EXPERIMENTAL-STUDY ON SWELLING CHARACTERISTICS OF COMPACTED BENTONITE

Compacted bentonites are attracting greater attention as back-filling (buffer) materials for repositories of high-level nuclear waste. Howev er, since there are few studies about the swelling characteristics of compacted bentonites, it is first necessary to clarify the fundamental swelling characteristics in detail. For this purpose, various laborat ory tests on the swelling deformation and swelling pressure of compact ed bentonites were performed and the results analyzed. The following c onclusions were drawn from the study. (i) The curve of swelling deform ation Versus time is strongly dependent on the initial dry density, ve rtical pressure, and initial water content. The maximum swelling defor mation, however, is almost independent of initial water content, and t he maximum swelling deformation increases in proportion to the initial dry density. (ii) The maximum swelling pressure increases exponential ly with increasing initial dry density, whereas the maximum swelling p ressure is almost independent of initial water content. (iii) The swel ling mechanism of compacted bentonite was considered on the basis of t he swelling behavior of swelling clay particles such as montmorillonit e. Furthermore, a model of the swelling characteristics and a new para meter (swelling volumetric strain of montmorillonite), which were able to evaluate the swelling characteristics of compacted bentonite, were proposed.