Abstract
Pellet-based expansive clay materials are considered as a sealing material for closing the galleries in radioactive waste disposal concepts. In repository conditions, the granular mixture progressively homogenises upon hydration by the host rock pore water. The present study focuses on the material behaviour before homogenisation. A grain-scale experimental characterisation is first performed in the laboratory. A model describing the hydromechanical behaviour of a pellet is proposed based on the experimental results. Then, suction-controlled swelling pressure tests are performed in the laboratory. Using Discrete Element Method (DEM) and the model proposed for a single pellet, the tests are successfully simulated. It is highlighted that (i) the swelling pressure evolves in two phases in the investigated suction range, controlled by the granular structure of the mixture; (ii) wall effects at the laboratory scale affects the material response; (iii) measurement variability associated to the sensor diameter is non-negligible; (iv) DEM is a valuable tool able to provide insight into the material behaviour.
Highlights
IntroductionCompacted expansive clay-based materials are candidate materials for engineered barriers in radioactive waste disposal concepts
Concepts of radioactive waste disposal vary between the different countries
Hydration is characterised by an increase of the measured swelling pressure
Summary
Compacted expansive clay-based materials are candidate materials for engineered barriers in radioactive waste disposal concepts. These materials are characterised by a low permeability, good radionuclide retention capacity, and ability to swell upon hydration and filling technological voids and exerting a confining pressure on the excavation damaged zone. Pellet-based materials have been considered as an alternative to compacted blocks [2,3,4,5]. Pellets are emplaced in the galleries as a granular material. The granular material undergoes hydration by the pore water of the host rock and progressively becomes homogeneous.
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