5 Common Major Errors with Geomembrane Terminations

Geomembranes that come from the factory, either as sheet materials or as panels from a second manufacturing process, rarely leak. Leaks occur primarily from three areas:

1. Field Seams
2. Field damage, primarily from overburden installation
3. Terminations (including protrusions)

This blog focuses on terminations, the third primary area of concern, and includes field seam considerations. Here are 5 mistakes which are often made when designing geomembrane terminations.

1. Thinking field seams are not terminations (connections). While this post is about terminations, as a designer, you should consider that any connection is subject to many of the same considerations as a termination. The primary example is geomembrane field seams, which are just as important as perimeter terminations. They require rigorous detail and quality control/assurance. Some geomembranes have as many as three times the number of field seams as others. Fewer field seams mean fewer chances for problems.
   
   
2. Not taking advantage of new technology (embeds). Historically, the only way to terminate a geomembrane at a vertical or horizontal concrete surface was by constructing batten bar terminations. This technique continues to be the most common for terminating at existing concrete surfaces. Now, however, certain geomembrane manufacturers offer an embedment strip that can be installed into new construction concrete. The strip is made from the same polymer as the geomembrane, allowing direct welding between the two, thus eliminating the need for mechanical batten attachments. These are much more cost-effective and time-saving.
   
   It does not allow for removal of the connection, in the case of geomembrane repairs, without rewelding. However, some would contend that rewelding is preferred.
   

            XR-5 Geomembrane Impoundment application, Oklahoma USA

   
3. Treating underwater connections the same as above-water connections. Underwater connections should be avoided, if possible, but inevitably, some are needed. Constant hydraulic head should dictate more robust sealing at edges. The adjacent photograph shows two inlet pipes that are at least partially submerged constantly. Here, the pipe boot connection to the pipe itself uses double clamps and the thermal weld between the boot and the geomembrane has been reinforced with cap stripping. Construction details should address the need for added security for submerged connections. This applies for round protrusions and flat connections.
   
                                                                                      Impoundment application, Kentucky USA
   
   
4. Not providing additional connection features for crystalline geomembranes. High thermal expansion and contraction are inherent properties of some geomembranes, such as many polyethylene types. This cyclic movement manifests stresses at connection points. Note connection points, not just terminations. So, field seams are also stress. There are various methods that attempt to relieve this stress and most involve some sort of mechanical restraint. Read our thermally induced wrinkles blog for additional information.
   
   
5. Thinking more is better. We sometimes see top-of-slope anchor trenches filled with concrete instead of soil or aggregate. Normally the idea was that it was more permanent, more secure, and more protective of the geomembrane. In most situations, however, this removes the option to adjust the geomembrane for maintenance over the life of the facility, which could normally be done with high-strength, flexible geomembranes. By evaluating the pull-out load on the trench, a heavier backfill is usually not needed.

Open anchor trench. Tennessee US
XR-5 PW Raw Water Impoundment

Design geomembrane terminations with a long-term perspective on how to make them as secure as the geomembrane barrier itself. For more information on typical termination details, visit our website.

All illustrations provided by Seaman Corporation.