Swelling Pressures of Compacted Bentonite/Sand Mixtures

Abstract

Compacted bentonitic clay/sand mixtures are being considered for use as buffer materials in the Canadian concept for nuclear fuel waste disposal. This paper describes a laboratory study of the swelling pressures that develop in statically compacted, air-dry specimens of mixtures of sodium bentonite and silica sand as they are saturated with double-distilled, deionized water. The results are interpreted with the aid of scanning electron microscope observations of the soils' structures.It is shown that the sand acts as an inert filler material, and swelling pressures are controlled by a parameter termed the effective clay dry density, γC, defined as the ratio of the mass of clay to the combined volume of the claq plus voids in the mixture. A threshold value of γC exists below which swelling pressures can be expected to be isotropic. Above the threshold value of γC, pressures parallel to the axis of compaction can be expected to be greatgr than those perpendicular to it. This is related to a change in soil fabric as γC is increased above the threshold value. For the Canadian disposal concept, γC would probably be below the limiting value and swelling pressures of 2.5 MPS or less are expected. The swelling pressures are likely to be isotropic within a saturated buffer mass.

Sealing performance of bentonite and bentonite/crushed rock borehole plugs

“…According to the results presented by Gray et al (1985), the swelling pressures of clays having dry densities larger than 1.7 g/cm3 may be predicted from Eq. (5.16), or from Eq.…”

“…For T = 293OK (20 OC) , v -1, B -1015 cm/mmole, G, -2.75, and X, -4 A, Gray et al (1985) obtain the following relation: Following the same approach and taking the correction factor into account, a more general form of Eq. (5.16) is proposed in this study:…”

“…(5.17), from Yong and Warkentin (1975) and Gray et al (1985), can be used for the prediction of swelling pressure of clays for dry clay densities up to 1.7 g/cm3. an appropriate value of the effective specific surface. Eq.…”

“…A generalized form of the Yong and Warkentin (1975) model has been derived for low salt concentrations with a correction factor of 1/3 as suggested by Gray et al (1985). In general, an appropriate composition for…”

Sorption and Diffusion of 1-125 and Sr-90 in a Mixture of Bentonite and Crushed Granite Backfill of a Radioactive Waste Repository

“…An attempt was made to explain this using the concept of "effective clay dry density" suggested by Gray et al [30]. The effective clay dry density q^^ is defmed as the ratio of the mass of clay to the volume of clay plus void in the system.…”