Modelling the Short- and Long-Term Hydro-Mechanical Behaviour of Argillaceous Limestone

Abstract of the technical presentation presented at:
IACMAG Conference, Wuhan, China
October 19–23, 2017

Prepared by:
T.S. Nguyen
Canadian Nuclear Safety Commission
Z. Li and X, Su

Abstract:

In Canada, the Cobourg limestone of the Michigan Basin is currently considered as one potential host formation for geological disposal. The understanding of the hydro-mechanical behaviour of such a host rock is an essential requirement for the assessment of its performance as a barrier against radionuclide migration. The excavation of galleries and shafts of a deep geologic repository (DGR) can induce damage in the surrounding rock. The excavation damage zone has higher permeability and reduced strength compared to the undisturbed rock and those factors must be considered in the design and safety assessment of the DGR.

In this research project initiated by the CNSC, the authors conducted experimental and theoretical research to assess the hydro-mechanical behaviour of the Cobourg limestone under undamaged and damaged conditions, both in the short and long terms. The short-term behaviour was investigated by a program of triaxial tests with the measurement of permeability evolution on specimens of Cobourg limestone. The authors formulated a coupled hydro-mechanical model to simulate the stress strain response and evolution of the permeability during those triaxial tests. Using creep and relaxation data from a similar limestone, the model was extended to include its long-term strength degradation. The model successfully simulated both the short-term and long-term hydro-mechanical behaviour of the limestone during those tests. This provides confidence that the main physical processes have been adequately understood and formulated.

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