An important step in your project involving a geomembrane liner is understanding the product’s strengths as well as the best course of action during each step of installation. This article will review the installation guidelines provided by AGRU, which references ASTM and the Geosynthetic Research Institute.
This article will focus on best practices for installing high-density polyethylene (HDPE) liners with a density of 0.940g/cc and up. This article will (1) describe ideal minimum conditions to start a construction project using an HDPE geomembrane liner, (2) identify ways to control for product quality, (3) explain subgrade preparation, (4) share geomembrane placement best practices, (5) highlight guidelines for optimal welding, and (6) review several field quality control procedures.
Core qualifications for geomembrane liners
Before starting a geomembrane project, ensure that your chosen geomembrane manufacturer and installer meet minimum qualifications for a successful project. The manufacturer should ideally have at least five years’ experience manufacturing geomembrane products that are similar to or specified by the design as well as an output of 100 million square feet of product during the last five years. Similarly, the installer should have at least three years’ experience with at least 10 projects in its portfolio totaling five million square feet of installed product.
Additional qualifications may be required, depending on the nature of your project. Once you have selected qualified manufacturing candidates and an installer, you can move on to product quality control to ensure the project will meet your specific project requirements.
Product selection and quality control
Despite specifications, it is good practice to test samples of the product. Manufacturing quality control is one important set of tests to ensure the product meets U.S. standards. HDPE geomembranes should, at a minimum, meet GRI GM 13 in most cases. You should ask for quality control certifications and results from those tests to ensure that the materials supplied for the project are in compliance and meet project specifications.
Furthermore, geomembrane liner should pass visual inspections. The liner should be new and without physical defects such as holes, blisters, or visual indications of contaminants. The final product should also be supplied as a continuous sheet without factory welds in the rolls.
If the chosen product passes all checks for quality control, you are ready to begin preparing the construction site for installation.
Preparing the subgrade for geomembrane installation
Your design requirements may vary, but in most cases ideal geomembrane subgrades require a uniform surface free of sharp objects that could damage the geomembrane. As installations can take several weeks, visual inspections should be conducted every day, especially for the construction area that is scheduled to be laid with geomembrane that day. The subgrade can also be damaged or disturbed by construction equipment. All necessary repairs to the subgrade should be done before construction continues.
Finally, the geomembrane should not be installed during rainfall or excessive winds.
Best practices for geomembrane placement
When your geomembrane arrives and the subgrade is prepared, you are ready to begin laying down the product. Here are a few tips and best practices for the best installation outcomes. First, it is best to only deploy the quantity of geomembrane that can be anchored and welded during that day. Laying down only what you can install will help you avoid unnecessary exposure of the liner. Second, it is recommended to avoid vehicular traffic over exposed geomembrane. If ground equipment is required, use only approved low ground pressure vehicles or vehicles that are able to pass over test pads without causing damage to the liner. Third, you should use sand bags or a similar type of ballast to temporarily hold the geomembrane liner in place during installation.
Fourth, during placement it is possible for the liner to bridge over voids or low areas in the subgrade. These areas should be flattened to ensure intimate contact between all sections of the liner and the subgrade. Furthermore, waves and wrinkles can be minimized by installing the geomembrane during optimal ambient temperatures to minimize thermal expansion and contraction (view our article on the subject).
Finally, check to ensure there is an overlap between geomembrane sections to allow for welding and testing. The overlap should not be less than 3 inches.
Once all the sections have been placed and adequately anchored, you are ready to begin welding the panels together. For most situations, the welding process should be done when the surface temperature of the geomembrane is above 0°C. It is possible to work outside these parameters, but additional steps should be taken to ensure onsite safety and proper welds. Fusion welding equipment is ideal, but extrusion welding can be used when necessary.
Tests for quality control should be conducted alongside the welding process.
Geomembrane installation quality control procedures
As environmental conditions can greatly affect the quality of each weld, it is recommended for welding technicians to perform a test weld prior to each welding session. The test weld should be done in accordance with ASTM D 6392 using the same conditions, equipment, and materials as would be used during production. Sections of the test weld should be cut and tested against minimum acceptable weld strength values.
Production welds should be tested upon completion using nondestructive methods before the geomembrane is covered. Any areas that do not pass their tests should be marked, repaired, and retested. Nondestructive weld test methods can use a vacuum box, air pressure, or spark testing equipment. Destructive weld testing is recommended for every 500 ft or another predetermined length as specified in GRI GM 14. If an independent weld test is required, it should be done in accordance with ASTM 5820 or ASTM D6392.