20 FAQs About Geomembranes: Everything You Need to Know About Geomembranes

These are answers to 20 questions engineers, contractors and buyers ask us about geomembranes: what they are made of, where they are used, how they are installed and tested, and what makes them fail.

1. What is a geomembrane?

A geomembrane is a continuous sheet of very low permeability, made from high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), polyvinyl chloride (PVC) or another synthetic polymer. It is used as a barrier to stop liquids or gases moving through the ground. Typical uses in civil engineering are landfills, dams, canals, ponds and wastewater treatment plants.

2. What are the different types of geomembranes?

HDPE and PVC are the two most widely used. HDPE geomembranes are the most common: they are stiff, strong and have very good chemical and UV resistance, which is why they are the default for landfills, effluent ponds and exposed water reservoirs. PVC geomembranes are more flexible and easier to fold around details, but they contain plasticisers and are generally less resistant to UV and chemicals than HDPE.

3. What are the benefits of using geomembranes?

Geomembranes offer several benefits:

• They stop seepage of water, leachate and other liquids.
• They are durable; HDPE can stay exposed in ponds and reservoirs.
• They usually cost less to install and maintain than concrete or thick clay lining.
• They suit many applications, from farm ponds to landfill cells.

4. What are the limitations of using geomembranes?

Geomembranes have a few limitations:

• They can be punctured or torn by sharp stones, roots or construction equipment, so they need a smooth subgrade and often a protective geotextile.
• Repairs need welding equipment and a trained technician, and damage under cover soil is hard to find.
• Some polymers (PVC, LDPE) degrade faster under UV or attack by certain chemicals; even HDPE needs the right grade for the liquid it holds.

5. How are geomembranes installed?

Geomembranes are usually installed by a specialist lining contractor. The sequence depends on the project, but generally runs like this:

1. Site preparation and excavation. The area is excavated to the design levels and slopes, and debris, roots and vegetation are removed.
2. Subgrade preparation. The base is compacted and trimmed smooth, free of sharp stones. A nonwoven geotextile cushion is often laid first to protect the liner from puncture.
3. Placement. Panels are unrolled, positioned with the specified overlap and held down with sandbags against wind uplift. Edges are fixed in an anchor trench at the crest of the slope.
4. Seaming. Adjacent panels are welded together, usually by hot wedge fusion for HDPE, with extrusion welding at patches and details.
5. Testing and cover. Seams are tested (see question 15), defects are repaired, and the liner is then covered with soil, a protective layer or the stored liquid as the design requires.

6. What are the common applications for geomembranes?

Geomembranes are used in many sectors, including:

• Landfills (base liners and caps)
• Dams and canals
• Wastewater treatment plants
• Oil and gas production (oil pits, secondary containment)
• Agriculture (farm ponds, water storage, aquaculture)
• Construction (basements, tunnels, moisture barriers)
• Mining (heap leach pads, tailings ponds)
• Transportation (road and rail cuttings, spill containment)

7. How long do geomembranes last?

Service life depends on the polymer, the thickness, the temperature and above all whether the sheet is exposed to sunlight. A buried or covered HDPE liner degrades very slowly and is expected to last for many decades. An exposed liner ages faster because of UV and heat, so exposed applications call for a thicker HDPE sheet with proper carbon black content and UV stabilisers.

8. How much do geomembranes cost?

Price depends mainly on the polymer, the thickness (in microns or mm), the area, the surface (smooth or textured) and whether installation and welding are included. For an indicative rate on a specific job, send the area and thickness to us; our pond liner and geomembrane pages list the grades we supply. Over the life of a project, a geomembrane is usually cheaper than concrete lining for the same containment.

9. What are the safety considerations for working with geomembranes?

The sheet is inert, but installing it carries some site risks:

• Wear PPE, including gloves, safety boots and eye protection near welding.
• Geomembrane surfaces, especially smooth HDPE, are slippery when wet or dusty, which is dangerous on slopes.
• Wind can lift unballasted panels, so lay sandbags as you go and stop deployment in high wind.
• Welding machines run hot; keep them on a stand and away from the sheet when idle.
• Keep knives and sharp tools away from laid liner, and dispose of offcuts properly.

10. Where can I learn more about geomembranes?

Useful sources include:

• The International Geosynthetics Society (IGS) and its Indian chapter
• The Geosynthetic Institute (GSI), which publishes the GRI-GM13 specification for HDPE and GRI-GM17 for LLDPE geomembranes
• ASTM Committee D35 on Geosynthetics, which maintains the test methods
• The American Society of Civil Engineers (ASCE) and its geotechnical publications

11. What are the different properties of geomembranes?

The properties that matter in a specification are:

• Tensile strength and elongation at yield and break
• Very low permeability to liquids and gases
• Chemical resistance to the stored liquid
• UV resistance (for HDPE, from 2–3% carbon black)
• Puncture and tear resistance
• Stress crack resistance and long-term durability (oxidative induction time)
• Density (at least 0.940 g/cc for HDPE under GRI-GM13)

12. How do HDPE, PVC, LLDPE, LDPE and CSPE geomembranes differ?

Each polymer has a different balance of strength, flexibility and resistance:

• HDPE geomembranes: stiff and strong, with the highest chemical and UV resistance of the group; the usual choice for landfills, effluent and exposed ponds.
• PVC geomembranes: very flexible and easy to fabricate into large panels; less UV and chemical resistance.
• LLDPE geomembranes: more flexible and better at following uneven subgrade than HDPE, with good puncture resistance; often used in caps and covered liners.
• LDPE geomembranes: low cost and flexible; used for lighter-duty moisture barriers and temporary lining.
• CSPE geomembranes: chlorosulfonated polyethylene, good weathering resistance in exposed applications, now less common.

13. What are the different methods for installing geomembranes?

Panels are joined and fixed by methods that depend on the polymer:

• Thermal fusion (hot wedge) welding: the main seaming method for HDPE and LLDPE
• Extrusion welding: for patches, pipe boots and details on polyethylene sheets
• Hot-air welding: mainly for PVC and for tacking polyethylene panels
• Solvent or chemical welding: for PVC
• Mechanical fastening: batten strips and anchors to fix the liner to concrete structures

14. What are the different types of geomembrane seams?

The common seam types are:

• Double-track fusion seams (hot wedge), which leave an air channel between the two welds for pressure testing
• Extrusion fillet seams, where a bead of molten polymer is laid along the edge of an overlap
• Extrusion flat seams, with the bead placed between the overlapped sheets
• Hot-air seams and solvent or adhesive seams, used mainly on PVC and other flexible sheets

15. How are geomembranes tested?

The sheet is tested in the factory or lab against a specification such as GRI-GM13, and seams are tested on site. Common tests include:

• Tensile strength and elongation (ASTM D6693 for HDPE)
• Thickness (ASTM D5199) and density (ASTM D1505 or D792)
• Carbon black content and dispersion (ASTM D4218, D5596)
• Puncture resistance (ASTM D4833) and tear resistance (ASTM D1004)
• Stress crack resistance (ASTM D5397) and oxidative induction time (ASTM D3895)
• Seam strength in shear and peel (ASTM D6392), plus on-site air pressure testing of fusion seams (ASTM D5820) and vacuum box testing of extrusion welds (ASTM D5641)

16. What are the common failures of geomembranes?

Geomembranes usually fail for one of these reasons:

• Punctures from stones in the subgrade or cover
• Tears during installation or from equipment
• Degradation due to UV radiation on exposed sheet with poor UV stabilisation
• Degradation due to chemicals the polymer was not selected for
• Poor installation: weak or untested seams, wrinkles, stress cracking at tight corners

17. How can geomembranes be repaired?

The repair method depends on the damage and the polymer:

• Patching: a piece of the same sheet, rounded at the corners, is extrusion welded over the hole (the usual HDPE repair)
• Bead or cap repairs for small holes and defective seam sections
• Hot-air welding of patches on PVC and other flexible sheets
• Solvent or adhesive patching for PVC

Every repair should be vacuum box or spark tested before cover is placed.

18. What are the environmental benefits of using geomembranes?

Geomembranes protect the environment in several ways:

• Reduced water pollution: landfill and effluent pond liners keep leachate and chemicals out of soil and groundwater
• Reduced air pollution: landfill caps contain landfill gas so it can be collected instead of escaping
• Water saved: lined canals, ponds and reservoirs lose far less to seepage
• Less earthworks: a thin liner replaces large volumes of imported clay

19. What are the economic benefits of using geomembranes?

The economic benefits are:

• Reduced construction costs compared with concrete or thick clay lining
• Reduced maintenance costs and water loss over the life of the structure
• Increased asset life of ponds, canals and containment structures
• Faster construction, since large panels are laid and welded quickly

20. What are the future trends for geomembranes?

Some developments already under way:

• Wider use in water conservation, aquaculture and mining
• New materials with improved properties, such as textured sheets for steep slopes and conductive-backed sheets that can be spark tested
• Better installation and repair checks, including electrical leak location surveys (ASTM D7007) on finished liners

Contact us to discuss the right geomembrane from Ocean Geosynthetics for your project.