Geosynthetic Clay Liners

Geosynthetic clay liners (GCL) are factory-manufactured hydraulic barrier products consisting of a thin layer of sodium bentonite clay (4–6 kg/m², 6–8 mm thickness when hydrated) encapsulated between two geotextile layers (needle-punched nonwoven + woven PP carrier, total 400–700 g/m²) or bonded to a geomembrane. Hydraulic conductivity of hydrated GCL is 5×10⁻¹¹ to 1×10⁻¹² m/s — equivalent to 300–600 mm of compacted clay at 10⁻⁹ m/s, but installed at 6–10 mm thickness providing 30–50× space saving. Bentonite swelling index of 24–40 mL/2g (ASTM D5890) and free swell 500–600% hydration capacity are critical quality parameters. GCL shear strength (peak internal friction angle 25–35°, ASTM D6243 direct shear) must exceed slope angle for stable installation. Desiccation cracking risk in arid climates (cycles above 50% swell capacity loss) is mitigated by polymer-enhanced bentonite (PEB-GCL, polyacrylamide 0.3–1.5% w/w, hydraulic conductivity maintained <10⁻¹¹ m/s after 5 wet-dry cycles). GCL installation cost of $8–15/m² is 40–60% lower than equivalent compacted clay liner at $20–35/m². GCL applications include landfill caps, secondary containment, canal lining, and tunnel waterproofing.