Swelling creep diagenesis damage model for the Callovo-Oxfordian claystone

The French National Agency for Radioactive Waste Management (ANDRA) has been constructing an Underground Research Laboratory (URL) in Meuse/Haute-Marne since 2000 to determine the viability and protection of deep geological formation for hosting industrial nuclear waste repositories. The purpose of this URL is to describe the in situ properties and behavior of the Callovo-Oxfordian (COx) claystone. At the same time, various types of computational models have been developed to reproduce the in situ phenomena.

This paper presents an elastoviscoplastic model called SC2D: Swelling, Creep, Diagenesis, with anisotropic Damage, taking into account in situ measurements. This phenomenological model was developed to contribute to the understanding of the short- and long-term behavior of the COx claystone around the excavated drift. The model parameters are calibrated using in situ measurements and observations.

The model assumes that intact COx claystone (around from the excavated drift) exhibits elastic behavior with anisotropic damage in extension as macropores are occupied by calcite fibers. The short-term behavior of damaged COx claystone (near the excavated drift) is also characterized by an elastic mechanism with anisotropic damage. Sampling causes hydromechanical unloading that breaks the calcite fibers. Upon reloading the sample to site mean pressure, the damaged COx claystone first presents elastic behavior and then elastoplastic behavior depending on the load surface. Triaxial tests in axial compression and axial extension are conducted to validate this model with satisfactory results. Its long-term behavior follows an elastoviscoplastic mechanism.