Interfacial self-healing behavior of densely compacted Gaomiaozi bentonite: physical and hydraulic aspects

In deep geological repositories for disposing of high-level radioactive waste, various types of bentonite interfaces exist in the engineered barrier system. The hydromechanical resistances of the bentonite buffer rely on the sealing and healing of these interfaces, especially the assembled bentonite-bentonite interfaces that can heal spontaneously upon bentonite hydration (i.e., self-healing). This study explored the interfacial self-healing behavior of densely compacted Gaomiaozi bentonite via laboratory tests and evaluated the interfacial self-healing capacity in terms of the physical and hydraulic properties. In detail, the interfacial healing test results indicate that self-healing of the assembled bentonite interface initiated at low suction values (total suction s < 20 MPa) under confined conditions (when the assembled interface is compressed by the swelling pressure). The infiltration test results suggest an increased interfacial hydraulic resistance after long-time water infiltration and a slightly higher permeability than the saturated intact bentonite specimen with the same final dry density. The swelling pressure test results show that the bentonite assembly developed much lower swelling pressure than the intact bentonite specimen (for a given total suction) and achieved a rotated and slightly enhanced swelling pressure anisotropy compared with the saturated intact bentonite specimen with the same final dry density. The MIP test results reveal that the healed interfacial zone has similar pore structure as its adjacent intact zone. Thus, it is concluded that densely compacted Gaomiaozi bentonite has strong interfacial self-healing capacity in physical and hydraulic aspects.