Geosynthetic Clay Liner (GCL) (GCL) is a low-permeability barrier consisting of a layer of sodium bentonite clay sandwiched between two geotextiles — or bonded to a geomembrane. When hydrated, the bentonite swells to form a self-sealing barrier with permeability typically below 1 × 10⁻¹¹ m/s.
How a GCL works
Sodium bentonite is a clay mineral that swells to many times its dry volume when hydrated. In a GCL, a layer of granular or powdered bentonite is held between two geotextiles by needle-punched bonding, stitching or adhesive. Once installed and hydrated by groundwater or applied water, the bentonite forms a continuous, self-sealing barrier.
The self-sealing property is the standout feature of GCLs: small punctures and pinholes are sealed automatically as the bentonite swells to fill any defect.
UK applications
- Landfill basal lining — typically beneath an HDPE geomembrane as a composite Environment Agency-compliant barrier.
- Landfill capping — final cover system to prevent infiltration of rainwater into closed waste cells.
- Contaminated land — barrier between contaminated material and clean cover, or beneath new development on remediated sites.
- Ponds and reservoirs — primary or secondary water containment, particularly attractive for irregular shapes and on-grade installation.
- Green roofs and podium decks — root barrier and waterproofing layer beneath substrate.
- Secondary containment — bund linings for fuel and chemical storage areas.
Specification and installation
UK specification follows BS EN 13361 and the Environment Agency’s LFE 3 framework for landfill applications. Key performance properties include hydraulic conductivity (typically below 5 × 10⁻¹¹ m/s), bentonite mass per unit area (3.5–5.5 kg/m²) and tensile strength.
Installation requires careful overlap (typically 300 mm minimum), protection from premature hydration during installation, and an immediate cover layer once installed. CQA procedures and trial seams are standard for landfill applications.
Related ViaCon solutions
ViaCon supplies geosynthetic clay liners as part of complete barrier systems alongside geomembranes, protection geotextiles and drainage geocomposites. See our geotechnical solutions. Related glossary entries: geomembrane, geotextile, geocomposite and permeability.
Frequently asked questions about geosynthetic clay liner (gcl)
What is a geosynthetic clay liner?
A geosynthetic clay liner (GCL) is a low-permeability barrier consisting of a layer of sodium bentonite clay sandwiched between two geotextiles, or bonded to a geomembrane. When hydrated, the bentonite swells to form a self-sealing barrier with hydraulic conductivity typically below 1 × 10⁻¹¹ m/s.
What is the difference between a GCL and a geomembrane?
A GCL is a clay-based hydraulic barrier that self-seals around small defects. A geomembrane is a continuous polymer sheet that relies on welded seams for integrity. They are often used together in composite landfill linings.
Where are GCLs used in the UK?
GCLs are specified for landfill basal linings and capping, contaminated land containment, pond and reservoir liners, green roofs, podium decks, and secondary containment around fuel and chemical storage.
How is a GCL installed?
Panels are unrolled and overlapped by at least 300 mm. The GCL must be protected from premature hydration during installation and covered on the same day to prevent damage. CQA procedures and trial seams are standard.