Method and apparatus for forming leak detectable geomembrane liners

Abstract

A method for forming a geomembrane liner testable for leaks by securing adjacent panels together with the conductivity of the lower surface of an overlying panel broken along a line adjacent the panel overlapping edge, and the overlapping edges sealed along the line. A heat welder has slots for the overlapping panel edges, with a heated wedge between the slots and having a projection to break the conductivity of the overlying panel bottom surface as it passes the wedge. The slots merge to press the liner edges together to heat weld them along the line of broken conductivity as the welder is moved along the panel edges.

Claims

1. A heating unit for use with a heat welder for securing overlapping edges of adjacent geomembrane liner panels together, said welder including upper and lower slots guiding the overlapping edges of adjacent liner panels toward a merged slot in which said adjacent panels are heat welded, said heating unit comprising: a wedge between said upper and lower slots whereby said wedge defines a portion of an upper wall of the lower slot and a portion of the lower wall of the upper slot, and said defined upper and lower walls taper together at the merged slot; and at least one projection extending upwardly from the wedge defined lower wall of the upper slot sufficiently to melt through and interrupt a bottom portion of a liner panel passing over the projection while still maintaining the overall structural integrity of the panel, wherein the wedge defined lower wall has a surface against which the liner panels can be directly guided up to and past the at least one projection and the at least one projection extends upwardly from the wedge defined lower wall surface, wherein the at least one projection is in the form of a pointed fin, said heating unit further comprising a heating element for heating the wedge defined lower wall and the at least one projection.

2. The heating unit of claim 1, wherein said fin has a base insert secured in said wedge defined lower wall.

3. The heating unit of claim 1, further comprising a second projection extending from said wedge defined lower wall, wherein said at least one projection and said second projection are adapted to melt through spaced parallel lines in said selected face of the first geomembrane liner panel sliding over said surface of the wedge defined lower wall while still maintaining the overall structural integrity of the first geomembrane panel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a partial perspective view of a heating element according to one aspect of the present invention;

(2) FIG. 2 is side view of the heating element of FIG. 1;

(3) FIG. 3 is a cross-sectional view showing a seam between adjacent panels of a prior art containment system liner;

(4) FIG. 4 is a side diagram view of a heat welder according to the present invention, having the heating element of FIG. 1;

(5) FIG. 5 is a top view of the heat welder of FIG. 4 shown welding adjacent geomembrane panels;

(6) FIG. 6 is a cross-sectional view showing a seam between adjacent panels of a containment system liner formed according to the present invention;

(7) FIG. 7 is a perspective view of the heating element of FIG. 1;

(8) FIG. 8 is a perspective view of the heat welder of FIG. 4 with the housing broken away for clarity;

(9) FIG. 9 is a perspective view like FIG. 8 but showing a bottom liner panel being fed into the heat welder;

(10) FIG. 10 is a perspective view like FIG. 8 but showing a both the top and bottom liner panels being fed into the heat welder;

(11) FIG. 11 is a perspective view like FIG. 8 but both liner panels continuing to be fed into the heat welder with a the panels passing out the rear of the welder having two seams formed therein according to the present invention;

(12) FIG. 12 is a cross-sectional view showing a seam between adjacent panels of a containment system liner formed according to another aspect of the present invention; and

(13) FIGS. 13 and 14 are partial and full perspective views, respectively, of a heat welder which may be used in accordance with the present invention, with the heat welder being shown in an open configuration with the contour rollers illustrated in phantom in their operative position when the welder is closed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(14) A heat welding apparatus 10 is disclosed in the Figures which may be used in accordance with the present invention to heat weld seams 14 between geomembrane panels 16, 18 (typically, rolls of plastic sheet) used to form a liner 20 for, for example, large containment areas, referred to herein generally as containment systems.

(15) The panels 16, 18 are geomembranes formed of a suitable leak proof non-conductive material having a suitable integral conductive lower surface 25. The lower conductive surfaces of the individual panels 16, 18 may also be interconnected with a series of conductive geomembranes, wires, or other conductive media in a grid pattern, or other materials suitable for connecting individual panels. Moreover, in accordance with the present invention, the formed seams 14 between panels 16, 18 maybe be suitably tested for leaks even after covered with, for example, water and/or soil, allowing performance of a reliable leak location survey

(16) In particular, in accordance with one aspect of the present invention, seams 14 may be easily formed so as to avoid the anomalies found in testing liner seams heretofore. Specifically, as illustrated in FIG. 3, the geomembrane panels 16, 18 have heretofore been connected in prior art liners 20 by overlapping two edges of the panels 16, 18 and then heat welding the overlapping edges together along a seam 14. Even where two such seams 14 are formed as illustrated to help to guard against leaks between the overlapping edge, the conductive lower surface 25 of the seam flap 26 of the top panel 16 will carry current from above the liner 20 through the seams 14 to the bottom of the liner 20 (i.e., at the right side of FIG. 3) where it is in contact with the underlying ground 27. Such conductivity through the seams 14 provides a false identification of a leak in the liner 20 along the seam 14. Moreover, ignoring such current flow as being anomalous (or as indicating a leak through the seam(s) 14) could cause actual leaks through the bottom panel 18 near the flap 26 of the overlying edge of the top panel 16 to be overlooked.

(17) In accordance with the present invention, the seam(s) 14 between adjacent panels may be advantageously heat welded continuously along the length of the overlapping edges of adjacent panels 16, 18 wherein the conductive layer 25 on the bottom of the top panel 16 is interrupted along the parallel lines of the seam(s) 14 during the heat welding process (see FIG. 6). As a result, the seam(s) 14 between adjacent panels 16, 18 will not allow electric current to flow between the top and bottom of the system through the liner seam(s), and thus reliable leak test readings may be obtained even at the seam(s) 14.

(18) The heat welding apparatus 10 and formation of the e seams 14 will now be described.

(19) Specifically, a heat welding apparatus 10 which may be advantageously used in connection with the present invention includes a body 40 having front and rear ends 42, 44. As best seen in FIG. 4, the body 40 defines top and bottom slots 50, 52 extending between the front and rear ends 42, 44, each slot 50, 52 being generally horizontally oriented and arranged to accept the overlapping edges of adjacent panels 16, 18.

(20) As best understood from FIGS. 4, 5 and 14, the slots 50, 52 of the apparatus (heat welder) 10 are also open on opposite lateral sides of the body 40, so that the welder 10 may be oriented so that it too overlaps with the overlapping edges of the panels 16, 18. The apparatus is suitably supported by front and rear wheels 60, 62 so that it may move relative to the panels 16, 18 and may be suitably driven by nip rollers 64 (as indicated by the arrows 65) to pull the heat welder 10 along the panels 16, 18 in the direction of arrow 66.

(21) It should be understood that while the apparatus slots 50, 52 may be described as extending horizontally, such horizontal orientation refers to the slots 50, 52 extending generally from the front to rear ends 42, 44, with the slots 50, 52 providing a non-planar path which merges together at the rear end 44 of the apparatus 10.

(22) Moreover, it should be understood that while the slots 50, 52 may be described as having top and bottom walls for simplicity of description, such description encompasses guiding members 70 such as contour rollers and/or partial walls. As such, slots as described generally herein would encompass any structure in which the edges of the panels 16, 18 may be moved through the apparatus while maintaining their generally horizontal orientation without buckling or folding.

(23) The welder 10 includes a heating unit 80 between the slots 50, 52 and forward of the merger of the slots 50, 52 at the apparatus rear end 44. Advantageously, the heating unit 80 defines a portion of a bottom wall of the top slot 50 and a portion of the top wall of the bottom slot 52 and is wedge shaped so as to be tapered together at its rear end. The heating unit 80 is suitably heated so that the panels 16, 18 which pass over the heating unit 80 have their faces heated sufficiently so that when the panels 16, 18 are pressed together in the merged path at the apparatus rear end 44, they are heat welded.

(24) As illustrated, the heating unit 80 includes two laterally spaced heating sections 82, 84, for forming a seal having two parallel seams 14, though it should be understood that it would be within the scope of the present invention to provide a single heat welded seam, or more than two seams if desired.

(25) Moreover, in accordance with the present invention, at least one heating section 82, 84 of the heating unit 80 also includes at least one projection or fin 90 extending partially into the top slot 50 from below.

(26) The fin 90 may advantageously be of any shape suitable to melt through the conductive thin layer on the bottom surface 25 of overlapping edge of the top panel 16 as it passes through the slot 50 and past the projection 90. Moreover, while the fin 90 may advantageously be shaped as illustrated, with a pointed leading (forward) edge, the shape and size could vary while still providing at least some of the advantages of the present invention.

(27) Further, the fin 90 may be an integral part of the heating unit 80, or it may advantageously be provided on an insert 92 in a recessed pocket in the heating unit 80 and removably secured therein by, for example, a countersunk screw 94. Still further, for heating units 80 such as illustrated which have more than one heating section 82, 84, it should be appreciated that a projection 90 may be provided on both sections 82, 84 to provide redundancy, although at least some of the advantages of the present invention could be provided with a projection 90 provided on only one of the sections 82, 84.

(28) It should thus be appreciated that as the two heated panels 16, 18 are pressed together behind the heating unit 80 by the nip rollers 64, each of which have two sections aligned with the two fins 90, respectively for forming the heat welded seams 14 along the length of the panels 16, 18. The welder 10 will thus form a pair of parallel seals 14 between the overlapping adjacent panels 16, 18 wherein, as shown in FIG. 6, there is no conductive layer passing through either of the seams 14that is, there will be no current flow through across the seams 14 such as has heretofore provided anomalous and erroneous readings when leak testing. (It should be appreciated also that it would be within the scope of the present invention to form only one such seam 14).

(29) Yet another embodiment of the present invention allows for reliable leak testing of liners formed of a plurality of panels even when used in applications where the liner may not be not maintained in good electrical contact with the earth (due to, e.g., use of double liners, irregularities in the subgrade, and/or wrinkles in the liner) and/or the earth is dry or not sufficiently conductive.

(30) Specifically, as illustrated in FIG. 12, in accordance with this aspect of the invention, a conductive member 100 may be provided beneath adjacent geomembrane liner panels 116, 118 having conductive bottom surfaces 125. As illustrated in FIG. 12, the conductive member 100 is an inverted section of a geomembrane liner panel with a conductive surface on one sidelaid upside down with the conductive surface 130 on top so that it contacts the conductive bottom surfaces 125 of both of the liner panels 116, 118.

(31) While the conductive member 100 may extend continuously underneath the adjacent liner panels 116, 118, spanning across the two so as to place them in electrical contact with each other, it should be appreciated that the member 100 may also consist of spaced short sections or strips of conductive geomembranes conductively connecting the adjacent panels 116, 118 at spaced locations along the seam(s). In fact, it should be appreciated that virtually any conductive member 100 could be used, including a grid of spaced wires or other conductive media laid beneath the liner, so long as it allows for the individual panels to effectively provide a single conductive bottom surface across the plurality of panels defining the liner 120.

(32) It should be appreciated that while FIG. 12 illustrates this aspect of the invention with a seam incorporating the first aspect of the invention (i.e., with the conductive bottom surface 25 of the top liner panel 16 broken), the advantages of this second aspect of the invention (i.e., a conductive interconnection of the bottom surfaces of adjacent liner panels) could be provided with even prior art seams such as illustrated in FIG. 3. However, the full advantages of both aspects of the invention may be provided by the configuration illustrated in FIG. 12.

(33) As previously noted, leak detection sensitivity depends on the conductivity of the materials above and below the geomembrane. As also previously noted, standard leak detection tests may use either water or moisture in the soil to transmit voltage above the geomembrane, and standard testing may utilize water or moisture in the soil below the liner for a grounding source. If there is a hole in the geomembrane then the voltage introduced in the above material will flow through the hole and to the grounding source underneath the geomembrane creating a current for leak detections. However, as also previously noted, where the material underneath the geomembrane does not have enough (or consistent) moisture to provide a suitable grounding source, such leak location testing could not heretofore be suitably performed.

(34) With a liner 120 formed according to this aspect of the invention, leak surveys can be accomplish with direct connection to a minimum number of panels (i.e., any one of interconnected panels). The bottom conductive surfaces 125 of the electrically interconnected geomembrane panels (e.g., 116, 118) provide a single grounding source underneath the liner 120 to allow the leak location survey to be performed over entire geomembrane surface. Since the conductive layer (bottom surfaces 125 and conductive member 100) is always in intimate contact with the geomembrane panels 116, 118, and the conductivity is consistent regardless of the conductivity of the underlying layers, leak surveys can be more effectively performed when the conductive layer is utilized.

(35) It should also be appreciated that leak detection of liners 20 formed of a plurality of panels 16, 18 according to the present invention may be performed using a variety of leak testing methods, including spark testing according to ASTM 7240. Moreover, leak detection of the seams of liners 20 formed according to the present invention could also be accomplished by spark testing according to ASTM 6365, with conductive material inserted into the seal (e.g., between the seams 14) and spark testing performed in the area of the seams 14.

(36) It should thus be appreciated that the present invention as disclosed herein allows for containment system liners to be more easily, economically and reliably inspected using an electrical inspection apparatus to detect leaks. Such inspections can be made without the need for maintaining good electrical contact with conductive natural surroundings outside the liner. Furthermore, other objects, features and advantages of the invention will become apparent from a review of the entire specification including any appended claims and drawings.

(37) It should be appreciated that the invention may include any or all of the above-described features, include only one of the above features, more than one of the above features, and any combination of the above features. Moreover, it should be appreciated that such features may be achieved by use of fewer than all of the above-described structural elements, including combinations less than all of the above-described structural elements.