The Underground Research Laboratory of Meuse/Haute-Marne (URL MHM) is being constructed by the French National Agency for Radioactive Waste Management (Andra) to study the feasibility of a geological repository in the Callovo-Oxfordian (COx) claystone. The URL MHM comprises a network of drifts excavated mainly in the direction of the main horizontal stresses. Instrumentation is used to monitor the behavior of the host rock, lining and support structures. The evaluation of these measurements provides a characterization of the time-dependent behavior of the drifts, which is essential information for the design of the future repository structures. The in-situ investigations carried out at the URL MHM have identified the development of an excavation-induced fracture zone whose horizontal and vertical extensions depend on the orientation of the drifts in relation to the state of stress. In addition, the monitoring of displacements at the wall and inside the rock indicates a highly anisotropic response intrinsically linked to the orientation of the fractured zones.

The thesis project is based on two main axes: the direct analysis of in-situ measurements and the numerical modelling of several drifts with variations related in particular to excavation directions and types of lining and support. Among the evaluation of various auscultation data, particular attention is given to the analysis of the convergence. The approach used considers an elliptical evolution of the drifts’ closure, which is approximated by the fitting of a semi-empirical convergence law. This allows us to identify the anisotropic ratios between vertical and horizontal convergences and to distinguish the influence of the excavation face advance and that of the time-dependent behavior of the rock on the observed response. For sections where it has not been possible to measure vertical convergence due to working site constraints, the evolution of convergence along this axis is estimated using the elliptical fitting. The convergence law curves are used to characterize the behavior of drifts over time and to extrapolate this behavior in the long term.

A numerical model is established to simulate the behavior of structures excavated in COx claystone, using in situ data from the drifts to validate the modelling assumptions. An isotropic viscoelastic-plastic behavior is assigned to the rock mass using the CVISC model. The approach considers the explicit introduction of the fractured zone and the assumption that only its time-dependent behavior is distinct from that of the intact rock. The viscoelastic parameters of the intact and fractured rocks are calibrated independently, allowing the model to reproduce the global in-situ response inside the rock mass. In addition, simulations of different excavation scenarios (orientation, geometry, excavation methods, and support types) are considered. This allows us to assess the influence of structural elements, such as compressible wedges, on the behavior of the temporary and final supports. This work proposes a new analysis approach based on a correlation between the in-situ evolution of convergence at the wall and the extension of the fractured zone to be introduced into the numerical model. The application of this analysis could be useful for design studies of future galleries excavated in the COx due to its simple implementation in existing calculation tools and its ability to predict the long-term evolution of the response of structures.