oa Cyclic Water Retention Behaviour of Compacted Granular Bentonite

The paper presents the analysis of the water retention behaviour of compacted MX80 granular bentonite when subjected to cyclic wetting and drying episodes. Bentonites are highly swelling materials and they experience strong modifications of their fabric when subjected to changes in their water content. Interestingly, the link between the evolution of the retention behaviour and the structural modifications during wetting and drying episodes has not been deeply investigated. To this regard, a new protocol has been designed to analyse the retention behaviour of swelling materials. The protocol allows to collect representative samples for microstructural investigations at different stages of the imposed hydraulic stress path. Microstructural analyses were run by combining mercury intrusion porosimetry tests and SEM observations. An irreversible modification of the retention behaviour was observed once the material approached the fully saturated state during the first wetting. The water retention capacity of the material was increased as a result of such modification. The microstructural analysis allowed relating this change in the retention properties to a strong modification of the fabric.