Here is a summary of AGRU’s installation guidelines for geomembrane.
An important step in a project involving a geomembrane 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) geomembranes. This article will (1) describe ideal minimum conditions to start a construction project using an HDPE geomembrane, (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.
Installation Guidelines for Geomembrane: Core Qualifications
Before starting a geomembrane project, ensure the chosen manufacturer and installer meet the 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 the product during the last five years. Similarly, the installer should have at least three years of experience with at least ten projects in its portfolio totaling five million square feet of installed product.
Additional qualifications may be required, depending on the nature of the project. Once a qualified manufacturing candidate and an installer are selected, the next step is product quality control to ensure the project will meet 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 GM13 in most cases. Follow up with quality control certifications and results from those tests to ensure that the materials supplied comply with and meet project specifications.
Furthermore, geomembranes should pass visual inspections. The liner should be new 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, the project is ready to begin preparing the construction site for installation.
Preparing the subgrade for geomembrane installation
The project’s 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 scheduled to be laid with a 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 the geomembrane arrives and the subgrade is prepared, the next step is to place the product. Here are a few tips and best practices for the best installation outcomes. First, it is best only to deploy the quantity of geomembrane that can be anchored and welded during that day. Placing only what can be installed that day will help avoid unnecessary liner exposure. Second, it is recommended to prevent vehicular traffic across the exposed geomembrane. If ground equipment is required, use only approved low-ground-pressure vehicles or vehicles that can pass over test pads without causing damage to the liner. Third, use sandbags or a similar ballast to hold the geomembrane in place during installation temporarily.
Fourth, during placement, the liner can 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 anchored, the team is 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 that welding technicians perform a test weld before each welding session. The test weld should be done per ASTM D6392 using the same conditions, equipment, and materials 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 per ASTM 5820 or ASTM D6392.