Swelling Pressures of some initially Saturated and Compacted Saturated Bentonites

Abstract

The swelling pressures of several bentonites (Bentonite S-2, Febex, Calcigel, Montigel, Kunigel, Kunigel V1, Na-Kunigel, Alaska, Ca-Fourges, MX80, Na-Ca MX80, Ca-Wyoming, and Na- Wyoming) were determined from the Gouy-Chapman diffuse double layer theory. Many of these bentonites have been considered as barrier and backfilling materials for the underground storage of nuclear waste in various countries. The theoretical swelling pressures were then compared with the reported experimental swelling pressures for both initially saturated and compacted saturated samples. Qualitative agreements between the theoretical predictions and the experimental results were noted for all the bentonites studied. However, it was noted that at low dry densities or high void ratios, the theory generally predicted higher swelling pressures with the reverse trend at high dry densities or low void ratios. The lesser magnitude of experimental swelling pressures at higher void ratios can possibly be attributed to the formation of clay domains. Such behaviour also supports the fact that the effects of counterion crowding near the surfaces of the clay platelets are to reduce the surface charge and the electric potential at the Gouy-Stern plane. At smaller void ratios, the overlapping of the Stern layers of adjacent clay platelets influenced the swelling pressures. In this case, much stronger swelling pressures were exhibited by the bentonites.