Mechanical and Hydromechanical Behavior of Host Sedimentary Rocks for Deep Geological Repository for Nuclear Wastes
Creators: name: Abdi, Hadj
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2014
Subjects: Development of a DGR within sedimentary rocks for the disposal of nuclear wastes
Laboratory investigation of the mechanical behavior of anisotropic rocks
Modeling of the mechanical behavior of anisotropic rocks
Numerical simulation of the hydromechanical behaviour of sedimentary rocks
Tournemire argillite
Coubourg limestone
Deep geological repositories for nuclear wastes
Excavation damaged zone (EDZ)
Transversely isotropic materials
Shales

description: Sedimentary rocks are characterized with very low permeability (in the order of 10-22 m2), low diffusivity, a possible self-healing of fractures, and a good capacity to retard radionuclide transport. In recent years, sedimentary rocks are investigated by many research groups for their suitability for the disposal of radioactive waste. Development of deep geologic repositories (DGRs) for the storage of radioactive waste within these formations causes progressive modification to the state of stress, to the groundwater regime, and to the chemistry of the rock mass. Thermal effects due to the ongoing nuclear activity can cause additional disturbances to the system. All these changes in the system are coupled and time-dependent processes. These coupled processes can result in the development of an excavation damaged zone (EDZ) around excavations. More permeable than the undisturbed rock, the EDZ is likely to be a preferential pathway for water and gas flow. Consequently, the EDZ could be a potential exit pathway for the radioactive waste to biosphere. An investigation of the Hydraulic-Mechanical (HM) and Thermal-Hydraulic-Mechanical-Chemical (THMC) behaviour of sedimentary rock formations is essential for the development of DGRs within such formations. This research work consists of (1) an experimental investigation of the mechanical behaviour of the anisotropic Tournemire argillite, (2) modeling of the mechanical behaviour of the Tournemire argillite, and (3) numerical simulations of the mechanical and hydromechanical behavior of two host sedimentary rocks, the Tournemire argillite and Cobourg limestone, for deep geological repository for nuclear wastes. The experimental program includes the measurements of the physical properties of the Tournemire argillite and its mechanical response to loading during uniaxial compression tests, triaxial compression tests with different confining pressures, unconfined and confined cyclic compression tests, Brazilian tests, and creep tests. Also, acoustic emission events are recorded to detect the initiation and propagation of microcracks within the rock during the uniaxial testing. The approach for modeling the mechanical behaviour of the Tournemire argillite consists of four components: elastic properties of the argillite, a damage model, the proposed concept of mobilized strength parameters, and the classical theory of elastoplasticity. The combination of the four components results in an elastoplastic-damage model for describing the mechanical behaviour of the Tournemire argillite. The capabilities of the model are evaluated by simulating laboratory experiments. Numerical simulations consist of: (1) a numerical simulation of a mine-by-test experiment at the Tournemire site (France), and (2) numerical simulations of the mechanical and hydromechanical behaviour of the Cobourg limestone within the EDZ (Canada). The parameters influencing the initiation and evolution of EDZ over time in sedimentary rocks are discussed.