AbstractGeosynthetic clay liners (GCLs) are widely used as hydraulic barriers in landfills and mine tailings facilities due to their low hydraulic conductivity. The average grain size of the granular bentonites (GBs) used in GCLs varies depending on the manufacturer and also between batches from the same manufacturer. The influence of GB grain size and plasticity on the sealing ability and volume-change characteristics under extreme chemical loads is important for long-term stability. Furthermore, GCLs are subjected to mechanical loading from landfill waste. The influence of different grain-size distributions in GB samples was assessed in terms of their self-sealing ability, hydraulic infiltration, and volume-change behavior under extreme chemical loadings and a 50-kPa mechanical load. The performance of fine-grained GBs was found to be satisfactory, in terms of hydraulic infiltration and volume change, under the test conditions. The plasticity of the GB also influenced its sealing and swelling ability under chemomechanical loading. The mechanism underpinning the influence of plasticity and grain size on the self-sealing behavior and hydraulic conductivity equilibrium is explained. We recommend fine-grained GBs for use in GCLs for containment applications.