ABSTRACT
The influence of chemo-mechanical couplings on the compressibility of bentonites has been satisfactorily explained from the high water content domain (stress lower than 0.01 MPa) to common geotechnical stresses (up to 1–2 MPa) on the basis of diffuse double layer (DDL) theories. However, this approach is less satisfactory for stresses higher than 2 MPa (Yong & Mohamed, 1992). The paper presents a study of the compressibility of three bentonites in a wide range of pressures (from 0.002 to 30 MPa). The studied smectites are considered as possible constituents of engineered clay barriers for nuclear waste disposal in Japan, France and Switzerland (Na Kunigel, Ca FoCa7 andWyoming Na/Ca MX80 clays respectively). Experimental testing also includes permeability measurements, mercury intrusion porosimetry and measurements of the consolidation coefficient cv . At high void ratios, cv decreases with decreasing void ratio, as expected, but at low void ratios, the opposite trend is observed. Related changes in the compression curves also suggest important changes in the nature of pore water when the clay is compressed at very low void ratios. The limitations of standard DDL models in this zone are discussed, and the predominant effects of adsorption phenomena related to the solvatation complexes that hydrate exchangeable cations, as suggested by Sposito & Prost (1982), are described.
