Regular Article

Effects of the initial granular structure of clay sealing materials on their swelling properties: experiments and DEM simulations

¹ Université Paris-Est, Laboratoire Navier, UMR 8205 (Ecole des Ponts ParisTech − Ifsttar − CNRS), 6-8 avenue Blaise Pascal, Cité Descartes, 77455 Marne-la-Vallée Cedex 2, France
² Andra R&D, 1-7 rue Jean Monnet, Parc de la Croix-Blanche, 92298 Châtenay-Malabry Cedex, France

^* e-mail: benjamin.darde@enpc.fr

Received: 20 October 2019
Accepted: 8 November 2019
Published online: 3 January 2020

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.