Rock Mechanics and Rock Engineering

, Volume 47, Issue 1, pp 57–70 | Cite as

Laboratory and In Situ Simulation Tests of the Excavation Damaged Zone Around Galleries in Opalinus Clay

  • Vincent Labiouse
  • Tim Vietor
Original Paper


In the context of nuclear waste disposal in clay formations, laboratory and in situ simulation experiments were performed to study at reduced scale the excavation damaged zone (EDZ) around tunnels in the indurated Opalinus Clay at Mont Terri, Switzerland. In the laboratory, thick-walled hollow cylindrical specimens were subjected to a mechanical unloading mimicking a gallery excavation. In samples cored parallel to bedding, cracks sub-parallel to the bedding planes open and lead to a buckling failure in two regions that extend from the borehole in the direction normal to bedding. The behaviour is clearly anisotropic. On the other hand, in experiments performed on specimens cored perpendicular to bedding, there is no indication of failure around the hole and the response of the hollow cylinder sample is mainly isotropic. The in situ experiment at Mont Terri which consisted in the overcoring of a resin-injected borehole that follows the bedding strike of the Opalinus Clay showed a striking similarity between the induced damaged zone and the fracture pattern observed in the hollow cylinder tests on samples cored parallel to bedding and such a bedding controlled “Excavation” Damaged Zone is as well consistent with the distinct fracture patterns observed at Mont Terri depending on the orientation of holes/galleries with respect to the bedding planes. Interestingly, the damaged zone observed in the hollow cylinder tests on samples cored parallel to bedding and in situ around URL galleries is found to develop in reverse directions in Boom Clay (Mol) and in Opalinus Clay (Mont Terri). This most probably results from different failure mechanisms, i.e. shear failure along conjugated planes in the plastic Boom Clay, but bedding plane splitting and buckling in the indurated Opalinus Clay.


Hollow cylinder test In situ simulation test Excavation damaged zone X-ray computed tomography Opalinus Clay Nuclear waste disposal 



The TIMODAZ project is co-funded by the European Commission and performed as part of the sixth EURATOM Framework Programme for nuclear research and training activities (2002-2006) under contract FI6 W-CT-2007-036449. The Mont Terri URL is an international project of 14 partners from 7 countries and is lead by Director P. Bossart of the Federal Office for Topography, Swisstopo. The support of the Mont Terri staff under the supervision of the Project Manager C. Nussbaum is gratefully acknowledged. Further acknowledgements go to Laurent Gastaldo and Shuang You who contributed to the LMR-EPFL experiment and to Martine Bernasconi of the Department of Diagnostic and Interventional Radiology of the CHUV (Lausanne Cantonal Hospital) for the X-ray computed tomography scans of the hollow cylinders. Finally, the Authors are grateful to two anonymous reviewers, whose suggestions and comments helped to improve the quality of the paper.


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Copyright information

© Springer-Verlag Wien 2013

Authors and Affiliations

  1. 1.Rock Mechanics Laboratory (LMR), Ecole Polytechnique Fédérale de Lausanne (EPFL)LausanneSwitzerland
  2. 2.National Cooperative for the Disposal of Radioactive Waste (NAGRA)WettingenSwitzerland

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