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With a newly developed swelling pressure apparatus, swelling pressure tests were conducted to elucidate initial water content and specimen preparation method effects on swelling pressures (swelling pressure evaluation curve and equilibrium swelling pressure) of Kunigel-V1 bentonite. X-ray diffraction (XRD) tests were conducted to investigate the initial water content and specimen preparation method effects on basal spacing, including basal spacings of specimens before and after wetting. Experiments produced the following results. (1) The swelling pressure evaluation curve changed from a line with peak and valley to a line with early-stage steady rise as increasing initial water content. (2) The initial water content and specimen preparation method exerted no apparent effect on the equilibrium swelling pressure. (3) Basal spacing of the specimen before wetting was affected not only by the initial water content but also by the specimen preparation method. (4) The initial water content did not influence the basal spacing of the specimen after wetting. It was only affected by the specimen preparation method. Based on the swelling pressure evaluation curve patterns, swelling mechanisms during saturation for specimens with different initial conditions were discussed. Initial water content and specimen preparation method effects on equilibrium swelling pressure were explained carefully with basal spacings. Key words: initial water content, specimen preparation method, swelling pressures, XRD, 1. Introduction The deep geological disposal method was selected to address high-level radioactive waste (HLW) from the nuclear power industry by different countries (e.g., SKB 2011; NUMO 2022). In Japan, [...]

A multi-ring and a newly developed swelling pressure apparatus were adopted for measuring swelling pressure of three low dry density bentonites (sodium type: MX-80 and Kunigel-V1; calcium type: Kunibond). Subsequently, slices from the multiring were observed using X-ray diffraction to obtain basal spacings. Distance between particles was calculated from a basal spacing database. Relations between microstructural changes, including basal spacing and distance between particles, and swelling pressure are discussed. Results show that calcium-type bentonites have greater swelling pressure than sodium-type bentonites during saturation. When bentonites have the same cation type, lower montmorillonite content bentonite obtains smaller swelling pressures than the high montmorillonite content ones. Basal spacing increases drastically first and then maintains a stable value during saturation. All three bentonites gradually reach the 3 w state along with wetting (MX-80 and Kunigel-V1: 1-3 w; Kunibond: 2-3 w). The distance between particles increases with the saturation time. During saturation, swelling pressure generally rises with increasing basal spacing and increasing distance between particles. The mechanism for swelling pressure development is discussed. Key words: bentonites, swelling pressure, development mechanism, XRD, Introduction The deep geological disposal method has been discussed as a safe and effective means to store high-level radioactive waste (HLW). In a Japanese project, a multi-barrier system consisting of [...]

This study starts from a question: how would initial water content (wi) affect equilibrium swelling pressure (peq) of compacted bentonites in swelling pressure tests (ps tests)? However, discussions based on experiments involving a bentonite, Kunigel V1 (K_V1), are extended to the following issues: (a) the effect of wi on peq; (b) pore water density (ρpw); (c) the co-existence of crystalline and osmotic swelling; and (d) relation between peq and compaction tests (pc tests). It is revealed that wi has an insignificant effect on peq in general, although a significant effect may appear for relatively high wi and dry density (ρd) conditions. Two swelling types, crystalline swelling with basal spacing of montmorillonite (d001 = 1·0–1·9 nm) and osmotic swelling (d001 ≥ ∼4·0 nm), co-exist in a w range from 36 to 65%. With the fact that ρpw of K_V1 may range from 1·1 to 1·2 Mg/m3, it is expected that crystalline swelling may mainly govern peq in ps tests if the final dry density of a specimen (ρdf) is larger than 1·46 Mg/m3, while osmotic swelling may mainly govern if ρdf < 1·05 Mg/m3. Together with the results of pc tests, the effects of wi on peq are explained by the proposed conceptual model. [ABSTRACT FROM AUTHOR]