HDPE geomembrane technical specifications

GRI GM13 is the specification published by the Geosynthetic Institute for smooth and textured HDPE geomembranes. It sets minimum property values and the testing methods and frequencies used to demonstrate them, covering thickness, density, tensile properties, tear and puncture resistance, stress crack resistance, carbon black content and dispersion, oxidative induction time and oven ageing. Most project specifications either reference GM13 directly or reproduce its table. The property set below follows that framework.

Oxidative induction time measures how much antioxidant protection is present in the polymer. Polyethylene itself is stable, but heat, ultraviolet light and oxygen slowly degrade it, and the antioxidant package is what holds that off. OIT is therefore a proxy for how long the liner will last. Two tests are used: standard OIT to ASTM D3895 and high pressure OIT to ASTM D5885. The oven ageing and UV resistance rows show how much of that protection remains after accelerated exposure, which is the number that actually predicts service life.

Environmental stress crack resistance measures the material's ability to resist cracking under sustained load in the presence of a surface active agent. It is tested by the notched constant tensile load method to ASTM D5397, with the requirement set at 500 hours minimum. It matters because geomembrane failures in service are far more often slow stress cracks at points of sustained strain, such as over a sharp subgrade feature or at a poorly supported penetration, than they are sudden tensile failures.

The last three rows of the table give the values. Seam shear strength and peel strength are tested to ASTM D6392, with separate peel values for hot wedge seams and extrusion fillet seams, because the two processes produce different joint geometry. A 1.50 mm liner, for example, requires 21 kN/m in shear, 15.9 kN/m peel on a hot wedge seam and 13.6 kN/m peel on an extrusion fillet. These are the numbers your field tensiometer is checking against.

Manufacturing tolerance. The specification sets both a minimum average value, which is the nominal thickness, and a lowest individual value, which is ten percent below it. A 1.00 mm sheet must average 1.00 mm with no single reading below 0.90 mm. This is normal and expected in extruded sheet. It becomes relevant on textured material, where core thickness is measured differently and comparing a textured sheet's nominal thickness against a smooth sheet's can mislead.