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.