The application of geomembrane landfill liners, particularly those made of polyethylene, has increased over the past two decades because they provide strength, ease of installation, durability and longevity as well as a competitive cost/benefit ratio.
There are two basic types of polyethylene: high-density polyethylene (HDPE) and very flexible polyethylene (VFPE). HDPE is the standard material for landfill containment applications (and for reservoirs, ponds and wastewater treatment plants). VFPE can be used in landfill caps where great amounts of differential settlement may occur.
Slope stability is an important issue for liner systems. Textured geomembranes provide frictional properties and allow engineers to design relatively steep slopes. Special grades of HDPE are often used to increase durability. These incorporate additives such as carbon black and chemical stabilizers. Light-reflective surfaces can also be applied to prevent heat buildup (which prevents material deformity and wrinkling).
Spark-testable geomembrane liners are also available. An electrically conductive undersurface allows the material to be spark-tested after installation. Since most damage to a liner occurs immediately following installation, the ability to identify holes prior to burial of the liner is advantageous.
Specially trained crews use heat to attach polyethylene pieces. There are two methods for this: fusion and extrusion welding. The length and geometry of the weld determines which method is used; fusion welds are long and straight and extrusion welds are short and curved. Both should be nondestructively tested to ensure quality.
Written by Matthew Adams, product manager of geomembranes at GSE Lining Technology, Inc., Houston, Texas.