Small-strain shear stiffness of compacted bentonites for engineered barrier system

Abstract

The shear modulus (G) of two different bentonites was measured by means of a resonant column apparatus. The samples were compacted at different dry densities and degrees of saturation and tested with different confinement pressures and strains levels for studying the influence of these parameters on the shear modulus. The results show similar tendencies in both bentonites: the shear modulus increases as the dry density increases and exhibits maximum shear modulus when degree of saturation is around 80%. An empirical equation, taking into account the microstructure of the clays, is used to evaluate the shear modulus at small strains as a function of dry density and degree of saturation. Although the values of the shear modulus measured are similar in both bentonites for a given stress and degree of saturation, there is difference in the elastic strain limit of the soil. Bentonite clay is going to be part of the Engineered Barrier System (EBS) in deep geological disposal facilities for the long-term confinement of spent nuclear fuel. In order to fully understand their long-term performance, their behaviour in shearing conditions should be assessed.