There are pros and cons to either leaving a geomembrane liner exposed (no cover) or burying it (complete cover). Let’s look at the issues.
Not all geomembrane liner materials can be left exposed because of the effect of either UV radiation or changes in temperature. The latter causes thermal expansion and contraction swings in highly crystalline products such as most polyethylenes, particularly HDPE. For HDPE geomembrane liners, long life exposure is not an option because the life will be greatly reduced, even if a lighter color is substituted.
Advantages of Covering a Geomembrane Liner
- No UV exposure; theoretically longer life
- Minimal thermal changes
- Protection from foot and vehicle traffic
- No uplift concerns
Advantages of an Exposed Geomembrane Liner
- Less damage potential during overburden installation
- Ability to view and monitor the geomembrane 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 require
- No differential loading due to shifting overburden
- No maintenance of overburden
- No added issues with the head drop from containment area to O/W separators (geomembrane must be placed lower to account for overburden thickness)
- Lower construction cost
Designers will often provide materials and features in a lining system that will incorporate the advantages of both covered and exposed geomembrane liners, including:
- Utilizing a geomembrane with a proven, long-term UV life, and negligible thermal and 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 (walkmats) in the roofing industry for many years.
- Providing a porous media (geonet, geotextile) 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.
Take a look at the project and consider the facility operation. Innovative design allows exposed membranes to offer many features also inherent in a covered application.