GRID COMPOSITE FOR BACKFILL BARRIERS AND WASTE APPLICATIONS

Abstract: A grid composite (108, 130) includes a regular polymer geogrid structure (40) formed by biaxially drawing a continuous sheet of select polypropylene material (28) which is heat bonded to a polyester fabric (46). The polymer grid composite (108, 130) is ideal for waste containment structures, backfill barriers, and silt barriers in construction and mining applications. In waste containment and backfill barriers, the grid composite (108, 130) is used to form a containment structure. Its principle function is to contain waste material usually consisting of a liquid with some percentage of solids.

Description: GRID COMPOSITE FOR BACKFILL BARRIERS AND WASTE APPLICATIONS Field of the Invention This invention relates to a high strength, lightweight polymer grid laminated with a material consisting of a non-woven polyester. It is utilized in waste containment structures, backfill barriers, and silt barriers in construction and mining applications. Summary of the Invention By the present invention, a polymer grid • is connected to a grid composite consisting of a polymer grid and a geotextile to provide a longwall screening package for use during longwall shield recovery. The grid composite is formed by use of a polymer grid which is typically heat bonded to an 8.0 oz./yd. 2 , 100% continuous filament polyester, non-woven needlepunched 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. The grid composite includes a regular polymer geogrid structure formed by biaxially drawing a continuous sheet of select polypropylene material which is heat bonded to a polyester fabric. The polymer geogrid of the grid composite shall typically conform to the following property requirements: PROPERTY TEST METHOD VALUE Material ASTM D 4101 97% (min) o copolymer Group 2/Class polypropylene 1/G-rade i o colorant and ASTM 4218 2 . 0% (min) UV inhibitor Interlock The geotextile of the grid composite typically conforms to the following property requirements: o Grab ASTM D1682 285/250 lbs tensile strength o EOS ASTM D422 70 US Std Sv Sz o Weight ASTM D1910 8.0 oz/sy The grid composite shall typically conform to the following property requirements: o roll length 200 ft o roll width 10 & 12 ft o roll weight 210 & 260 lb 1 MD (machine direction) dimension is along roll length. CMD (cross machine direction) dimension is across roll width. 2 Maximum inside dimension in each principal direction measured by calipers. Percent open area measured without magnification by Corps of Engineers method as specific in CW 02215 Civil Works Construction Guide, November 1977. 4 ASTM D 1388-64 modified to account for wide specimen testing as described in Tensar test method TTM-5.0 "Stiffness of Geosynthetics" . 5 Secant modulus at 2% elongation measured by Geosynthetic Research Institute test method GG1-87 "Geogrid Tensile Strength" . No offset allowances are made in calculating secant modules. 6 Geogrid junction strength and junction efficiency measured by Geosynthetic Research Institute test method GG2-87 "Geogrid Junction Strength". The polymer grid composite of the present invention is also ideal for use in a wide range of applications in the mining, industrial and construction markets. An important application of the polymer grid composite is in waste and containment applications. The polymer grid composite may be used in the mining industry, for use as a containment structure to contain and de-water waste by-products of the various types of processes utilized by the mining industry. By the present invention, a grid composite consisting of a polymer grid and a geotextile is used to provide a containment structure in waste related applications. The grid composite is formed by use of a polymer grid which is typically heat bonded to a 100% continuous filament polyester, non-woven needle-punched engineering fabric. The fabric may consist of various weights and types of geotextile or engineering fabric. Its primary purpose is to act as a filter medium which will allow water to pass through while containing solids within the containment structure. The fabric is bonded to the polymer grid using an open flame heat source of a heated roll as a heat source. The polymer grid composite is ideal for waste containment structures, backfill barriers, and silt barriers in construction and mining applications. In waste containment and backfill barriers, the grid composite is used to form a containment structure. It principle function is to contain waste material usually consisting of a liquid with some percentage of solids. The polymer grid is utilized to provide the strength required for the structure while the geo-fabric "filters" the liquids involved. Typically, the containment structure is constructed utilizing the grid composite as the walls of the structure. The waste or backfill material is then pumped into the structure. Various pH adjusting material may be added or the material may be pre-treated to aid in the flocculation of solids which would aid differential settling of the solids. Due to the physical nature of the grid composite, the solids are contained within the waste containment structure or backfill barrier and the liquid is allowed to decant or pass through the fabric utilized. The liquid can then be disposed of or treated as required. The structure typically utilizes wire ropes to provide additional tensile strength to the structure. These wire ropes are spaced at various intervals throughout the structure as required in the design of the structure. The wire ropes are attached to the grid composite by a wire or nylon tie to reinforce the grid composite walls. The spacing and size of these wire ropes depends on the anticipated hydraulic pressure within the backfill barrier or waste containment structure. The grid composite, when utilized as a silt barrier at construction sites by anchoring to the ground, performs in exactly the same manner. It is utilized in an open trench to prevent silts or other small particles from washing onto streets or in some way contaminating adjacent properties. The grid composite includes a regular polymer geogrid structure formed by biaxially drawing a continuous sheet of select polypropylene material which is heat bonded to a polyester fabric. The polymer geogrid of the grid composite typically conforms to the property requirements outlined above, plus the following property requirements: PROPERTY MATERIAL TEST METHOD VALUE Vertical Water Flow at 2" head ASTM D4491 135 gpm/ft 2 Coefficient of Permeability, k ASTM D4491 .55 cm/sec AOS (Mod. to 10 min.) ASTM D4751 70/ 120 Sieve Size It is an object of the present invention to provide a grid composite including a polymer grid and a geotextile for use as a containment structure to contain a body of water and to filter water passing through the grid composite from the containment structure. It is another object of the present invention to provide a grid composite including a polymer grid and a geotextile for use as a containment structure to contain a body of water and to filter water passing through the polymer grid composite from the containment structure where waste is being contained. It is another object of the present invention to provide a grid composite including a polymer grid and a geotextile for use as a containment structure to contain a body of water and to filter water passing through the polymer. grid composite from the containment structure where the grid composite is used as a silt barrier at a construction site. Brief Description of the Drawings Figure 1 is a schematic flowchart for formation of a polymer geogrid with Figs. 1A-1C illustrating enlarged areas of Figure 1. Figure 2 illustrates a grid composite including a polymer geogrid and a geotextile secured to each other. Figure 3 is a plan view of a backfill barrier used in a room and pillar mining operation. Figure 4 is a detailed front view of a backfill barrier used in a room and pillar mining operation. Figure 5 is a side view of a backfill barrier. Figure 6 is a front view of a grid composite used- at a construction site. Figure 7 is a sectional view taken along line 7-7 of Figure 6. Detailed Description of the Preferred Embodiments Production of the grid composite is accomplished in a four stage manufacturing process as schematically shown in Figure 1: I. SHEET EXTRUSION A multi-component blending system allows for precise control of the raw material additives mix. This on-line blender feeds directly to an extruder, which compresses and melts plastic pellets, and then pumps the molten extrudate. A gear pump and a melt mixer are included in the extrusion system, to provide for a very accurate, consistent flow of a homogeneous melt. At the end of the extruder is a sheet die, which evenly distributes the melt flow across the desired sheet width. UBSTITUTESHEET The sheetline portion of the process accepts the molten sheet, cools it slowly and uniformly, controls the sheet thickness, and provides for a smooth surface finish. The sheet thickness tolerances are very tight in the sheet process, with a +/- 1.0% specification in both the machine and transverse direction. The sheet thickness is monitored at all times with an on-line thickness profiler. The finished sheet 20 is then wound onto large reel carts for transfer to the next process. II. SHEET PUNCHING The second stage of the polymer grid production process involves punching a solid sheet 22 with a pattern of holes, prior to its orientation. Specially designed punch tools and heavy duty presses 24 are required. . Several hole geometries and punch arrangements are possible, depending upon the finished product properties of the grid, in order to meet the requirements of the ground control application. III. ORIENTATION The polymer raw materials used in the manufacture of the grids are selected for their physical properties. However, the very high strength properties of the finished grid are not fully realized until the base polymer's long chain molecules are stretched (oriented) for the mining grid or finished product. This is accomplished in a two stage process. Initially, the punched sheet is heated to a critical point in the softening range of the polypropylene polymer. Once heated, the sheet is stretched in the machine direction, through a series of heated rollers located within a housing 26. During this uniaxial stretching, polymer is drawn from the junctions into the ribs as the orientation effect passes through the junction zones. This guarantees continuity in molecular orientation in the resultant structure. In the second stage, the uniaxially oriented grid 28 enters a heated tenter frame (stenter) 30 where the material is stretched in the transverse direction, at right angles to the initial stretch. This biaxial stretch process imparts a high degree of orientation and stretch throughout all regions of the grid. Exiting the stretching process, the biaxial grid material 32 is quenched (stabilized) , and then slip and wound into a roll 34 to meet customer roll dimension requirements. IV. LAMINATION A polyester geotextile is bonded to the biaxial grid material by two methods. Of the two methods for forming the-grid composite of polymer grid and geotextile, the flame method exposes both mating surfaces of the polyester geotextile and the polymer grid to an open flame. Immediately thereafter, the two materials are joined together in a nip roll and allowed to cool. The other method, the heated roll method, is accomplished by running both the polyester geotextile and the polymer grid around a heated roll with the polyester geotextile against the heated roll surface. Upon leaving the heated roll, the composite is run through a nip roll and allowed to cool. As shown in Figure 2, the polymer geogrid 40, having nodes 42 and ribs 44, is secured across the nodes and ribs 42 to a polyester geotextile 46 by the open flame method. In the heated roll method, only the nodes are bonded to the polyester geotextile. In Figure 3, a mine site 100 is shown as is found in a room and pillar mining operation. Typically, • excavated portions of the mine 102 are formed between separated pillars 104 which remain after excavation is completed. The pillars 104 consist of unexcavated material and support the roof above the excavated areas 102. In Figure 3, a backfill barrier 106 formed of a grid composite 108 is used to separate a waste containment area on one side of the backfill barrier 106 from a filtrate area located on an opposite side of the backfill barrier. As shown in greater detail in Figure 4, lengths of wire rope 110 extend between adjacent support pillars 104. Schematically shown are lengths of grid composite 108 secured between stretched sections of wire rope 110 by ties 112. The grid composite 108 is intended to extend completely between adjacent vertically spaced, horizontally extending sections of wire rope 110. Liquids contained in the waste containment area filter through the grid composite by first passing through a polyester geotextile liner 46 secured to the rear face of the structurally supporting polymer geogrid 40. The grid composite filters liquid contained in the waste containment area, allowing only filtered liquid to pass through the backfill barrier 106 while retaining solids in the waste containment area. In Figure 5, a backfill barrier 114 made of a grid composite, as shown in Figure 2, extends from one end 116 located adjacent to the ground and rises vertically towards an opposite terminal end 118. The backfill barrier 114 includes polymer geogrid 40 with interstitial nodes 42 secured to a polyester geotextile 46 which is located adjacent to a backfill or waste material containment area 120. Decanted water or effluent passes in the direction of arrows 122 into area 124. Horizontally extending wire ropes 126 support back ill barrier 114 for the filtering of backfill or waste material. In a further embodiment of the * present invention, as shown in Figures 6 and 7, a barrier 128 includes a grid composite 130 including a polyester geotextile 46 secured to a polymer geogrid 40. The grid composite is supported on stakes 132 which are anchored in an anchor trench 134. A portion 136 of the grid composite 130 is located at the bottom of the anchor trench 134 and is folded to form a U-shape. The opposite end 138 of the grid composite 130 is secured to the top of the stakes 132. This arrangement may be used for the filtering of silt or other aqueous solutions, such as, for example, at construction sites.

Claims: I CLAIM: 1. A system for separating liquid from a solution of solids and liquid located in a waste containment area, said system comprising: a containment area filled with a solution- of solids and liquid, a grid composite formed of polymer geogrid and a geotextile, a backfill barrier including said grid composite extending substantially vertically from the ground and separating said containment area from a filtrate area, and a plurality of support means spaced along a peripheral edge of said containment area for supporting said backfill barrier substantially vertically between adjacent support means so that said liquid of said solution is allowed to pass through said geotextile of said grid composite to said filtrate area while said solids are retained in said containment area. 2. A system for separating liquid from a solution of solids and liquid as claimed in claim 1, wherein said geotextile is bonded to said polymer geogrid at nodes of said polymer geogrid. 3. A system for separating liquid from a solution of solids and liquid as claimed in claim 1, wherein said support means includes pillars formed in a room and pillar mining operation. 4. A system for separating liquid from a solution of solids and liquid as claimed in claim 1, wherein said support means includes stakes. 5. . A method of separating liquid from a solution of solids and liquid located in a waste containment area, said method comprising: forming a grid composite from a polymer geogrid and a geotextile, arranging a plurality of supports at a periphery of a containment area containing the solution of solids and liquids, securing said grid composite to said plurality of supports so as to form a backfill barrier extending substantially vertically from the ground and between said plurality of supports, said backfill barrier separating said containment area from a filtrate area, and filtering liquid from the solution of liquid and solids in said containment area as said liquid passes to said filtrate area through said grid composite. 6. A method of separating liquid from a solution of solids and liquid as claimed in claim 5, wherein said geotextile is bonded to said polymer grid. 7. A method of separating liquid from a solution of solids and liquid as claimed in claim 6, wherein said geotextile is bonded to said polymer grid at nodes of said polymer grid. 8. A method for separating liquid from a solution of solids and liquid as claimed in claim 5, wherein said plurality of supports includes pillars formed in a room and pillar mining operation. 9. A method for separating liquid from a solution of solids and liquid as claimed in claim 5, wherein said plurality of supports includes stakes. 10. A system for separating liquid from a solution of solids and liquid located in a waste containment area, said system comprising: an underground mine area formed by a room and pillar mining operation so that a roof of said underground mine area is supported by a plurality of pillars having " excavated portions of said underground mine area between said plurality of pillars and having a containment area filled with a solution of solids and liquid in said underground mine area, a grid composite formed of polymer geogrid and a geotextile, ■ and a backfill barrier including said grid composite extending substantially vertically from the ground between adjacent ones of said plurality of pillars and separating said containment area from a filtrate area so that said liquid of said solution is allowed to pass through said geotextile of said grid composite to said filtrate area while said solids are retained in said containment area. 11. A system for separating liquid from a solution of solids and liquid as claimed in claim 10, wherein said geotextile is bonded to said polymer geogrid at nodes of said polymer geogrid. 12. A method of separating liquid from a solution of solids and liquid located in a waste containment area, said method comprising: forming a grid composite from a polymer geogrid and a geotextile, forming an underground mine by a room and pillar mining operation so that • a roof of said underground mine area is supported by a plurality of pillars having excavated portions of said underground mine between said plurality of pillars, positioning said plurality of pillars of said underground mine at a periphery of a waste containment area containing a solution of solids and liquids, securing said grid composite to extend substantially vertically from the ground between said plurality of pillars so as to form a backfill barrier, said backfill barrier separating said containment area from a filtrate area, and filtering liquid from the solution of liquid and solids in said containment area as said liquid passes to said filtrate area through said grid composite. 13. A method of separating liquid from a solution of solids and liquid as claimed in claim 12, wherein said geotextile is bonded to said polymer grid. 14. A method of separating liquid from a solution of solids and liquid as claimed in claim 13, wherein said geotextile is bonded to said polymer grid at nodes of said polymer grid. 15. A system for separating liquid from a solution of solids and liquid in a waste containment area, said system comprising: a containment area filled with a solution of solids and liquid, a grid composite formed of polymer geogrid and a geotextile, and a backfill barrier including said • grid composite extending substantially vertically from the ground and separating said containment area from a filtrate area, a plurality of stakes anchored in a trench and spaced along a peripheral edge of said containment area for supporting said backfill barrier substantially vertically between adjacent stakes so that said liquid of said solution is allowed to pass through said geotextile of said grid composite to said filtrate area while said solids are retained in said containment area. 16. A system for separating liquid from a solution of solids and liquid as claimed in claim 15, wherein said geotextile is bonded to said polymer geogrid at nodes of said polymer geogrid. 17. A system for separating liquid from a solution of solids and liquid as claimed in claim 15, wherein a lowermost end of said backfill barrier is buried in said trench. 18. A method of separating liquid from a solution of solids and liquid located in a waste containment area, said method comprising: forming a grid composite from a polymer geogrid and a geotextile, arranging a plurality of stakes anchored in a trench at a periphery of a containment area containing a solution of solids and liquids, securing said grid composite to extend substantially vertically from the ground between said plurality of stakes so as to form a backfill barrier, said backfill barrier separating said containment area from a filtrate area, and filtering liquid from the solution of liquid and solids in said containment area as said liquid passes to said filtrate area through said grid composite. 19. A method of separating liquid from a solution of solids and liquid as claimed in claim 18, wherein said geotextile is bonded to said polymer grid. 20. A method of separating liquid from a solution of solids and liquid as claimed in claim 19, wherein said geotextile is bonded to said polymer grid at nodes of said polymer grid. 21. A method of separating liquid from a solution of solids and liquid as claimed in claim 18, wherein a lowermost end of said backfill barrier is buried in said trench. 22. A system for separating liquid from a solution of solids and liquid located in a waste containment area, said system comprising: . a containment area filled with a solution of solids and liquid, a grid composite formed of polymer geogrid and a geotextile, a backfill barrier including said grid composite extending substantially vertically from the ground and separating said containment area from a filtrate area, and a plurality of substantially horizontally oriented cables spaced vertically along a peripheral edge of said containment area for supporting said backfill barrier substantially vertically between adjacent ones of said substantially horizontally oriented cables so that said liquid of said solution is allowed to pass through said geotextile of said grid composite to said filtrate area while said solids are retained in said containment area. 23. A system for separating liquid from a solution of solids and liquid as claimed in claim 22, wherein said geotextile is bonded to said polymer geogrid at nodes of said polymer geogrid. 24. A method of separating liquid from a solution of solids and liquid located in a waste containment area, said method comprising: forming a grid composite from a polymer geogrid and a geotextile, arranging a plurality of substantially horizontally oriented cables at a periphery of a containment area containing a solution of solids and liquids, securing said grid composite to said plurality of substantially horizontally oriented cables so as to form a backfill barrier extending substantially vertically from the ground and between said plurality of substantially horizontally oriented cables, said backfill barrier separating said containment area from a filtrate area, and filtering liquid from the solution of liquid and solids in said containment area as said liquid passes to said filtrate area through said grid composite. 25. A method of separating liquid from a solution of solids and liquid as claimed in claim 24, wherein said geotextile is bonded to said polymer grid. 26.- A method of separating liquid from a solution of solids and liquid as claimed in claim 25, wherein said geotextile is bonded to said polymer grid at nodes of said polymer grid.

Inventors: TRAVIS BRIAN E, TRAVIS, BRIAN, E.
Applicants: TENSAR CORP, THE TENSAR CORPORATION
Application year: 1993
Main classification: E21D19
IPC codes: E02D29, E02D31, E21D11