Arnaud Dizier

Hollow Cylinder Tests on Boom Clay: Modelling of Strain Localization in the Anisotropic Excavation Damaged Zone

Boom Clay is extensively studied as a potential candidate to host underground nuclear waste disposal in Belgium. To guarantee the safety of such a disposal, the mechanical behaviour of the clay during gallery excavation must be properly predicted. In that purpose, a hollow cylinder experiment on Boom Clay has been designed to reproduce, in a small-scale test, the Excavation Damaged Zone (EDZ) as experienced during the excavation of a disposal gallery in the underground. In this article, the focus is made on the hydro-mechanical constitutive interpretation of the displacement (experimentally obtained by medium resolution X-ray tomography scanning). The coupled hydro-mechanical response of Boom Clay in this experiment is addressed through finite element computations with a constitutive model including strain hardening/softening, elastic and plastic cross-anisotropy and a regularization method for the modelling of strain localization processes. The obtained results evidence the directional dependency of the mechanical response of the clay. The softening behaviour induces transient strain localization processes, addressed through a hydro-mechanical second grade model. The shape of the obtained damaged zone is clearly affected by the anisotropy of the materials, evidencing an eye-shaped EDZ. The modelling results agree with experiments not only qualitatively (in terms of the shape of the induced damaged zone), but also quantitatively (for the obtained displacement in three particular radial directions).

Multi-physical processes in geomechanics

ABSTRACT This paper is the basis for a course dedicated to the geomechanics modelling, taking into account multiphysics couplings. A number of different coupling are discussed, with respectively the fluid flow (saturated and unsaturated) and the thermal transfers in deformable porous media. Eventually some aspects on the numerical modelling with the finite element method are discussed.

Multi-physical processes in geomechanics – an introduction to constitutive modelling and coupling aspects

This paper is the basis for a course dedicated to the geomechanics modelling, taking into account multiphysics couplings. A number of different coupling are discussed, with respectively the fluid flow (saturated and unsaturated) and the thermal transfers in deformable porous media. Eventually some aspects on the numerical modelling with the finite element method are discussed.

Hydro-Mechanical Modelling of the Boom Clay Excavation, Convergence and Contact with Concrete Lining

The Boom Clay is considered as one of the potential host rock formation in Belgium for radioactive waste repository in deep geological layers. Gallery excavations will induce large hydro-mechanical disturbances around disposal system that need to be well understood and characterised. This study discusses particularly the role of interactions between the lining of the galleries and the host formation in the numerical characterisation of excavations in Boom Clay. The excavation and the convergence of the connecting gallery of the HADES underground research facility in Mol is modelled in a hydro-mechanical framework. Zero-thickness interface elements are used to manage numerically the contact between the host rock and the lining. Numerical predictions are compared with strains measurements recorded within the concrete segments of the lining in the underground research laboratory in Mol. The study highlights the impact of the anisotropic behavior of the host rock on the response of the model.