SWELLING PRESSURES OF SOME BENTONITES

摘要

The swelling pressures of several bentonites (Bentonite S-2, Febex, Calcigel, Montigel, Kunigel, Kunigel VI, Na-Kunigel, Alaska, Ca-Fourges, MX80, NaCa 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 compared with the reported experimental swelling pressures for both initially saturated and compacted-saturated conditions. Qualitative agreements between the theoretical predictions and the experimental results were noted for all the clays 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 higher 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-SteM plane. At smaller void ratios, the overlapping of the hydration layers influenced the swelling pressures. In this case, much stronger swelling pressures were exhibited by the clays.