Competing effects of volume change and water uptake on the water retention behaviour of a compacted MX-80 bentonite/sand mixture

Abstract

Bentonite-based materials have been studied as potential barriers for the geological disposal of radioactive waste. In this context, the hydro-mechanical behaviour of the engineered barrier is first characterized by free swelling conditions (as a consequence of the progressive filling of technological gaps) followed by constant volume conditions. This paper presents an experimental study conducted in order to characterize the water retention behaviour of a compacted MX-80 bentonite/sand mixture. The water retention properties upon wetting were investigated under both free swelling and constant volume conditions. In the high suction range, the water content was not influenced by the imposed volume constraints. On the contrary, swelling significantly affected the water retention behaviour at low suctions, and the quantity of water stored was higher under free swelling conditions than it was under prevented swelling. In this case, competing effects between bentonite swelling and water uptake did not lead to an increase of the degree of saturation upon wetting, as it was observed for samples wetted under constant volume conditions. The influence of the very strong hydro-mechanical coupling is further discussed.

Water retention model for compacted bentonites

“…The existence of two water retention domains in compacted bentonite-based materials has been highlighted by several Authors (see for instance Lloret et al 2003;Villar 2007;Loiseau et al 2002;Agus et al 2013;Seiphoori et al 2014;Wan et al 2015;Gatabin et al 2016). Experimental data show that:…”

“…Experimental data on compacted bentonites show that, for a given suction, the quantity of water stored under free swelling conditions is greater than it is under prevented swelling (Loiseau et al 2002;Lloret et al 2003;Ye et al 2009;Seiphoori et al 2014;Gatabin et al 2016). In bentonites, coupled hydromechanical processes are indeed extremely strong, so 180 that under free swelling conditions, suction changes yield significant swelling or shrinkage (in the order of several tens, even hundreds percent of the initial volume), resulting in important changes of dry density.…”

Estimation of water retention behaviour of MX-80 bentonite partially saturated with saline solution

“…The paper adds to significant existing body of knowledge on MX-80 bentonite water retention behaviour e.g. [1][2][3][4][5][6][7][8].…”

A nonlinear elastic approach to modelling the hydro-mechanical behaviour of the SEALEX experiments on compacted MX-80 bentonite

“…Collapse of the macrostructure is associated with macro-structure compressive strains which are partially offset by expansion of the microstructure to fill the voids Gatabin et al 2016). As a result, the stress reduces until the microstructure strain leads to a further build-up in stress.…”