Effect of gap-sealing on hydro-mechanical behaviour of granular bentonite

Abstract

Granular bentonite (GB), offering better pourability and workability than traditional powder bentonites, has been proposed as a candidate material for engineered barriers in deep geological repositories of radioactive waste. During service, involving complex hydro-mechanical (HM) stress paths, GB barriers are expected to seal technological gaps within the system. However, few studies have examined the HM behaviour of GB related to gap sealing. To address this, a technological gap was initially fabricated within the compacted GB samples used for HM testing. The gap enhanced the compressibility of the sample, promoting a hardening effect under high stress and thereby reducing the volumetric collapse during subsequent wetting. Under low stress, the gap accelerated the hydration swelling, while the final swelling strain depended on the sample’s initial global dry density. Similarly, gap sealing had little effect on the development of swelling pressure when the sample was wetted under constant volume. Furthermore, the water permeability after saturation at a comparable global void ratio was higher in the initially gapped sample than in the intact one. These findings are anticipated to support a long-term safety assessment of GB barriers.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme ‘European Joint Programme on Radioactive Waste Management’ EURAD (2019-2024) WP GAS ‘Mechanistic understanding of gas transport in clay materials’ under grant agreement No. 847593. The authors acknowledge the support of NAGRA through the project ‘Scientific work related to barrier integrity’ Ref 18722 (2019-2024). All authors also thank project PID2022141429OB-I00, funded by the Spanish Ministry of Science/Research Agency 501100011033/FEDER EU (2023-2027).

Postprint (published version)