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<p>In the construction of deep geological repository for high-level radioactive waste (HLW), bentonite is pre-compacted and then positioned in galleries, inevitably producing technological voids. Upon hydration, self-sealing of technological voids happens, inducing a certain heterogeneity of dry density. The subsequent self-healing promotes homogenization, but this homogenization process stops after a certain time, when the swelling forces are lower than the friction forces at each element throughout the cross-section of the sample. This study investigates the mechanical behaviour of the density homogenization process and then proposes a theoretical method of swelling pressure prediction for compacted bentonite with different initial technological voids. The good performance is verified by the experimental results of the MX80 bentonite/Callovo-Oxfordian (COx) claystone mixture, a buffer material considered in the Cigéo project in France. On this basis, the effects of the technological void ratio on homogenization and in turn on overall swelling pressure development are analysed. For the homogenization process, the intersection points of the equilibrium and non-equilibrium zones reveal that the compacted bentonite with a lower initial technological void does not necessarily have an accelerated self-healing process, although the gradient of dry density is flatter and the variation of swelling pressures is higher throughout the cross-section. For swelling pressure development, a comparison between the predicted final equilibrium state and the measured non-equilibrium state interprets the decline of overall swelling pressure with the homogenization process observed in previous laboratory tests.</p>

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Investigation on the density homogenization and swelling pressure evolution of compacted bentonite with technological voids based on friction analysis

  • 期刊论文

  • 发表日期：

    2026年7月20日

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  • Jing Ma,
  • Yong-gui Chen,
  • Yu-jun Cui,
  • Zhao Sun,
  • Wei-min Ye,
  • Qiong Wang

摘要

In the construction of deep geological repository for high-level radioactive waste (HLW), bentonite is pre-compacted and then positioned in galleries, inevitably producing technological voids. Upon hydration, self-sealing of technological voids happens, inducing a certain heterogeneity of dry density. The subsequent self-healing promotes homogenization, but this homogenization process stops after a certain time, when the swelling forces are lower than the friction forces at each element throughout the cross-section of the sample. This study investigates the mechanical behaviour of the density homogenization process and then proposes a theoretical method of swelling pressure prediction for compacted bentonite with different initial technological voids. The good performance is verified by the experimental results of the MX80 bentonite/Callovo-Oxfordian (COx) claystone mixture, a buffer material considered in the Cigéo project in France. On this basis, the effects of the technological void ratio on homogenization and in turn on overall swelling pressure development are analysed. For the homogenization process, the intersection points of the equilibrium and non-equilibrium zones reveal that the compacted bentonite with a lower initial technological void does not necessarily have an accelerated self-healing process, although the gradient of dry density is flatter and the variation of swelling pressures is higher throughout the cross-section. For swelling pressure development, a comparison between the predicted final equilibrium state and the measured non-equilibrium state interprets the decline of overall swelling pressure with the homogenization process observed in previous laboratory tests.