3.4 Field Seaming

Approved seaming processes are fusion and extrusion welding. On side slopes, seams shall be oriented in the general direction of maximum slope, i.e., oriented down, not across the slope. In corners and odd-shaped geometric locations, the number of field seams shall be minimized.

No base T-seam shall be closer than 5 feet from the toe of the slope. Seams shall be aligned with the least possible number of wrinkles and "fishmouths". If a fishmouth or wrinkle is found, it shall be relieved and cap-stripped.

3.4.1 Seam Overlap

Geomembrane panels must have a finished minimum overlap of 4 inches for fusion welding and 6 inches for extrusion welding.

Cleaning solvents may not be used unless the product is approved by the liner manufacturer.

3.4.2 Seaming Equipment and Accessories

Approved equipment for field seaming are fusion welders and extrusion fillet welders.

1. Fusion Welder, 110 Volt (220 Volt).
2. Extrusion Welder, 220 Volt.
3. High-speed, 10,000 rpm, 4¹/2 inch side grinder with 80-grit discs.
4. 6.5 KW Generator, single-phase with 110/200 Volt Outputs.
5. Power Cord, minimum S.O. type, 12 gauge O.S.H.A. approved electrical cord with O.S.H.A. approved twist-type plugs and connections.
6. Vacuum Box Test Equipment for non-destructive seam testing.
7. Air pressure test equipment for non-destructive seam testing.
8. Field Tensiometer, capable of performing quantitative shear and peel tests.

3.4.3 Test Seams

Field test seams shall be conducted on the liner to verify that seaming conditions are satisfactory. Test seams shall be conducted at the beginning of each seaming period and at least once each 4 hours, for each seaming apparatus and personnel used that day.

All test seams shall be made in contact with the subgrade. Welding rod used for extrusion welding shall have the same properties as the resin used to manufacture the geomembrane. The test seam samples shall be 10 feet long for fusion welding and 3 feet long for extrusion welding with the seam centered lengthwise. Five specimens shall be cut from each end of the test seams by the inspector. The inspector shall use a tensiometer to test 5 specimens for shear and 5 specimens for peel. Each specimen shall be one inch wide with a grip separation of 4 inches plus the width of the seam. The seam shall be centered between the clamps. The rate of grip separation shall be 2 inches per minute. Test results for seam strength properties shall be the average of five specimens. Four out of five specimens shall pass seam acceptance criteria. Shear and peel tests shall return in Film Tearing Bond (FTB), which is a failure in ductile mode of one of the bonded sheets by tearing prior to complete separation in the bonded area. If a test seam fails to meet field seam specifications, the seaming apparatus and/or seamer shall not be used for seaming until the deficiencies are corrected and a successful test seam is achieved.

3.4.4 Non-Destructive Seam Testing

The installer should non-destructively test all field seams over their full length.

1. Vacuum Box Testing

   Equipment for testing extrusion seams shall be comprised of the following:

   1. A vacuum box assembly consisting of a rigid housing, a transparent viewing window, a soft rubber gasket attached to the bottom, port hole or valve assembly, and a vacuum gauge.

   2. Soapy solution in a plastic bucket with a mop.

   The following procedures shall be followed by the installer:
   1. Excess sheet overlap shall be trimmed away.

   2. Wet a strip of geomembrane approximately 12 inches by the length of box with the soapy solution.

   3. Place the box over the wetted area and compress.

   4. Create a vacuum of 3 - 5 psi.

   5. Ensure that a leak tight seal is created.

   6. For a period of approximately 15 seconds, examine the geomembrane through the viewing window for the presence of animated soap bubbles.

   7. If no animated bubbles appear after 15 seconds, close the vacuum valve and open the bleed valve, move the box over the next adjoining area with a minimum 3 inches overlap and repeat the process.

   8. All areas where animated soap bubbles appear shall be marked, repaired and then retested.

   The following procedures shall apply to locations where seams cannot be non-destructively tested.
   1. If the seam is accessible to testing equipment prior to final installation, the seam shall be non-destructively tested prior to final installation.

   2. If the seam cannot be tested prior to final installation, the seams shall be spark tested according to the spark tester manufacturer's procedures.

2. Air Pressure Testing (For Double Fusion Seams Only)

   Equipment for testing double vision seams shall be comprised of the following:
   

   1. An air pump equipped with pressure gauge capable of generating and sustaining a pressure between 25 and 30 psi.

   2. A pressure gauge equipped with a sharp hollow needle.

   The following procedures shall be followed by the installer:
   1. Seal one end of the seam to be tested.

   2. Insert needle or other approved pressure feed device through the sealed end of the channel created by the double wedge fusion weld.

   3. Energize the air pump to verify the unobstructed passage of air through the channel.

   4. Seal the other end of the channel.

   5. Energize the air pump to a pressure between 25 and 30 psi, close valve, allow 2 minutes for the injected air to come to equilibrium in the channel, and sustain pressure for approximately 5 minutes.

   6. If loss of pressure exceeds 4 psi, or pressure does not stabilize, locate faulty area, repair and retest.

   7. If pressure does not drop below the acceptable value after five minutes, cut the air channel open at the opposite end from the pressure gauge. The air channel should deflate immediately indicating that the entire length of the seam has been tested.

3.4.5 Destructive Seam Testing

Destructive seam testing should be minimized to preserve the integrity of the liner. The installer shall provide the inspector with one destructive test sample per project specifications (usually once per 500 feet of seam length) from a location specified by the inspector.

1. Sampling Procedure

   In order to obtain test results prior to completion of liner installation, samples shall be cut and marked by the installer as the seaming progresses. The installer shall also record the date, location, and pass or fail description. all holes in the geomembrane resulting from obtaining the seam samples shall be immediately patched and vacuum tested.

2. Size and Disposition of Samples

   The samples shall be 12 inches wide by 36 inches long with the seam centered lenghtwise. The sample shall be cut into three equal-length pieces, one to be given to the inspector, one to be given to the owner and one to the installer.

3. Field Laboratory Testing

   The inspector shall test ten 1 inch wide specimens from his sample, five specimens for shear strength and five for peel strength. To be acceptable, four out of the five specimens must pass the project seam requirements.

4. Independent Laboratory Testing

   The owner, at his discretion and expense, may send seam samples to a laboratory for testing. The test method and procedures to be used by the independent laboratory shall be the same as used in field testing.

5. Procedures for Destructive Test Failure

   The following procedures shall apply whenever a sample fails the field destructive test:

   1. The installer shall cap strip the seam between the failed location and any passed test locations.

   2. The installer can retrace the welding path to an immediate location (usually 10 feet from the location of the failed test), and take a sample for an additional field test. If this test passes, then the seam shall be cap stripped between that location and the original failed location. If the test fails, then the process is repeated.

   3. Over the length of seam failure, the installer shall either cut out the old seam, reposition the panel and reseam, or add a cap strip.

3.4.6 Defects and Repairs

All seams and non-seam areas of the geomembrane shall be inspected by the inspector for defects, holes, blisters, undispersed raw materials, and any sign of contamination by foreign matter. The surface of the geomembrane shall be clean at the time of inspection.

1. Evaluation

   Each suspect location in seam and non-seam areas shall be non-destructively tested as appropriate in the presence of the inspector. Each location that fails the non-destructive testing shall be marked by the inspector, and repaired accordingly.

2. Repair Procedures
   1. Defective seams shall be cap stripped or replaced.

   2. Small holes shall be repaired by extrusion welding. If the hole is larger than ¹/4 inch, it shall be patched.

   3. Tears shall be repaired by patching. If the tear is on a slope or an area susceptible to stress and has a sharp end it must be rounded prior to patching.

   4. Blisters, large cuts and undispersed raw materials shall be repaired by patches.

   5. Patches shall be done by extrusion welding. The weld area shall be ground no more than 10 minutes prior to welding. No more than 10% of the thickness shall be removed by grinding. Welding shall commence where the grinding started and must overlap the previous seam by at least 2 inches. Reseaming over an existing seam without regrinding shall not be permitted. The welding shall restart by grinding the existing seam and rewelding a new seam.

   Patchess shall be round or oval in shape, made of the same geomembrane, and extend a minimum of 6 inches beyond the edge of defects.

3. Verification of Repairs

   Each repair shall be non-destructively tested. Repairs that pass the non-destructive test shall be taken as an indication of an adequate repair. Failed tests indicate that the repair shall be repeated and retested until passing test results are achieved.

   The inspector shall keep daily documentation of all non-destructive and destructive testing. This documentation shall identify all seams that initially failed the test and include evidence that these seams were repaired and sucessfully retested.

The anchor trench shall be backfilled by the earthwork contractor. Trench backfill material shall be placed and compacted in accordance with the project specifications.

Care shall be taken when backfilling the trenches to prevent any damage to the geomembrane. If damage occurs, it shall be repaired prior to backfilling.

3.6 Geomembrane Acceptance

The installer shall retain all ownership and responsibility for the geomembrane until acceptance by the owner.

Final acceptance is when all of the following conditions are met:

1. Installation is finished.

2. Verification of the adequacy of all filled seams and repairs, including associated testing, is complete.