A hydromechanical material model for compacted bentonite

Abstract

This paper presents a new hydromechanical model, developed with the intention to be used for predicting the mechanical evolution of compacted bentonite components in repositories for spent nuclear fuel. The model is based on a thermodynamic relation for the chemical potential of the clay water, and uses empirical functions which are parametrized and calibrated with data on water retention properties at free swelling conditions, swelling pressure, and shear strength; the latter two are central for defining technical requirements for the bentonite buffer components. This results in a model which at its core incorporates all these properties, as well as the hysteresis behaviour. The validity of the model was investigated by analysing nine experimental test conditions, using COMSOL Multiphysics®, with a single set of parameter values. Model results were compared with experimental data for both saturated conditions (free swelling retention test; oedometer tests and triaxial compression tests) and for unsaturated conditions (swelling pressure build-up; swelling or shrinkage at constant load; compression at constant water or constant suction and unconfined compression tests). These comparisons gave a broad demonstration of the predictive capabilities of the model. Some limitation of the model regarding the representation of shrinkage, the shear strength at lower water contents, and the path dependence can nevertheless be noted.