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Kaylie: Hi and welcome to the AGRU America podcast. Today, we will discuss our recent blog titled: “General installation guidelines for HDPE geomembranes.” Joining me in today’s discussion is Cody Miles. Together, we’ll review a number of HDPE geomembrane installation guidelines suggested by AGRU. Thanks for joining me today, Cody.
Cody: Happy to be here, as always.
Kaylie: I suppose we should start by putting these installation guidelines into context. Why are they important and why should projects lean to them for guidance?
Cody: I think it is always helpful to have guidelines like these as a baseline for anyone considering HDPE geomembrane products for the first time or for those who like to keep up with industry trends.
Kaylie: Yeah, I found it quite telling that core qualifications were the first items discussed in the guidelines. Even if you are a manufacturer or installer with years of experience, if you haven’t been involved with a project during the last five years your experience doesn’t count for much.
Cody: For sure. Holding manufacturers and installers to high standards helps ensure project success and can reduce costs by avoiding waste and preventable mistakes.
Kaylie: Product selection was the next section covered. What are some important points you noticed?
Cody: One thing that stood out is the importance of test samples. Product specifications are certainly helpful to get an idea of a product’s performance, but it should never be blindly trusted. Testing a product before its used in a product is essential and these tests help ensure that the product will meet the minimum design specifications for a project.
Kaylie: That part caught my attention too. I know most industries set standards to help set a benchmark for quality, and the geosynthetics industry is no different. What is GRI GM 13?
Cody: As you mentioned, industries are built on standards. For HDPE geomembranes, many manufacturing standards followed by the industry in the United States have been set by the Geosynthetic Research Institute, or GRI. GRI GM 13 is a manufacturing specification that sets the minimum, physical, mechanical, and chemical properties that must be met, or exceeded, by the HDPE geomembrane being manufactured.
Kaylie: So those manufacturing specifications are a way to set the minimum requirements to call your product an HDPE geomembrane?
Cody: Yeah, exactly. And of course, some products will be manufactured at a higher standard to provide solutions for niche applications. In those cases, the product should be tested and compared with more restrictive values depending on the exact design specifications.
Kaylie: Let’s say the product passes all the tests for a given project, the next set of guidelines points to preparing the construction site for installation. This part seems pretty intuitive to me. For instance: “the geomembrane subgrade should be uniform and clear of sharp objects.”
Cody: Some things stay pretty much the same in the world of geomembrane installation and subgrade preparation is one of them.
Kaylie: It sure seems that way. How about the next section on the best practices for geomembrane installation? I know some parts of this section have been discussed in detail for years.
Cody: I think waves and wrinkles have been a central topic in HDPE geomembrane installation for such a long time due to oversight when it comes to general guidelines and best practices during installation.
Kaylie: Can you give a short summary of the topic?
Cody: We’ve published several posts about it and I’ll be sure to include a link to a recent one in the transcript (https://agruamerica.com/hdpe-liner/), but in general the problem stems from some installers following old industry dogma when it comes to HDPE geomembranes and thermal expansion. It was thought that thermal expansion-induced waves and wrinkle across geomembranes would flatten out on their own once pressure is applied from the final soil cover.
Kaylie: But it doesn’t work that way, does it?
Cody: No and it was found that what actually happens is that those wrinkles tend to fold over to form areas of high stress in the liner where cracks can form.
Kaylie: So poor installation practices led to poor performing geomembranes and sparked the discussions. What are the solutions?
Cody: The guidelines build on EPA requirements. Specifically, that a HDPE geomembrane is only effective when it has “intimate contact” with the underlying subgrade. I think one of the most common strategies is to prevent waves from occurring in the first place by controlling the temperature of the geomembrane. A typical practice during the summer months is to modify the installation schedule so that work is only done during low sunlight. If that isn’t practical, then a HDPE geomembrane with reflective white coating can be used to absorb less heat.
Kaylie: Can you go into more detail with the installation schedule approach? What are some best practices?
Cody: An important concept advocated in the guideline is to only lay out the quantity of geomembrane that can be anchored and welded that same day. This way, installers can avoid unnecessary exposure to the geomembrane.
Kaylie: OK, so let’s say waves occur despite these preventative efforts. What can installers do in that situation?
Cody: One strategy in that situation is to push, accumulate, cut, and seam. Basically, you push the wave to flatten the geomembrane. The gathered crest is then cut, with the excess material folded over and welded.
Kaylie: On the subject of welding, it seems like many of the quality control procedures are associated with this step in the installation. I suppose that makes sense since poor welding can pretty much ruin the whole project.
Cody: That’s definitely the case. The whole point of the geomembrane is to provide an impermeable layer so, yeah, if a weld fails then everything falls apart.
Kaylie: What are some important steps in welding?
Cody: I found it interesting that the guidelines emphasize test welding. It is a process where the technician welds a test section under the same conditions, equipment, and materials. A portion of the test weld, which is done in accordance with the associated ASTM method, is then cut and tested against the acceptable weld strength values for the project.
Kaylie: And this is done before every welding session, right?
Cody: That’s the recommendation, yes.
Kaylie: The impressive thing is that the testing doesn’t stop there, either. After the test weld, the actual production weld is then tested too.
Cody: Yeah, each section of the production weld should be tested using a nondestructive method. And after a given length, typically about 500 feet, a destructive test is recommended.
Kaylie: From what I understand, it looks like in the destructive tests a seamed portion of the actual geomembrane is cut out and tested. That is quite a lot of work.
Cody: It is, but then again, welding is such an essential part of the installation and the success of the project so can I appreciate the effort taken for quality control. Thankfully the majority of the installation is tested using the nondestructive methods, which helps save time. The destructive tests are there as an additional layer of quality assurance.
Kaylie: A few options were mentioned for the nondestructive weld tests, can you explain how the spark test works?
Cody: Spark testing refers to ASTM D7240, a test method that relies on a geomembrane that either has an integrated conductive layer or is in intimate contact with a conductive surface. Rather than testing purely for seam integrity, this test is a sweeping construction quality assurance test that allows installers to identify possible holes, tears, or other breaches.
Kaylie: OK so to get this done you’ll need a conductive layer. What else do you need?
Cody: The installer will use an apparatus that includes a power supply, a coupling pad, and a test wand. When the coupling pad is charged and is in contact with the geomembrane and underlying conductive liner, a capacitor is formed. The area is swept over with the test wand to locate points where the capacitor discharges through a leak.
Kaylie: It sounds like you can pinpoint any leak in the geomembrane with this test, that’s very cool. What about the conductive layer though? You mentioned that it can be integrated with the geomembrane, right? That would definitely save installation time.
Cody: Definitely! Some manufacturers like AGRU offer the ability to purchase a geomembrane that has an integrated conductive layer. AGRU’s Conductive Liner, for instance, combines all the benefits of a geomembrane with the benefits of a conductive layer without compromising on the liner’s strength or durability. With Conductive Liner, you can perform the spark test without additional installation time.
Kaylie: Thank you Cody! And with that, I think we’ve covered every section in our general installation guidelines for geomembranes. To our listeners, thank you for tuning in. We hope you’ve enjoyed this podcast. For more information about AGRU geomembranes, installation guidelines, or our conductive liner, please visit us on the web at AGRU America dot COM. As always, we hope you’ve enjoyed listening and we welcome your feedback.