Hydro-mechanical response of a bentonite pellets/powder mixture upon infiltration

Abstract

A series of infiltration tests on a 50/50% bentonite pellets/powder mixture compacted at different dry densities are reported and analysed. This mixture was proposed as sealing material in the Belgian concept for radioactive waste disposal. The tests have been performed with the French FoCa bentonite at two laboratories following analogous methodologies. The water intake, swelling pressure and axial strain have been measured during the tests. A common pattern of swelling pressure development has been found in all the tests, regardless the density of the mixture, the dimensions of the specimen, or the initial fabric, since a similar behaviour has also been found for specimens of compacted powder. At the beginning of saturation the swelling pressure increases sharply and then decreases, what gives place to an initial peak pressure. This decrease is interpreted as a collapse of the macrostructure on suction reduction. As saturation proceeds the swelling pressure increases again and eventually reaches a steady final value, what is a result of the redistribution of water towards the microstructure. The dry density and the initial water content of the mixture are two key factors affecting the particulars of this behaviour. After full saturation, the mixture becomes homogeneous with respect to water content and dry density, and the swelling pressure developed is analogous to that expected for a specimen of powder compacted at the same dry density.