A failed liner will, obviously, not provide its intended service. Geomembranes can be compromised by mechanical events (dropped tools, rocks in boots, etc.) by chemical attack (hydrocarbons, high or low pH, etc.) and by weathering (UV, harsh weather).
It is possible to leave the liner exposed and take advantage of the benefits that an exposed geomembrane offers. Three items must be addressed in order to do so.
First, assuming the liner is chemically resistant to the contained substance, it must be able to resist mechanical and weathering damage. There are a number of geomembrane types available today which have excellent puncture, tear and weathering resistance. Some types of liners offer 20 or 30-year warranties in exposed applications. The geomembrane industry has a long track record of projects wherein the liner has been serviceable (exposed) for over 30 years. The liner used in the aeration basin at the Mammoth Cave National Park WWTP, for instance, has been in service for over 30 years:
Second, care must be taken to provide resistance to wind uplift. Proven methodologies for determining ballast plans with sand tubes are readily available (see Design of Geomembrane Anchorage Against Wind Action, J.P, Ghiroud & M.H. Gleason; Geosynthetics International 1999, Vol 6, No. 6 p.481).
Finally, provision should be made for access by personnel and vehicular traffic. The geomembrane industry offers pedestrian traffic mats that not only protect the liner but offer visual guidance and slip resistance as well.
What are your thoughts on protecting geomembrane liners? Tell us about them in the comments!