Numerical Investigation of the Mechanical Behaviour of Tournemire Argillite

"In this paper, the mechanical properties of Tournemire argillite are modeled using a mathematical framework which employs the microstructure tensor approach (Pietruszczak & Mroz, 2000). The experimental data incorporates the results of a series of triaxial tests (Abdi & Evgin, 2013) conducted at different orientation of bedding planes relative to the direction of loading. First, a plasticity framework is presented which involves the specification of the conditions at failure as well as the description of the irreversible deformation process. Later, a systematic procedure is outlined for identification of material functions/parameters involved. The paper is concluded by presenting the results of numerical simulations of the triaxial tests. It is demonstrated that the model can adequately reproduce the primary effects of anisotropy in the stable deformation regime as well as the onset of fracture.INTRODUCTIONThe understanding of the mechanical behaviour of argillaceous rocks is important in many types of geotechnical projects, including petroleum extraction, carbon dioxide sequestration as well as deep geological disposal of radioactive waste. In all these cases, the primary concern is the onset and propagation of damage due to excavation, transport of pore fluids and/or elevated temperature. The Canadian Nuclear Safety Commission (CNSC), Canada’s nuclear regulator, will be responsible for the licensing of future deep geological repositories. In order to evaluate the safety of deep geological repositories, CNSC staff keep abreast of scientific developments by collaborating with national and international partners on experimental and theoretical research on the long-term performance of those engineered and natural barriers. Through that collaboration, the CNSC has access to data resulting from experiments performed at different Underground Research Laboratories (URL). Such an URL is situated in Tournemire, France, in an argillaceous rock formation, the Tournemire argillite. The Tournemire argillite is characterized by the presence of closely spaced bedding planes and exhibits a strong anisotropic behaviour, so that its strength as well as deformation properties are directionally dependent."