Strain-controlled oedometer test for the measurement of the chemico-osmotic properties of bentonites

The possibility of relating the macroscopic transport properties and the swelling behaviour of bentonites to a limited number of physico-chemical and fabric parameters has been investigated by means of a new laboratory apparatus, which allows the reflection coefficient, which is also known as the membrane efficiency coefficient, and the swell coefficient to be simultaneously determined on the same clay specimen. The results of two multi-stage tests, which were performed on a natural sodium bentonite under fully saturated conditions, while varying both the specimen porosity and the salt concentration of the equilibrium solutions, have been interpreted through a physically-based model in which the pore-scale electro-chemical interactions be-tween the solid skeleton, the aqueous phase and the ion species are explicitly taken into account. The efficiency of the tested bentonite in acting as a semi-permeable membrane and its swelling behaviour have been found to be accurately simulated when a single fabric parameter, referred to as the solid charge coefficient, is calibrated on the available experimental dataset, thus suggesting that the containment performance of bentonite-based barriers, used for a number of geoenvironmental applications, may be predicted on the basis of the results of a strain-controlled oedometer test.