A Novel Coupled Elastoplastic Hydromechanical Model for Unsaturated Swelling Bentonite

The interaction between the hydraulic and the mechanical properties of bentonite poses a significant challenge in designing barriers for radioactive waste repositories. Tackling the complexities of joint elastoplastic deformations and hydration swelling, this paper introduces a novel coupled hydromechanical (HM) model based on the mixture coupling theory for unsaturated bentonite. The HM model integrates the elastoplastic deformations and hydration swelling of bentonite into a single theoretical framework, enabling comprehensive HM analyses across different scales and physical processes. By integrating entropy generation and Helmholtz free energy, it establishes a connection between macroscopic mechanical deformations and molecular-scale hydration swelling. The stress–strain relationship considers elastoplastic deformations. Deriving Darcy's law based on nonequilibrium thermodynamics, the model, illustrated using a numerical example, quantitatively describes the hydraulic and mechanical properties of unsaturated bentonite. The model reveals the notable impact of soil plasticity and expansiveness on the stress and strain in HM coupling.