Experimental and numerical characterisation of the mechanical anisotropic properties of Boom Clay PhD Glusica Nemanja

Experimental and numerical characterisation of the mechanical anisotropic properties of Boom Clay.

The underground geological disposal of radioactive waste is today the most widely adopted solution in many countries to ensure long-term safety. In Belgium, Boom Clay represents a stable and potential host formation for the disposal of radioactive waste.

The research on Boom Clay was initiated in 1974 by the Belgian Nuclear Research Centre (SCK CEN). So far, many studies have been undertaken to understand its behaviour. Both laboratory test campaigns and in situ experiments in HADES URL have allowed a good understanding of the hydro-mechanical behaviour of the Boom Clay. However, open questions remain on the short- and long-term behaviour of clay around galleries. Dizier et al. (2022) have recently demonstrated that the clay mechanical anisotropy and the anisotropic in situ stress states have a major impact on the deformation modes of galleries.

So far, the role of the anisotropy of the strength properties was neglected in Boom Clay. Except very few triaxial tests that have been performed with different orientations of the bedding (Dao, 2015), only in situ experiments offered the opportunity to explore the anisotropy in Boom Clay. In that way, Chen et al. (2011) have shown that considering the anisotropic elastic properties of the Boom Clay in the analysis of the small-scale ATLAS heater test allowing bettering reproducing the main thermo-hydro-mechanical behaviour when the clay is submitted to an increase of temperature. However, in his study, parameters were deduced by back analysis of in situ measurements. 

This project aims to complement the current knowledge by focusing on the anisotropic behaviour of the Boom Clay and more particularly on the characterisation of the mechanical plastic anisotropy of the Boom Clay. The objective is to improve our understanding of the deformation mechanisms in the clay during the different phases of a geological disposal facility from the excavation to the thermal phase. It will be an added value in the optimisation of the disposal galleries by evaluating more precisely the loads acting on the galleries.

To reach this goal, this research project will be divided into three main phases:

1.  An experimental programme focusing on triaxial tests on Boom Clay with different orientations to the bedding and at different confining pressure values.
2. The development and the implementation of a new constitutive law taking into account the anisotropic plasticity. This model will be inspired by Pardoen (2015) who developed an anisotropic elaso-visco-plastic model for Callovo-Oxfordian claystone.

3. Modelling of a long-term in situ experiment such as the Connecting gallery, for which more than 20 years of experimental data are available during and after the construction.

Other relevant information:
This project is funded by SCK CEN. Because of that I have four supervisors, but only one of them is from ULiège. Since I am not sure whether you need details about all of them, I have included the information just in case.