grid opening. The net-structured fabric is then passed through a heat treatment causing the low-melting point staple fibers to melt and thereby ubiquitously bind the individual composite yarn. After cooling, a soft geogrid with excellent mechanical and chemical properties is produced. The grid structure can be made in a plant off-site or at the construction site.
The composite yarn disclosed in the present invention comprises at least one high-melting point filament yarn and a plurality of low-melting point staple fibers. The high-melting point filament yarn should possess the qualities of high strength, high modules and low strain rate, so as to provide the function as a reinforcement material for the woven geogrid. Examples of the high-melting point filament yarns that can be used in the present invention include polyesters, such as polyethylene terphthalate (PET), polybutylene terephthalate (PBT), etc; polyamides, such as nylon 6, nylon 66, etc; glass fibers; polyvinyl alcohol fibers; carbon fibers; and aramid fibers. On the other hand, the main function of the low-melting point staple fibers is to serve as a matrix or binder, and its strength is of relatively secondary consideration. Examples of the low-melting point staple fibers that can be used in the present invention include polyethylene, polypropylene, co-polyesters, polyamides such as nylon, etc. It is preferred that low-melting point staple fibers are selected such that the melting point of the high-melting point filament yarns is at least 20°C greater than that of the low-melting point staple fibers. The low-melting point staple fibers can be selected from the same class of polymers that can be used as the high-melting point filament yarns, the main point is they must have a lower melting point.
It is preferred that the composite yarn contains the high-melting point filament yarns and the low-melting point staple fibers in a weight ratio of 50 ∼ 70% to 30 ∼ 50%. These two types of fibers are spun into a bobbing. Thereafter, the composite yarn can be subjected to the weaving operation. Because the yarns formed in the present invention belong to the type of spun yarns, they can be used in various types of weaving machines, such as rapier loom or warp knitting machines, to form the desired grid structures. Typically, the grid dimension can be square 20 x 20 or rectangular 20 x 30 mm, etc. After the weaving process, the woven product can be placed in an oven, or other heat treatment devices, and heated at temperatures preferably about 10 ∼ 50 °C above the melting point of the low-melting point staple fibers, to thereby form the final geogrid product.
By using the composite yarn, the present invention does not require the costly and messy prepregging step which has always been required in the prior art processes. By doing so, the process disclosed in the present invention eliminates the need for the coating facility, its also reduces the size of the processing plant as well as the cost of other related equipment. But more importantly, the process disclosed in the present invention greatly reduces the processing time and minimizes potential environmental pollution problems. Furthermore, with the process disclosed in the present invention, the high-strength fibers (i.e., the high-melting point fibers) are intimately bonded by the binder or matrix resin (formed from the low-melting point staple fibers), excellent adhesion is provided between the individual composite yarn and at the intersections of the yarns. This results in greatly improved junction strength and overall strength of the geogrids so produced.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be described in detail with reference to the drawing showing the preferred embodiment of the present invention, wherein:
Fig. 1 is a schematic drawing showing the steps of forming a polymeric geogrid according to the most common prior art processes.
Fig. 2 is a schematic drawing showing the steps of form a polymeric geogrid according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention discloses an improved process for making polymeric geogrids, which can be used with foundations, soils, rock, earth, or other geomechanical materials to provide selective separation and reinforcement. The method disclosed in the present invention provides many distinct advantages. First, the process can be readily and easily implemented on-site without requiring excessive extra equipment. Second, it reduces the manufacturing time and cost and is highly environmentally compatible. Third, the geogrids manufactured from the process disclosed in the present invention exhibit superior qualities, including high junction strength, low elongation, and high overall strength. As discussed earlier, one of the distinct advantages of the method disclosed in the present invention is that the geogrids so prepared can retain a significant portion of their designed strength after elongation, without incurring substantially increased manufacturing cost.
As described above, the process disclosed in the present invention does not require the equipment and steps for receiving, containing and melting a thermoplastic (or asphalt) feed, nor does it requires the equipment and steps for coating the molten thermoplastic onto a geotextile fabric. Both of these elements are required by the prior art processes, which involve the handling of a very hot (typically above 150 °C) molten polymer or asphalt mass. As a result, the prior art processes often require relatively expensive equipment and often result in a highly hazardous work environment. Furthermore, the unused thermoplastic resin or asphalt mass can cause serious disposal problems and often present environmental headaches.
The process disclosed in the present invention also allows the binder composition (i.e., the low melting point stable fibers) to effectively and intimately cover the filament yarn. This is another distinct advantage over all of the prior art processes, in which the binder composition only covers the filament bundles. The wrapping of the binder fiber composition outside and around the individual composite yarn allows the geogrids made from the process disclosed in the present invention to exhibit superior qualities over those made from the prior art processes, especially with regard to the junction strength and retained strength after elongation. The present invention thus not only allows a superior geogrid to be made, it also enables the product to be made in a more cost-effective and environmentally-conscientious manner.
In the process disclosed in the present invention, at least one high-melting point fiber filament yarn and a plurality of low-melting point fibers are first spun to form a composite yarn. The composite yarn is then woven into a net structure with a predetermined grid opening, which can be a rectangular or square shape with a predetermined grid dimension. The woven net structure made from the composite yarns is then heated to cause the low-melting point staple fiber to melt and thereby forming a wrapping outside and around the high-melting point fibers. After cooling, a soft geogrid with excellent mechanical and chemical properties is provided. The grid structure can be made from a manufacturing plant or at the construction site.
The composite yarn disclosed in the present invention preferably comprises one or more high-melting point multi-filament yarns and a plurality of low-melting point staple fibers. It is preferred that the composite yarn contain the high-melting point filament yarns and the low-melting point multi-filament yam at a ratio of 50 ∼ 70% to 30 ∼ 50%, by weight, of the fibers. The high-melting point and low-melting point fibers can be provided as simple fibers, or the low-melting point fibers can be provided as bi-component fibers. If bi-component staple fibers are used, they can be either sheath-and-core type or side-by-side type. The high-melting point filament yarn, which provides the function as a reinforcement material for the polymeric geogrid, should possess the desired qualities of high strength, high modules and low strain rate. Preferred examples of the high-melting point fibers that can be used in the present invention include polyesters, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc; and polyamides, such as nylon 6, nylon 66, etc. Glass fibers, polyvinyl alcohol fibers, carbon fibers, and aramid fibers may also be used as the reinforcement component. The main function of the low-melting point staple fibers is to serve as a matrix or binder to wrap the reinforcement component (i.e., the high-melting point multi-filament yarn), and its strength is of secondary consideration. Preferred examples of the low-melting point staple fibers that can be used in the present invention include polyethylene, polypropylene, polyester copolymers, polyamides such as nylon, etc. It is preferred that low-melting point fibers are selected such that the melting point of the high-melting point fibers is at least 20°C greater than that of the low-melting point fibers.
The high- and low-melting point fibers are spun then subjected to warp beaming; optionally, they can be subject to other processing steps before warp beaming. Thereafter, the yam bundles can be subjected to the weaving operation. Because the yarns formed in the present invention belong to the type of spun yarns, they can be used in various types of weaving machines, such as rapier loom, warp weaving or warp twisting machines, to form the desired grid structures. Preferably, the grid dimensions are 20 x 20 or 20 x 30 mm. Other dimensions can be easily implemented. After the weaving process, the woven product is placed in an oven and heated at temperatures preferably about 10 ∼ 20 °C above the melting point of the low-melting point fibers, to thereby form the final geogrid product.
A distinct feature of the process disclosed in the present invention is that the present invention does not require the costly and messy coating step which has always been required in the prior art processes. Rather, the present invention uses the composite yarn comprising high-melting point filament yarns and low-melting point staple fibers in the weaving process. This novel approach allows the process disclosed in the present invention to eliminate the need for the coating equipment, its also reduces the plant size and the cost for other equipment. As a result the process disclosed in the present invention was able to greatly reduce the processing time and minimize potential environmental pollution problems. In addition to the cost savings, the geogrids produced from the process disclosed in the present invention also exhibit unexpectedly superior qualities. With the process disclosed in the present invention, the reinforcement fibers are intimately wrapped by the binder fibers, thus, excellent bonding is provided between the individual fibers and at the intersections of these fibers. This resulted in greatly improved junction strength as well as excellent overall strength. The wrapping of the filament yarns by the staple fibers also allows eventually excellent enclosure by the binding component.
Now refer to the drawings. Fig. 1 is a schematic drawing showing the steps of forming a polymeric geogrid according to the most common prior art processes. High strength filament fibers 2 are provided from the bobbin support 1 and combined to form yarns 3. The yarns are processed through a warp beam 4 and are woven in a weaving machine 5 to form a woven net structure consisting of grid ribs and nodes formed of fiber bundles. The net structure is then passed through a dipping bath 6, and a pair of padders 7. The dipping bath 6 contains a coating composition, typically polyvinyl chloride, to apply a layer of protective and binder composition covering the fiber bundles. Finally the coated woven net structure is heated and dried in an oven 8 and taken up by a take-up roller 9 to form a geogrid.
Fig. 2 shows a schematic drawing showing the steps of forming a polymeric geogrid according to a preferred embodiment of the present invention. Composite yam bobbins 12 are provided from the roll support, or creel, 10. The composite yarn are processed through a tension unit 15 and woven in a weave machine 13 to form a woven net structure consisting of grid ribs and nodes formed of composite yams. Instead of passing through the dipping bath as shown in Fig. 1 of the prior art processes, the woven net structure is directly fed to the oven 15, through guide rollers 14, where the woven net structure is heated and dried, and then is cooled and taken up by a take-up device 16 to form a geogrid. The elimination of the dipping bath greatly simplifies the manufacturing process, reduces the manufacturing cost (in both the capital cost and operation cost), improves the manufacturing condition, and ameliorates environmental pollution concerns.
The present invention will now be described more specifically with reference to the following example. It is to be noted that the following descriptions of examples, including the preferred embodiment of this invention, are presented herein for purposes of illustration and description, and are not intended to be exhaustive or to limit the invention to the precise form disclosed.

Example 1

In this example, the high-melting point fibers were high-strength polyethylene terephthalate (PET) filament yarns of 2,000d/192f, and the low-melting point fibers were a polypropylene staple fibers with a fiber denier of 2.5 and nominal fiber length of 2 inches. Three bundles of the high-strength PET filament yarns were combined then spun with the polypropylene staple fibers to form a composite yarn. The composite yarn was then woven into a net structure having a grid opening of 20 x 20 mm. The woven net structure was heated at a temperature of 190 °C for 2 min so as to cause the low-melting point staple fibers to melt and bind the high-strength PET filament yarns. After cooling, the net structured solidified to form the geogrid ready for use.

Table 1 shows a comparison of relevant physical properties between a commercial geogrid and the geogrid of the present invention. Both geogrids have same specification, i.e., nominal strength, of 150 kN/m.

	Commercial Geogrid	Example 1
Weaving type	Weaving	Weaving
Polymer type	150 kN/m	150 kN/rn
Specification	PET/PVC	PET/PP
Ultimate Strength	168.9 kN/m	164.0 kN/m
Ultimate Elongation	15.21 %	13.1 %
Strength at 5% Elongation	39.3 kN/m	60.1 kN/m
(% of Ultimate Strength)	23.3 %	36.6 %
Junction Strength	11.7 Kg	15.5 Kg
Basis Weight	796.5 g	502.7 g

The comparative results Table 1 clearly show that the geogrid of the present invention provided superior results, an improvement of about 32.5% over the commercial product of the same specification, with regard to junction strength. But at least equally importantly, the geogrid of the present invention exhibited better than 57 % improvement over the commercial product, in the retention of the ultimate strength at 5% elongation.
The foregoing description of the preferred embodiments of this invention has been presented for purposes of illustration and description. Obvious modifications or variations are possible in light of the above teaching. The embodiments were chosen and described to provide the best illustration of the principles of this invention and its practical application to thereby enable those skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

1. A method for manufacturing geogrids comprising the steps of:

(a) combining at least a high-melting point fiber in the form of a filament yarn with at least a low-melting point fiber in the form of a staple fiber to form a composite yarn, wherein said low-melting point fiber has a melting point that is at least 10 °C lower than the melting point of said high-melting point fiber;

(b) weaving said composite yarn to form a net-structured fabrics;

(c) heating said net-structured fabrics to cause said low-melting point fiber to melt and wrap about said high-melting point fiber; and

(d) cooling said net-structured fabrics to form a geogrid.

2. A method for manufacturing geogrids according to claim 1 wherein the melting point of said low-melting point fiber is at least 20 °C lower than the melting point of said high-melting point filament fiber.

3. A method for manufacturing geogrids according to claim 1 wherein said composite yarn comprises a plurality of said high-melting point filament yarns and a plurality of said low-melting point staple fibers

4. A method for manufacturing geogrids according to claim 1 wherein said high-melting point fiber is selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyamides, glass fibers, aramid fibers, and carbon fibers.

5. A method for manufacturing geogrids according to claim 4 wherein said polyamide is nylon 6 or nylon 66.

6. A method for manufacturing geogrids according to claim 1 wherein said low-melting point fiber is selected from the group consisting of polyethylene, polypropylene, polyester copolymers, and polyamides.

7. A method for manufacturing geogrids according to claim 6 wherein said polyamide is nylon 6 or nylon 66.

8. A method for manufacturing geogrids according to claim 1 wherein said low-melting point fiber is a bi-component fiber.

9. A method for manufacturing geogrids according to claim 8 wherein said bi-component fiber is a sheath-and-core type or side-by-side type fiber.

10. A method for manufacturing geogrids according to claim 1 wherein said composite yarn comprises about 50 to 70 percent by weight of said high-melting point fiber and about 30 to 50 percent by weight of said low-melting point fiber.

11. A method for manufacturing geogrids according to claim 1 wherein said high-melting point fiber has a melting point above 150 °C.

12. A method for manufacturing geogrids according to claim 1 wherein said high-melting point fiber and said low-melting point fiber are combined by co-spinning to form said composite filament yarn.

13. A method for manufacturing geogrids comprising the steps of:

(a) co-spinning at least one first fiber in the form of a filament yarn with at least one second fiber also in the form of a staple fiber to form a composite yam, wherein said first fiber has a melting point above 150 °C and said second fiber has a melting point that is at least 10 °C lower than the melting point of said first fiber;

(b) weaving said composite yam to form a net-structured fabrics;

(c) heating said net-structured fabrics at a temperature which causes said second fiber to melt and wrap about said first fiber; and

(d) cooling said net-structured fabrics to form a geogrid.

14. A method for manufacturing geogrids according to claim 13 wherein the melting point of said second fiber is at least 20 °C lower than the melting point of said first fiber.

15. A method for manufacturing geogrids according to claim 13 wherein said composite yarn comprises a plurality of said first filament yarns and a plurality of said staple fibers.

16. A method for manufacturing geogrids according to claim 13 wherein said composite yarn comprises about 50 to 70 percent by weight of said first fiber and about 30 to 50 percent by weight of said second fiber.

16. A polymeric geogrid comprising a plurality of intersecting longitudinal and transversal composite yarns, each of said composite yarns comprising a plurality of first fibers wrapped by a polymeric binder resin in a spaced-apart manner, said polymeric geogrid being made from a process comprising the steps of:

(a) co-spinning a plurality of said first fibers in the form of filament yarns with a plurality of second fibers in the form of staple fibers which is made from said polymeric binder to form a composite yarn, wherein said first fiber has a melting point that is at least 10 °C greater than the melting point of said second fiber;

(b) weaving said composite yarn to form a net-structured fabrics;

(d) cooling said net-structured fabrics to form a geogrid.

18. A geogrid according to claim 17 wherein said first fiber is selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyamides, glass fibers, aramid fibers, and carbon fibers.

19. A geogrid according to claim 17 wherein said first fiber wherein said second fiber is selected from the group consisting of polyethylene, polypropylene, polyester copolymers, and polyamides.