GRI Standard GM 13
by George Yazdani, MSc., P.E.

The National Sanitation Foundation (NSF) will withdraw their Standard 54 "Flexible Membrane Liners" at the end of 1997. The NSF Standard 54 provides minimum physical properties and manufacturing quality control testing frequencies for smooth HDPE and VLDPE liners, but has no specifications for textured polyethylene liners. NSF is not an active participant in research in the area of polyethylene geomembranes.

The Geosynthetic Research Institute (GRI) at Drexel University, was established 10 years ago and has since been actively involved in research for all geosynthetics including HDPE geomembranes. During this period, GRI has created 13 geomembrane related standards, some of which have been adopted by the American Society for Testing and Materials. The latest GRI standard is GM 13 "Test Properties, Testing Frequency and Recommended Warranty for High Density Polyethylene (HDPE) Smooth and Textured Geomembranes". This standard was developed by the GRI polyethylene focus group-consisting of Dr. Robert M. Koerner, Director of GRI, Dr. Grace Hsuan, Assistant Director of GRI, and major polyethylene resin and sheet manufacturers-and was rigorously reviewed by the GRI member organizations-including design engineers, third party quality assurance engineers, regulators, and owner/operators. GM 13 was developed over a period of more than two years and cost over $500,000. This standard sets forth a set of minimum physical properties and manufacturing quality control testing frequencies for HDPE liners. GRI has authorized the general use of this document by the public. Please take advantage of this standard and use it as the industry standard when contacting your clients and design engineers. The polyethylene focus group is working on a similar standard for Very Flexible Polyethylene, VFPE (LLDPE), liners which should be released later this year or next year. A copy of the GRI Standard GM 13 is included with this newsletter.

As you review this standard, I would like to draw your attention to the Asperity Height for textured sheets, under Table 2(a). The specified minimum average value is 7 mils as compared to Poly-Flex's 17 mils. This indicates that Poly-Flex textured sheet has more than twice the texturing as the minimum industry standard. This is an added design value which enhances the stability of liner systems and increases the factor of safety against liner systems failure on side slopes. Please feel free to contact me at 888-765-9359, extension 7314, if you would like to discuss this topic in more detail or if you should have any questions.

GRI TEST METHODS & STANDARDS

Conformance Testing
by James Nobert, Laboratory Manager

When sending material samples to a laboratory for testing it is necessary to always send a full roll width sample.

Poly-Flex, Inc. minimum properties are based on average roll values. Average roll values is defined as the average value obtained when testing individual specimens randomly across the full width of the sample. When machine and cross direction are tested, the average roll values are the average of both directions.

Test results which do not represent the full width sample are not representative of the average roll value. When cutting samples to send to a laboratory for testing, always ask how big of a sample they need. Typically a sample 1' by the roll width is adequate for testing by most labs. Larger samples are a waste of material and freight charges.