BCV bentonite hydromechanical behaviour and modelling

Abstract

It is assumed that clay materials such as bentonites will be used as the buffer and backfill of high-level radioactive waste disposal. Due to the very long timescale, the design can be based only on mathematical models that have been thoroughly validated via the use of high-quality laboratory data. The presentation of an extensive laboratory dataset, accompanied by the validation of a bentonite constitutive model, comprises the main topic of this paper. The objectives of the laboratory research were to determine the basic hydromechanical properties of BCV bentonite and to study the stress path behaviour of this bentonite. The laboratory results revealed that the hydromechanical behaviour is highly dependent on the stress path assumed, as well as the method of water introduction into the sample. The results further indicate that the micro- and macrostructures are constantly evolving, which exerts a significant impact on the determination of the material properties and the development of mathematical models. Moreover, it was demonstrated that swelling pressure tests, although they are typically considered to be element tests (with constant fields of state variables), when adopted by researchers for the calibration of constitutive models, do not in fact constitute element tests. A hypoplastic model of the behaviour of bentonite was implemented and validated using the experimental data obtained. It was demonstrated that the hypoplastic model accurately predicted the main behavioural features of bentonite that are important in terms of the prediction of the behaviour of the buffer in nuclear waste repositories.