Environmental Geology

, Volume 57, Issue 6, pp 1325–1335 | Cite as

Study of the initiation and propagation of excavation damaged zones around openings in argillaceous rock

  • Alain Millard
  • Jobst Maßmann
  • Amel Rejeb
  • Shin Uehara
Special Issue

Abstract

The study of the creation and evolution of the excavation disturbed zone (EDZ) in argillaceous rocks is a major issue for the safety of nuclear wastes underground repositories. In this context, the argillaceous Tournemire site has provided a unique opportunity to study the evolution of the EDZ with time thanks to the existence of three openings of different ages. A thorough characterization of the EDZ has been conducted by different means such as visual observation, analysis of samples extracted from drilled boreholes, EDZ permeability measurements, etc. On the basis of these measurements, a conceptual model of the EDZ initiation and propagation at the Tournemire site has been proposed. In order to validate this model, numerical simulations of increasing complexity have been carried out. In a first attempt, the response of the rock mass to the excavation phase, followed by seasonal cyclic variations of temperature and relative humidity inside the opening, has been simulated by means of a purely mechanical analysis, using a simple elastic material model. The EDZ has been estimated by post-processing the calculated stress states, using a Mohr–Coulomb failure criterion. The results obtained show that no EDZ could be predicted unless adopting a low cohesion value for the rock mass. Moreover, the deferred nature of the EDZ formation in Tournemire could not be reproduced. These limitations have then been suppressed by using a coupled viscoplastic-damaging mechanical model, the parameters of which have been identified from different laboratory experiments. With this model, a time evolution of the EDZ could be predicted, but the EDZ pattern could not match the one observed in situ. Finally, in view of the importance of the hydraulic couplings, unsaturated hydro-mechanical calculations have been carried out to investigate the effect of the numerous seasonal variations cycles and the resulting shrinkage.

Keywords

Excavation Argillite Damage Numerical simulation Hydro-mechanical coupling 

Notes

Acknowledgments

The authors like to acknowledge the Institut de Radioprotection et de Sûreté Nucléaire (IRSN), France, for providing the in situ data. The work was supported in parts by the Commisariat à l’Energie Atomique (CEA), France.

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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Alain Millard
    • 1
  • Jobst Maßmann
    • 2
  • Amel Rejeb
    • 3
  • Shin Uehara
    • 4
  1. 1.Commissariat à l’Energie Atomique, CEN SaclayGif sur YvetteFrance
  2. 2.Institute of Fluid Mechanics and Computer Applications in Civil EngineeringLeibniz Universität HannoverHannoverGermany
  3. 3.Institut de Radioprotection et de Sûreté NucléaireFontenay-aux-RosesFrance
  4. 4.Department of Urban and Environmental EngineeringKyoto UniversityNishikyo-KuJapan

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