A numerical study on the coupled hydro-mechanical behaviour of compacted bentonite

Jose A Bosch,Lyesse Laloui,Alessio Ferrari

doi:10.1051/e3sconf/202020510001

Jose A Bosch, Lyesse Laloui + Show 1 more

Open Access

https://doi.org/10.1051/e3sconf/202020510001

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Abstract

Understanding the mechanical behaviour of compacted bentonite upon re-saturation is of outmost importance in most designs of nuclear waste disposal repositories. The behaviour of bentonite is characterized by its stress-path dependency and it is typically interpreted on the basis of its microstructural interactions. Up to now, effective stress-based models have had limited success in reproducing consistently the main responses. Here a recently proposed model for the modelling of volumetric behaviour of compacted bentonites is extended to triaxial stress states. The model is formulated using a conventional effective stress expression and the degree of saturation. Because these two variables are directly related to the water retention, a suitable formulation for bentonites is used. The resulting equations are characterised by a high degree of hydro- mechanical couplings and a low number of material parameters, which can be obtained on the basis of well- established laboratory procedures. In order to demonstrate its capabilities, the model is used to simulate the behaviour of MX-80 bentonite for several stress paths under oedometric conditions. The emphasis is put on the process of parameter determination. The predictive capabilities of the model are also highlighted.

Highlights

One of the main challenges in the analysis of underground nuclear waste repositories that use bentonite as a sealing material, is the long-term prediction of dry density evolution and distribution of the bentonite
The model is based on the recently developed volumetric model presented in Bosch et al [2] which is formulated in terms of a single effective stress and the degree of saturation
The calibration procedure of all material parameters is shown for MX-80 bentonite, demonstrating that the determination of parameters can be done in a robust way on the basis of quantitative data from laboratory tests

Summary

Introduction

One of the main challenges in the analysis of underground nuclear waste repositories that use bentonite as a sealing material, is the long-term prediction of dry density evolution and distribution of the bentonite. In this regard, it is paramount the use of numerical models that can be calibrated on a well-defined basis and preferably with measurable properties, while being able to describe and predict the behaviour of bentonite satisfactorily. The model is based on the recently developed volumetric model presented in Bosch et al [2] which is formulated in terms of a single effective stress and the degree of saturation.

Numerical models

Determination of parameters

Model predictions

Conclusions