Fundamental aspects of the hydromechanical behaviour of Callovo-Oxfordian claystone: From experimental studies to model calibration and validation

Within the framework of feasibility studies for a reversible, deep geological repository of high- and intermediate-level long-lived radioactive waste (HLW, IL-LLW), the French National Radioactive Waste Management Agency (Andra) is investigating the Callovo-Oxfordian (COx) claystone formation near Bure (northeast France) as a potential host formation for the repository. In 2000, Andra initiated construction of the Meuse Haute-Marne Underground Research Laboratory (MHM URL). Concurrently with on-site construction work, an extensive research program has been conducted, including theoretical and experimental studies and constitutive modelling. In-situ experiments provide an extensive data set for performance evaluation of models describing the thermo-hydro-mechanical behaviour of COx claystone under different conditions (excavation, heat, etc.). In 2012, a benchmark exercise was initiated to evaluate proposed models, including basic assumptions, mathematical descriptions, input variables and parameters, and to determine how these assumptions influence model outcomes with respect to in-situ experimental observations. The present paper outlines the main features of the hydromechanical behaviour of COx claystone and presents a series of laboratory test results (triaxial compression and creep tests) providing model development teams with a coherent database for model calibration and validation.