Mechanical constitutive models of unsaturated expansive clays: A review of BExM

Mechanical constitutive models of unsaturated expansive clays are essential for the performance assessment and design of engineered barrier system (EBS) in the repository. Mechanical constitutive models of unsaturated expansive clays have been studied by many researchers. Among them, the BBM (Barcelona Basic Model) presented by Alonso et al. has been widely used. It is a model for nonexpansive or slightly swelling clays, considering only the macrostructural level responsible for major structural rearrangement and also allowing for the small reversible swelling in the elastic zone. The BExM (Barcelona Expansive Model), which overcomes the limitations of the BBM, has been used to describe the mechanical behavior of unsaturated expansive clays. The present paper reviews the model concept and mathematical formulation of the BExM and intends to provide the technical knowledge and information needed to test and model the mechanical behavior of the bentonite buffer for the KRS repository