Compacted bentonite and sand-bentonite mixtures are attracting greater attention as buffer materials for repositories of high-level nuclear waste. Buffer material must have the swelling characteristics and is expected to fill up the space between buffer material and surrounding ground by swelling. This role is called as "Self-sealing." To design the buffer material from the viewpoint of "Self-sealing", we must evaluate the swelling characteristics of compacted bentonite and sand-bentonite mixtures. For the purpose described above, we performed various laboratory tests on the swelling deformation and swelling pressure of compacted bentonite and sand-bentonite mixtures. This study proposed a model of the swelling characteristics and a new parameter "Swelling volumetric strain of montmorillonite," which were able to evaluate the swelling characteristics of buffer materials on the basis of laboratory test results and observation of swelling behavior of bentonite in the buffer materials. Furthermore, this study proposed the prediction method for swelling characteristics of buffer material, which can evaluate the swelling behavior of buffer materials at various environmental conditions. The applicability of this method was investigated by comparing the predicted results with laboratory test results on the swelling deformation and swelling pressure of buffer materials.
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