Authors: Vincent Labiouse Claire Sauthier Shuang You
Publish Date: 2013/02/15
Volume: 47, Issue: 1, Pages: 43-55
Abstract
In the context of nuclear waste disposal in clay formations laboratory experiments were performed to study at reduced scale the excavation damaged zone EDZ induced by the construction of galleries in the Boom clay formation For this purpose thickwalled hollow cylindrical samples were subjected after recovery of in situ stress conditions to a decrease in the inner confining pressure aiming at mimicking a gallery excavation Xray computed tomography XRCT scans of the specimens were carried out through the testing cell before and after the mechanical unloading and allowed to quantify the displacements undergone by the clay as a result of the mechanical unloading The deformation of the hollow cylinders and the inferred extent of the damaged zone around the central hole are found to depend on the orientation of the specimen with respect to the bedding planes and show a great similarity with in situ observations around galleries and boreholes at Mol URL in the Boom clay formation In the experiments performed on samples cored parallel to the bedding the damaged zone is not symmetrical with respect to the hole axis and extends more in the direction parallel to the bedding It is the same for the radial convergence of the hole walls which is larger in the direction parallel to bedding than in the perpendicular one In contrast a test on a sample cored perpendicularly to the bedding did not show any ovalisation of the central hole after the mechanical unloading These observations confirm the significance of the preexisting planes of weakness bedding planes in Boom clay and the need for a correct consideration of the related mechanical anisotropyThe authors acknowledge the financial support provided by the European Commission for the TIMODAZ project performed as part of the sixth EURATOM framework programme for nuclear research and training activities 2002–2006 under contract FI6WCT2007036449 They are grateful to Laurent Gastaldo LMREPFL for the experiments and to Martine Bernasconi of the Department of Diagnostic and Interventional Radiology of the CHUV Lausanne Cantonal Hospital for the Xray computed tomography scans of the hollow cylinders The third author also wishes to thank the China Scholarship Council CSC for the financial support provided for her stay at LMREPFL The authors are also grateful to Joël Sarout CSIRO and to anonymous reviewer whose suggestions and comments have helped to improve the quality of the paper
Keywords: