Hydrodynamic Simulation of Swelling of Bentonite Granules and Hydraulic Conductivity of Geosynthetic Clay Liner

Sodium bentonite geosynthetic clay liners (NaB GCLs) rely on the hydration-induced swelling of bentonite to achieve low hydraulic conductivity. However, the pore scale evolution linking nonuniform granule swelling to changes in intergranular flow path remains insufficiently understood. In this study, an idealized two-dimensional multiphysics finite element model was developed to investigate the coupled evolution of bentonite hydration, granule swelling and deformation, intergranular pore structure, and fluid flow. An effective moisture concentration diffusion field was coupled with hygroscopic swelling, solid deformation, fluid–structure interaction, deformation domain treatment, and laminar flow to represent the progressive hydration and swelling process. The simulations showed pronounced spatially nonuniform swelling, with the domain-averaged particle area swelling ratio increasing from 1.85% to 22.79% across the selected states. During this process, the areal porosity decreased from 0.63 to 0.55, whereas the hydraulic conductivity decreased from 3.46 × 10−5 to 2.11 × 10−7 m/s, corresponding to an approximately 164-fold reduction. The hydraulic response was strongly nonlinear relative to the reduction in total pore area. In particular, the minimum connected pore throat width decreased from approximately 3.37 to 0.45 μm between the selected 33% and 44% swelling states, accompanied by substantial flow path constriction and redistribution. These results indicate that localized pore throat narrowing, pore connectivity, and flow path tortuosity can exert a stronger influence on hydraulic response than bulk porosity alone. The developed model provides a mechanistic interpretation of the coupling between bentonite swelling, pore structure evolution, and hydraulic response within an idealized two-dimensional granular system rather than a direct quantitative prediction of real GCL performance.