Simulation of Bentonite Swelling Pressure and Pore Structure Evolution with a Particle-Based Finite-Element Framework

The highly expansive behavior of bentonite makes it a widely used sealing material in engineered barrier systems. This study develops a finite-element (FE) model to simulate the swelling behavior of compacted granular bentonite at the particle scale. Volumetric swelling strain is defined as a function of water content, and a new constitutive law is introduced to capture hydration-induced softening by linking particle stiffness to water content. The model, implemented in COMSOL 6.2, is validated against constant-volume swelling pressure tests on FEBEX bentonite. Simulation results show that higher dry density significantly increases maximum swelling pressure, while higher initial water content reduces it due to stress path effects. At the microstructural level, interparticle voids progressively close and the pore size distribution curve shifts toward smaller radii during hydration, while stress transmission remains heterogeneous even after full saturation. These findings provide new insight into the interplay between particle-scale mechanics and macroscopic swelling behavior, offering a predictive tool for evaluating the performance of bentonite-based barrier systems.