The GMA Techline

Geomembranes for canal lining

Q: Our company is an international member of the Industrial Fabrics Association International (IFAI). Our government is planning to line their water canals with a geomembrane to prevent water seepage into the soil. We have been approached by many to suggest the most suitable material with specifications to guide them in making the tender documents. The quantity involved will be substantial, as there are miles of canal irrigation in our country. We would appreciate receiving any guidance with regards to the different types of geomembranes available in the industry and their advantages and disadvantages. Thanks, and looking forward to your support and help.

A: Canals are invariably lined with polymeric geomembranes of which there are many resin types. Go to https://geosynthetic-institute.org/specifications.htm for a number of generic specifications. They are free for you to download and use. Also, go to www.geosynthetic-institute.org/papers/paper12.pdf for a selection guide depending on your site-specific needs. Regarding design, Marilyn Ashley will send a short section from my book Designing with Geosynthetics, 6th edition, Xlibris Publ. Co., 2012. It is available from Amazon as an e-book, softbound or hardbound. After looking things over, doget back with specific questions.

TCLP test for a geomembrane?

Q: This is an odd question we were asked, and I was wondering if you had anything on this. Apparently, a contractor doing sampling at a local landfill thinks that per- and polyfluoroalkyl substances (PFAS) found in runoff may be coming off a landfill cap or drain piping during rain events. The contractor was theorizing that the PFAS could be coming from the low-density polyethylene liner and/or high-density polyethylene underdrain piping in the landfill cap. The landfill cap was installed in the 1990s.

A: Nice to hear from you and thanks for asking the question. PFAS (PFOS, OFOA and Gen X) have been widely used to make products more stain-resistant, waterproof and/or nonstick. They are used in textile carpets, not in geomembranes. Australia is going through problems with this class of compounds as a result of poor fire-retardant containment at airports. Military bases in the U.S. have issues for the same reason. I am hearing a lot about these materials lately, but this is the first time someone has suggested they are coming from an unstable geomembrane formulation. One could do a toxicity characteristic leaching procedure (TCLP) test on the suspect geomembrane to verify.

Destructive testing of field seams?

Q: I am overseeing a construction project involving linear low-density polyethylene (LLDPE) for capping of a landfill. I have some questions regarding GRI-GM19a, in particular the use of shear elongation for acceptance of destructive testing results of a field seaming project. It is footnoted in Table 2(a) that for shear elongation, “Elongation measurements should be omitted for field testing.” My questions are as follows:

1. Does acceptance of a destructive test of a field seamed sample that is tested by a third-party laboratory include the need to exceed 50% in shear elongation?
2. Can you provide more information on the intent of the footnote or its applicability? I have tried to find additional information in white papers on your website and in your Designing with Geosynthetics books and have not found an answer.
3. Is there an intended difference between the term “field testing” and “laboratory testing”? I note that the applicability section states that this is for laboratory testing only, so I am trying to understand the footnote reference to field testing.
4. If these answers point to a direction that shear elongation is not a relevant test result in passing a fusion seam, then what would be a scenario(s) where that result of the seam test would be applicable?

A: The following is in regard to your questions about GRI-GM19a and in particular how they relate to ASTM D6392.

1. Please note, most field tensiometers do not measure or record deflection. This is the reason for excluding shear elongation for acceptance of destructive testing results of a field seaming project, as per footnote in Table 2(a) that for shear elongation, “Elongation measurements should be omitted for field testing.” That said, one does not want to see a brittle failure (overheated) seam situation.
2. Please note destructive field testing of seams was only intended for qualification of the equipment and personnel on-site. The production seaming and subsequent laboratory testing is where the one in 500 feet (152 m) sampling comes into play. For both the peel and shear tests, per ASTM D6392, one needs to satisfy three criteria: For peel testing: load, proper location of break code and percent peel separation (or incursion); and for shear testing: load, proper location of break code and elongation.
3. es, field testing is less rigorous and generally not accredited. It is usually done by the construction quality control (CQC) organization and is performed in the field under nonenvironmentally controlled conditions. Incursion and elongation are not recorded due to the nature of the typical field tensiometer versus a controlled laboratory CRE testing device.
4. Not sure about the answer to this one. I will give you a call to discuss.