Experimental study on swelling pressure of low dry density compacted bentonites during saturation combining X-ray diffraction

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 multi -ring 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.

Automated summary

In this study, a multi-ring and a newly developed swelling pressure apparatus were used to measure the swelling pressure of three low dry density bentonites. X-ray diffraction was employed to observe slices from the multi-ring and obtain basal spacings, and the distance between particles was calculated using a basal spacing database. The relationship between microstructural changes (including basal spacing and distance between particles) and swelling pressure was discussed. Results showed that calcium-type bentonites had higher swelling pressure than sodium-type bentonites during saturation. When bentonites had the same cation type, those with lower montmorillonite content had smaller swelling pressures. Basal spacing increased significantly at the beginning and then remained stable during saturation. All three bentonites gradually reached the 3 w state with wetting. The distance between particles increased with saturation time. Swelling pressure generally increased with increasing basal spacing and distance between particles during saturation. The mechanism of swelling pressure development was also discussed.