Abstract:
A geomembrane comprising a unitary structure fabricated by co-extrusion including a center core, a thermoplastic adhesive layer secured on one side of the center core, and a textured layer secured on the opposite side of the center core. The geomembrane is utilized in the manufacture of a liner for earthen constructions by employing the thermoplastic layer of the geomembrane to secure the geomembrane to a geosynthetic clay liner.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates generally to geomembranes of the type utilized in the fabrication of liners for earthen constructions such as landfills, canals, ponds, etc., and more particularly to an improved geomembrane comprising a unitary structure fabricated by co-extrusion.  
         BACKGROUND AND SUMMARY OF THE INVENTION  
         [0002]    Ground water contamination is a primary environmental concern. One method of controlling ground water contamination comprises the lining of landfills, canals, ponds, and similar earthen constructions with a liner comprising a geosynthetic clay liner and an underlying geomembrane. In this manner seepage from the lined construction into the underlying ground water is prevented.  
           [0003]    More particularly, liners for landfills, canals, ponds, and similar earthen constructions may comprise a layer of bentonite. The upper surface of the bentonite layer is secured by a layer of woven polypropylene. A layer of non-woven polypropylene textile is positioned below the bentonite layer. A geomembrane is secured to the lower surface of the non-woven polypropylene textile which may be provided with a textured lower surface to prevent shifting of the liner relative to the underlying construction.  
           [0004]    Heretofore the fabrication of liners in which a geomembrane is secured beneath a geosynthetic clay liner has been complicated by the necessity of applying a glue layer to the upper surface of the geomembrane in order to secure the geomembrane to the geosynthetic clay liner. The application of the glue layer has required a separate manufacturing step which has typically been carried out at a remote location. The cost of manufacturing the liner is therefore substantially increased.  
           [0005]    The present invention comprises an improved geomembrane and method of manufacture which overcomes the foregoing and other difficulties which have long since characterized the prior art. More particularly, the present invention comprises an improved geomembrane construction which is directly bondable to a geosynthetic clay liner to complete the construction of a liner for landfills, canals, ponds, and similar constructions. In accordance with the preferred embodiment of the invention, the geomembrane comprises a unitary structure including an adhesive layer and a barrier layer which are fabricated by co-extrusion. The geomembrane of the present invention may further include a third co-extruded layer which may be textured.  
           [0006]    By means of the present invention the fabrication of liners for earthen constructions such as landfills, canals, ponds, and the like is greatly simplified. The improved geomembrane of the present invention is directly bondable to a geosynthetic clay liner to complete the construction of the liner, thereby eliminating the necessity of a separate adhesive application step. The use of the invention also results in an improved liner construction wherein the possibility of separation of the geomembrane from the remaining components of the liner is substantially eliminated.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    A more complete understanding of the invention may be gained by reference to the following Detailed Description when presented in conjunction with the accompanying Drawings, wherein:  
         [0008]    [0008]FIG. 1 is a diagrammatic illustration of the installation of a liner in a landfill, canal, pond, or similar earthen construction;  
         [0009]    [0009]FIG. 2 is a sectional view illustrating a liner for landfills, canals, ponds, and similar construction incorporating the geomembrane of the present invention;  
         [0010]    [0010]FIG. 3 is an exploded view of the liner of FIG. 2 further illustrating the invention;  
         [0011]    [0011]FIG. 4 is a sectional view illustrating a first embodiment of the method of the present invention; and  
         [0012]    [0012]FIG. 5 is a sectional view illustrating a second embodiment of the method of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0013]    Referring now to the Drawings, and particularly to FIG. 1 thereof, the use of a liner incorporating the geomembrane of the present invention is diagrammatically illustrated. An excavation  10  is formed in the earth. The excavation  10  may ultimately comprise a landfill, a canal, a pond, or similar earthen construction. A trench  12  is formed along the sides of the excavation  10 , it being understood that the configuration of the trench  12  depends upon the configuration of the excavation  10 . A liner  14  incorporating the geomembrane of the present invention is provided in rolls. The liner  14  is unrolled in overlapping strips utilizing an appropriate vehicle  16 . Each end of each strip comprising the liner  14  extends into the trench  12 . Following installation of the liner  14 , backfill  18  is installed in trench  12  to secure the liner in place.  
         [0014]    Referring to FIG. 2, liner  14  includes a geosynthetic clay liner  20  and a geomembrane  22  comprising the present invention. The geosynthetic clay liner  20  comprises a clay layer  24  which may comprise bentonite. The clay layer  24  is retained by a layer of woven polypropylene fabric  26  extending across the upper surface thereof. A layer of non-woven polypropylene material  28  extends across the lower surface of the clay layer  24 .  
         [0015]    The geomembrane  22  of the liner  14  is further illustrated in FIG. 3. The geomembrane  22  comprises a two layer construction, including a thermoplastic adhesive layer  30  and a barrier layer  32 . The geomembrane  22  may also include a third layer  34 , which may be textured as shown. In accordance with the invention, the geomembrane  22  comprises a unitary structure fabricated by co-extrusion.  
         [0016]    The adhesive layer  30  of the geomembrane  22  may be formed from any of the following materials:  
         [0017]    Ethylene Vinyl Acetate(EVA)  
         [0018]    Ionomer  
         [0019]    Ethylene Methyl Acrylate(EMA)  
         [0020]    Ethylene Acrylic Acid(EAA)  
         [0021]    Ethylene Methyl Acrylic Acid(EMAA)  
         [0022]    Ethylene Ethyl Acrylate(EEA)  
         [0023]    Polyethylene with density below 0.915 gm/cc  
         [0024]    Polyolefins, copolymers and terpolymers of polyolefins with melt points below the melt point of the barrier layer  32 .  
         [0025]    The barrier layer  32  and the third layer  34 , if used, may be formed from any of the following materials:  
         [0026]    High Density Polyethylene  
         [0027]    Linear Low Density Polyethylene  
         [0028]    Low Density Polyethylene  
         [0029]    Ultra Low Density Polyethylene  
         [0030]    Very Low Density Polyethylene  
         [0031]    Polypropylene  
         [0032]    Polypropylene copolymers and terpolymers  
         [0033]    Polyethylene with natural density between 0.880 and 0.950 gm/cc.  
         [0034]    Any of the following techniques may be used to provide a textured surface on the third layer, if desired:  
         [0035]    Use of chemical blowing agents  
         [0036]    Use of compressed gas blowing agents including nitrogen  
         [0037]    Use of post extrusion texturing process such as lamination, spray-on, or embossing.  
         [0038]    [0038]FIG. 4 illustrates a first embodiment of the method of the present invention. A conventional co-extrusion die  36 , of the type used to make cast co-extrusions, receives a molten thermoplastic adhesive which will eventually form the adhesive layer of the geomembrane  22  through an inlet  38 . Molten thermoplastic material which eventually will form the barrier layer  32  of the geomembrane  22 , is received through inlet  40 . If the geomembrane  22  is to include a third layer, molten thermoplastic material which eventually will form the layer  34  of the geomembrane  22 , is received through inlet  42 . The materials received through the inlets of the die  36  are directed through a combining adapter  44  and are co-extruded to form the geomembrane  22  of the present invention.  
         [0039]    [0039]FIG. 5 illustrates a second embodiment of the method of the present invention. A blown film co-extrusion die  46  receives molten thermoplastic adhesive material which eventually will comprise the adhesive layer  30  of the geomembrane  22  through a cylindrical inlet  48 . Molten thermoplastic material, which eventually will form the core  32  of the geomembrane  22 , is received through a cylindrical inlet  50 . If the geomembrane is to include a third layer, molten thermoplastic material, which eventually will form the layer  34  of the geomembrane  22 , is received through inlet  52 . Within the die  46 , the materials received through the inlets are co-extruded to form a blown film comprising the geomembrane  22  of the present invention.  
         [0040]    Referring again to FIG. 2, the geomembrane of the present invention is hot as it leaves the die  36  or the die  46 . Therefore, immediately following the manufacture thereof, the geomembrane  22  may be secured to the outer surface of the non-woven polypropylene textile layer  28  comprising the geosynthetic clay liner  20 . The adhesive layer  30  of the geomembrane  22  adhesively secures the geomembrane  22  to the non-woven polypropylene material layer  28  thereby securely joining the geomembrane  22  of the present invention to the geosynthetic clay liner  20 . The use of the adhesive layer  30  to secure the geomembrane  22  to the geosynthetic clay liner  20  assures complete bonding between the geomembrane  22  and the geosynthetic clay liner  20  thereby preventing separation during use.  
         [0041]    Alternatively, the geomembrane  22  may be cooled following its manufacture. The geomembrane is then formed into rolls for transport to a separate assembly location. The geomembrane is unrolled and the adhesive layer thereof is heated to facilitate bonding of the geomembrane  22  to the geosynthetic clay liner  20 .  
         [0042]    Although preferred embodiments of the invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions of parts and elements without departing from the spirit of the invention.