2007:09 DECOVALEX-THMC - Task C

This report describes the results of Task C1 of the international DECOVALEX– THMC project devoted to Excavation Damage Zone (EDZ) in argillaceous rock at the Tournemire site in France. Task C of the project is aimed to understand the physical phenomena induced by excavation in the argillaceous rock. The task is to develop adequate numerical models for interpretation of observed damaged zones around three different openings excavated at different time at the Tournemire site. The research teams are asked to model the evolution of the EDZ with time and to compare the results with measurements performed at the site.

Three research teams are participating in this task:

  • CEA (Commissariat of Atomic Energy, France) and the IRSN (Institute of Radioprotection and Nuclear safety, France);
  • ISEB (Institute of Fluid Mechanics and Computer Applications in Civil Engineering, University of Hanover, Germany) supported by the BGR (Federal Institute for Geosciences and Natural Resources, Germany);
  • KU (Department of Urban and Environmental Engineering, Kyoto University, Japan) supported by the JAEA (Japan Atomic Energy Agency, Japan).

This report presents a description and definition of Task C including a geological description of the site, the geomechanical characterisation of the argillaceous rocks and in particular the stress field, mechanical properties and hydraulic properties. Thereafter, the EDZ characterization from geological mapping and permeability measurements are presented. The EDZ in the 100 years old tunnel drilled manually and with its reinforcement of limestone blocks is very different from the EDZ observed in drifts excavated with road-headers 3 and 10 years ago.

According to the task definition, Task C1 concerns the understanding of the EDZ development around the 100 years old tunnel. The failure mechanism should be identified by analysing the in situ stress field and the orientation of the bedding planes with respect to the axis of the tunnel and the degree of anisotropy. Numerical models have to be developed to predict the extent of the EDZ around the tunnel. The results of the calculations using various approaches should be compared with measured data in order to understand the physical processes and validate the computer models used in the simulations.