Hydraulic Performance of Polymer-Modified Bentonites for Development of Modern Geosynthetic Clay Liners: A Review

Smectite-based geosynthetic clay liners (GCLs) are popularly employed as hydraulic barriers due to their low permeability and high swelling capacity. The exposure of GCLs to aggressive inorganic permeants is inevitable in the majority of field applications. GCLs exhibit inferior hydraulic properties and low swelling in these scenarios due to the concomitance of various physico–chemical interactions. To confront such aggressive environmental conditions, bentonites are modified chemically to enhance their resistance against increased permeability. Several polymer-modified clays have been developed with improved hydraulic properties; however, the efforts made to comprehend the overview of available literature are scarce. Limited studies have focussed on addressing the fundamental mechanism ascribing to their enhanced hydraulic performance. Given this, the present review article comprehends the insights into different types of modifications on smectite-based GCLs from their hydraulic performance perspective. Osmotic swell enhancement and pore clogging phenomena were found to be the primary mechanisms responsible for the improved hydraulic performance of polymer-treated GCLs. Further, the study reviewed the variation of permeability of various polymer-modified GCLs with the swell index based on the data published in the literature till date and proposed a relationship correlating them considering the wide range of permeants. The regression analysis results evidenced the suitability of the swell index as one of the index properties for ascertaining its hydraulic performance. Also, the study advocated the use of the dielectric constant of permeant for correlating the hydraulic behaviour of polymer-modified GCLs.