ABSTRACT:

Laboratory experiments carried out at the LMR-EPFL on thick-walled hollow cylindrical samples aim at modelling at small-scale conditions similar to those that will be experienced by host rocks around disposal galleries for heat emitting radioactive waste. The paper presents results on a Boom Clay sample cored parallel to the bedding planes and subjected to a decrease of the confining pressure in the central hole of the hollow cylinder. It focuses on medium resolution X-Ray Computed Tomography (XRCT) scans of the sample inside the testing cell that were carried out with a medical scanner. By comparing the scans before and after the mechanical unloading (tracking of the movement of pyrite inclusions), quantitative analyses of the displacements undergone by the clay can be performed.The observations point out a significant mechanical anisotropy of Boom Clay related to its bedding planes.

1 INTRODUCTION

Within the 6th EURATOM Framework Program of the European Community, the TIMODAZ project (Thermal Impact on the Damaged Zone Around a RadioactiveWaste Disposal in Clay Host Rocks) aims at studying the fracturing and self-sealing processes that develop in the Excavation Damaged Zone (EDZ) around disposal galleries for heat emitting radioactive waste and at assessing the impact of the thermal phase on their evolution. Three different potential geological formations for deep radioactive waste repositories are investigated in the project, i.e. the Boom, Opalinus and Callovo-Oxfordian clayey formations. This paper presents results on a sample of Boom Clay (N° 13A) cored parallel to the bedding planes. After a short presentation of the testing device and procedure, the paper focuses on medium resolution X-Ray Computed Tomography (XRCT) scans of the sample carried out at the CHUV (Cantonal Hospital in Lausanne) before and after the mechanical unloading and provides some explanations about the image processing performed to analyse the displacements undergone by the clay.

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