AbstractThe composite nature of geosynthetic clay liners and the contrasting water retention behavior of its bentonite and geotextile components has presented a unique challenge that current water retention models do not fully address. This paper proposes a new water retention model that can accurately describe the bimodal behavior of geosynthetic clay liners across the entire suction range (10−2–106 kPa) on the adsorption path. The model was formulated based on the pore structures and dominant suction regimes present in geosynthetic clay liners. In addition to the soil adsorptive and capillary water, it incorporates the geotextile capillary regime, which encompasses the pore water fraction in the geotextile, bentonite extrusion into the geotextile, and additionally, any volume changes due to bentonite swelling (including polymer effects). The parameters defined in this conceptual model describe the physical characteristics of bentonite and the geotextile fraction in the geosynthetic clay liner (GCL). The proposed model’s performance was assessed and validated using extensive experimental water retention data sets. The statistical analysis indicated that the proposed model provides a better fit than other models, especially in the low-suction range, and is adept at predicting the water retention behavior of the geosynthetic clay liners on the wetting path.