Abstract:
A geocomposite for use in a landfill, including a geonet and a geotextile bonded to at least one side of the geonet. The geonet includes a first plurality of substantially parallel strands, and a second plurality of substantially parallel strands disposed on top of the first plurality of strands, the second plurality of strands being at an angle relative to the first plurality of strands. The first and second plurality of strands are substantially incompressible and secured to one another at crossover locations, and are substantially round in cross-section.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not applicable. 
     TECHNICAL FIELD 
     The present invention is directed toward geocomposites for use in geotechnical construction sites, and particularly toward geonets usable with geotextiles in forming such geocomposites. 
     BACKGROUND OF THE INVENTION AND TECHNICAL PROBLEMS POSED BY THE PRIOR ART 
     Geotechnical engineering and the usage of geosynthetic materials are very common in today&#39;s civil engineering marketplace. One of the most common geosynthetic materials available today are drainage products. Drainage products are generally comprised of a geonet or a geonet combined with a filtration fabric which may be one of many varieties. These products are used for a broad variety of applications. Common applications include drainage/leachate collection layers in waste storage facilities, leak detection layers in waste storage facilities, the use of a geosynthetic drainage material for gas venting in water and wastewater storage and treatment facilities, the use of geosynthetic drainage layers in roadway, rail and transportation applications and many others. In all of these applications, there are generally two performance factors which determine the suitability of the drainage media. These performance factors are the transmissivity (flow capacity) of the drainage media and the maximum allowable overburden pressure which the drainage media can support and still perform the functions required of it. 
     Waste collection sites are, of course, one well known type of geotechnical construction site, and are unavoidably required in today&#39;s societal structures. Such sites can require large amounts of valuable land, particularly in urban areas where land is most in demand. Also, while desirable uses can be made of such lands (for example, golf courses have been built on such sites), such desirable uses typically have to wait until the land is no longer being used to collect further waste and the often high pile of waste has stabilized. While use and stabilization of such sites can take many years, there is nevertheless a desire to have that accomplished as quickly as possible, not only to increase the safety of those who might have to be at the site but also to allow for the desired use of others (for example, golfers) and to enhance the environment of those who live in the area as soon as is reasonably possible. 
     Toward that end, bioreactor landfills have been used to modify solid waste landfills by re-circulating and injecting leachate/liquid and air to enhance the consolidation of waste and reduce the time required for landfill stabilization. To accomplish this, generally horizontal flow of the leachate/liquid beneath the surface of the landfill is required. In some instances, vertical injection pipes and horizontal pipe fields have often been used to facilitate this leachate/liquid flow. With these structures, a liner is commonly provided at the bottom of the site, which liner may be used to trap leachate which has run through the collected waste above, with pipes in that area used to collect the leachate and draw it out for re-circulation by pumping it out and distributing/dispersing the leachate back into the upper portions of the waste site through, for example, perforated pipes and/or horizontal trenches. 
     Unfortunately, vertical injection pipes and horizontal pipe fields have been costly, time consuming to install and maintain, and not entirely effective for a number of reasons. U.S. Pat. No. 6,802,672 discloses an advantageous system which addresses such problems. 
     Moreover, geocomposites have heretofore been used with many different types of systems where it is desirable to provide for fluid flow below the surface of built up land masses. As shown in  FIGS. 1-3 , such prior art geocomposites  10  have, for example, included a geonet  12  having high density polyethylene (HDPE) longitudinal strands  14  in the form of a grid  16  (see  FIG. 1 ), with geotextiles  18  (such as, e.g., nonwoven needlepunched geotextiles) secured to one or both sides of the geonet (see  FIG. 3 ). The geonet strands  14  have been long and oblong in cross-section, and oriented with the long dimension in a generally vertical orientation (see  FIGS. 2-3 ), whereby the strands  14  provide a height for the geonet  12  which serves to facilitate flow along the plane of the geocomposite. However, while the strands  14  are themselves substantially incompressible HDPE, it has been the experience in the industry that under higher loading (which occurs, e.g., under greater depths of fill and/or pressures above the geocomposite), the rate of fluid flow along the plane of the geocomposite may be substantially reduced to undesirably low levels, which reduced flow can significantly inhibit the desired benefits of, for example, fluid drainage or recirculation. 
     The present invention is directed toward overcoming one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a geonet for use in a landfill is provided, including a first plurality of substantially parallel strands, and a second plurality of substantially parallel strands disposed on top of the first plurality of strands, the second plurality of strands being at an angle relative to the first plurality of strands. The first and second plurality of strands are substantially incompressible and secured to one another at crossover locations, and at least one of the first and second plurality of strands is substantially round in cross-section. 
     In one form of this aspect of the present invention, the strands are high density polyethylene (HDPE). 
     In another form of this aspect of the present invention, both of the first and second plurality of strands are substantially round in cross-section. 
     In still another form of this aspect of the present invention, a geotextile is bonded to at least one side of the of the geonet. 
     In another aspect of the present invention, a geocomposite for use in geotechnical applications is provided, including a geonet and a geotextile bonded to at least one side of the geonet. The geonet includes a first plurality of substantially parallel strands, and a second plurality of substantially parallel strands disposed on top of the first plurality of strands, the second plurality of strands being at an angle relative to the first plurality of strands. The first and second plurality of strands are substantially incompressible and secured to one another at crossover locations, and at least one of the first and second plurality of strands is substantially round in cross-section. 
     In one form of this aspect of the present invention, the strands are high density polyethylene (HDPE). 
     In another form of this aspect of the present invention, both of the first and second plurality of strands are substantially round in cross-section. 
     In still another form of this aspect of the present invention, a geotextile is non-woven textile heat laminated to the geonet strands. In a further form, the strands are high density polyethylene (HDPE). In another further form, the geotextile is non-woven needlepunched textile heat laminated to strands on both sides of the geonet and, in a still further form, the strands are high density polyethylene (HDPE). 
     In yet another form of this aspect of the present invention, the geotextile is spun-bonded or heat laminated textile heat laminated to strands on both sides of the geonet and, in a further form, the strands are high density polyethylene (HDPE). 
     In still another aspect of the present invention, a landfill comprising alternating layers of fill and geocomposites is provided, where the geocomposites are each disposed beneath a layer of fill to facilitate draining of liquid from the landfill. The geocomposites include a geonet and a geotextile bonded to at least one side of the geonet. The geonet includes a first plurality of substantially parallel strands, and a second plurality of substantially parallel strands disposed on top of the first plurality of strands, the second plurality of strands being at an angle relative to the first plurality of strands. The first and second plurality of strands are secured to one another at crossover locations, and at least one of the first and second plurality of strands is substantially round in cross-section. 
     In one form of this aspect of the present invention, the strands are high density polyethylene (HDPE). 
     In another form of this aspect of the present invention, both of the first and second plurality of strands are substantially round in cross-section. 
     In still another form of this aspect of the present invention, a geotextile is non-woven needlepunched textile heat laminated to strands on both sides of the geonet and, in a further form, the strands are high density polyethylene (HDPE). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a prior art geonet; 
         FIG. 2  is a cross-sectional view of the  FIG. 1  prior art geonet, taken along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is an enlarged cross-section view of a geocomposite including the geonet of  FIGS. 1-2 ; 
         FIG. 4  is a perspective view of one embodiment of a geonet according to the present invention; 
         FIG. 5  is a cross-sectional view of the geonet of the present invention, taken along line  5 - 5  of  FIG. 4 ; 
         FIG. 6  is an enlarged cross-section view of a geocomposite according to the present invention including the geonet of  FIGS. 4-5 ; and 
         FIG. 7  is a cross-section of a landfill in which the geocomposite of the present invention is used. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A geonet  30  according to the present invention is shown in  FIGS. 4-5 . The geonet  30  consists of substantially incompressible longitudinal strands  34  (e.g., formed of high density polyethylene [HDPE]), including a lower set of a plurality of substantially parallel strands  34   a  and an upper set of a plurality of substantially parallel strands  34   b , with the two sets of strands  34   a ,  34   b  being at an angle relative to one another whereby a crisscrossed grid  36  is formed (see  FIG. 4 ). It should be understood that as used herein, “substantially incompressible” is meant to refer to materials such as HDPE which, though susceptible to bending, breaking, fracture and/or creep, does not appreciably compress in the vertical direction when vertical forces are applied. 
     At their overlapping intersection, the strands  34   a ,  34   b  are suitably secured together whereby a relatively rigid geonet  30  is provided in the plane of the geonet  30  (i.e., the geonet  30  is substantially rigid against compressive forces directed along the plane of the geonet  30 , while still providing some flexibility for bending when laid on uneven ground). 
     In accordance with the present invention, the strands  34   a ,  34   b  of the geonet  30  are substantially round in cross-section with connected areas  38  at the overlapping intersections. Advantageously, the diameter of the strands  34   a ,  34   b  may, for a given design use, be substantially the same as the longer dimension of the prior art flat strands as described with respect to  FIGS. 1-3 . 
     As a result of this configuration, it has been found that at higher pressures such as 15,000 pounds per square foot or more, such as may be encountered in site designs involving several hundred thousand to over a million square feet and projected overburden heights of zero to over two hundred feet, significantly greater fluid flow along the generally horizontal geonet  30  may be provided than with comparable prior art geonets. It is believed that with geonets  30  configured as with the present invention, the round strands  34   a ,  34   b  will provide a reliable height of the geonet  30  and thereby serve to facilitate flow along the plane of the geocomposite. By contrast, with the prior art strands  14  shown in  FIGS. 1-3 , even though they are themselves substantially incompressible HDPE, creep of the strands  14  of such geonets will, eventually, result in the strands  14  folding over in a relatively short amount of time once begun. For example, testing has shown that under loading of 7500 to 15,000 psi, the strands  14  of such geonets  12  may be caused to fold over flat in 10,000 hours or less. Such rollover will, of course, cause the two groups of strands  14  to present a height which is substantially less than the combined long dimension of two sets of strands and thereby significantly and undesirably reducing the transmissivity (flow capacity) provided by such prior art geocomposite  10 . 
     Testing has also shown that at higher loadings such as 30,000 psi, transmissivity for geonets according to the present invention is higher than it is for prior art geonets of  FIGS. 1-3  having comparable material usages (i.e., transmissivity per mass per unit area is greater with the geonets of the present invention). 
     A geocomposite  50  incorporating the geonet  30  of the present invention is shown in  FIG. 6 . In the illustrated geocomposite  50 , geotextiles  54 ,  56  (such as, e.g., nonwoven needlepunched geotextiles, spun-bonded or heat laminated textiles, as are known in the art) are suitably secured to both sides of the geonet  30 , such as by heat laminating. 
       FIG. 7  illustrates, in cross-section, a landfill  70  in which geocomposites  50  according to the present invention may be advantageously used. As the landfill is made, a first layer of geocomposites  50   a  is laid down on the surface of the area on which the landfill  70  is being formed. Of course, the area being covered may be extremely large, and therefore more than one section of geocomposite  50   a  will typically be required to cover the entire area at each layer. Fill  74   a  will then be placed on top of the geocomposite  50   a  to a desired depth such as is known in the art, and then a second layer of geocomposites  50   b  is then laid down on that area. Further layers of fill  70   b - 70   e  and geocomposites  50   c - 50   e  are similarly added according to the design of the landfill  70 . As is known to those skilled in the art, geocomposites  50   a - 50   e  such as illustrated may be used to facilitate fluid flow through the landfill  70 . Moreover, other structures, such as pumps and vertical and horizontal pipes, may also be used in conjunction with such geocomposites  50   a - 50   e  to intentionally circulate leachate through the landfill and thereby facilitate stabilization of the landfill  70  so that it may thereafter be returned to other productive uses more quickly. Further, geocomposites  50  only about 0.200 inch thick may be used, for example, in place of twelve inch layers of sand and aggregate, thereby requiring much less height and concomitantly having less environmental impact and/or allowing for more fill (e.g., waste in a landfill). 
     Geocomposites  50  such as described herein may be advantageously used particularly in large landfills where they are subjected to high pressures over long periods of time. However, it should further be understood that geonets  30  and geocomposites  50  according to the present invention, though advantageously usable in geotechnical construction sites such as landfills  70  as described above, may also be advantageously usable in a wide variety of geotechnical construction sites, including not only common horizontal orientations facilitating drainage over a site but also vertical orientations such as in mechanically stabilized earth walls. 
     Still other aspects, objects, and advantages of the present invention can be obtained from a study of the specification, the drawings, and the appended claims. It should be understood, however, that the present invention could be used in alternate forms where less than all of the objects and advantages of the present invention and preferred embodiment as described above would be obtained.