Effect of Dry Density and Salt Solution on Swelling Pressure of Compacted Bentonite

Abstract

In many underground nuclear waste disposal facilities, bentonite has been referred as buffer and backfilling materials due to its high swelling capability, high water holding ability and low permeability. Since bentonite gets limited space for occupying itself around the underground nuclear waste containers and in case of water intrusion to the nuclear waste disposal repository, it exerts swelling pressure, therefore, the determination of swelling pressures of compacted bentonites is a significant aspect for such kind of bentonite-built barrier systems. Many of the waste repositories are commissioned in locations where the ground water either contains significant amount of salts or the repositories are anticipated to receive saline water from sea. Hence in this current research, an effort has been made to find out the swelling pressure of compacted bentonites under the influence of dry density and salt solution. Constant volume swelling pressure tests were carried out with compacted bentonite specimens of targeted dry densities varying between 1.2 to 1.8 Mg/m3 using distilled water and solutions of NaCl (0.5 and 1.0 M) as the hydrating ?uids. It was found that the swelling pressure of compacted bentonite specimens increased with increase in dry density.In all the cases,the equilibrium swelling pressures were found to reach within about 7 days for all cases irrespective of the dry density and the bulk solution. However, the influence of saline solutions was found to decrease the swelling pressure of the bentonite.