Geomechanics and Engineering

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Research on sealing ability of granular bentonite material after 10.5 years of engineered barrier experiment

  • Ni, Hongyang (State Key Laboratory for GeoMechanics and Deep Underground Engineering, and School of Mechanics and Civil Engineering, China University of Mining & Technology) ;
  • Liu, Jiangfeng (State Key Laboratory for GeoMechanics and Deep Underground Engineering, and School of Mechanics and Civil Engineering, China University of Mining & Technology) ;
  • Pu, Hai (State Key Laboratory for GeoMechanics and Deep Underground Engineering, and School of Mechanics and Civil Engineering, China University of Mining & Technology) ;
  • Zhang, Guimin (State Key Laboratory for GeoMechanics and Deep Underground Engineering, and School of Mechanics and Civil Engineering, China University of Mining & Technology) ;
  • Chen, Xu (State Key Laboratory for GeoMechanics and Deep Underground Engineering, and School of Mechanics and Civil Engineering, China University of Mining & Technology) ;
  • Skoczylas, Frederic (Laboratoire de Mechanique de Lille (LML), and Ecole Centrale de Lille)
  • Received : 2020.07.28
  • Accepted : 2021.11.10
  • Published : 2021.12.25
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Abstract

The gas permeability behavior of unsaturated bentonite-based materials is of major importance for ensuring effective sealing of high-level radwaste repositories. This study investigated this by taking a sample of Granular Bentonite Material (GBM) at the end of the Engineered Barrier Emplacement (EB) experiment in the Opalinus Clay, placing it under different humidity conditions until it achieved equilibration, and testing the change in the gas permeability under loading and unloading. Environmental humidity is shown to have a significant effect on the water content, saturation, porosity and dry density of GBM and to affect its gas permeability. Higher sensitivity to confining pressure is exhibited by samples equilibrated at higher relative humidity (RH). It should be noted that for the sample at RH=98%, when the confining pressure is raised from 1 MPa to 6 MPa, gas permeability can be reduced from 10-16 m2 to 10-19 m2, which is close to the requirements of gas tightness. Due to higher water content and easier compressibility, samples equilibrated under higher RH show greater irreversibility during the loading and unloading process. The effective gas permeability of highly saturated samples can be increased by 2-3 orders of magnitude after 105℃ drying. In addition, cracks possibly occurred during the dehydration and drying process will become the main channel for gas migration, which will greatly affect the sealing performance of GBM.

Keywords

Acknowledgement

The research described in this paper was financially supported by the Agence Nationale pour la Gestion des Dechets Radioactifs (ANDRA), the National Natural Science Foundation of China (No. 52174133, 51974296 and U1803118).

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