As is the case with political views, religious beliefs or how to best build a fire, experts have strong opinions about whether geomembranes should be buried or left exposed. In truth, the correct answer is often dependent upon the needs of each specific project. That’s why making an informed decision requires taking a closer look at the advantages of both options.
However, your first consideration should be geomembrane material. Not all materials can be left exposed to UV rays or even changes in temperature. The latter causes thermal expansion-contraction swings in highly crystalline products such as most polyethylenes, particularly HDPE. For these materials, long-term exposure to the elements isn’t an option. Even if a lighter color material is substituted, the material’s life cycle will still be greatly reduced.
But it’s not that easy. Below are the clear advantages to keep in mind when deciding whether a geomembrane should be buried or left exposed:
Advantages of a Buried Geomembrane:
- No UV exposure, theoretically extending life cycle
- Minimal thermal changes
- Less potential for damage once successfully installed.
- Minimizes uplift concerns
Advantages of an Exposed Geomembrane:
- Less damage potential from overburden installation
- Ability to view and monitor the geomembrane’s condition at all times
- Ability to remove or repair sections
- Ability to use steeper side slopes because overburden sliding concerns are eliminated
- No contaminated overburden, which will ultimately require disposal
- No maintenance of overburden
- Lower construction cost
Designers will often suggest lining system materials and features that take into account the advantages of both buried and exposed geomembranes. These include:
- Using a geomembrane with a proven, long-term UV life and negligible thermal-expansion contraction
- Covering selected areas where foot traffic or other disturbances are expected during the project life; exposed membranes have been covered by other membrane products (e.g., walk mats) in the roofing industry for many years
- Providing a porous medium (e.g., geonets, geotextiles and granular materials) under the geomembrane and providing a positive slope to the dikes from the center; this is a particularly good practice in a geomembrane-lined liquid impoundment for passive venting of the subgrade
When considering the advantages and disadvantages of burying or leaving a geomembrane exposed, be sure to take a look at the project details and consider the facility operation. Whichever you choose, remember that today’s innovative design capabilities allow exposed membranes to offer many of the features also inherent in a buried application.