laboratory and numerical investigation of the anisotropy behaviour of natural Boom clay (PhD)

In the course of the characterisation programme of the Boom Clay, a potential host rock for geological disposal of radioactive wastes, the roles of anisotropy of key thermo-hydro-mechanical (THM) properties in the perturbation of Boom clay have been put in evidence. A lot of phenomena observed in underground laboratory HADES and in surface laboratories can only be explained by the anisotropy behaviour of the Boom clay, such as the fractures pattern around gallery excavation and the large extent hydraulic disturbed zone due to the excavation. In parallel, evidences of anisotropic THM behaviour of the clay massif were obtained through laboratory tests. Recent laboratory tests on Boom clay performed in the frame of EC project TIMODAZ (Thermal Impact on the Damaged Zone around a Radioactive Waste Disposal in Clay Host Rocks) shows clearly the important anisotropic characteristics of Boom clay.

Consequently, a deep investigation on the anisotropy reveals necessary to understand the THM process of Boom clay around a disposal repository. Indeed, till now, the characterisation programme of Boom clay focuses on the isotropic geomechanical characterisation.

The objectives of this PhD proposal are to characterise the anisotropy of THM properties in the laboratory and develop an elasto-plastic-damage constitutive model including anisotropy of Boom clay. To this end, the research program will cover two aspects:

·       Laboratory testing: advanced (non destructive) measurement techniques (Digital Image Deformation Measurement System based on sub-pixel accurate corner detection method, mCT, etc.) will be applied to tri-axial tests to obtain precisely the strain localisation and damage evolution with stress states.

·       Numerical investigation: based on the laboratory test results and collected anisotropy evidences from in situ experiments and observation in HADES, an elasto-plastic-damage model will be developed with consideration of anisotropy (intrinsic and induced) of Boom clay. The developed constitutive model will be applied to model the in situ experiments: excavation of connecting gallery.

The research program will focus on the role of anisotropy on the damage generation of Boom clay.