The New Industry Standard for Polyethelene Geomembrane Seams
by George Yazdani, MSc., P.E.

The Geosynthetic Research Institute (GRI) has developed many standards for Geomembranes, including GRI GM13 and GM17 for HDPE and LLDPE geomembranes. The latest GRI Standard GM19, “Seam Strength and Related Properties of Thermally Bonded Polyolefin Geomembranes”, came out on February 18, 2002. The Standard was developed with active participation of the members of the GRI Polyethylene Focus Group, including five raw material manufacturers and seven geomembrane manufacturers.
GM19 provides minimum properties for hot wedge and fillet extrusion seams for smooth and textured HDPE and LLDPE geomembranes. The Standard refers to ASTM D 6392 test method, “Determining the Integrity of Nonreinforced Geomembrane Seams Produced Using Thermo-Fusion Methods”, for the details of the test method and specific testing procedures.

Seam Properties
The following are from Tables 1(a) and Table 2(a) of the GRI Test Method GM19. The test method is based on the ASTM D 6392.

Assessment of Seam Test Results
Four out of five 1.0 inch wide strip specimens in shear and peel should meet or exceed the values given in the Tables. The fifth must meet or exceed 80% of the given value. Additionally, the shear elongation should exceed 50%. The shear percent elongation is based on the assumed gage length of the unseamed sheet material on either side of the welded area. It generally will be 1.0 inch from the edge of the seam to the grip face. The peel separation should not exceed 25%. The peel separation is based on the proportion of the area of separated bond to the area of the original bonding.
Regarding the locus-of-break patterns of the hot wedge and fillet extrusion seaming methods in shear and peel, the following are unacceptable break codes per their description in FIG. 3 and FIG. 4 of ASTM D 6392;

• Hot Wedge: AD and AD-Brk (unless separation is less than 25%)

• Fillet Extrusion: AD1, AD2 and AD-WLD (unless strength is achieved)

There is a difference in the observation of the peel test between the GM19 Standard and ASTM D 6392 test method. GM19 calls for the peel separation not to exceed 25% of the proportion of the area of separated bond to the area of the original bonding. Based on the ASTM D 6392, the estimation for seam separation should be made to the nearest 25% of the proportion of the linear length of separated bond to the length of original bonding. The members of the Polyethylene Focus Group at GRI agree with GM19 in that a geomembrane seam acts as a unit and should be judged based on the quality of the entire bonded area of the seam specimen rather than its weakest point.

GRI Test Method GM19 Highlights
• Seam properties are the same for hot wedge and fillet extrusion welds.
• Seam properties are the same for smooth and textured geomembranes.
• Shear elongation measurements are for laboratory testing and should be omitted for field testing.
• Separation In the Plane of the sheet (SIP), as shown in FIG. 3 and FIG. 4 of the ASTM D 6392, is an acceptable break code.

The Poly-Flex published seam values meet or exceed the new GRI Test Method GM19. For more information on the new GRI GM19 Standard please contact George Yazdani at (972) 337-7314.

1. GRI Test Method GM19, February 18, 2002, GRI Test Methods and Standards, Geosynthetic Research Institute, Folsom, PA
2. ASTM D 6392 Standard Test Method, July 1999, Annual Book of ASTM Standards. Vol. 04.09, American Society for Testing and Materials, W. Conshohoken, PA