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<p>Compacted bentonite has been selected as the preferred buffer material for its remarkable swelling potential. This study, framed within the context of China’s deep geological disposal, aims to investigate the swelling of compacted Gaomiaozi (GMZ) bentonite into technological voids under Beishan granite host-rock. A series of laboratory experiments including short-term visualized hydration, long-term soaking, interfacial shearing, and swelling pressure tests were conducted. The experimental setup mainly involved a cake-shaped bentonite sample centrally embedded within a ring-shaped granite, with annular technological voids of varying volume ratios generated by employing bentonite samples of different diameters. Macro–micro characterization and hydro-mechanical responses were systematically analyzed upon hydration, thereby elucidating the underlying mechanisms of the swelling behavior of compacted bentonite into technological voids under granite boundary. Beyond the well-reported three phenomenological stages (filling, cracking, and homogenizing), the investigation also captured distinct granite fracturing and bentonite intruding phenomena, a finding markedly different from steel boundary. Compacted bentonite with annular technological voids exhibited significant initial radial heterogeneity. As hydration time increased, technological voids gradually closed, and the heterogeneity in the physical state (dry density, water content, and saturation degree) and pore size distributions decreased and then tended to stabilize. Nevertheless, the radial spatial heterogeneity persisted at the final stable state, implying that complete homogeneity cannot be achieved. The radial swelling pressure after bentonite swelling into technological voids was smaller than that of samples with the same montmorillonite void ratio under constant volume condition, which was suspected to be due to energy dissipation caused by sidewall friction during bentonite swelling deformation. The interfacial shear strength between bentonite and granite was predominantly governed by swelling pressure, satisfying the Mohr–Coulomb criterion. Notably, the interfacial shear strength under long-term soaking conditions was significantly higher than the stable value observed in short-term visualized hydration tests, primarily attributed to bentonite&#xa0;gel intruding into granite micro-fissures, strengthening the interfacial bonds.</p>

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Swelling of Compacted Bentonite into Technological Voids under Granite Boundary: Macro–micro Characterization and Hydro-mechanical Responses

  • 期刊论文

  • 发表日期：

    2025年10月14日

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  • Kun-peng Li,
  • Yong-gui Chen,
  • Wei-min Ye,
  • Zhao Sun,
  • Qiong Wang,
  • Xing-guang Zhao

摘要

Compacted bentonite has been selected as the preferred buffer material for its remarkable swelling potential. This study, framed within the context of China’s deep geological disposal, aims to investigate the swelling of compacted Gaomiaozi (GMZ) bentonite into technological voids under Beishan granite host-rock. A series of laboratory experiments including short-term visualized hydration, long-term soaking, interfacial shearing, and swelling pressure tests were conducted. The experimental setup mainly involved a cake-shaped bentonite sample centrally embedded within a ring-shaped granite, with annular technological voids of varying volume ratios generated by employing bentonite samples of different diameters. Macro–micro characterization and hydro-mechanical responses were systematically analyzed upon hydration, thereby elucidating the underlying mechanisms of the swelling behavior of compacted bentonite into technological voids under granite boundary. Beyond the well-reported three phenomenological stages (filling, cracking, and homogenizing), the investigation also captured distinct granite fracturing and bentonite intruding phenomena, a finding markedly different from steel boundary. Compacted bentonite with annular technological voids exhibited significant initial radial heterogeneity. As hydration time increased, technological voids gradually closed, and the heterogeneity in the physical state (dry density, water content, and saturation degree) and pore size distributions decreased and then tended to stabilize. Nevertheless, the radial spatial heterogeneity persisted at the final stable state, implying that complete homogeneity cannot be achieved. The radial swelling pressure after bentonite swelling into technological voids was smaller than that of samples with the same montmorillonite void ratio under constant volume condition, which was suspected to be due to energy dissipation caused by sidewall friction during bentonite swelling deformation. The interfacial shear strength between bentonite and granite was predominantly governed by swelling pressure, satisfying the Mohr–Coulomb criterion. Notably, the interfacial shear strength under long-term soaking conditions was significantly higher than the stable value observed in short-term visualized hydration tests, primarily attributed to bentonite gel intruding into granite micro-fissures, strengthening the interfacial bonds.