Bentonite　is　widely　used　as　an　engineering　barrier　in　radioactive　waste　disposal.　This　study　examined　the　hydromechanical　behavior　and　microstructural　evolution　of　a　bentonite　mixture　under　controlled　hydration,　utilizing　real-time　X-ray　micro-CT　imaging　to　capture　transitions　from　granular　to　dense　homogeneous　states.　The　results　demonstrated　that,　during　the　early　stages　of　hydration,　bentonite　pellets　experienced　substantial　swelling,　filling　inter-pellet　voids　and　transforming　from　a　loosely　packed　granular　structure　to　a　compact,　homogeneous　matrix.　This　transformation　significantly　reduced　the　porosity　from　an　initial　value　of　20%　to　below　0.1%　after　60　days,　thereby　substantially　lowering　the　material’s　permeability.　Particle　displacement　analysis,　employing　digital　image　correlation　techniques,　revealed　axial　displacements　of　up　to　2.6　mm　and　radial　displacements　of　up　to　0.9　mm,　highlighting　pronounced　void　closure　and　structural　reorganization.　The　study　also　examined　the　influence　of　initial　dry　density　heterogeneities　on　swelling　pressure　and　permeability,　providing　insights　for　optimizing　barrier　design.　The　findings　affirm　that　hydrated　bentonite　serves　as　a　highly　effective　low-permeability　barrier　for　sealing　deep　geological　repositories.　Its　capacity　for　environmental　adaptation,　demonstrated　through　self-healing　and　densification,　further　reinforces　its　suitability　for　critical　and　long-term　engineering　applications.　©　2025　by　the　authors.